Search Results for: surface anatomy female

The Anatomical Basis of Medical Practice will be on view at the OBJECTIFY THIS opening Friday, Sept. 7th in Chicago

In researching the use of female anatomy in medical textbooks for our upcoming OBJECTIFY THIS: Female Anatomy Dissected and Displayed exhibition, I came across The Anatomical Basis of Medical Practice, and could not believe what I saw.  I’ll give you a little background…

In 1971, at a time when anatomy hours were being drastically cut, a trio of Duke professors set out to write an anatomy textbook that was different from the rest.  One of the professors, Dr. R. Fredrick Becker had an affinity for hanging female Playboy centerfolds up in his office to teach surface anatomy.  This would inspire one of the most unique and somewhat scandalous anatomy textbook of our time.

The professors, Becker, James S. W. Wilson, and John A. Gehweiler, set out to write a textbook in an “easy-going, literary style so that any student could read ahead on his own without difficulty.” Furthermore, they go on to state their inspiration to use seductive female nudes to display surface anatomy,

“In our own student days we discovered that studying surface anatomy with a wife or girl friend proved to be not only instructive, but highly entertaining. Since the majority of medical students still tend to be males, we have liberalized this text by making use of the female form. But, more to the point, we have done so because a large portion of your future patients will be women and few texts have pointed out surface landmarks on the female.”

They were quite liberal in their use of female nudes of the pin-up girl variety as you can see in the images above.  And the “easy-going, literary style,” often lent itself to cheeky comments about women.  In the discussion about the effects of UV light on skin, the authors state, “the contrast between exposed and unexposed parts of the epidermis is quite stark when the bathing suit is removed.”

In the preface of the textbook, the authors justify their use of gorgeous females to show surface anatomy,

“Perhaps we should have included photographs of garden-variety, American males and females who have let their physiques go to pot.  Instead, we used female models as model females.  The student will see the ordinary specimen every day.  Only on rare occasions will the attractive, well-turned specimen appear before him for consultation.  He should be prepared for this pleasant shock. For the growing ranks of female medics, we inlcuded the body beautiful of a robust, healthy male.  We are sorry that we cannot make available the addresses of the young ladies who grace our pages. Our wives burned our little address books at our last barbecue get-together.”

Needless to say, the book was eventually banned from publication at a time when the feminist movement was on everyone’s radar.  It has now become a bit of a collectors item and many university libraries have listed it as “missing” from their collection.  I know because I tried borrowing a copy with absolutely no luck.  Thankfully a Street Anatomy fan reached out and allowed us to borrow the book for our exhibition!

Feminism aside, I do have to say that after going through the book myself, it is rather fun and entertaining.  The writing style is conversational and the “pin-up girl” photographs make learning surface anatomy quite engaging.  The women in the photographs are not the stick thin models that we are used to seeing today, but curvy healthy women that happen to be in very feminine and oftentimes seductive poses.  While not everyone will agree with me, I do applaud the authors for trying to create a different experience in anatomy education and overall for having fun with it.

Is it objectification of women or is it simply appreciation of the beauty that is the female form?  You can decide by seeing the book in person at the OBJECTIFY THIS exhibition opening this Friday September 7th at Design Cloud Gallery in Chicago!

RSVP for OBJECTIFY THIS via Facebook!

To read more about the Anatomical Basis of Medical Practice, view the journal article “The pornographic anatomy book? The curious tale of the Anatomical Basis of Medical Practice.” [Halperin EC. The pornographic anatomy book? The curious tale of the AnatomicalBasis of Medical Practice. Acad Med. 2009 Feb;84(2):278-83. PubMed PMID:19174685.]

[A huge thank you to Charlotte W. for lending the textbook for the OBJECTIFY THIS exhibition!]

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EXCLUSIVE: In a competitive situation, Roughcut TV, the BAFTA-winning British producer behind Stath Lets Flats and People Just Do Nothing, has swooped for the rights to adapt Sarah Vaughans fourth novel into a television series.

The company, spearheaded by The Office producer Ash Atalla, considers the deal for Little Disasters to be an important moment in its strategy to move into high-end drama. It follows Vaughan becoming a hot property in TV after Netflix set an adaptation of her third book, Anatomy Of A Scandal, with Big Little LiescreatorDavid E. Kelley showrunning and Sienna Miller starring.

Little Disasters is apsychological thriller, centering on pediatrician, Dr Liz Trenchard, who is surprised to find the child of her close friend, Jess, has been admitted to accident and emergency. Jess is an attentive mother, but Trenchard has a dreadful feeling that her friends explanation for what happened doesnt reflect the childs injuries. As she alerts the authorities, Jess life unravels and guarded secrets surface, with consequences for their friendship group.

Related StorySky Preps Paramedic Comedy 'Bloods' Starring 'Timewasters' Samson Kayo & 'Ab Fab's Jane Horrocks From 'People Just Do Nothing' Producer Roughcut

Roughcut TV is currently interviewing writers for the series and is yet to take the project to market. Vaughan said she was blown away by the companys pitch for the book, saying it has a commitment to being brave and true to the darkness of the story.

Roughcuts drama development producer Marianna Abbotts, who works alongside head of scripted Alex Smith, added: Sarahs meticulously researched story bravely explores the dark reaches and intense love of motherhood through a taut, compelling psychological thriller. The female friendships at the heart of the book and the way mothers judge each other make this a hugely universal and relatable subject.

Roughcut TV is currently working on a third season of Channel 4s BAFTA-winning realtor comedy Stath Lets Flats, which has been picked up by HBO Max in the U.S., as well as a movie based on BBC Threes pirate radio mockumentary People Just Do Nothing.

Anatomy Of A Scandal is currently shooting in the UK. Michelle Dockery(Downton Abbey) andRupert Friend(Strange Angel) co-star in the anthology series about a high-flying Westminster politician whose marriage unravels when he is accused of rape. House Of CardsshowrunnerMelissa James Gibson is collaborating with Kelley on the drama, which is directed by S.J. Clarkson(Succession).

Roughcut TV is repped by CAA. Vaughans deal was brokered by Penelope Killick at David Higham Associates.

See the rest here:
Roughcut TV Lands Rights To Little Disasters From Sarah Vaughan, The Author Behind Netflix Series Anatomy Of A Scandal - Deadline

The pathogen has already done a fair bit of damage. It has only been five days since the patient began exhibiting typical COVID-19 symptoms, but already, menacing shadows can be seen in the CT scans of the lungs.

"It's like frosted glass," is how Christian Strassburg, a professor of internal medicine at the Bonn University Hospital, describes the changes made visible by the scan. "The lung tissue is saturated with fluid." Secretions and dead cells are gumming up the walls of the pulmonary alveoli "like Jell-O," he says.

"It is extremely difficult for oxygen to permeate a layer like that to get from the lung into the bloodstream," the professor explains. It is a phenomenon he has been seeing frequently in recent weeks and it is caused by the novel coronavirus, SARS-CoV-2. The number of confirmed COVID-19 patients worldwide is now well over 4.2 million and the number of deaths is approaching 300,000. Meanwhile, doctors and biologists are doing all they can to gain a better understanding of the pathogen behind the pandemic.

SARS-CoV-2 behaves differently than almost any other virus that humans have faced before, and even now, several months into the pandemic, there is disagreement as to what percent of COVID-19 patients experience severe symptoms. Estimates tend to come in at around 5 percent of all infections. And in those cases, the virus unfolds unfathomable destructive power.

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The article you are reading originally appeared in German in issue 20/2020 (May 09, 2020) of DER SPIEGEL.

The epicenter of such infections is almost always the lungs. But as medical professionals now realize, the virus can also affect other organs and tissues - including the heart, the brain, the kidneys and the bowels. In the worst case, the body begins attacking itself. When the immune system spins out of control like that, doctors call it a "cytokine storm," and when patients die as a result, multiple organ failure tends to be the cause.

Over 100 vaccine candidates are currently being developed worldwide to combat SARS-CoV-2, but in the worst-case scenario, it could take years before a vaccine is available. Until it is, the virus will still be with us. Even if the pandemic does weaken a bit, experts believe a second wave is just around the corner.

Early talk of COVID-19 as being mostly a mild illness has been proven to be "dangerously false," Richard Horton, editor-in-chief of the medical journal The Lancet, has written. At the bedside, he says, it is "a story of terrible suffering, distress and utter bewilderment." U.S. cardiologist Harlan Krumholz described the ferocity of COVID-19 in the magazine Science as "breathtaking and humbling." The disease, he continued, "can attack almost anything in the body with devastating consequences."

The best way to learn more about SARS-CoV-2 is to start small. Coronaviruses are a mere 160 nanometers in size. In order to multiply, the tiny pathogens are reliant on the cells belonging to a different organism.

The novel coronavirus likely comes from bat viruses, and it is thought that, even before it made the jump to humans, it developed the mechanism allowing it to bind with human cells. Some bat viruses are able to bind to a receptor called ACE2. This molecule can be found on the surface of human cells and helps regulate blood pressure. But it also functions as a kind of doorway to the interstices of the cell, and viruses that have the key can get inside.

Researchers believe that bats carry around 3,200 different coronaviruses. Chance, time and opportunity fueled the creations of the SARS-CoV-2 virus, which ultimately managed to jump to humans.

But how exactly does the virus find its way into the human body? Internal medicine professor Strassburg is quite familiar with the process. At the Bonn University Hospital, he is currently in charge of between 10 and 20 COVID-19 patients. On one day recently, eight of them were intubated, having become so ill that they were forced to rely on ventilators. "Luckily, that is the minority," Strassburg says. "Most of those infected by the virus get away with only mild symptoms."

Early on, virologists thought that the novel coronavirus would spread only slowly, in part due to the similarities between SARS-CoV-2 and the SARS coronavirus that appeared in China in 2002. From November 2002 and July 2003, almost 800 people died of the disease, the full name of which is Severe Acute Respiratory Syndrome. But then, the epidemic disappeared. It was a stroke of luck for humanity: That pathogen appears to have been more deadly than SARS-CoV-2, but it focused its attentions on the lungs. The virus multiplied deep within the body, making it less contagious. Furthermore, it was easy to identify and isolate those who had fallen ill from the virus.

Experts initially hoped that the same would hold true of SARS-CoV-2, but they were mistaken. The novel coronavirus doesn't just attack the lungs. Throat swabs from patients revealed early on that the pathogen first goes after the mucous membrane in the upper respiratory tract.

That is advantageous for the virus. The distance from one throat to another throat is much shorter than the distance from one person's lung to another. "That means that those carrying the virus are highly contagious," says Strassburg. A huge number of the viruses are found in the nasal cavity and pharynx, "even in people who aren't yet experiencing symptoms," he adds, "which is why the pathogen was able to circle the globe so quickly."

There are three stages in the attack on the human body. Initially, the coronavirus binds with club-shaped protein complexes on the ACE2 receptors of human cells. That opens up the host cell and allows genetic material from the pathogen to enter. The virus then converts the cell into a virus factory. Huge numbers of viruses thus produced then leave the host cell and attack other cells.

The SARS-CoV-2 Virus focuses its attack on the lungs. The delicate alveoli are most at risk.

The resulting viral load is enormous, particularly in the first week following infection. And initially, there are hardly any symptoms. Often, there is merely a dry cough, says Strassburg, with the body's temperature hardly rising at all. "Even patients who are more severely affected generally have a temperature below 38 degrees Celsius (100.4 degrees Fahrenheit)." That is a significant difference to the flu: "For influenza, a sudden rise in temperature is typical, along with a distinctive feeling of being sick. But that's not the case here."

In this initial phase of the illness, much depends on the patient's immune system. Immune cells attack the invaders, but because the body isn't yet familiar with the virus, the weapons at their disposal are relatively basic.

A battle of attrition ensues, one that determines whether the patient will quickly recover or whether the disease will get the upper hand. Will the immune system stop the attack in the upper respiratory tract? Or will the pathogen be able to find its way into the lungs? The answers to those questions determine whether the illness becomes life threatening or not.

Researchers are still trying to figure out why the virus is able to reach the lungs of some patients but is stopped short in others. One of the factors appears to be the number of pathogens that attack the body at the beginning. More than anything, though, patients with underlying medical conditions seem to have the most to fear from SARS-CoV-2. According to estimates, about a quarter of the population in Central Europe has such an underlying condition.

Those at risk include people suffering from obesity, diabetes and high blood pressure. And smokers: "Their mucous membranes and lung ventilation are already impaired," says Strassburg. Tiny hair-like projections known as cilia, which normally help keep pathogens and mucous out of the lungs and respiratory tract, no longer function appropriately.

In such cases, there are hardly any hurdles for the virus on the way to the lungs. Gravity is sufficient for the tiny pathogens to reach their target. Once the virus advances into the smaller, branch-like bronchioles, it meets a particularly vulnerable layer of cells, the membranes of which are also covered with ACE2 receptors. Directly in the pulmonary alveoli, the tiny sacs where oxygen is transferred into the bloodstream, SARS-CoV-2 finds perfect conditions.

To depict the precise damage the virus does in the lungs, thoracic surgeon Keith Mortman of George Washington University Hospital in Washington, D.C., turned to computer modelling. The 3-D imagery from the clinic shows the lungs of a man in his late 50s. Yellow-tinged deposits can be seen in many areas within the organ.

"The damage we are seeing is not isolated to any one part of the lung," says Mortman. Initially, he says, the patient experienced a fever and a cough, before then developing serious breathing difficulties. He was intubated and attached to a ventilator, but when that proved insufficient, he was hooked up to a so-called ECMO machine.

The machine infuses blood with oxygen outside of the body before pumping it back inside. The hope is that the procedure will give the lungs the time they need to recover.

Doctors now have a deeper understanding of how SARS-CoV-2 damages lung tissue. White blood cells discover the virus and attract other immune cells to the site, which attack the infected lung cells and kill them. They leave behind cell detritus, which clog up the alveoli. If the body isn't able to gain control over the reaction to the infection, acute lung failure looms.

But other organs can also be damaged as a result of the infection. The more SARS-CoV-2 patients are treated around the world, the clearer it has become just how comprehensive the attack staged by the virus is.

According to data from China, around 20 percent of patients requiring hospitalization suffer damage to the heart. It remains unclear whether the virus goes after heart muscle cells directly or if damage to the coronary blood vessels is to blame. The blood clotting function is also disrupted, leading to clumps that could result in heart attacks, lung embolisms and strokes.

The kidneys of some hospitalized patients also come under attack, as evidenced by blood or protein in urine samples. As a result, dialysis machines have had to join ventilators in ICUs devoted to treating COVID-19 patients.

Doctors have likewise observed brain inflammation and seizures in some patients. The virus apparently advances all the way into the brain stem, where important control centers are located, such as the one responsible for breathing. The virus likely gets to the brain via the mucous membrane inside the nose and the olfactory nerve. This could also be the reason that many patients temporarily lose their sense of smell.

SARS-CoV-2 can also attack the digestive tract, with patients complaining of bloody diarrhea, nausea and abdominal pain.

Doctors have also reported a possible link between COVID-19 and a rare blood vessel syndrome in children called Kawasaki Disease. In Britain, the disease has even killed a few children who became infected with SARS-CoV-2. The disease involves the inflammation of blood vessels throughout the body and can damage the heart.

Doctors now believe that SARS-CoV-2 attacks tissue and organs virtually everywhere in the body. And the disease can also apparently leave behind long-term damage. Chinese researchers have examined the blood of patients and found that even after the infection has passed, certain blood values remain abnormal for an extended period. Despite the virus no longer being present in the body, for example, their livers still don't exhibit normal functionality.

The virus can make it all the way into the brain, triggering seizures and inflammation.

The lungs, too, likely suffer lasting damage in severe cases. "When inflammation does not subside with time, then it becomes essentially scarring in the lungs, creating long-term damage," says Mortman, the doctor from George Washington University Hospital.

It is still too early for a comprehensive understanding of the long-term consequences of COVID-19. But doctors are familiar with cytokine storms and acute lung failure from other severe infections. Some of the survivors of the first SARS epidemic, for example, experienced limited lung functionality for up to 15 years after the illness.

But why do some people emerge virtually unscathed from this multifaceted attack while others do not? Thus far, researchers do not have an answer to this question. There are indications that the virus - similar to the pathogen that causes AIDS is able to attack certain white blood cells, thus damaging precisely that line of defense that is supposed to stop the infection.

Are some patients more susceptible than others to that phenomenon for genetic reasons? The biotechnology company 23andMe intends to comb through the DNA of its 10 million customers in the search for sequences that could be predictive of their susceptibility to severe COVID-19.

Until the question is answered for sure, however, most patients can continue to rely on hope. After all, most people do not experience severe symptoms from the disease. "Among patients without underlying conditions, even severe cases have an 80 percent survival rate," estimates Christian Strassburg, the internal medicine specialist. Still, it is by no means time to let down our guard, he says, particularly now that restrictions on public life are increasingly being lifted. "The danger remains extremely high that a large number of patients will soon have to be treated in hospitals."

That will heap even more pressure on doctors and nurses. The condition of some patients, after all, can worsen dramatically within just a few days.

Should death be the ultimate result, it is often not the virus itself that causes it, but the immune system of the infected patient, which can disastrously overreact and attack the body.

In such instances, huge numbers of so-called cytokines are released. These chemical signaling molecules produced by the body trigger a cascade of biochemical reactions that affect the immune system. The development of a fever accelerates the metabolism and helps kill the virus. Blood vessel walls are made more permeable, allowing easier access for immune cells, such as phagocytes, to attack the virus. The heartrate speeds up.

"The reaction is actually quite sensible," says Strassburg. But in cases of severe infection, the immune system can overreact and trigger a cytokine storm.

"The result is a reaction that looks like a massive blood infection, but isn't one," says Strassburg. It can lead, however, to multiple organ failure. "If the immune system overreaction to the pathogen continues for too long or is too severe, it will kill the body."

Vast destruction is the result, as pathologists can attest. Johannes Friedmann is a professor at Ldenscheid Hospital just south of Dortmund and has examined the bodies of several patients who succumbed to COVID-19. In the alveoli of these patients, he has found epithelial cells in the lung that have been "scaled off" in addition to protein "deposits" in the blood resulting from blood vessels that have become permeable. He has also discovered cells with multiple or enlarged nuclei, a phenomenon that is typical of viral illnesses.

The walls of the vast majority of the alveoli in the lungs are "widened to many times their normal thickness," Friemann says, adding that the lungs of many COVID-19 casualties are "insufficiently inflated." That impedes oxygen transfer.

Friemann's findings have been consistent with those of medical professionals in Hamburg, the United States, Switzerland and elsewhere: Most of those who died were sick before they came into contact with SARS-CoV-2. Friemann has found cases of liver cirrhosis, severe arterial sclerosis and extremely high blood pressure.

Did these patients die of SARS-CoV-2 or from other maladies? "You can't live with such a lung, so I would point to the virus as being the cause of death," says Friemann. "Many of these people would still be alive without the infection."

Indeed, a recent calculation by British epidemiologists casts significant doubt on claims that most COVID-19 victims would have died soon anyway. They found that female victims of the disease lose an average of 11 years of life. For men, the number was 13 years.

See the original post here:
Anatomy of a Killer: What the Coronavirus Does Inside the Body - DER SPIEGEL

What should I know about breast?

What are the breasts (mammary glands)?

The breasts, located on the front of the chest, are medically known as the mammary glands. The term "breast" is sometimes used to refer to the area at the front of the chest.

Ms. G. is a 40-year-old woman with two smallchildren. Like most women, she is concerned about her chances of developingbreast cancer. She asks her doctor about her risks. Although breast cancer is a worry for most women, Ms. G. is especially worried because of a family history of breast cancer. Her mother and sister had breast cancers that were diagnosedat young ages.

What are the anatomical features of the breast?

The mammary gland is made up of lobules -- glandular structures that produce milk in females when stimulated to do so. The lobules drain into a system of ducts, connecting channels that transport the milk to the nipple. Between the glandular tissue and ducts, the breast contains fat tissue and connective tissue.

Both males and females have breasts. The structure of the male breast is nearly identical to that of the female breast, except that the male breast tissue lacks the specialized lobules, as there is no physiologic need for milk production by the male breast. Abnormal enlargement of the male breasts is medically known as gynecomastia.

The breast does not contain muscles. Breast tissue is located on top of the muscles of the chest wall. Blood vessels and lymphatic vessels (a system of vessels that drains fluid) are located throughout the breast. The lymphatic vessels in the breast drain to the lymph nodes in the underarm area (axilla) and behind the breast bone (sternum).

In females, milk exits the breast at the nipple, which is surrounded by a darkened area of skin called the areola. The areola contains small, modified sweat glands known as Montgomery's tubercules. These glands secrete fluid that serves to lubricate the nipple during breastfeeding.

What are the most common medical conditions affecting the breasts?

Breast health is a source of concern for most women. Although breast cancer is a fairly common malignancy affecting one out of every eight women in the U.S. at some point in life, benign (non-cancerous) conditions of the breast are much more common. In fact, most masses and lumps in the breasts are not cancer. Breast cancer occurs in males as well, but it accounts for a small percentage of all breast cancers.

Among the benign breast conditions, cysts and fibrocystic changes are common. One type of benign tumor in particular, known as a fibroadenoma, is common in young women. Infections of the breast tissue can also occur, particularly during breastfeeding. Mastitis is the medical term for inflammation of the breast.

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What happens to the breasts in pregnancy?

During pregnancy, the breasts grow further due to stimulation by estrogens (female hormones). The growth during pregnancy is more uniform than that observed at puberty. The amount of tissue capable of producing milk is approximately the same in all women, so women with smaller breasts produce the same amount of milk as women with larger breasts. During pregnancy, the areola becomes darker and enlarges in size.

How does breast tissue develop?

Breast tissue begins to form in the fourth week of fetal life. In the fetus, breast tissue develops along two "milk lines" that start at the armpit and extend to the groin. Uncommonly, an extra (ancillary) breast can develop along this line. On the skin surface, an extra nipple (supernumerary nipple) may develop along this line.

How are human breasts different from other species?

In other primates (such as apes), the breasts develop only when they are producing milk. After the young have been weaned, the breasts flatten again. In humans, the breasts enlarge at puberty and stay enlarged throughout a woman's life.

Medically Reviewed on 10/12/2018

References

REFERENCE: MedscapeReference.com. Breast Anatomy.

Link:
Breast Anatomy: Learn About the Structure and Blood Supply

INTRODUCTION

Since the extinction of non-avian dinosaurs, the northern Neotropics have harbored now-extinct vertebrates that have been at the extreme of large size within their respective clades (1). Among them are the largest snake (2), caimanine crocodile (3), gharial (4), and some of the largest rodents (5). One of the most iconic of these species is the gigantic turtle Stupendemys geographicus, as it is the largest nonmarine turtle ever known from a complete shell (until now rivaled only by the extinct marine turtle Archelon ischyros from the Late Cretaceous). It was first described in 1976 from the Urumaco Formation in northwestern Venezuela (6), but our knowledge of this animal has been based on partial specimens that have resulted in a problematic taxonomy, especially due to a lack of specimens with associated skull and shell elements. The species diversity of the giant turtles inhabiting northern South America during the Miocene is thus unclear (7, 8), with several forms having been proposed: the postcrania-based S. geographicus from the late Miocene, Urumaco region (6, 912); the skull-based Caninemys tridentata from the late Miocene, Acre region, Brazil (8); the controversial postcrania-based S. souzai, also from the late Miocene of Acre, Brazil (8, 13), currently attributed as Podocnemididae incertae sedis (14); and the skull-based Podocnemis bassleri from the late Miocene, Acre region (Loretto), Peru (15). The fossil record of large-sized littoral-freshwater Podocnemididae turtles of South America also includes the skull-based Carbonemys cofrinii, and the shell-based Pelomedusoides indet., from the middle to late Paleocene of Colombia (12).

We here describe several new shells and the first lower jaw specimens from discoveries made during regular fieldwork in the Urumaco region since 1994 (10, 16) and recent finds from La Tatacoa Desert in Colombia. Together, these fossils shed new light on the biology, past distribution, and phylogenetic position of giant neotropical turtles. First, we report a new size record for the largest known complete turtle shell. Second, our findings support the existence of a sole giant erymnochelyin taxon, S. geographicus, with an extensive geographical distribution in what were the Pebas and Acre systems (pan-Amazonia during the middle Miocene to late Miocene in northern South America). Third, we hypothesize that S. geographicus exhibited sexual dimorphism in shell morphology, with horns in males and hornless females.

Testudines Batsch, 1788.

Pleurodira Cope, 1864 sensu Joyce et al., 2004.

Podocnemididae Cope, 1868.

Eymnochelyinae sensu Ferreira et al., 2018.

Stupendemys geographicus Wood, 1976.

Caninemys tridentata (8)

Stupendemys souzai (7, 13)

Stupendemys sp. (17)

Podocnemididae indet. (17)

Holotype. MCNC-244, medial portion of the carapace with associated left femur, fragments of scapulocoracoid and a cervical 8? (6).

Hypodigms. Specimens described in Wood (6): MCZ(P)-4376, much of the carapace, fragments of plastron, cervical 7?, both scapula-coracoids and a caudal vertebra; MCNC-245, a plastron lacking the epiplastra and entoplastron, two nearly complete costals, several peripherals, and one neural; MCZ(P)-4378, a right humerus. Specimen described as C. tridentata (8): DNPM-MCT-1496-R, nearly complete skull (Fig. 4, A to D). Specimens referred to as S. souzai (13): UFAC-1764, incomplete right humerus; UFAC-1163, cervical vertebra; UFAC-1294, left peripheral 1; UFAC-1544, left costal 2; UFAC-1547, right xiphiplastron; UFAC-1553, cervical vertebra; UFAC-1554, cervical vertebra; UFAC-4370, pelvic girdle; UFAC-5275, cervical vertebra; UFAC-5508, anterior margin of the carapace and left hypoplastron, and LACM-131946, nuchal bone, originally attributed to Stupendemys sp. (17). Specimens referred to as Podocnemididae ind. (17): LACM-141498, left lower jaw ramus, and Stupendemys sp. (17): LACM-138028, right scapula. New specimens described here: CIAAP-2002-01 (allotype), nearly complete carapace (Fig. 1, A to E); AMU-CURS-85, nearly complete carapace, left humerus, and right scapula-coracoid (Figs. 2, B and C, and 3, A to D); AMU-CURS-1098, plastron and anterior portion of carapace (Fig. 2, D and E); MPV-0001, nearly complete carapace and complete plastron (Fig. 2, F to M); OL-1820, left humerus (Fig. 3, E to H); AMU-CURS-233, fragment of femur (Fig. 3, I to P); AMU-CURS-706, lower jaw (see fig. S6); VPPLT-979, lower jaw (Fig. 4, E to L).

(A and B) CIAAP-2002-01 carapace in dorsal view. (C) Close-up of the left horn in CIAAP-2002-01 [see red square in (B)]. (D) Medial-right view of the left horn showing its ventral projection. (E and F) Close-up of one of bone surface of the carapace showing the pitted sculpture [see red circle in (B)]. (G) General reconstruction of CIAAP-2002-01 including the horns covered with keratinous sheath (light gray). co, costal bone; M, marginal scute; P, pleural scute; pe, peripheral bone; py, pygal bone; sp., suprapygal; V, vertebral scute. Blue lines indicate sulci. Photo credit: Edwin-Alberto Cadena, Universidad del Rosario.

(A) Reconstruction of S. geographicus male (front) and female (middle-left), together with the giant caimanine Purussaurus mirandai and the large catfish Phractocephalus nassi. (B and C) AMU-CURS-85 nearly complete carapace in ventral view. (D and E) AMU-CURS-1098 nearly complete plastron in ventral view. (F to N) Female shell anatomy of S. geographicus MPV-0001 from Colombia. (F and G) Carapace in dorsal view. (H and I) Plastron in ventral view. (J and K) Close-up of the right anterior portion of the carapace in dorsoposterior view, showing bite marks and punctured bone [(J) and rectangle in (G)]. (L and M) Nuchal-anterior peripheral in dorsomedial view, showing thickened and moderately to strongly upturned (arrows) [(L) and circle in (G)]. (N) Close-up of the bone surface of one of the costal bones [(N) and circle in (G)], exhibiting microvermiculation sculpturing pattern. Abd, abdominal scute; Ana, anal scute; bm, bite mark; bp, bridge peripheral; co, costal bone; ent, entoplastron; epi, epiplastron; Ext, extragular scute; Fem, femoral scute; Hum, humeral scute; hyo, hyoplastron; hyp, hypoplastron; Int, intergular scute; isc, ischium scar; Lpg, left pelvic girdle; M, marginal scute; mes, mesoplastron; ne, neural bone; nu, nuchal bone; pe, peripheral bone; Pec, pectoral scute; pub, pubis bone; py, pygal bone; Rco, right coracoid; Rpg, right pelvic girdle; Rsc, right scapula; sp., suprapygal; tv, thoracic vertebra; V, vertebral scute; xip, xiphiplastron. Blue lines indicate sulci. Art: Jaime Chirinos. Photo credit: Edwin-Alberto Cadena, Universidad del Rosario.

(A to D) AMU-CURS-85 left humerus in ventral (A), medial (B), dorsal (C), and proximal (D) views. (E to H) OL-1820 left humerus in ventral (E), lateral (F), dorsal (G), and proximal (H) views. (I and J) AMU-CURS-233 partial femur in ventral (I) and dorsal (J) views. (K) Outline of the femur indicating the region where the thin section was elaborated. (L) Thin section of the partial femur, indicating the close-up presented in (M) to (P). (M) Close-up of the cortical region of the bone. (N) Close-up of the deeper part of the cortex. (O) Close-up of the central region of the bone. (P) Close-up of the transitional region of the bone. Outlines of the largest extant and extinct turtles ever, indicating their maximum carapace length (see table S2): (Q) S. geographicus. (R) A. ischyros. (S) D. coriacea (extant). (T) M. cf. sivalensis. (U) R. swinhoei (extant). (V) C. niger (extant). pco, primary cortex; SO, secondary osteon. Photo credit (A to H): Edwin-Alberto Cadena, Universidad del Rosario; (I to P): Torsten Scheyer, University of Zurich.

(A to D) DNPM-MCT-1496 skull described by Meylan et al. (8), from Acre, Brazil in dorsal (A), ventral (B), and right lateral (C) views. (D) Composite skull and lower jaw (not a scale) of S. geographicus using relief images of DNPM-MCT-1496 skull and VPPLT-979 lower jaw. (E to L) VPPLT-979 lower jaw from La Tatacoa Desert, Colombia in dorsal (E and F), ventral (G and H), and right-lateral (I and J) views. (K and L) VPPLT-979 articular bone and facet in posterior view, exhibiting the foramen posterius chorda tympani. (M to T) Right articular region of the lower jaw, Podocnemis expansa NHMW-137 (M and N), S. geographicus VPPLT-979 (O and P), S. geographicus AMU-CURS-706 (Q and R), P. dumerilianus AMNH-1886 (S and T). (U) Lower jaw of P. dumerilianus AMNH-1886 in dorsal view. (V) P. expansa NHMW-137 lower jaw in dorsal view. ang, angular; arf, articular facet; art, articular; cor, coronoid; den, dentary; fm, fossa Meckelii; fna, foramen nervi auriculotemporalis; fos, fossa articularis mandibularis; fpc, foramen posterius chorda tympani; pra, processus retroarticularis; pre, prearticular; sr, symphisis ridge; sur, surangular. Photo credit (A to C): Orangel Aguilera-Socorro, Universidade Federal Fluminense; (E to V): Edwin-Alberto Cadena, Universidad del Rosario.

Range and distribution. Middle to late Miocene, Tatacoa Desert, Villavieja, Departamento del Huila, Colombia; late Miocene, Urumaco, Falcn State, Venezuela; late Miocene, Acre region, Brazil; Loretto region, Peru (Fig. 5).

(A) The phylogeny is based on the single MPT, resulting from the analysis of 245 characters [L = 1180, consistency index (CI) = 0.319, and retention index (RI) = 0.748]. Bremer support indices are indicated next to the internodes. (B) A time-calibrated cladogram of South American Erymnochelyinae; the bars indicate the stratigraphic occurrence of taxa; internode length is hypothetical. (C) Paleogeographic reconstruction of northern South America during the late Miocene (10 Ma), including the localities with fossil record of S. geographicus and extension of the Pebas system, modified from Hoorn (44). (D) General stratigraphic column of Urumaco Formation, including the four localities where the new fossils of S. geographicus described here were found. (E) Excavation of AMU-CURS-85 carapace from To Gregorio locality. H, Holocene; L, tree length; Oligo, Oligocene; Paleo, Paleocene; Pleisto, Pleistocene; Plio, Pliocene. Pr, present.

Diagnosis. S. geographicus is recognized as a pleurodire based on (i) sutural articulation of pelvis with shell, (ii) loss of medial contact of mesoplastra, (iii) well-developed anal notch, (iv) fusion of gulars, (v) formed central articulations of cervical vertebrae, (vi) a well-developed processus trochlearis pterygoidei, and (vii) quadrate-basioccipital contact. It is a podocnemidid based on (i) a fully developed, medially extensive cavum pterygoidei with a completely developed pterygoid flange; (ii) an incisura columellae auris enclosing stapes and eustachian tube; (iii) an exoccipital-quadrate contact absent; and (iv) a cervical centra with saddle-shaped posterior condyles. It shares with Peltocephalus dumerilianus and Erymnochelys madagascariensis (i) a long parietal-quadratojugal contact; (iii) large postorbital bones; (iii) cheek emargination potentially reduced or absent; (iv) potentially advanced posterior roofing of the skull (reduced temporal emargination); (v) an articular with a processus retroarticularis posteroventromedially projected, differing from the ventrally projected Podocnemis spp. (Fig. 4, M to T, and fig. S6) acute tip of dentary at symphysis; and (vii) foramen chorda tympani enclosed in processus retroarticularis.

Further description and dimensions. Detailed anatomical descriptions, comparisons, and measurements of the fossilized bones and body mass estimation for S. geographicus and other fossil and extant giant turtles are presented in Fig. 3 (Q to V) and in the Supplementary Materials (text, figs. S1 to S6, tables S1 and S2, and data files S1 and S2).

Remarks. Skull: Unique among podocnemidids (and all other pleurodires, the side-necked turtles) in having greatly inflated maxillae, each with a ventral, tooth-like process, which, together with a single process formed on the midline of the premaxillae, form a tridentate condition in the upper triturating surfaces. Lower jaw: Triturating surface deep, forming an oval concavity, deeper than in any known living or extinct podocnemidid, labial ridge curved anteriorly ending in acute tip; lingual ridge is a blunt margin forming an accessory ridge that increases in height and width anteriorly and runs as a narrow ridge at the medial symphysis; high coronoid process; large dorsal opening of fossa Meckelii; the fossa Meckelii fills the posterior end of the jaw to such an extent that the area articularis mandibularis forms part of the posterior margin, and the fossa opens posterolaterally next to the jaw articulation. Shell: Carapace 2 m straight midline length, carapace low-arched, with irregular nodular contours on external surface and deep median notch at front; anterior border of nuchal-peripheral bones thickened and moderately to strongly upturned; carapace with massive anterolateral horns slightly projected ventrally in forms attributed as male; carapace dorsal bone surface smooth to striated or slightly pitted; posterior peripheral bones moderately scalloped along margins; thickness of carapace relatively thin at the costals. Shell (plastron): Pectoral-abdominal sulcus very anterior to mesoplastra, reaching almost the hyoplastra lateral notch level. Neck: Cervical vertebrae (probably 7 and 8) with neural arches relatively high in relation to anteroposterior lengths of centra, and articular facets of postzygapophyses forming acute angle of less than 90; cervical 8? neural arch with large horizontal plane, prezygapophyses directed perpendicularly, thin bladelike spine on anterior face of neural arch and no ventral keel on centrum. Humerus: Humerus squat, massive; deep bicipital fossa between lateral and medial articular facets on ventral surface; prominent ridge traversing ventral surface of shaft from medial process to distal end, terminating just above lateral condyle; medial condyle broadest at anterior end; medial and lateral condyles facing very ventrally; straight to slightly slender shaft and triangular in cross section than circular. Femur: Femur squat, massive, greatly flattened dorsoventrally; breadth of tibial condyle approximately one-third total length of bone. Scapula: A dorsal strongly bowed scapular process with a flattened flange projecting laterally from the main axis.

The first analysis (all taxa separated) produced 156,070 most parsimonious trees [MPTs; length = 1154, consistency index (CI) = 0.326, and retention index (RI) = 0.749]. The strict consensus tree (fig. S7) shows the lower jaws from Acre, Urumaco, and La Tatacoa in polytomy at the base of the Stereogenyini clade, sensu Ferreira et al. (18), with the same position for C. tridentata and S. geographicus as presented in Ferreira et al. (18). The second analysis [C. tridentata + Acre jaw and S. geographicus + (Urumaco, La Tatacoa jaws)] produced 1157 MPT (length = 1157, CI = 0.325, and RI = 0.748). Here, the strict consensus tree (fig. S7) shows C. tridentata and S. geographicus forming a monophyletic clade inside the Erymnochelyinae clade sensu Ferreira et al. (18), suggesting them to be closely related or potentially the same taxon. We favor the latter monospecific scenario based on the following considerations: (i) the three lower jaws from Urumaco, La Tatacoa, and Acre resemble each other in all morphological aspects, varying only in size and in preservation; (ii) the lower jaws from Urumaco, La Tatacoa, and Acre were found in localities and/or formations where shell material of S. geographicus was also found; and (iii) as Meylan et al. (8) stated, there is a higher probability that the lower jaw, LACM-141498, does belong to Caninemys, and they are sufficiently complementary to suggest that they are from closely related taxa. This scenario receives additional support from the third phylogenetic analysis, which produced 36 MPTs (length = 1180, CI = 0.319, and RI = 0.748). The strict consensus tree (Fig. 5A) and the time-calibrated cladogram pruned to the South American Erymnochelyinae clade (Fig. 5B) show S. geographicus at the base, as sister taxon to all remaining erymnochelyin turtles. This position is in agreement with the hypothesis presented by Meylan et al. (8) for C. tridentata (now S. geographicus), based on a relatively different character-taxon matrix. Jointly considering all these lines of evidence, we hypothesize that the skull of C. tridentata and the lower jaws described here together correspond to the skull of S. geographicus. It is thus both telling and fitting that turtle expert Eugene Gaffney, when supervising the exhibit of the reconstructed skeleton of S. geographicus at the American Museum of Natural History in New York, provided the skull of Caninemys for that model.

The measurements of the new specimens are given in fig. S2 and table S2. Of particular interest is the new S. geographicus specimen CIAAP-2002-01 that we describe here. With its 286 cm parasagittal straight carapace length, it is not only the largest known specimen for this taxon but also the largest turtle shell found to date, considering that the hitherto largest known specimen is the so-called Vienna specimen of the turtle A. ischyros (NHMW-1977/1902/0001) with a shell length of 220 cm (19). Among Asian trionychids, giant forms have been reported from the Eocene of Pakistan, some reaching up to 2 m in shell length (20). Badam (21) reported on giant tortoises from the Pliocene of India that, based on reconstructed shell fragments, may have been larger than 3 m in carapace length.

We estimated the body mass using the straight carapace length method (see data file S1) (22). For the largest specimen, CIAAP-2002-01, we obtained an estimate of 871 kg [compared to the 744 kg obtained by Iverson (22) for MCZ(P)-4376, previously the largest and most complete specimen]. However, in the case of S. geographicus, to compensate for the effect of the large nuchal embayment, calculating the body mass estimate as the average between estimations based on the carapace midline and parasagittal lengths likely yields a more precise body mass estimate. Doing this results in a body mass estimate of 1145 kg for the CIAAP-2002-01 specimen.

The thin section of AMU-CURS-233 (Fig. 3, L to P) reveals an overall dense microanatomy with a central medullary region completely filled by cancellous bone, surrounded by a transitional zone with regular formed smaller spaces, which leads into a compact, external cortex. Because of erosion of the femur surface, the external-most layers of the bone are visible only in a few places.

The cortical tissue is increasingly dense toward the outer bone surface (Fig. 3M). The deeper parts of the cortex show a dense Haversian bone (Fig. 3N), consisting mostly of longitudinally arranged or slightly angled secondary osteons. In the more surficial parts of the cortex, remodeling into dense Haversian bone is prominent, but remnants of primary parallel-fibered bone matrix with numerous longitudinally arranged primary osteons are still present. In these remnants, cell lacunae are more irregular or of a roundish shape. The cortex also does not reveal growth marks that could be counted, with the exception of a single spot in the external-most cortical fragment that splits off from the main section due to delamination processes and gypsum growth. In this outermost-cortical layer, a few closely spaced lines (five lines?), interpreted as lines of arrested growth (LAGs), form an outer circumferential layer.

The cancellous bone in the center of the section (Fig. 3O) consists of short bone trabeculae and few irregular larger intertrabecular spaces. The trabeculae are secondarily remodeled and consist of lamellar bone.

The transitional bone (Fig. 3P) does not have distinct margins but is a zone of decreasing size of individual extravascular spaces and increasing bone compactness. Vascularization of the tissue is found in the form of longitudinally arranged osteons and only few circumferentially oriented ones. Remodeling by secondary osteons is extensive so that only interstitial pockets of primary parallel-fibered bone tissue are discernible. The overall bone compactness is 0.873, with modeled values at the center of 0.543 and at the periphery of 0.97 (see data file S2).

In vertebrates, different body parts have independently evolved into protruding structures that are associated with a wide variety of purposes, e.g., defense or attack, mating, display, communication, or thermoregulation. Some of the most remarkable of these structures include horns, antlers, spikes, spurs, plates, tail clubs, and tusks (2325). In turtles, a notable example is the posterolateral horns of the skull of the extinct meiolaniids (26, 27). Most examples, though, are connected to their shell, covering a diversity of types. Knobby ridges can be found on the carapaces of the extant matamata Chelus fimbriatus (28) and the alligator snapping turtle Macrochelys temminckii (29) and the extinct stem turtle Proganochelys quenstedti possessed serrations along the posterior shell margin (30). Among other examples, the extant spiny turtle Heosemys spinosa has peripherals with marginal spines (31) that disappear ontogenetically, and many groups of testudinid tortoises have highly lobulated and protruded anterior and posterior peripherals or anterior plastron edges (32). Horn-like structures at the anterolateral margin of the carapace, such as those we report here for S. geographicus, have previously only been documented in the Cretaceous nanhsiungchelyid Anomalochelys angulata (see fig. S8) (33). For this medium-sized (~65-cm straight parasagittal carapace length) extinct terrestrial turtle, one interpretation of the horns purpose was proposed as the protection of a large skull.

This hypothesis may also apply for S. geographicus, considering that we here interpret the massive skull DNPM-MCT-1496-R as its head. This specimen was previously described as C. tridentata, and it had lower jaws, which in several morphological aspects resemble the lower jaw of the extant South American big-headed turtle P. dumerilianus (Fig. 5 and the Supplementary Materials), including an acute symphyseal tip. Another feature that supports the robustness of the head of S. geographicus is the posterolateral opening of the fossa Meckelii in the newly recovered lower jaws described here (AMU-CURS-706 and VPPLT-979), implying a large main adductor tendon and associated musculature (17).

The occurrence of deep grooves in the massive horns of all three new specimens of S. geographicus from Urumaco described here (Fig. 1, C and D, and the Supplementary Materials) indicates that they were true horns with a bony core covered by a keratinous sheath that was strongly attached via the grooves, similar to horns of extant artiodactyl bovid mammals (34), and has been argued for meiolanid horns (26).

If the horns were for protection, then why do several S. geographicus specimens lack horns? The anteroventrally facing orientation of the horns is a distinct feature, suggesting that potentially they were exclusively used not only for protection but also for combat. We therefore hypothesize that the horned shells from Venezuela described here represent males of S. geographicus and that the horns served the main purpose of weapons in male-male combat behaviors. This hypothesis is consistent with the occurrence of similar structures in males of other groups of vertebrates, for example, in artiodactyl mammals (23, 34). In addition, in snapping turtles (Chelydridae), some of the largest extant freshwater turtles, males that occupy overlapping areas often establish dominance through fights (35). The elongated and deep scar in the left horn of CIAAP-2002-01 (see the Supplementary Materials) could be interpreted as a mark resulting from combat between males. Many extant tortoises use their protruding epiplastral horns for combat, often with the goal of flipping the opponent (3638).

The putative S. geographicus males would also have been larger than females (see table S1), a pattern similar to that documented in the closely related extant taxon P. dumerilianus, which exhibits a male-biased sexual size dimorphism (39). Other sexually dimorphic traits of the turtle shell, such as a xiphiplastral concavity in males, or a deeper anal notch in males than in females (40, 41), are not distinct in S. geographicus, at least from a comparison between the specimens AMU-CURS-1098 (attributed to a male) and MPV-0001 (attributed to a female).

The climate and the productivity of the environment, habitat size, and predation-competition interactions are some of the factors usually considered as triggers or in favor of gigantism (42, 43). We hypothesize that in the case of S. geographicus, a combination of several factors favored the evolution of its large size.

Habitat size, both in terms of individuals (home ranges large enough to sustain giant body sizes) and in terms of populations (species distribution ranges that can sustain long-term viable populations), was surely a major determinant. During the Paleogene and until the late Miocene [~66 to 5 million years (Ma)], after the retreat of the dominant marine conditions of the Cretaceous, northern South America harbored the most extensive freshwater and littoral ecosystems in its geological history. The coverage reached a particular peak during the Miocene, with the development of a large wetland and lake system known as the Pebas system (44), which offered not only increased connectivity between habitats but also the opportunity for the diversification and migration of faunas, including turtles. It seems that the size of these wetland habitats in northern South America during the Miocene facilitated the occurrence of gigantism not only in turtles (this study) but also in several vertebrate lineages such as crocodylians (Fig. 6 and table S3) and rodents (35).

Deep-sea benthic foraminifer oxygen isotope curve for 0 to 23 Ma, redraw from Zachos et al. (46), showing major global climatic events (left). Major geological and geographical events for northern South America (light brown bars). Maximum skull or lower jaw (green values) and carapace (black values) for turtles and crocodylians from northern South American fossil sites. Formations are represented by yellow stars: 1, Barzalosa Fm., early Miocene, Colombia; 2, Castillo Fm., early Miocene, Venezuela; 3, Castilletes Fm., early-middle Miocene, Colombia; 4, La Victoria and Villavieja Fms., middle-late Miocene, Colombia; 5, Pebas Fm., middle Miocen, Peru; 6, Urumaco Fm., late Miocne, Venezuela; 7, Madre de Dios and Ipururo Fms., late Miocene, Brazil; 8, Pisco Fm., late Miocene, Peru; 9, Solimes Fm., late Miocene-Pliocene, Brazil; 10, San Gregorio Fm., early Pliocene, Venezuela; 11, Ware Fm., Pliocene-Pleistocene, Colombia; 12, Mesa Fm., Pleistocene, Venezuela. Carap, carapace; MMCO, middle Miocene climatic optimum; MMCT, middle Miocene climatic transition; Magda, Magdalena; Pleist; Pleistocene. Detailed information on localities, specimens, and sources are in table S3.

Predation interactions could have also been involved in the evolution of large body size in S. geographicus, as it shared its habitat with gigantic crocodylians, including Purussaurus spp. and Gryposuchus spp., which could reach up to 10 m or more in body length. There is direct evidence of interactions between S. geographicus and large South American crocodylians, in the form of bite marks in Colombian and Venezuelan specimens, and an isolated tooth attached on the ventral surface of the carapace in the CIAAP-2002-01 specimen (see fig. S3).

Climate, particularly warmer temperatures, could have been a potential factor favoring the evolution of large body size in Miocene South American reptiles. For example, this causal link has been inferred for the Paleocene fauna of Cerrejn, Colombia, which includes the largest snake ever, Titanoboa cerrejonensis (2), and the largest Paleogene pelomedusoid turtles and crocodylians (12, 45). Although less warm than the Paleocene and the Eocene, the Miocene was also an epoch with notable climatic events that could have affected the body size of neotropical animal species, for example, the warm middle Miocene climatic optimum (MMCO) (46, 47), the global cooling between ~15 and 13 Ma known as middle Miocene climatic transition (MMCT), and continuous decreasing of global temperature during the late Miocene (48). The time range so far known for S. geographicus (middle Miocene to late Miocene) (this study) indicates that this taxon overcame the MMCT event. It exhibited a gigantic (and potentially its maximum) size during global cooling times (late Miocene) (Fig. 6). The latter rules out a direct and rather unlikely simple effect of climate on gigantism in neotropical Miocene reptiles. Thermally imposed upper limits to body mass are more likely than a simple tracking of changing temperature in body size evolution (49). Unfortunately, the climatic conditions of terrestrial ecosystems during the Miocene in tropical South America are still poorly known, and better reconstructions of climatic conditions await information from geochemical analyses of paleosols and carbonate isotopes. In addition, for neotropical faunas in general and reptiles in particular, the considerable gap in the South American Eocene and Oligocene fossil record is a major obstacle to a clear understanding of the effect of these climatic events on body size trends through time. It is therefore currently impossible to track the evolutionary path of evolution of body size that started during the Paleocene in detail or to establish whether body sizes of late Eocene and Oligocene neotropical reptiles remained large or decreased due, in part, to other cooling events such as the late Eocene-Oligocene transition from greenhouse to icehouse. To test the existence of a passive or driven trend in body size evolution (50), better sampling of the neotropical fossil record is needed. Both internal or external factors could be associated with such trends (51), and discoveries such as that reported here provide the primary evidence with which to start to understand the range of possibilities in morphospace occupation.

Turtles are a particularly challenging group when it comes to the identification of potential causal correlates in body size evolution, given the atypical patterns in relation to latitude they show in body size and in geographic range (52), as opposed to major tendencies identified for other vertebrate groups.

Last, the phylogenetic framework is likely an additional important factor, given the association of biological attributes such as body size and physiology to clades. Teasing out the relative importance of physiological boundaries related to clades is currently equally limited by the Eocene and Oligocene gap in neotropical faunas. For example, the large body size of S. geographicus could be an inherited ancestral trait, rooted in the Paleocene forms from Cerrejn, Colombia [Carbonemys cofrinii and its potential shell, Pelomedusoides indet. (12)]. Our phylogenetic analysis (Fig. 5) supports the view that S. geographicus and Ca. cofrinii both belong to the Erymnochelyinae clade but not as closely related taxa. What is clear is that at least two separate clades inside Podocnemididae exhibited large body size during the Miocene: one including S. geographicus and another with P. bassleri (15) (15.7-cm skull length, potentially 2 m carapace length) in the line of Podocnemis group. In other turtle clades of the neotropics, this trend is represented by Chelonoidis sp. (1 m carapace length estimate) inside the terrestrial Testudinidae and Chelus colombianus (70 cm carapace length estimate) within the freshwater-inhabitant Chelidae (Fig. 6).

Adding to the previously known records of S. geographicus from Urumaco and Acre (68, 13, 17), we here report the first occurrence of this taxon in the well-known fauna of La Venta, Tatacoa Desert. This notably expands the known distribution of S. geographicus, highlighting that it likely was a common taxon throughout the entire Pebas system, well adapted to both fluvial conditions (La Venta and Acre) and fluvial-littoral conditions (Urumaco) (Fig. 5C). It is likely that the changes in the configuration of the Pebas and the posterior Acre systems due to the uplifting of the Andes starting in the middle Miocene (ca. 12.5 Ma) (53) (Fig. 6) had a deep impact on the populations of S. geographicus, considerably reducing their habitat size and leading to its final extinction, probably during the early Pliocene.

Taking into account the morphology of the massive skull elements (skull and lower jaws, Fig. 4D) of S. geographicus, Meylan et al. (8) interpreted this turtle as a pleurodiran snapping turtle, involving a vacuum feeding system and capable of capturing and holding prey of very large size, including fish, small caimanines, and snakes. In this questionable interpretation, it was a carnivore much like the extant cryptodires Macrochelys, Claudius, and Staurotypus, which also exhibit a depression in the upper triturating surface and have lower jaws with a well-developed symphyseal hook (8). The very acute symphysial end and wider anteromedial triturating surface of the well-preserved jaw (VPPLT 979 specimen) from La Tatacoa described here indicate that S. geographicus may have had a diet much broader than one consisting of the abovementioned vertebrate preys. It could have had a more diverse diet. For example, it could have had a generally durophagous diet, crushing hard-shelled prey such as mollusks with the help of its large triturating surface and facilitated by its large main adductor tendon and associated musculature. Increasing the diet niche breadth would have favored maintaining a very large body size in this turtle, resulting in a body sizeenvironment productivity correspondence (42).

Another previously underestimated aspect of paleodiet is the potential of large extinct turtles having acted as seed dispersers for many plant species. A recent review of frugivory and seed dispersal in extant turtles (54) highlighted that many species consume fruits, and thus potentially disperse the seeds, even if fruits are not considered part of their standard diet. Seasonally, high-energy fruits from, e.g., palms (Araceae) can even form the major part of Amazonian turtles diets. This is the case for the closest extant relative of S. geographicus, the big-headed Amazon river turtle, P. dumerilianus, where (55) found that fruits and seeds formed the most diverse component of its stomach contents and that palm seeds were the most common item (55).

Because of its huge gape size, S. geographicus could have swallowed even the largest South American fruits and thus qualify as a megafaunal frugivore and seed disperser [sensu (56)]. In general, larger turtles also include more fruits in their diet than do smaller ones; for example, in the extant Asian big-headed turtle, Platysternon megacephalum, there is a positive relationship between body size and amount of fruit in their diet (57). Overall, S. geographicus could thus have been a highly efficient seed disperser [sensu (58)].

As with the previously analyzed shell bones of S. geographicus (from CIAAP-2002-01) (59), our histological analysis of the femur did not reveal anything unusual about Stupendemys growth, only that it is overall comparable to the microanatomical build and the histology of smaller turtles. The high amount of Haversian bone in the femur fragment might be related to the giant size as pointed out by Foote (60) or by advanced age of a skeletally mature specimen, as is tentatively indicated by the tightly spaced LAGs in the outer circumferential layer. The estimated compactness values of AMU-CURS-233 are comparable to those of other aquatic, nonmarine turtles (61).

We see the almost universal conserved arrangement of scutes of turtles in the gigantic specimen described here, emphasizing how the developmental program of turtles (62) results in early differentiation in which prolonged growth does not result in changes in epidermal structures. S. geographicus probably lived for at least 110 years to be able to reach the largest recorded size we report here, assuming a growth rate similar to that of extant, large turtles (59).

The fossils referred here are in the collections of American Museum of Natural History, New York, USA; Alcada Bolivariana de Urumaco, Urumaco, Falcn State, Venezuela (AMU-CURS); Centro de Investigaciones Antropolgicas, Arqueolgicas y Palentolgicas (CIAAP) of the Universidad Nacional Experimental Francisco de Miranda, Coro, Falcn State, Venezuela; Departmento Nacional de Produa Mineral, Divisa de Geologia e Mineralogia, Cincias da Terra, Rio de Janeiro, Brazil (DNPM-MCT); The Geological Museum, Geology Survey Institute, Bandung, Indonesia (K); Natural History Museum of Los Angeles, Los Angeles, USA (LACM); Museo de Ciencias Naturales de Caracas, Caracas, Venezuela (MCNC); Museum of Comparative Zoology-Harvard University, Cambridge, USA [MCZ(P)]; Museo Paleontolgico de Villavieja, Villavieja, Huila Department, Colombia (MPV); Naturhistorisches Museum Wien, Vienna, Austria (NHMW); Universidad Simn Bolvar, Caracas, Venezuela (OL; specimens housed in the Museo Paleontgico de Urumaco); and Museo de Historia Natural La Tatacoa, La Victoria, Huila Department, Colombia (VPPLT).

To explore the phylogenetic position of S. geographicus, three separate maximum parsimony analyses were run using PAUP 4.0 (63) and using the character-taxon matrix of Ferreira et al. (18) as the original template with some modifications (see the Supplementary Materials). For all the analyses, Pr. quenstedti, Notoemys laticentralis, and Platychelys oberndorferi comprised the outgroup taxa; all the 245 characters were considered equally weighted, and multistate states were treated as polymorphic. Heuristic search, random search for 10,000 replicates, and tree-bisection reconnection option were performed, seed 1000, holding one tree per replicate and collapse branches if minimum length is zero. Strict consensus trees and their decay index (Bremer support) were also obtained. For the first analysis, we considered each of the three giant lower jaws from Acre (17), Urumaco, and La Venta (described here) as separate taxa, as well as C. tridentata (8) and S. geographicus, with the addition of information from previous and the new specimens described here. A second analysis considering the lower jaw LACM-141498 from Acre as belonging to C. tridentata as considered originally by Meylan et al. (8) and the lower jaws AMU-CURS-706 from Urumaco and VPPLT-979 from La Tatacoa as belonging to S. geographicus was performed. For the third analysis, we considered a single taxon, S. geographicus, formed by the new and previously described S. geographicus shells and postcrania; the three lower jaws from Acre, Urumaco, and La Tatacoa; and the skull of C. tridentata (see fig. S7). Twelve morphocline characters were treated as ordered characters (14, 18, 19, 71, 95, 96, 99, 101, 119, 129, 174, and 175) following Ferreira et al. (18). Results are also presented in a time-calibrated cladogram of South American Erymnochelyinae turtles (Fig. 5B) based on this and previous studies (12, 64).

Body mass estimation of S. geographicus and some other taxa mentioned in table S1 was obtained using the correspondence between carapace length and body mass reported by Iverson (22) in extant representative of all lineages of turtles. Specifically, we used the general allometric equation y = axb, where y is the body mass (in grams), x is the carapace length (in centimeters), and a and b are the correlation coefficients established for each of the taxa (see the Supplementary Materials) (22). Considering that none of the taxa included in this study were part of Iversons study, we used the coefficients of the closest phylogenetic and/or similar lifestyle representative, for example, in the case of S. geographicus as it was also used by Iverson (22), we used the coefficients established for Podocnemis unifilis; for A. ischyros and D. coriacea (both marine turtles), we used the coefficients of Chelonia mydas; for Megalochelys sivalensis and Chelonoidis niger (both tortoises), we used the coefficients of Geochelone elegans; and for Rafetus swinhoei (freshwater soft-shelled turtle), we used the coeficientes of Apalone (Trionyx) spinifera.

We sectioned a shaft fragment of a femur of S. geographicus (AMU-CURS-233) recovered from a site next to the gas pipeline at El Mamn locality, Urumaco, Falcn state, Venezuela (11131.46N; 701651.2W). The shaft section was roughly oval shaped, with the longest axis of 8 cm and a perpendicular shorter axis of 6.2 cm. The bone was cut with an iron hand saw and processed afterward, following standard petrographic thin-sectioning procedures (65). The thin section was studied and analyzed using a compound microscope (DM 2500M, Leica) with a digital camera (DFC 420C, Leica). Comparative material of S. geographicus included already published shell bone sections (59), and overall bone compactness was calculated using Bone Profiler software (66).

We plotted the largest as-preserved or estimated length of skull, lower jaw, and/or carapace of turtles and crocodylians from each of the neotropical Neogene to Quaternary fossil sites, putting them in context with the global climatic curve of Zachos et al. (46) and the major geological and geographical events of northern South America. We included the following lineages of turtles: Erymnochelyinae, Podocnemidinae, Chelidae, and Testudinidae, and for the crocodylians: Alligatoridae, Gavialidae, and Crocodylidae (Fig. 6, fig. S9, and table S3), adding also the largest reported extant representatives. We excluded from this plot very recently immigrant lineages of turtles: Geoemydidae, Kinosternidae, Emydidae, and Chelydridae, and turtles that occasionally reached South America, for example, Trionychidae, as well as sea turtles and the extant Galpagos tortoises (gigantism due to phylogenetic history and island isolation). The extremely fragmentary Charactosuchus spp. were also excluded considering that they are still controversial if they are truly members of Crocodylidae (67).

Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/7/eaay4593/DC1

Supplementary Text

Fig. S1. S. geographicus CIAAP-2002-01 details.

Fig. S2. Outlines and indication of the measurements of the new specimens described here and reported in tables S1 and S2.

Fig. S3. S. geographicus CIAAP-2002-01 carapace.

Fig. S4. AMU-CURS-85 carapace of S. geographicus from Venezuela.

Fig. S5. Details of S. geographicus AMU-CURS-1098 from Venezuela.

Fig. S6. Lower jaws of S. geographicus from Venezuela, Colombia, and extant podocnemidids.

Fig. S7. Additional strict consensus trees.

Fig. S8. A. angulata from the Cretaceous of Japan.

Fig. S9. Phylogeny versus skulllower jaw length for Miocene neotropical crocodylians.

Table S1. Measurements and body mass estimation for S. geographicus and other extant and extinct giant turtles as preserved in centimeters and kilograms.

Table S2. Specific measurements and thickness (see fig. S2) of new specimens of S. geographicus.

Table S3. Data on size for the Neogene to extant neotropical turtles and crocodylians.

Data file S1. Body mass estimation calculations.

Data file S2. Bone compactness calculations using Bone Profiler.

Data file S3. Character-taxon matrix Nexus file raw data.

Data file S4. Character-taxon matrix Nexus file final version.

Movie S1. Video of CIAAP-2002-01 specimen.

Movie S2. Video of the excavation of AMU-CURS-85 specimen.

References (6893)

Acknowledgments: We are indebted to D. Gutirrez and F. Parra for helping with the preparation of fossil specimens and collaboration in fieldwork. We thank R. Hirayama for color photos of Anomalochelys; M. Clauss for discussion on the early stages of this work; and editors J. Jackson and D. Erwin, reviewer W. Joyce, and an anonymous reviewer for input to improve this paper. We thank the curators and museum staff of the following institutions for permits and access to collections and specimens: American Museum of Natural History; Alcada Bolivariana de Urumaco; Chelonian Research Institute; Instituto de Ciencias Naturales Universidad Nacional de Colombia; Instituto del Patrimonio Cultural de Venezuela; Museo Paleontolgico de Urumaco; Centro de Investigaciones Antropolgicas, Arqueolgicas y Paleontolgicas de la Universidad Experimental Francisco de Miranda; Museo de Ciencias Naturales de Caracas; Museum of Comparative Zoology-Harvard University; Museo Paleontolgico de Villavieja; Museo de Historia Natural La Tatacoa; Naturhistorisches Museum Wien; Servicio Geolgico Colombiano; Divisa de Geologia e Mineralogia Museu de Cincias da Terra do Rio de Janeiro; Smithsonian Natural History Museum Collections; and University of Florida Herpetology Collection. We thank H. Moreno, C. Morn, G. Ojeda, A. Blanco, A. Reyes-Cespedes, J. Hernndez, and the communities of Urumaco and La Victoria for their valuable assistance. We thank the Brazilian Council of Science and Technological Development (productivity researches 305269/2017-8). We thank J. Moreno for information on some fossil crocodylians. Funding: This research was funded by grant 40215 from the National Geographic SocietyWaitt Foundation Grants Program and the Vicerrectora Universidad del Rosario. Author contributions: R.S., O.A.A.-S., M.P., A.V., M.R.S.-V., J.D.C.-B., and E.-A.C. collected the fossils. E.-A.C. and T.M.S. designed the study. E.-A.C., T.M.S., M.R.S.-V., and J.D.C.-B., collected data, made comparisons, and wrote the paper. All authors gave final approval for publication. Competing interests: The authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors.

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The anatomy, paleobiology, and evolutionary relationships of the largest extinct side-necked turtle - Science Advances

Bones are an important part of the musculoskeletal system. This article, the first in a two-part series on the skeletal system, reviews the anatomy and physiology of bone

The skeletal system is formed of bones and cartilage, which are connected by ligaments to form a framework for the remainder of the body tissues. This article, the first in a two-part series on the structure and function of the skeletal system, reviews the anatomy and physiology of bone. Understanding the structure and purpose of the bone allows nurses to understand common pathophysiology and consider the most-appropriate steps to improve musculoskeletal health.

Citation: Walker J (2020) Skeletal system 1: the anatomy and physiology of bones. Nursing Times [online]; 116: 2, 38-42.

Author: Jennie Walker is principal lecturer, Nottingham Trent University.

The skeletal system is composed of bones and cartilage connected by ligaments to form a framework for the rest of the body tissues. There are two parts to the skeleton:

As well as contributing to the bodys overall shape, the skeletal system has several key functions, including:

Bones are a site of attachment for ligaments and tendons, providing a skeletal framework that can produce movement through the coordinated use of levers, muscles, tendons and ligaments. The bones act as levers, while the muscles generate the forces responsible for moving the bones.

Bones provide protective boundaries for soft organs: the cranium around the brain, the vertebral column surrounding the spinal cord, the ribcage containing the heart and lungs, and the pelvis protecting the urogenital organs.

As the main reservoirs for minerals in the body, bones contain approximately 99% of the bodys calcium, 85% of its phosphate and 50% of its magnesium (Bartl and Bartl, 2017). They are essential in maintaining homoeostasis of minerals in the blood with minerals stored in the bone are released in response to the bodys demands, with levels maintained and regulated by hormones, such as parathyroid hormone.

Blood cells are formed from haemopoietic stem cells present in red bone marrow. Babies are born with only red bone marrow; over time this is replaced by yellow marrow due to a decrease in erythropoietin, the hormone responsible for stimulating the production of erythrocytes (red blood cells) in the bone marrow. By adulthood, the amount of red marrow has halved, and this reduces further to around 30% in older age (Robson and Syndercombe Court, 2018).

Yellow bone marrow (Fig 1) acts as a potential energy reserve for the body; it consists largely of adipose cells, which store triglycerides (a type of lipid that occurs naturally in the blood) (Tortora and Derrickson, 2009).

Bone matrix has three main components:

Organic matrix (osteoid) is made up of approximately 90% type-I collagen fibres and 10% other proteins, such as glycoprotein, osteocalcin, and proteoglycans (Bartl and Bartl, 2017). It forms the framework for bones, which are hardened through the deposit of the calcium and other minerals around the fibres (Robson and Syndercombe Court, 2018).

Mineral salts are first deposited between the gaps in the collagen layers with once these spaces are filled, minerals accumulate around the collagen fibres, crystallising and causing the tissue to harden; this process is called ossification (Tortora and Derrickson, 2009). The hardness of the bone depends on the type and quantity of the minerals available for the body to use; hydroxyapatite is one of the main minerals present in bones.

While bones need sufficient minerals to strengthen them, they also need to prevent being broken by maintaining sufficient flexibility to withstand the daily forces exerted on them. This flexibility and tensile strength of bone is derived from the collagen fibres. Over-mineralisation of the fibres or impaired collagen production can increase the brittleness of bones as with the genetic disorder osteogenesis imperfecta and increase bone fragility (Ralston and McInnes, 2014).

Bone architecture is made up of two types of bone tissue:

Also known as compact bone, this dense outer layer provides support and protection for the inner cancellous structure. Cortical bone comprises three elements:

The periosteum is a tough, fibrous outer membrane. It is highly vascular and almost completely covers the bone, except for the surfaces that form joints; these are covered by hyaline cartilage. Tendons and ligaments attach to the outer layer of the periosteum, whereas the inner layer contains osteoblasts (bone-forming cells) and osteoclasts (bone-resorbing cells) responsible for bone remodelling.

The function of the periosteum is to:

It also contains Volkmanns canals, small channels running perpendicular to the diaphysis of the bone (Fig 1); these convey blood vessels, lymph vessels and nerves from the periosteal surface through to the intracortical layer. The periosteum has numerous sensory fibres, so bone injuries (such as fractures or tumours) can be extremely painful (Drake et al, 2019).

The intracortical bone is organised into structural units, referred to as osteons or Haversian systems (Fig 2). These are cylindrical structures, composed of concentric layers of bone called lamellae, whose structure contributes to the strength of the cortical bone. Osteocytes (mature bone cells) sit in the small spaces between the concentric layers of lamellae, which are known as lacunae. Canaliculi are microscopic canals between the lacunae, in which the osteocytes are networked to each other by filamentous extensions. In the centre of each osteon is a central (Haversian) canal through which the blood vessels, lymph vessels and nerves pass. These central canals tend to run parallel to the axis of the bone; Volkmanns canals connect adjacent osteons and the blood vessels of the central canals with the periosteum.

The endosteum consists of a thin layer of connective tissue that lines the inside of the cortical surface (Bartl and Bartl, 2017) (Fig1).

Also known as spongy bone, cancellous bone is found in the outer cortical layer. It is formed of lamellae arranged in an irregular lattice structure of trabeculae, which gives a honeycomb appearance. The large gaps between the trabeculae help make the bones lighter, and so easier to mobilise.

Trabeculae are characteristically oriented along the lines of stress to help resist forces and reduce the risk of fracture (Tortora and Derrickson, 2009). The closer the trabecular structures are spaced, the greater the stability and structure of the bone (Bartl and Bartl, 2017). Red or yellow bone marrow exists in these spaces (Robson and Syndercombe Court, 2018). Red bone marrow in adults is found in the ribs, sternum, vertebrae and ends of long bones (Tortora and Derrickson, 2009); it is haemopoietic tissue, which produces erythrocytes, leucocytes (white blood cells) and platelets.

Bone and marrow are highly vascularised and account for approximately 10-20% of cardiac output (Bartl and Bartl, 2017). Blood vessels in bone are necessary for nearly all skeletal functions, including the delivery of oxygen and nutrients, homoeostasis and repair (Tomlinson and Silva, 2013). The blood supply in long bones is derived from the nutrient artery and the periosteal, epiphyseal and metaphyseal arteries (Iyer, 2019).

Each artery is also accompanied by nerve fibres, which branch into the marrow cavities. Arteries are the main source of blood and nutrients for long bones, entering through the nutrient foramen, then dividing into ascending and descending branches. The ends of long bones are supplied by the metaphyseal and epiphyseal arteries, which arise from the arteries from the associated joint (Bartl and Bartl, 2017).

If the blood supply to bone is disrupted, it can result in the death of bone tissue (osteonecrosis). A common example is following a fracture to the femoral neck, which disrupts the blood supply to the femoral head and causes the bone tissue to become necrotic. The femoral head structure then collapses, causing pain and dysfunction.

Bones begin to form in utero in the first eight weeks following fertilisation (Moini, 2019). The embryonic skeleton is first formed of mesenchyme (connective tissue) structures; this primitive skeleton is referred to as the skeletal template. These structures are then developed into bone, either through intramembranous ossification or endochondral ossification (replacing cartilage with bone).

Bones are classified according to their shape (Box1). Flat bones develop from membrane (membrane models) and sesamoid bones from tendon (tendon models) (Waugh and Grant, 2018). The term intra-membranous ossification describes the direct conversion of mesenchyme structures to bone, in which the fibrous tissues become ossified as the mesenchymal stem cells differentiate into osteoblasts. The osteoblasts then start to lay down bone matrix, which becomes ossified to form new bone.

Box 1. Types of bones

Long bones typically longer than they are wide (such as humerus, radius, tibia, femur), they comprise a diaphysis (shaft) and epiphyses at the distal and proximal ends, joining at the metaphysis. In growing bone, this is the site where growth occurs and is known as the epiphyseal growth plate. Most long bones are located in the appendicular skeleton and function as levers to produce movement

Short bones small and roughly cube-shaped, these contain mainly cancellous bone, with a thin outer layer of cortical bone (such as the bones in the hands and tarsal bones in the feet)

Flat bones thin and usually slightly curved, typically containing a thin layer of cancellous bone surrounded by cortical bone (examples include the skull, ribs and scapula). Most are located in the axial skeleton and offer protection to underlying structures

Irregular bones bones that do not fit in other categories because they have a range of different characteristics. They are formed of cancellous bone, with an outer layer of cortical bone (for example, the vertebrae and the pelvis)

Sesamoid bones round or oval bones (such as the patella), which develop in tendons

Long, short and irregular bones develop from an initial model of hyaline cartilage (cartilage models). Once the cartilage model has been formed, the osteoblasts gradually replace the cartilage with bone matrix through endochondral ossification (Robson and Syndercombe Court, 2018). Mineralisation starts at the centre of the cartilage structure, which is known as the primary ossification centre. Secondary ossification centres also form at the epiphyses (epiphyseal growth plates) (Danning, 2019). The epiphyseal growth plate is composed of hyaline cartilage and has four regions (Fig3):

Resting or quiescent zone situated closest to the epiphysis, this is composed of small scattered chondrocytes with a low proliferation rate and anchors the growth plate to the epiphysis;

Growth or proliferation zone this area has larger chondrocytes, arranged like stacks of coins, which divide and are responsible for the longitudinal growth of the bone;

Hypertrophic zone this consists of large maturing chondrocytes, which migrate towards the metaphysis. There is no new growth at this layer;

Calcification zone this final zone of the growth plate is only a few cells thick. Through the process of endochondral ossification, the cells in this zone become ossified and form part of the new diaphysis (Tortora and Derrickson, 2009).

Bones are not fully developed at birth, and continue to form until skeletal maturity is reached. By the end of adolescence around 90% of adult bone is formed and skeletal maturity occurs at around 20-25 years, although this can vary depending on geographical location and socio-economic conditions; for example, malnutrition may delay bone maturity (Drake et al, 2019; Bartl and Bartl, 2017). In rare cases, a genetic mutation can disrupt cartilage development, and therefore the development of bone. This can result in reduced growth and short stature and is known as achondroplasia.

The human growth hormone (somatotropin) is the main stimulus for growth at the epiphyseal growth plates. During puberty, levels of sex hormones (oestrogen and testosterone) increase, which stops cell division within the growth plate. As the chondrocytes in the proliferation zone stop dividing, the growth plate thins and eventually calcifies, and longitudinal bone growth stops (Ralston and McInnes, 2014). Males are on average taller than females because male puberty tends to occur later, so male bones have more time to grow (Waugh and Grant, 2018). Over-secretion of human growth hormone during childhood can produce gigantism, whereby the person is taller and heavier than usually expected, while over-secretion in adults results in a condition called acromegaly.

If there is a fracture in the epiphyseal growth plate while bones are still growing, this can subsequently inhibit bone growth, resulting in reduced bone formation and the bone being shorter. It may also cause misalignment of the joint surfaces and cause a predisposition to developing secondary arthritis later in life. A discrepancy in leg length can lead to pelvic obliquity, with subsequent scoliosis caused by trying to compensate for the difference.

Once bone has formed and matured, it undergoes constant remodelling by osteoclasts and osteoblasts, whereby old bone tissue is replaced by new bone tissue (Fig4). Bone remodelling has several functions, including mobilisation of calcium and other minerals from the skeletal tissue to maintain serum homoeostasis, replacing old tissue and repairing damaged bone, as well as helping the body adapt to different forces, loads and stress applied to the skeleton.

Calcium plays a significant role in the body and is required for muscle contraction, nerve conduction, cell division and blood coagulation. As only 1% of the bodys calcium is in the blood, the skeleton acts as storage facility, releasing calcium in response to the bodys demands. Serum calcium levels are tightly regulated by two hormones, which work antagonistically to maintain homoeostasis. Calcitonin facilitates the deposition of calcium to bone, lowering the serum levels, whereas the parathyroid hormone stimulates the release of calcium from bone, raising the serum calcium levels.

Osteoclasts are large multinucleated cells typically found at sites where there is active bone growth, repair or remodelling, such as around the periosteum, within the endosteum and in the removal of calluses formed during fracture healing (Waugh and Grant, 2018). The osteoclast cell membrane has numerous folds that face the surface of the bone and osteoclasts break down bone tissue by secreting lysosomal enzymes and acids into the space between the ruffled membrane (Robson and Syndercombe Court, 2018). These enzymes dissolve the minerals and some of the bone matrix. The minerals are released from the bone matrix into the extracellular space and the rest of the matrix is phagocytosed and metabolised in the cytoplasm of the osteoclasts (Bartl and Bartl, 2017). Once the area of bone has been resorbed, the osteoclasts move on, while the osteoblasts move in to rebuild the bone matrix.

Osteoblasts synthesise collagen fibres and other organic components that make up the bone matrix. They also secrete alkaline phosphatase, which initiates calcification through the deposit of calcium and other minerals around the matrix (Robson and Syndercombe Court, 2018). As the osteoblasts deposit new bone tissue around themselves, they become trapped in pockets of bone called lacunae. Once this happens, the cells differentiate into osteocytes, which are mature bone cells that no longer secrete bone matrix.

The remodelling process is achieved through the balanced activity of osteoclasts and osteoblasts. If bone is built without the appropriate balance of osteocytes, it results in abnormally thick bone or bony spurs. Conversely, too much tissue loss or calcium depletion can lead to fragile bone that is more susceptible to fracture. The larger surface area of cancellous bones is associated with a higher remodelling rate than cortical bone (Bartl and Bartl, 2017), which means osteoporosis is more evident in bones with a high proportion of cancellous bone, such as the head/neck of femur or vertebral bones (Robson and Syndercombe Court, 2018). Changes in the remodelling balance may also occur due to pathological conditions, such as Pagets disease of bone, a condition characterised by focal areas of increased and disorganised bone remodelling affecting one or more bones. Typical features on X-ray include focal patches of lysis or sclerosis, cortical thickening, disorganised trabeculae and trabecular thickening.

As the body ages, bone may lose some of its strength and elasticity, making it more susceptible to fracture. This is due to the loss of mineral in the matrix and a reduction in the flexibility of the collagen.

Adequate intake of vitamins and minerals is essential for optimum bone formation and ongoing bone health. Two of the most important are calcium and vitamin D, but many others are needed to keep bones strong and healthy (Box2).

Box 2. Vitamins and minerals needed for bone health

Key nutritional requirements for bone health include minerals such as calcium and phosphorus, as well as smaller qualities of fluoride, manganese, and iron (Robson and Syndercombe Court, 2018). Calcium, phosphorus and vitamin D are essential for effective bone mineralisation. Vitamin D promotes calcium absorption in the intestines, and deficiency in calcium or vitamin D can predispose an individual to ineffective mineralisation and increased risk of developing conditions such as osteoporosis and osteomalacia.

Other key vitamins for healthy bones include vitamin A for osteoblast function and vitamin C for collagen synthesis (Waugh and Grant, 2018).

Physical exercise, in particular weight-bearing exercise, is important in maintaining or increasing bone mineral density and the overall quality and strength of the bone. This is because osteoblasts are stimulated by load-bearing exercise and so bones subjected to mechanical stresses undergo a higher rate of bone remodelling. Reduced skeletal loading is associated with an increased risk of developing osteoporosis (Robson and Syndercombe Court, 2018).

Bones are an important part of the musculoskeletal system and serve many core functions, as well as supporting the bodys structure and facilitating movement. Bone is a dynamic structure, which is continually remodelled in response to stresses placed on the body. Changes to this remodelling process, or inadequate intake of nutrients, can result in changes to bone structure that may predispose the body to increased risk of fracture. Part2 of this series will review the structure and function of the skeletal system.

Bartl R, Bartl C (2017) Structure and architecture of bone. In: Bone Disorder: Biology, Diagnosis, Prevention, Therapy.

Danning CL (2019) Structure and function of the musculoskeletal system. In: Banasik JL, Copstead L-EC (eds) Pathophysiology. St Louis, MO: Elsevier.

Drake RL et al (eds) (2019) Grays Anatomy for Students. London: Elsevier.

Iyer KM (2019) Anatomy of bone, fracture, and fracture healing. In: Iyer KM, Khan WS (eds) General Principles of Orthopedics and Trauma. London: Springer.

Moini J (2019) Bone tissues and the skeletal system. In: Anatomy and Physiology for Health Professionals. Burlington, MA: Jones and Bartlett.

Ralston SH, McInnes IB (2014) Rheumatology and bone disease. In: Walker BR et al (eds) Davidsons Principles and Practice of Medicine. Edinburgh: Churchill Livingstone.

Robson L, Syndercombe Court D (2018) Bone, muscle, skin and connective tissue. In: Naish J, Syndercombe Court D (eds) Medical Sciences. London: Elsevier

Tomlinson RE, Silva MJ (2013) Skeletal blood flow in bone repair and maintenance. Bone Research; 1: 4, 311-322.

Tortora GJ, Derrickson B (2009) The skeletal system: bone tissue. In: Principles of Anatomy and Physiology. Chichester: John Wiley & Sons.

Waugh A, Grant A (2018) The musculoskeletal system. In: Ross & Wilson Anatomy and Physiology in Health and Illness. London: Elsevier.

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Skeletal system 1: the anatomy and physiology of bones - Nursing Times