Were Dinosaurs Undergoing Long-Term Decline Before Mass Extinction?
ScienceDaily (May 1, 2012) — Despite years of intensive research about the extinction of non-avian dinosaurs about 65.5 million years ago, a fundamental question remains: were dinosaurs already undergoing a long-term decline before an asteroid hit at the end of the Cretaceous? A study led by scientists at the American Museum of Natural History gives a multifaceted answer.
The findings, published online May 1 in Nature Communications, suggest that in general, large-bodied, “bulk-feeding” herbivores were declining during the last 12 million years of the Cretaceous. But carnivorous dinosaurs and mid-sized herbivores were not. In some cases, geographic location might have been a factor in the animals’ biological success.
“Few issues in the history of paleontology have fueled as much research and popular fascination as the extinction of non-avian dinosaurs,” said lead author Steve Brusatte, a Columbia University graduate student affiliated with the Museum’s Division of Paleontology. “Did sudden volcanic eruptions or an asteroid impact strike down dinosaurs during their prime? We found that it was probably much more complex than that, and maybe not the sudden catastrophe that is often portrayed.”
The research team, which includes Brusatte; Mark Norell, chair of the Museum’s Division of Paleontology; and scientists Richard Butler of Ludwig Maximilian University of Munich and Albert Prieto-M‡rquez from the Bavarian State Collection for Palaeontology, both in Germany, is the first to look at dinosaur extinction based on “morphological disparity”-the variability of body structure within particular groups of dinosaurs. Previous research was based almost exclusively on estimates of changes in the number of dinosaur species over time. However, it can be very difficult to do this accurately.
“By looking just at trends in taxonomic diversity, you get conflicting answers about the state of dinosaurs prior to extinction,” Brusatte said. “This is because the results can be biased by uneven sampling of the fossil record. In places where more rock and fossils were formed, like in America’s Great Plains, you’ll find more species. We wanted to go beyond a simple species count for this study.”
By looking at the change in biodiversity within a given dinosaur group over time, researchers can create a rough snapshot of the animals’ overall well-being. This is because groups that show an increase in variability might have been evolving into more species, giving them an ecological edge. On the other hand, decreasing variability might be a warning sign of extinction in the long term.
The researchers calculated morphological disparity for seven major dinosaur groups using databases that include wide-ranging characteristics about the intricate skeletal structure of nearly 150 different species.
“People often think of dinosaurs as being monolithic-we say ‘The dinosaurs did this, and the dinosaurs did that,'” Butler said. “But dinosaurs were hugely diverse. There were hundreds of species living in the Late Cretaceous, and these differed enormously in diet, shape, and size. Different groups were probably evolving in different ways and the results of our study show that very clearly.”
The researchers found that hadrosaurs and ceratopsids, two groups of large-bodied, bulk-feeding herbivores-animals that did not feed selectively-may have experienced a decline in biodiversity in the 12 million years before the dinosaurs ultimately went extinct. In contrast, small herbivores (ankylosaurs and pachycephalosaurs), carnivorous dinosaurs (tyrannosaurs and coelurosaurs), and enormous herbivores without advanced chewing abilities (sauropods) remained relatively stable or even slightly increased in biodiversity.
As a complication, hadrosaurs showed different levels of disparity in different locations. While declining in North America, the disparity of this dinosaur group seems to have been increasing in Asia during the latest Cretaceous.
“These disparity calculations paint a more nuanced picture of the final 12 million years of dinosaur history,” Brusatte said. “Contrary to how things are often perceived, the Late Cretaceous wasn’t a static ‘lost world’ that was violently interrupted by an asteroid impact. Some dinosaurs were undergoing dramatic changes during this time, and the large herbivores seem to have been mired in a long-term decline, at least in North America.”
In North America, extreme fluctuations of the inland Western Interior Sea and mountain building might have affected the evolution of dinosaurs in distinct ways from species on other continents. Therefore, the authors say, the North American record might not be representative of a global pattern, if one exists. They also note that there is no way to tell whether a declining dinosaur group would have survived if the asteroid had not struck Earth.
“Even if the disparity of some dinosaur clades or regional faunas were in decline, this does not automatically mean that dinosaurs were doomed to extinction,” Norell said. “Dinosaur diversity fluctuated throughout the Mesozoic, and small increases or decreases between two or three time intervals may not be noteworthy within the context of the entire 150-million-year history of the group.”
Funding for this study was provided by the National Science Foundation through the Division of Earth Sciences, the Division of Biological Infrastructure, a Graduate Research Fellowship, and a Doctoral Dissertation Improvement Grant; the German Research Foundation’s Emmy Noether Programme; the Alexander von Humboldt Foundation; the Charlotte and Walter Kohler Charitable Trust; the American Museum of Natural History; and Columbia University.
Egg-Laying Beginning of the End for Dinosaurs
ScienceDaily (Apr. 17, 2012) — Their reproductive strategy spelled the beginning of the end: The fact that dinosaurs laid eggs put them at a considerable disadvantage compared to viviparous mammals. Together with colleagues from the Zoological Society of London, Daryl Codron and Marcus Clauss from the University of Zurich investigated and published why and how this ultimately led to the extinction of the dinosaurs in the journal Biology Letters.
The dinosaur’s egg and the tiny dino baby
Weighing in at four tons, the mother animal was 2,500 times heavier than its newly hatched dinosaur baby. By way of comparison, a mother elephant, which is just as heavy, only weighs 22 times as much as its new-born calf. In other words, neonates are already big in large mammal species. The staggering difference in size between newly hatched dinosaurs and their parents was down to the fact that there are limits to the size eggs can become: After all, larger eggs require a thicker shell and as the embryo also needs to be supplied with oxygen through this shell, eventually neither the shell nor the egg can grow any more. Consequently, newly hatched dinosaur babies cannot be larger in the same way as in larger species of mammal.
Many species occupy one niche each; one species occupies many niches
In addition, new-born mammals occupy the same ecological niche as their parents: As they are fed with milk directly by the mother, they do not take any niche away from smaller species. With large dinosaurs, however, it was an entirely different story: They did not only occupy the adults’ one niche during their lifetime, but also had many of their own to pass through — from niches for animals with a body size of a few kilos and those for ten, 100 and 1,000-kilo animals to those that were occupied by the fully grown forms of over 30,000 kilograms.
Daryl Codron explains what this means for biodiversity: “The consensus among researchers is that animals of particular body sizes occupy particular niches. In the case of the dinosaurs, this would mean that a single species occupied the majority of the ecological niches while mammals occupied these through numerous species of different sizes.” Accordingly, the research results reveal that dinosaurs of a small and medium body size were represented with far fewer individual species than was the case in mammals — because their niches were occupied by the young of larger species.
“An overview of the body sizes of all dinosaur species — including those of birds, which are also dinosaurs after all — reveals that few species existed with adults weighing between two and sixty kilograms,” specifies Codron. And Marcus Clauss sums up the consequences of this demonstrated by the researchers using computer simulations: “Firstly, this absence of small and medium-sized species was due to the competition among the dinosaurs; in mammals, there was no such gap. Secondly, in the presence of large dinosaurs and the ubiquitous competition from their young, mammals did not develop large species themselves.” The third insight that the computer simulation illustrates concerns small dinosaurs: They were in competition both among their own ranks and with small mammals. And this increased pressure brought the small dinosaurs either to the brink of extinction or forced them to conquer new niches. The latter enabled them to guarantee their survival up to the present day, as Codron concludes, since “back then, they had to take to the air as birds.”
Catastrophe: Small dinosaurs take to the air and large ones die out
The dinosaurs’ supremacy as the largest land animals remained intact for 150 million years. The mass extinction at the Cretaceous-Tertiary boundary, however, spelled trouble as the species gap in the medium size range turned out to be disastrous for them. According to the current level of knowledge, all the larger animals with a body weight from approximately ten to 25 kilos died out. Mammals had many species below this threshold, from which larger species were able to develop after the calamity and occupy the empty niches again. The dinosaurs, however, lacked the species that would have been able to reoccupy the vacant niches. That was their undoing.
Duck-Billed Dinosaurs Endured Long, Dark Polar Winters
ScienceDaily (Apr. 11, 2012) — Duck-billed dinosaurs that lived within Arctic latitudes approximately 70 million years ago likely endured long, dark polar winters instead of migrating to more southern latitudes, a recent study by researchers from the University of Cape Town, Museum of Nature and Science in Dallas and Temple University has found.
The researchers published their findings, “Hadrosaurs Were Perennial Polar Residents,” in the April issue of the journal The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology.
Anthony Fiorillo, a paleontologist at the Museum of Nature and Science, excavated Cretaceous Period fossils along Alaska’s North Slope. Most of the bones belonged to Edmontosaurus, a duck-billed herbivore, but some others such as the horned dinosaur Pachyrhinosaurus were also found.
Fiorillo hypothesized that the microscopic structures of the dinosaurs’ bones could show how they lived in polar regions. He enlisted the help of Allison Tumarkin-Deratzian, an assistant professor of earth and environmental science, who had both expertise and the facilities to create and analyze thin layers of the dinosaurs’ bone microstructure.
Another researcher, Anusuya Chinsamy-Turan, a professor of zoology at the University of Cape Town, was independently pursuing the same analysis of Alaskan Edmontosaurus fossils. When the research groups discovered the similarities of their studies, they decided to collaborate and combine their data sets to provide a larger sampling. Half of the samples were tested and analyzed at Temple; the rest were done in South Africa.
“The bone microstructure of these dinosaurs is actually a record of how these animals were growing throughout their lives,” said Tumarkin-Deratzian. “It is almost similar to looking at tree rings.”
What the researchers found was bands of fast growth and slower growth that seemed to indicate a pattern.
“What we found was that periodically, throughout their life, these dinosaurs were switching how fast they were growing,” said Tumarkin-Deratzian. “We interpreted this as potentially a seasonal pattern because we know in modern animals these types of shifts can be induced by changes in nutrition. But that shift is often driven by changes in seasonality.”
The researchers questioned what was causing the dinosaurs to be under stress at certain times during the year: staying up in the polar region and dealing with reduced nutrition during the winter or migrating to and from lower latitudes during the winter.
They did bone microstructure analysis on similar duck-billed dinosaur fossils found in southern Alberta, Canada, but didn’t see similar stress patterns, implying that those dinosaurs did not experience regular periodic seasonal stresses. “We had two sets of animals that were growing differently,” said Tumarkin-Deratzian.
Since the Alaska fossils had all been preserved in the same sedimentary horizon, Fiorillo examined the geology of the bonebeds in Alaska where the samples were excavated and discovered that these dinosaurs had been preserved in flood deposits.
“They are very similar to modern flood deposits that happen in Alaska in the spring when you get spring melt water coming off the Brooks Mountain Range,” said Fiorillo. “The rivers flood down the Northern Slope and animals get caught in these floods, particularly younger animals, which appear to be what happened to these dinosaurs.
“So we know they were there at the end of the dark winter period, because if they were migrating up from the lower latitudes, they wouldn’t have been there during these floods,” he said.
“It is fascinating to realize how much of information is locked in the bone microstructure of fossil bones,” said Chinsamy-Turan. “It’s incredible to realize that we can also tell from these 70 million-year-old bones that the majority of the polar hadrosaurs died just after the winter season.”
The study was funded through a grant from the National Science Foundation.
T. Rex’s Killer Smile Revealed
ScienceDaily (Mar. 18, 2012) — One of the most prominent features of life-size models of Tyrannosaurus rex is its fearsome array of flesh-ripping, bone-crushing teeth.
Until recently, most researchers who studied the carnivore’s smile only noted the varying sizes of its teeth. But University of Alberta paleontologist Miriam Reichel discovered that beyond the obvious size difference in each tooth family in T. rex’s gaping jaw, there is considerable variation in the serrated edges of the teeth.
“The varying edges, or keels, not only enabled T. rex’s very strong teeth to cut through flesh and bone,” says Reichel, “the placement and angle of the teeth also directed food into its mouth.”
Reichel analyzed the teeth of the entire tyrannosaurid family of meat-eating dinosaurs and found T. rex had the greatest variation in tooth morphology or structure. The dental specialization was a great benefit for a dinosaur whose preoccupation was ripping other dinosaurs apart.
Reichel’s research shows that the T. rex’s front teeth gripped and pulled, while the teeth along the side of the jaw punctured and tore flesh. The teeth at the back of the mouth did double duty: not only could they slice and dice chunks of prey, they forced food to the back of the throat.
Reichel says her findings add strength to the classification of tyrannosaurids as heterodont animals, which are animals with teeth adapted for different functions depending on their position in the mouth.
One surprising aspect of T. rex teeth, common to all tyrannosaurid’s, is that they weren’t sharp and dagger-like. “They were fairly dull and wide, almost like bananas,” said Reichel. “If the teeth were flat, knife-like and sharp, they could have snapped if the prey struggled violently when T. rex’s jaws first clamped down.”
Reichel’s research was published in The Canadian Journal of Earth Science.
Ancestor of Biggest Dinosaurs: First Dinosaur Discovered in Spain Dates Back 15 Million Years Earlier Than Thought
ScienceDaily (Mar. 12, 2012) — A research group from Aragon, that has the same name as the first Aragosaurus ischiaticus dinosaur discovered 25 years ago in Teruel, reveals that it lived 15 million years earlier than originally believed. Its new dating means that it was the ancestor of the Titanosauriforms, which includes the biggest dinosaurs.
The Aragosaurus was the first sauropod dinosaur described in Spain some 25 years ago in Galve (Teruel), but its age was never clear. The new dating would make it the only dinosaur of the Hauterivian age (between 136 and 130 million years ago) to be found in Spain.
“This is the only dinosaur of this period found in Spain and is also the most intact in Europe. It can be categorised amongst the well known sauropods of the Jurassic-Cretaceous transition (135 million years ago), the most abundant species during the Barremian age (116 million years ago). As this group has been studied the least, the Aragosaurus fills the gap,” explains José Ignacio Canudo, lead author of the study and researcher in the University of Zaragoza’s Aragosaurus-IUCA Group, which stands for the Aragon Research Institute of Environmental Sciences.
Its new age means that Aragosaurus fills in the transitional period between the Jurassic and Cretaceous periods, of which there is little record in the world. Canudo points out that, “Aragosaurus would have therefore been a primitive ancestor of the titanosauraus sauropods that would later dominate Europe and Asia during the Late Cretaceous Period.”
Published in Geological Magazine, the study shows that Aragosaurus, found by José Luis Sanz and his team in 1987, is the oldest of its kind ever found and it could even be a common ancestor. The researcher said that, “the group could have originated in Europe, or even in Iberia, but there is still a lot more to be found out.”
The new finding also reveals that in the Early Cretaceous Period (135 million years ago), what we now know as the European Continent was made up of a series of large islands that could have been, “the point of origin for many vertebrate groups including sauropod dinosaurs like the Basal Titanosauriform.”
Fossil dating: An “almost” impossible mission
In order to situate the dinosaurs on their corresponding branch of the evolutionary tree, their remains require dating. In some cases though, this is lacking. Dating dinosaur remains can be problematic due the little information available on the age of the sediments where the fossils lie.
In relation to Aragosaurus ischiaticus “there are some lagoons that allude to its stratigraphic position,” outlines Candudo, adding that dating “can often be complicated due to imprecision in continental scales.” For this reason, the age of some dinosaur species can vary “even by tens of millions of years,” assures the geologist.
The research group carried out their detailed geological field work to find the remains in the lower part of the Castellar Formation site in Teruel. As the lower part is “not as rich” in fossils compared to the upper part, the only Aragosaurus remains that could be dated were a pollen fossil assemblage.
In Canudo’s opinion, specifying the age of dinosaurs is “fundamental” in determining the paleobiogeography and evolution of these beings. As the scientist concludes, “incorrect aging provides the wrong results when determining the correlation between continents.”
Polysternon Isonae, a New Species of Turtle That Lived With Dinosaurs in Isona (Spanish Pyrenees)
ScienceDaily (Feb. 27, 2012) — Researchers* have recently published in the online edition of the journal Cretaceous Research the discovery and description of a turtle from the end of the age of dinosaurs.They have named this new species as Polysternon isonae, in recognition of the municipality of Isona I Conca Dellà (Catalonia, Spain), where the fossil remains of the specimen type have been found.
The abundance of dinosaur fossils that lived between 65 and 70 million years ago in the area currently occupied by the Pyrenees It is well known. In this range we find dozens of sites with bones, footprints and eggs of the last dinosaurs that inhabited our planet, the Tremp basin being one of the areas with the highest concentration of fossils.
However, lesser-known are the other organisms that completed the ecosystems at the end of the Cretaceous period, consisting of other vertebrates, invertebrates, plants, fungi, etc. A common feature of these ecosystems were turtles. In the Pyrenean sites, their fossils are relatively abundant and, in general, consist of isolated shell plates or small sets of plates that can help us get a general idea of the morphology and size of the animal. Instead, the entire shell finding is rare and even more exceptional are the findings where parts of the skeleton are preserved within the shell.
In recent years, in the municipality of Isona i Conca Dellà (Catalonia) numerous discoveries of turtle remains have been made, spread over several sites. One of these sites, that of Barranc de Torrebilles, has given fairly complete remains that allowed describing a new species: Polysternon isonae. The remains found consist of dozens of isolated plates derived from the fragmentation of shells through their sutures, and what is more important: a fragment of the ventral side of a shell and an almost entire shell, which without being totally complete, show morphological features of great interest to paleontologists and have allowed to describe this new species. These remains were recovered during two excavation campaigns conducted during the summers of 2008 and 2009.
So far, two species of the genus Polysternon were known : P. provinciale and P. Atlanticum (plus a possible third P. Mechinorum), distributed only in what is know the south of France and the Iberian Peninsula. They were animals adapted to swimming and living in fresh waters, in the deeper areas of rivers and lakes. Specifically, the shell of the new species P. isonae was oval, measuring about 50 centimeters long and 40 wide. The remains were found preserved in a very hard sandstone strata now exposed in the Barranc de Torrebilles. Just over 65 million years ago, when the animal died, this was not a lithified sandstone and consisted of fine sand that was washed away by river streams and that was deposited, along with the remains of other turtles of the Barranc de Torrebilles, at the bottom of one of these rivers.
Unlike other kinds of turtles, it seems that Polysternon did not survive the end of Cretaceous and went extinct with the dinosaurs. The close proximity of the site Barranc de Torrebilles to the geological level that marks the end of the Cretaceous extinction, indicates that Polysternon isonae was possibly one of the last species of the genus Polysternon.
* Josep Marmi, Angel Lujan, Angel Galobart from Institut Català de Paleontologia Miquel Crusafont (ICP), Rodrigo Gaete from the Museu de la Conca Dellà (MCD) and Violeta and Oms Oriol Riera from the Universitat Autònoma de Barcelona (UAB
Why Do Dinosaur Skeletons Look So Weird?
ScienceDaily (Feb. 16, 2012) — Many fossilized dinosaurs have been found in a twisted posture. Scientists have long interpreted this as a sign of death spasms. Two researchers from Basel and Mainz now come to the conclusion that this bizarre deformations occurred only during the decomposition of dead dinosaurs.
More or less complete and articulated skeletons of dinosaurs with a long neck and tail often exhibit a body posture in which the head and neck are recurved over the back of the animal. This posture, also known from Archaeopteryx, has been fascinating paleontologists for more than 150 years. It was called “bicycle pose” when talking with a wink, or “opisthotonic posture” in a more oppressive way of speaking.
The latter alludes to an accessory symptom of tetanus, well known in human and veterinarian medicine. Usually, an “opisthotonic posture” like that is the result of vitamin deficiency, poisoning or damage to the cerebellum.
Basically, the cerebellum is a brain region that controls fine muscle movement, which includes the body’s antigravity muscles that keep the head and tail upright. If the cerebellum ceases to function, the antigravity muscles will clench at full force, tipping the head and tail back, and contracting the limbs.
A syndrome like that as a petrified expression of death throes was discussed for the first time about 100 years ago for some vertebrate fossils, but the acceptance of this interpretation declined during the following decades. In 2007, this “opisthotonus hypothesis” was newly posted by a veterinarian and a palaeontologist. This study, generously planned, received much attention in the public and the scientific community.
Now, five years later, two scientists from Switzerland and Germany have re-evaluated the revitalized “opisthotonus hypothesis” and examined one of its icons, the famous bipedal dinosaur Compsognathus longipes from the “Solnhofen Archipelago” (Germany). It is widely acknowledged that this 150-millions-years-old land-living dinosaur was embedded in a watery grave of a tropical lagoon.
“In our opinion, the most critical point in the newly discussed scenario of the preservation of an opisthotonic posture in a fossil is the requirement that terrestrial vertebrates must have been embedded immediately after death without substantial transport. But consigning a carcass from land to sea and the following need of sinking through the water column for only a few decimetres or meters is nothing else” says sedimentologist Achim Reisdorf from University of Basel’s Institute of Geology and Paleontology.
Biomechanics in Watery Graves Convinced that the back arching was generated, not by death throes, but by postmortem alterations of a decaying carcass, the researchers made experiments with plucked chicken necks and thoraxes, immersed in water. Submersed in water, the necks spontaneously arched backwards for more than 90°. Ongoing decay for some months even increased the degree of the pose. Thorough preparation and dissection combined with testing revealed that a special ligament connecting the vertebrae at their upper side was responsible for the recurved necks in the chickens. This ligament, the so-called Ligamentum elasticum, is pre-stressed in living chickens, but also in dead ones.
“Veterinarians may often have to do with sick and dying animals, where they see the opisthotonic posture in many cases. Vertebrate palaeontologists, however, who want to infer the environment in which the animals perished and finally were embedded have to elucidate postmortem processes and biomechanical constraints too” says palaeontologist Michael Wuttke from the Section of Earth History in the General Department for the Conservation of Cultural History Rhineland Palatinate in Mainz (Germany).
“A strong Ligamentum elasticum was essential for all long necked dinosaurs with a long tail. The preloaded ligament helped them saving energy in their terrestrial mode of life. Following their death, at which they were immersed in water, the stored energy along the vertebra was strong enough to arch back the spine, increasingly so as more and more muscles and other soft parts were decaying” conclude the researchers. “It is a special highlight that, in the Compsognathus specimen, these gradual steps of recurvature can be substantiated, too. Therefore, biomechanics is ruling the postmortem weird posture of a carcass in a watery grave, not death throes.”
Fossils in South Africa Reveal Dinosaur Nesting Site: 190 Million Years Old
ScienceDaily (Jan. 23, 2012) — An excavation at a site in South Africa has unearthed the 190-million-year-old dinosaur nesting site of the prosauropod dinosaur Massospondylus — revealing significant clues about the evolution of complex reproductive behaviour in early dinosaurs.
A new study, published in the Proceedings of the National Academy of Sciences (PNAS), was led by Canadian palaeontologist Prof. Robert Reisz, a professor of biology at the University of Toronto at Mississauga, and co-authored by Drs. Hans-Dieter Sues (Smithsonian Institute, USA), Eric Roberts (James Cook University, Australia), and Adam Yates (Bernard Price Institute (BPI) for Palaeontological Research at Wits).
The study reveals clutches of eggs, many with embryos, as well as tiny dinosaur footprints, providing the oldest known evidence that the hatchlings remained at the nesting site long enough to at least double in size.
Prof. Bruce Rubidge, Director of the BPI at Wits, says: “This research project, which has been ongoing since 2005 continues to produce groundbreaking results and excavations continue. First it was the oldest dinosaur eggs and embryos, now it is the oldest evidence of dinosaur nesting behaviour.”
The authors say the newly unearthed dinosaur nesting ground is more than 100 million years older than previously known nesting sites.
At least ten nests have been discovered at several levels at this site, each with up to 34 round eggs in tightly clustered clutches. The distribution of the nests in the sediments indicate that these early dinosaurs returned repeatedly (nesting site fidelity) to this site, and likely assembled in groups (colonial nesting) to lay their eggs, the oldest known evidence of such behaviour in the fossil record.
The large size of the mother, at six metres in length, the small size of the eggs, about six to seven centimetres in diameter, and the highly organised nature of the nest, suggest that the mother may have arranged them carefully after she laid them.
“The eggs, embryos, and nests come from the rocks of a nearly vertical road cut only 25 metres long,” says Reisz. “Even so, we found ten nests, suggesting that there are a lot more nests in the cliff, still covered by tons of rock. We predict that many more nests will be eroded out in time, as natural weathering processes continue.”
The fossils were found in sedimentary rocks from the Early Jurassic Period in the Golden Gate Highlands National Park in South Africa. This site has previously yielded the oldest known embryos belonging to Massospondylus, a relative of the giant, long-necked sauropods of the Jurassic and Cretaceous periods.
“Even though the fossil record of dinosaurs is extensive, we actually have very little fossil information about their reproductive biology, particularly for early dinosaurs,” says David Evans, a University of Toronto at Mississauga alumnus and a curator of Vertebrate Palaeontology at the Royal Ontario Museum.
“This amazing series of 190 million year old nests gives us the first detailed look at dinosaur reproduction early in their evolutionary history, and documents the antiquity of nesting strategies that are only known much later in the dinosaur record,” says Evans.
‘Skin Bones’ Helped Large Dinosaurs Survive, New Study Says
ScienceDaily (Nov. 29, 2011) — Bones contained entirely within the skin of some of the largest dinosaurs on Earth might have stored vital minerals to help the massive creatures survive and bear their young in tough times, according to new research by a team including a University of Guelph scientist.
Guelph biomedical scientist Matthew Vickaryous co-authored a paper published in Nature Communications about two sauropod dinosaurs — an adult and a juvenile — from Madagascar.
The study suggests that these long-necked plant-eaters used hollow “skin bones” called osteoderms to store minerals needed to maintain their huge skeletons and to lay large egg clutches. Sediments around the fossils show that the dinosaurs’ environment was highly seasonal and semi-arid, with periodic droughts causing massive die-offs.
“Our findings suggest that osteoderms provided an internal source of calcium and phosphorus when environmental and physiological conditions were stressful,” he said. As a researcher in the Department of Biomedical Sciences in Guelph’s Ontario Veterinary College, Vickaryous studies how skeletons develop, regenerate and evolve.
He worked with paleontologist Kristina Curry Rogers and geologist Raymond Rogers at Macalaster College in Minnesota, and paleontologist Michael D’Emic, now at Georgia Southern University on the study. Vickaryous helped to interpret the results of CT scans and fossilized tissue cores taken from the dinosaurs.
Shaped like footballs sliced lengthwise and about the size of a gym bag in the adult, these bones are the largest osteoderms ever identified. The adult specimen’s bone was hollow, likely caused by extensive bone remodelling, said Vickaryous.
Osteoderms were common among armoured dinosaurs. Stegosaurs had bony back plates and tail spikes, and ankylosaurs sported heavily armoured bodies and bony tail clubs. Today these “skin bones” appear in such animals as alligators and armadillos.
Such bones were rare among sauropod dinosaurs and have appeared only in titanosaurs. These massive plant-eaters included the largest-ever land animals. “This is the only group of long-necked sauropods with osteoderms,” he said.
Other studies have shown that female titanosaurs laid dozens of volleyball-sized eggs. Modern crocodiles and alligators also lay clutches of dozens of eggs and are known to reabsorb minerals from their osteoderms.
The researchers found the new osteoderms along with two skeletons of the titanosaur Rapetosaurus. Unlike the hollow adult specimen, the juvenile specimen was solid and showed little evidence of remodelling. That suggests that osteoderms became more important mineral stores as the animals grew, Vickaryous said.
LARGE NEST OF JUVENILE DINOSAURS, FIRST OF THEIR GENUS EVER FOUND
The findings were reported in the most recent issue of the Journal of Paleontology.
David Fastovsky, URI professor of geosciences, said the bowl-shaped nest measuring 2.3 feet in diameter was found in the Djadochta Formation at Tugrikinshire, Mongolia.
“Finding juveniles at a nest is a relatively uncommon occurrence, and I cannot think of another dinosaur specimen that preserves 15 juveniles at its nest in this way,” he said.
The analysis of the 70-million-year-old nest by Fastovsky and his colleagues found that all 15 dinosaurs — at least 10 of which are complete specimens — were about
the same size and had achieved the same state of growth and development, suggesting they represent a single clutch from a single mother. The discovery also indicates that the young dinosaurs remained in the nest through the early stages of postnatal development and were cared for by their parents.
Protoceratops grew to about 6 feet long and may have taken as long as 10 years to reach full size. Those Fastovsky found in the nest were likely less than one year old when they died.
“I suspect that the preserved animals were rapidly buried by the shifting, accumulating sands that must have constituted the bulk of sedimentation in this setting,” he said. “Death likely occurred during a desert sandstorm. My guess is that the initial and present-day dryness contributed significantly to the superb preservation, not just of Protoceratops, but of all the fossils from this unit.”
Fastovsky calls Protoceratops “a fascinating and unexpected mass of contradictions.” It is an herbivore that lived in a sand sea much like the Sahara Desert and likely bestowed significant parental care on a relatively large number of offspring, perhaps because it lived where mortality was quite high.
A wide variety of theropod dinosaurs lived in Mongolia at the time, some of which, including the notorious Velociraptor, probably ate young Protoceratops‘.
“Juvenile Protoceratops mortality may have been rather high, not only from predation but from a potentially stressful environment, and large clutches may have been a way of ensuring survival of the animals in that setting,” he said. “Nonetheless, if preservation is any indicator of abundance in life, then during the time represented by the Djadochta Formation, Protoceratops were a very common feature of Mongolian Late Cretaceous desert landscapes.”