The “Morphotype 1″ tunnel complex: points marked “a” represent tunnels, and points marked “b” signify vertical shafts. From Colombi et al., 2012.

Dinosaurs never cease to surprise. Even though documentaries and paleoart regularly restore these creatures in lifelike poses, the fact is that ongoing investigations into dinosaur lives have revealed behaviors that we never could have expected from bones alone. Among the most recent finds is that dinosaurs were capable of digging into the ground for shelter. Burrows found in Australia and Montana show that some small, herbivorous dinosaurs dug out cozy little resting places in the cool earth.

But when did dinosaurs develop burrowing behavior? The distinctive trace fossils found so far are Cretaceous in age, over 100 million years after the first dinosaurs evolved. That’s why a new PLoS One paper by paleontologist Carina Colombi caught my eye. In the Triassic rock of Argentina’s Ischigualasto Basin, Columbi and coauthors report, there are large-diameter burrows created by vertebrates that lived approximately 230 million years ago. Archaic dinosaurs such as Eoraptor and Herrerasaurus roamed these habitats–could dinosaurs be responsible for the burrows?

Colombi and colleagues recognized three different burrow forms in the Triassic rock. Two distinct types–differentiated by their diameter and general shape–were “networks of tunnels and shafts” that the authors attributed to vertebrates. The third type showed a different pattern of “straight branches that intersect at oblique angles” created by the burrowing organism and the plant life. The geology and shapes of the burrows indicate that they were created by living organisms. The trick is figuring out what made the distinct tunnel types.

In the case of the first burrow type, Colombi and collaborators propose that the structures were made by small, carnivorous cynodonts–squat, hairy protomammals. In the other two cases, the identities of the burrow makers isn’t clear. The second type included vertical shafts that hint at a vertebrate culprit. Dinosaurs would have been too big, but, Colombi and coauthors suggest, other cynodonts or the bizarre, ancient cousins of crocodiles–such as aetosaurs or protosuchids–could have created the burrows. Unless remains of these animals are found associated with the burrows, it is impossible to be sure. Likewise, the third type of trace might represent the activities of animals that burrowed around plant roots, but there is no clear candidate for the trace-maker.

As far as we know now, Triassic dinosaurs didn’t burrow. Even though they were not giants, they were still too large to have made fossils reported in the new research. Still, I have to wonder if predatory dinosaurs such as Herrerasaurus, or omnivores like Eoraptor, dug poor little cynodonts out of their burrows much like the later deinonychosaurs scratched after hiding mammals. There’s no direct evidence for such interactions, but, if small animals often sheltered from heat and drought in cool tunnels, perhaps predators tried to nab prey resting in their hiding places. One thing is for sure, though: we’ve only just started to dig beyond the surface of Triassic life.

References:

Colombi, C., Fernández, E., Currie, B., Alcober, O., Martínez, R., Correa, G. 2012. Large-Diameter Burrows of the Triassic Ischigualasto Basin, NW Argentina: Paleoecological and Paleoenvironmental Implications. PLoS ONE 7,12: e50662. doi:10.1371/journal.pone.0050662

An illustration showing the only known bones from Genyodectes. Art in Woodward, 1901, image from Wikipedia.

Paleontologists are naming new dinosaurs at an astonishing rate. In fact, they’re only just begun to skim the diversity of dinosaurs preserved in the world’s Mesozoic formations–hundreds of unknown dinosaur species are undoubtedly hiding in stone. But even among dinosaurs that have a formalized identity, there are many that we know relatively little about. Among them is Genyodectes serus, a carnivorous dinosaur known from the tip of its fearsome jaws and little else.

Though it’s far from being a household name, Genyodectes holds a significant place in the history of South American paleontology. Aside from a tooth found a few years before, the incomplete fossil snout of a Genyodectes was the first definitive non-avian theropod dinosaur found on the continent. As described by paleontologist A.S. Woodward in 1901, the remains of Genyodectes mostly consisted of pieces from the lower jaw, as well as the premaxillary bones and fragments of the maxillary bones in the upper jaw, all of which sported frighteningly long, curved teeth.

There was never any question that Genyodectes was a theropod dinosaur. All the principally carnivorous dinosaurs that we know of fell among various branches of this group. But what sort of theropod dinosaur was it? During the 20th century, different paleontologists proposed that it was a megalosaurid (then a generalized term for big predatory dinosaurs), a tyrannosaur or, after additional theropod remains started to come out of South America, one of the stubby-armed abelisaurids.

After the specimen was given a fresh cleaning, paleontologist Oliver Rauhut reexamined Genyodectes with an eye towards what the dinosaur was and where it came from. Based on notes and geological details, Rauhut proposed that the dinosaur was found in Cañadón Grande in Argentina’s Chubut province in a Cretaceous deposit that probably dates to around 113 million years old. And, based on the limited remains, Rauhut hypothesized that Genyodectes was a later, southern cousin of North America’s Ceratosaurus. While the only known specimen of Genyodectes was cracked and damaged by erosion, the size and the anatomy of the dinosaur’s teeth most closely resembled that of Ceratosaurus–especially in having extremely long teeth in the maxilla. Given this relationship, we might expect that Genyodectes had some kind of skull ornamentation like the nasal and eye horns of its cousin, but we need more fossils to be sure.

Reference:

Rauhut, O. 2004. Provenance and anatomy of Genyodectes serues, a large-toothed ceratosaur (Dinosauria: Theropods) from Patagonia. Journal of Vertebrate Paleontology. 24, 4: 894-902

The giant sauropod Futalognkosaurus (at left) with some of its Cretaceous neighbors. Art by Maurilio Oliveira.

Which was the biggest dinosaur ever? We don’t know. Even though the size-based superlative draws a great deal of attention, paleontologists have uncovered so many scrappy sauropod skeletons that it’s difficult to tell who was truly the most titanic dinosaur of all. But, among the current spread of candidates, Futalognkosaurus dukei is one of the most complete giant dinosaurs yet found.

Discovered in 2000, and named in 2007 by Universidad Nacional del Comahue paleontologist Jorge Calvo and colleagues, Futalognkosaurus was one of many dinosaurs found in an exceptionally rich, roughly 90-million-year0old deposit in northwest Argentina. From fossil plants to pterosaurs, fish and dinosaurs, the one site entombed vestiges of a vibrant Cretaceous ecosystem. And, on that landscape, no dinosaur was as grand the newly named titanosaur.

Contrary to what you might expect given their skeletal sturdiness, the biggest sauropods are often found as partial skeletons. Our knowledge of Argentinosaurus, Puertasaurus, Supersaurus, Diplodocus hallorum and other giants is frustratingly incomplete, and figuring out how large they truly were relies on estimation from more complete representatives of other species.

The lack of complete tails from these dinosaurs makes the matter even more problematic. Dinosaur tails varied in length from individual to individual, and different subgroups had proportionally longer or shorter tails. In the case of Diplodocus hallorum, for example, a great deal of the dinosaur’s estimated  100-foot-plus length comes from the fact that other Diplodocus species had very long, tapering tails.

We don’t really know how long Futalognkosaurus was because, with the exception of a single vertebra, the dinosaur’s tail is entirely missing. Nevertheless, the sauropod that Calvo and coauthors described is remarkable for encompassing the entire neck, back and associated ribs, and the majority of the hips. Together, these elements represent over half the skeleton and comprise the most complete giant sauropod individual yet known.

Even if skeletal incompleteness keeps us from knowing exactly how big Futalognkosaurus was, the collected bones can leave no doubt that this was a truly enormous dinosaur. Calvo and coauthors estimated that the whole animal stretched between 105 and 112 feet in length, which would put it in the same class as the more famous (and less complete) Argentinosaurus. As the paleontologists at SV-POW! said when they posted images of Futalognkosaurus bones next to Juan Porfiri, who helped describe the dinosaur, there’s no doubt that the sauropod was “darned big.” The challenge is finding and filling in the parts of the dinosaur’s body that have not yet been found. There will undoubtedly be other challengers for the title of biggest dinosaur, but, for now, Futalognkosaurus remains our most detailed representative of the biggest of the big.

References:

Calvo, J., Porfiri, J., González-Riga, B., Kellner, A. 2007. A new Cretaceous terrestrial ecosystem from Gondwana with the description of a new sauropod dinosaur. Anais da Academia Brasileira de Ciências. 79, 3: 529-541

Calvo, J., Porfiri, J., González-Riga, B., Kellner, A. 2007. Anatomy of Futalognkosaurus dukei Calvo, Porfiri, González Riga, & Kellner, 2007 (Dinosauria, Titanosauridae) from the Neuquen Group, Late Cretaceous, Patagonia, Argentina. Arquivos do Museu Nacional 65, 4: 511–526.

Novas, F. 2009. The Age of Dinosaurs in South America. Bloomington: Indiana University Press. pp. 201-202

Only hindlimb elements of Alnashetri are known so far, but, based on the dinosaur’s relationships, the tiny theropod probably looked something like this Alvarezsaurus. Photo by FunkMonk, image from Wikipedia.

Many dinosaurs have gained fame thanks to their gargantuan size. A creature in the form of a dipldodocid or tyrannosaur would be wonderful at any scale, but the fact that Apatosaurus was an 80-foot-long fern-sucker and Tyrannosaurus was a 40-foot carnivore make their skeletal frames all the more spectacular. Even as an adult, long after my first encounter with their bones at the American Museum of Natural History in New York City, I still feel tiny when I look up at what’s left of the great dinosaurs.

But not all non-avian dinosaurs were gigantic. There were 100-foot giants, like the sauropod Argentinosaurus, but there were also pigeon-sized theropods such as the strikingly-colored Anchiornis. Indeed, a significant part of how we know dinosaurs really ruled the earth is because they occupied such a wide range of body sizes–from the breathtakingly large to the diminutive. And, earlier this month, Field Museum of Natural History paleontologist Peter Makovicky and colleagues added a previously unknown tiny dinosaur to the ever-growing roster of Mesozoic species.

Named Alnashetri cerropoliciensis, the small dinosaur is mostly a mystery. All that we know of it, Makovicky and coauthors report, are a set of articulated hindlimbs from a single animal found in the roughly 95-million-year-old rock of La Buitrera, Argentina. (The dinosaur’s genus name, the paper says, means “slender thighs” in a dialect of the Tehuelchan language.) Yet those appendages contain enough clues about the dinosaur’s identity that the researchers were able to figure out that the specimen represented a new species of alvarezsaur–one of the small, possibly ant-eating dinosaurs recognizable by their short, stout arms and long skulls set with tiny teeth. While the paleontologists acknowledge that their Alnashetri specimen might be a juvenile, Makovicky and collaborators estimate that the dinosaur was comparable to its relative Shuvuuia in size–about two feet long.

How Alnashetri resembled other alvarezsaurs, and where it departed in form, will have to wait for more complete specimens. Further research is also needed to narrow down when this dinosaur lived, but for the moment, Alnashetri appears to be the oldest alvarezsaur found in South America. If only we knew more of this dinosaur! As Makovicky and coauthors conclude, “continued fieldwork and future discoveries hopefully will provide more information on the anatomy of Alnashetri and allow a more definitive evaluation of its affinities and its significance for understanding biogeography and evolutionary trends such as body size evolution within alvarezsaurids.” At least the enigma has a name.

Reference:

Makovicky, P., Apesteguía, S., Gianechini, F. 2012. A new coelurosaurian theropod from the La Buitrera fossil locality of Rio Negro, Argentina. Fieldiana Life and Earth Sciences, 5: 90-98

When paleontologists at the Argentine Museum of Natural Science in Buenos Aires threw the curtain back on the new dinosaur Bicentenaria argentina last month, they showed off a beautiful mount of tussling dinosaurs. But I couldn’t help but wonder about the reconstruction. Just how much of the dinosaur had been found, and was there any direct evidence that these dinosaurs fought each other?

Frustratingly, I couldn’t obtain immediate answers. The press event preceded the actual paper describing Bicentenaria. But last night I finally got my claws on the description of this archaic, peculiar dinosaur and its possible behavior.

Although Bicentenaria is new to science, the dinosaur’s remains were first discovered years ago. In 1998, during a drop in the water level at Argentina’s Ezequiel Ramos Mexía Reservoir, Rauel Spedale discovered and collected the disarticulated, scattered remains of several Bicentenaria from a small quarry. There was no single complete skeleton, but the quarry contained multiple skull and postcranial bones from several animals. The largest of these dinosaurs would have been about 10 feet long.

According to the analysis of the accumulated bones by paleontologist Fernando Novas and colleagues, Bicentenaria was an archaic form of coelurosaur. This is the major group of theropod dinosaurs that includes tyrannosaurs, the fluffy compsognathids, the sickle-clawed deinonychosaurs, the utterly strange therizinosaurs and birds, among other disparate lineages. Bicentenaria didn’t belong to any of these subgroups but was near the base of the coelurosaur family tree.

Yet, despite its old school anatomy, Bicentenaria was definitely not the ancestral coelurosaur. Not even close. Coelurosaurs were already a diverse group by the Late Jurassic, meaning that they started to proliferate before 150 million years ago. Yet Bicentenaria lived around 95 million years ago during the Late Cretaceous. It was over 55 million years too late to be a true ancestor of the other coelurosaur groups.

Bicentenaria can still help paleontologists visualize the anatomy early coelurosaurs, though. Based on the evolutionary analysis in the new paper, Bicentenaria preserved features seen in much, much older dinosaurs that were at the base of the coelurosaur family tree. While not an ancestor of coelurosaurs, the skeleton of Bicentenaria can help scientists figure out what the actual progenitors of the group were like.

The study also speculated about the dinosaur’s social life. Since the small quarry yielded multiple individuals, Novas and collaborators concluded that these dinosaurs must have been socializing when they died. More than that, the paleontologists tie in other theropod bonebeds to suggest that a gregarious lifestyle was the ancestral condition of theropod dinosaurs, “if not Dinosauria as a whole.”

I’m not so sure. The fact that multiple dinosaurs of the same species died in the same place, by itself, isn’t evidence that the animals lived together. It is only evidence that the dinosaurs were buried together. Even though there have been many claims of “dino gangs” and “dueling dinosaurs” based upon associated skeletons, we need to know the details of how those animals died and became buried before we can accurately reconstruct their behavior. Just because we find dinosaurs buried together doesn’t necessarily mean they were socializing before they perished. Some bonebeds really do seem to contain dinosaurs that were in a social group when they perished, while others represent assemblages of individuals that died at different times and were later washed together. The geologic and taphonomic context is critical.

In this case, unfortunately, Spedale did not take any notes on the arrangement of the bones or the context in which they were found. That data is lost. But one quarry block indicates that the bones of the dinosaurs were transported by water and stirred together. The dinosaurs died elsewhere and only parts of them ultimately became preserved in the same spot. This complicates the social Bicentenaria hypothesis. Did all the dinosaurs in the quarry die together, or did their bodies accumulate in a particular place–perhaps due to a drought or other event–over time before being washed together? We don’t know. Bicentenaria very well could have been a social dinosaur, but the evidence isn’t strong enough to say for sure, much less hypothesize that a gregarious lifestyle was the ancestral condition for all theropods. There’s a lot that we can learn about dinosaur lives from their bones, but the intricacies of their social lives remains obscured by the quirks of the fossil record.

Reference:

Novas, F., Ezcurra, M., Agnolin, F., Pol, D., Ortíz, R. 2012. New Patagonian Cretaceous theropod sheds light about the early radiation of Coelurosauria. Rev. Mus. Argentino Cienc. Nat., n.s. 14(1): 57-81 (PDF)

Last week, paleontologists at the Argentine Museum of Natural Science in Buenos Aires literally unveiled a new dinosaur. Named Bicentenaria argentina to celebrate the museum’s 200th anniversary and just over two centuries of Argentine independence, the dinosaur was presented in a dramatic mount in which two of the predatory dinosaurs face off against each other.

As yet, there’s not very much to say about the dinosaur. The paper officially describing Bicentenaria has yet to be published. Based on various news reports, though, Bicentenaria appears to be a 90 million year old coelurosaur. This is the major group of theropod dinosaurs that contains tyrannosaurs, deinonychosaurs, therizinosaurs, and birds, among others, and Bicentenaria is reportedly an archaic member of this group that represents what the earliest coelurosaurs might have looked like. It wouldn’t be an ancestor of birds or other coelurosaur groups – by 90 million years ago, birds and other coelurosaurs had already been around for tens of millions of years – but Bicentenaria may have had a conservative body plan that preserved the form of the dinosaurs that set the stage for other coelurosaurs. For now, though, we’re left to admire the impressive skeletal mount until the paper comes out.

The rebbachisaurid Limaysaurus. This sauropod was similar to the ones discovered by Salgado and colleagues in the Patagonian bonebed. Image by FunkMonk, from Wikipedia.

Dinosaur skeletons are marvelous things. The reconstructed bones of Allosaurus, Stegosaurus, Styracosaurus, Barosaurus and the like are beautiful monuments of natural architecture. But what really makes the skeletons so fantastic is that we know they once cradled viscera and were wrapped in flesh. It’s impossible to look at a dinosaur’s skeleton and not wonder about how the animals looked and acted in life.

How social dinosaurs were is one of the most persistent mysteries of their natural history. Rare trackways record the steps of dinosaurs that walked together, and bonebeds containing the bones of multiple individuals of a particular species have sometimes been taken as evidence that the dinosaurs must have been traveling together when they died. But the evidence is never straightforward. Sometimes multiple dinosaurs walked over the same patch of ground at different times, creating trackway slabs that record the independent activities of several dinosaurs rather than a coordinated herd. And just because dinosaurs were preserved together doesn’t necessarily mean that they composed a social group—natural disasters such as drought and flood, as well as transportation of carcasses by water, can create assemblages of animals that didn’t actually flock together in life. Great care is required in piecing together dinosaur lives.

With this in mind, I was curious to read a paper by Leonardo Salgado and colleagues in the latest Journal of Vertebrate Paleontology about possible evidence for social sauropods from Cretaceous Patagonia. While searching for a previously discovered dinosaur quarry in Argentina, Salgado and collaborators stumbled across a small bonebed containing the jumbled remains of three sauropods. The deposit was formed over 100 million years ago.

The largest dinosaur at  the site—presumably an adult—was primarily represented by strings of articulated vertebrae arranged in the classic dinosaur death pose, while two smaller sauropod skeletons were scattered in other parts of the quarry. The dinosaurs are still undergoing study and don’t have a formal identity yet, but they appear to be rebbachisaurids, a group of sauropods that were distant cousins of the more familiar Diplodocus.

The juvenile dinosaurs alone were a significant find—no one had identified juvenile rebacchisaurids before. But the association of those skeletons is the focus of the new paper. Evidence from trackways and bonebeds has hinted that different sauropods had distinct social structures. Some, such as Alamosaurus, seemed to group together in small herds as juveniles and either become solitary as they grew or form age-segregated adult herds. Other sauropods seemed to live in mixed-age herds, where juveniles remained with older individuals. In the case of the bonebed in Argentina, it would seem that juveniles and adults traveled together.

But how do we know these dinosaurs really lived together? The skeletons are incomplete and mostly disarticulated—perhaps they were all washed up to the same spot and buried. Salgado and co-authors present a different interpretation.  The bonebed doesn’t seem to be a trap or mire, and the paleontologists noted that the skeletons show “few signs of transport.” It would seem that the sauropods died all at once. The reason why is a mystery. While they frustratingly do not provide details about this scenario, the researchers speculate that “the death of the adult triggered the death of the two juvenile individuals.”

The fact that the three dinosaurs were preserved in place, without evidence of transport, seems to be fair evidence that this species of sauropod was social. But even that hypothesis brings up a series of other questions. Did individuals stay with the herd from the time they were born? Was there any form of parental care after the babies left the nest? Did these dinosaurs really form large herds, or did the young simply stick with one of their parents? We still have a lot to learn about the lifestyles of the big and extinct.

References:

Myers, T., & Fiorillo, A. (2009). Evidence for gregarious behavior and age segregation in sauropod dinosaurs Palaeogeography, Palaeoclimatology, Palaeoecology, 274 (1-2), 96-104 DOI: 10.1016/j.palaeo.2009.01.002

Salgado, L., Canudo, J., Garrido, A., & Carballido, J. (2012). Evidence of gregariousness in rebbachisaurids (Dinosauria, Sauropoda, Diplodocoidea) from the Early Cretaceous of Neuquén (Rayoso Formation), Patagonia, Argentina Journal of Vertebrate Paleontology, 32 (3), 603-613 DOI: 10.1080/02724634.2012.661004

A skeleton reconstruction of Eoabelisaurus, showing the recovered parts of the skeleton. From the LMU press release.

Some dinosaur lineages are more famous than others. I can say “tyrannosaur” and most anyone immediately knows what I’m talking about: a big-headed, small-armed predator similar to the notorious Tyrannosaurus rex. The same goes for “stegosaur,” and of course it helps that Stegosaurus itself is the famous emblem of this bizarre group. But public understanding hasn’t kept up with new discoveries. In the past two decades, paleontologists have identified various dinosaur lineages vastly different from the classic types that gained their fame during the Bone Wars era of the late 19th century. One of those relatively obscure groups is the abelisaurids: large theropod dinosaurs such as Carnotaurus with high, short skulls and ridiculously stubby arms that make T. rex look like Trogdor the Burninator. And paleontologists Diego Pol and Oliver Rauhut have just described an animal close to the beginning of this group of supreme predators—a dinosaur from the dawn of the abelisaurid reign.

Pol and Rauhut named the dinosaur Eoabelisaurus mefi. Discovered in roughly 170-million-year-old Jurassic rock near Chubut, Argentina, the mostly complete dinosaur skeleton is about 40 million year older than the next oldest abelisaurid skeleton. Eoabelisaurus, placed in context with other theropod dinosaurs of the same era, represents a time when predatory dinosaurs were undergoing a major radiation. Early members of many terrifying Cretaceous predators such as the tyrannosaurs and abelisaurids had already appeared by the Middle to Late Jurassic.

Not all of these Jurassic predators looked quite like their later Cretaceous counterparts. Jurassic tyrannosaurs such as Juratyrant and Stokesosaurus were relatively small predators, unlike their bulky, titanic relatives from the Late Cretaceous. Eoabelisaurus was a little closer to what was to come.

Despite being many tens of millions of years older than relatives such as Carnotaurus and Majungasaurus, the newly described dinosaur displays some tell-tale features that characterize the group. While a significant portion of the dinosaur’s skull is missing, the head of Eoabelisaurus had the short, deep profile seen among other abelisaurids. And this dinosaur already had distinct forelimbs. Much like its later relatives, Eoabelisaurus had a strange combination of heavy shoulder blades but wimpy forelimbs, with a long upper arm compared to the lower part of the arm. The dinosaur’s condition was not as extreme as in Carnotaurus—a dinosaur whose lower forelimbs were so strange that we have no idea what, if anything, Carnotaurus was doing with its arms—but they were still comparatively small and tipped with little fingers good for wiggling but probably useless in capturing prey.

And with a 40-million-year gap between Eoabelisaurus and its closest kin, there are plenty of other abelisaurids to find. The question is where  they are. Is their record so poor that very few were preserved? Or are they waiting in relatively unexplored places? Now that the history of these blunt-skulled predators has been pushed back, paleontologists can target places to look for the carnivores.

Reference:

Pol, D., Rauhut, O. (2012). A Middle Jurassic abelisaurid from Patagonia and the early diversification of theropod dinosaurs. Proceedings of the Royal Society B, 1-6 : 10.1098/rspb.2012.0660

A clutch of sauropod eggs at the geothermal nesting site in Argentina. Eggs are outlined by black dashes. From Fiorelli et al., in press.

Imagine a dinosaur as massive as Apatosaurus sitting on a nest. It doesn’t really work, does it? We know without a doubt that these large sauropod dinosaurs laid eggs, but there is no conceivable way that the gargantuan dinosaurs could have sat on their grapefruit-sized eggs without crushing them all. There must have been some other way that the eggs could have been kept safe and warm enough to develop properly. One special site in Argentina suggests that some sauropods had a geological solution to the problem.

Two years ago, paleontologists Lucas Fiorelli and Gerald Grellet-Tinner announced the discovery of a unique nesting site that sauropods returned to multiple times. During a stretch between 134 million and 110 million years ago, expectant mother sauropods came to this site to deposit clutches of up to 35 eggs within a few feet of geysers, vents and other geothermal features. This basin held naturally heated dinosaur nurseries.

A new, in-press paper about the site by Fiorelli, Grellet-Tinner and colleagues Pablo Alasino and Eloisa Argañaraz reports additional details of this site. To date, more than 70 clutches of eggs have been found across an area spanning more than 3,200,00 square feet in a section of rock about four feet thick. Rather than focusing on the habits of the dinosaurs, however, the new study fills out the geological context of the place as a possible explanation for why the dinosaurs came here.

On the basis of geological features and minerals, the authors suggest that the site may have resembled the Norris Geyser Basin of present-day Yellowstone National Park. A series of underground pipes and tubes fed geysers, hot springs and mud pots scattered across an ancient terrain crossed by rivers. The fact that the egg clutches are consistently found near the heat-releasing features is taken by Fiorelli and co-authors as an indication that parent dinosaurs were seeking out these spots to lay their eggs. And this site isn’t the only one. Fiorelli and collaborators also point out that similar sauropod egg sites have been found in South Korea.

Exactly what happened to preserve so many nests is not immediately clear, but the eggs were buried in sediments at least partly produced by the surrounding geothermal features. The eggs were eroded and thinned by the acidic nature of the entombing sediment. Some eggs were destroyed by these and other processes, but others held out and became preserved in place.

Not all sauropod dinosaurs selected such sites for nests. Particular populations near geothermal features may have received a benefit from the natural heat, but how did other populations and species far removed from these hot spots lay and protect their nests? We still have much to learn about how baby sauropods came into the world.

References:

Fiorelli, L., Grellet-Tinner, G., Alasino, P., & Argañaraz, E. (2011). The geology and palaeoecology of the newly discovered Cretaceous neosauropod hydrothermal nesting site in Sanagasta (Los Llanos Formation), La Rioja, northwest Argentina Cretaceous Research DOI: 10.1016/j.cretres.2011.12.002

A reconstruction of Patagonykus. The newly-described Bonapartenykus was a close relative of this dinosaur. Image from Wikipedia.

Alvarezsaurs are Cretaceous mysteries. These small dinosaurs, a feathered subgroup of coelurosaurs, had long jaws studded with tiny teeth, and their arms were short, stout appendages that some researchers hypothesize were used to tear into anthills or termite mounds. But no one knows for sure. We understand very little about the biology of these dinosaurs, but even as we puzzle over their natural history, more previously unknown genera are being found. The latest is Bonapartenykus ultimus from the Late Cretaceous of Patagonia, and what makes this dinosaur so special is what was found with its bones.

Paleontologists Federico Agnolin, Jaime Powell, Fernando Novas and Martin Kundrát describe the new dinosaur in an in-press Cretaceous Research paper. The alvarezsaur was not in good shape when the researchers found it. While some of the bones, particularly those of the leg, were close to their original articulation, Bonapartenykus is represented by an incomplete set of partially damaged bones, without a skull. In life, the dinosaur is estimated to have been about eight and a half feet long. (Subtle characteristics of the preserved vertebra, shoulder girdle, and hips are what led Agnolin and co-authors to identify this animal as an alvarezsaur despite the paucity of bones.) But there was also something else. Next to the bones were the battered remnants of at least two dinosaur eggs. Could these be fossil evidence of a Bonapartenykus that was protecting its nest?

Determining who laid those eggs is a difficult task. No evidence of embryos has been found inside the egg, so we can’t entirely be sure of what kind of dinosaur was growing inside. The close association between the fossils is the primary line of evidence that the eggs might be attributable to Bonapartenykus. This is the hypothesis favored by Agnolin and co-authors, but they doubt that the small site represents parental care. There is no evidence of a nest. Instead the scientists suggest that the two eggs may still have been inside the dinosaur when it died—a hypothesis based on the previous discovery of an oviraptorosaur from China with a pair of eggs preserved where the dinosaur’s birth canal would have been. When the alvarezsaur perished, the eggs may have fallen out of the body and been preserved with the bones.

Yet I wonder if there might be alternative explanations. Just because fossils are found together does not necessarily mean that the organisms those fossils represent interacted in life. Making connections between organisms found at the same site requires a detailed understanding of taphonomy—what happened to those organisms from the time of death to discovery. In this case, the bones of  Bonapartenykus are scattered and poorly preserved, and the eggs were also partially broken. Did the animal simply fall apart, as the authors seem to suggest, or were the bones and eggs brought together through rushing water? Perhaps the body of Bonapartenykus was carried by a water flow to the location of the eggs, fell apart after the water receded and then was buried again. This is a bit of armchair speculation on my part, and the hypothesis proposed by Agnolin and co-authors is a reasonable one, but we need a detailed understanding of how this little fossil pocket formed if we are to understand the relationship between the eggs and the bones. The geological and taphonomic details of the fossil site are important for framing hypothesis about what happened so many millions of years ago. We may have to wait for more intricately preserved fossils to be sure. A Bonapartenykus preserved on a nest, or a female dinosaur with eggs preserved within her hips, would do nicely.

References:

Agnolin, F., Powell, J., Novas, F., & Kundrát, M. (2011). New alvarezsaurid (Dinosauria, Theropoda) from uppermost Cretaceous of north-western Patagonia with associated eggs Cretaceous Research DOI: 10.1016/j.cretres.2011.11.014

A reconstruction of Leyesaurus marayensis, showing the bones found so far. The scale bar is 25cm. From Apaldetti et al., 2011.

The evolution of the sauropod dinosaurs has to be one of the most fantastic transitions in the fossil record. Though some were the largest creatures to ever walk the land—long-necked behemoths such as Giraffatitan and Argentinosaurus—this impressive group of dinosaurs has its evolutionary roots in much smaller, bipedal dinosaurs that ran about during the Late Triassic. Rather than there being a single, straight evolutionary line from the small sauropod forerunners to famous Jurassic and Cretaceous giants, however, there were multiple flowerings of diversity among the early forms. Yet another new discovery from South America adds some resolution to the big picture.

Within the broad dinosaur family tree, the sauropodomorpha is one of the most prominent branches. This group contains the great sauropod dinosaurs as well as their closest relatives and evolutionary forerunners. Within this scheme, the sauropods were a particular and specialized lineage of a wider group of sauropodomorph dinosaurs that began to spread and diversify many millions of years before there was anything like Diplodocus stomping around. The roughly 231-million-year-old dinosaur Panphagia found in Argentina comes quite close to the beginnings of the sauropodomorph lineage. This dinosaur, named just two years ago, was a bipedal and relatively slender animal that nevertheless represents the approximate ancestral stage for the sauropodomorphs.

This month, another, more specialized sauropodomorph from Argentina was described in the journal PLoS One by paleontologists Cecilia Apaldetti, Ricardo Martinez, Oscar Alcober and Diego Pol. They have named the animal Leyesaurus marayensis. Relatively little of the approximately 199-million-year-old dinosaur was found: A skull, several neck and tail vertebrae, and a few elements of the limbs were all that were recovered, and the animal is estimated to be about eight and a half feet long. Nevertheless, these bones appear to be distinctive enough to separate the new dinosaur out as a previously unknown genus and species from the latest Triassic or earliest Jurassic of northwestern Argentina.

Leyesaurus falls in an intermediate place between the earliest, Panphagia-type forms and the earliest true sauropod dinosaurs. While this sauropodomorph dinosaur already had an elongated neck and spoon-shaped teeth suited to an herbivorous diet, Leyesaurus lacked the column-like limbs of the giant sauropods and could probably switch between walking on two legs or all fours. This can be inferred from the hypothesis of Apaldetti and co-authors that Leyesaurus was most closely related to Massospondylus, a better-known sauropodomorph from the Early Jurassic of South Africa that had shorter forelimbs than hindlimbs. But Leyesaurus was not ancestral to the giant sauropods of later Mesozoic time. Instead this dinosaur, like its close relatives, was part of an array of sauropodomorph dinosaurs which spread all over the world during the later part of the Triassic and Early Jurassic. This time period was one of great change for dinosaurs, and the more we understand about creatures such as sauropodomorphs from this time the better we will be able to comprehend how the giants of the Jurassic and Cretaceous came to be.

References:

Apaldetti, C., Martinez, R., Alcober, O., & Pol, D. (2011). A New Basal Sauropodomorph (Dinosauria: Saurischia) from Quebrada del Barro Formation (Marayes-El Carrizal Basin), Northwestern Argentina PLoS ONE, 6 (11) DOI: 10.1371/journal.pone.0026964

A dinosaur egg with preserved wasp cocoons inside. From Genise and Sarzetti, 2011.

Dinosaur eggs were wonderful things. For the dinosaurs, reproducing by laying eggs may have played an important role in why many species reached enormous sizes. And for the animals that fed on them, dinosaur eggs were tasty packages of protein. Early last year, for example, researchers announced the discovery of a prehistoric snake that probably crushed sauropod eggs to reach the dinosaur embryos inside. Now paleontologists Jorge Genise and Laura Sarzetti have proposed that wasps may have made the most of dinosaur eggs, too.

The Cretaceous rock of Argentina has yielded many dinosaur eggs. The egg at the center of the new study was part of a clutch found in rock dating between about 77 million and 67 million years ago. There were five spherical eggs altogether, but one was special. Cracked in half, the fossil preserved eight cocoons inside. These were delicate structures—the sort that could not be transported without damaging or destroying the cocoons—and so it seems that the association between the egg and cocoons is real and not attributable to some accident of preservation. Invertebrates had been using this dinosaur egg, but what sort of creatures, and why?

As reconstructed by Genise and Sarzetti, the cocoon-containing egg was probably broken by some kind of force which did not affect the other eggs in the clutch. (If the egg had been crushed during burial in sediment, for example, the other eggs in the clutch would have been similarly broken, yet they were not.) Exactly what cracked the egg is unknown, but as the paleontologists point out, the egg would have filled in with sediment while still decaying. This turned the egg into a food source and place where insect scavengers could burrow into the soil filling the structure.

Exactly what species of insect the cocoons belonged to is unknown, but the structure of the preserved cocoons most closely resembles that of wasp cocoons. This finding helps flesh out the story of what happened to the egg after it was crushed. The location and orientation of the cocoons seems to fit a pattern for parasitoid wasps that track down spiders and crickets in their own burrows, immobilize them, and then lay eggs on them. If correct, this means that the wasps were relatively late arrivals at the rotten dinosaur egg—the wasps were there to take advantage of the other invertebrates that had come to feed on and burrow into the impromptu home. Still, even though they did not directly feed on the dead dinosaur egg, the wasps would have been part of a prehistoric cleaning crew—a temporary ecosystem whose existence we now know of thanks to the chance preservation of a special egg.

References:

GENISE, J., & SARZETTI, L. (2011). Fossil cocoons associated with a dinosaur egg from Patagonia, Argentina Palaeontology, 54 (4), 815-823 DOI: 10.1111/j.1475-4983.2011.01064.x

Eodromaeus, as restored by artist Todd Marshall.

Tracking the origin of the dinosaurs has been one of the most difficult tasks paleontologists have faced, but since the 1990s, multiple discoveries in South America have provided scientists with a look at what some of the earliest dinosaurs were like. Eoraptor, Herrerasaurus and the recently-described Panphagia are among the oldest representatives of the famous vertebrate group, and all come from the 231-million-year-old rock of Argentina’s Ischigualasto Formation. A new species from the same slice of time, described yesterday in the journal Science, has added to the diversity of early dinosaurs.

Named Eodromaeus murphi by Ricardo Martinez, Paul Sereno and colleagues, this early dinosaur is currently represented by a partial skeleton which is still missing a few parts of the skull, tail, ribs and other parts of the skeleton. Despite this missing fragments, however, it is clear what sort of dinosaur it was. The long, low skull of Eodromaeus was filled with sharp, recurved teeth, and anatomically it resembles both its contemporary Herrerasaurus and the 215-million-year-old predatory dinosaur Tawa. Even though our knowledge of early dinosaurs remains scrappy, comparison with its relatives shows Eodromaeus to be a theropod dinosaur, which was one of the earliest-known carnivorous groups.

But one of the most significant aspects of the new paper does not directly relate to Eodromaeus. Paleontologists are constantly reexamining ideas about early dinosaur evolution as new species are found, and thanks to the discovery of both Eodromaeus and Panphagia, one of the more famous Ischigualasto dinosaurs has been given a new identity. Eoraptor was thought to have been one of the earliest theropod dinosaurs and representative of the humble beginnings of this group, but the new study by Martinez and co-authors repositions this dinosaur as a sauropodomorph closely related to Panphagia.

If the new study is correct, Eoraptor was not a precursor to Allosaurus, Tyrannosaurus, and other predators giants, but instead was on the evolutionary stem which eventually gave rise to the immense sauropod dinosaurs. This seems especially apparent in the teeth of Eoraptor. Compared to the teeth of Eodromaeus, the teeth of Eoraptor are more leaf-shaped and seem better suited to a varied diet, indicating that it was probably an omnivore that regularly consumed plants. Nevertheless, it should be kept in mind that this new interpretation of Eoraptor is a hypothesis; it will require further discovery, investigation, and analysis to determine just what sort of dinosaur it was.

The researchers behind the Eodromaeus description also use the opportunity to appraise the pattern of early dinosaur evolution. By 231 million years ago there were already multiple genera of different dinosaur carnivores and omnivores (if not dedicated herbivores), and they appear to have made up a significant part of the local fauna. This might indicate that the oft-discussed “rise of the dinosaurs” may have occurred later than thought, but as has been recently stressed in reference to other dinosaur sites, we must be careful in our counts of dinosaur diversity at any one place and time. An exceptional richness in dinosaurs or a particular type of dinosaur may mean that those species actually accumulated over a longer span of time and did not live side-by-side after all. This well-known concept is called time-averaging, and parsing the fine details of what dinosaurs lived alongside one another will be critical to studies of their early evolution.

For more, see Bill Parker’s post on Eodromaeus at Chinleana.

References:

Martinez, R., Sereno, P., Alcober, O., Colombi, C., Renne, P., Montanez, I., & Currie, B. (2011). A Basal Dinosaur from the Dawn of the Dinosaur Era in Southwestern Pangaea Science, 331 (6014), 206-210 DOI: 10.1126/science.1198467

Bite marks - indicated by white arrows - along the side of an articulated crocodile tail close to the hips. From Fiorelli, 2010.

The traditional, simplified recipe for how to make a fossil goes something like this: take a dead animal, keep it safe from scavengers, cover it up with sediment, add a heaping dollop of time and presto!, you have a petrified skeleton. The second step is often cited as being especially important—a skeleton can’t enter the fossil record if it is destroyed—but sometimes predator kills and scavenged carcasses do make it into the fossil record. This year alone there has been a report of Tarbosaurus scavenging a hadrosaur carcass and a study confirming that Tyrannosaurus picking at the deceased of its own kind. Now paleontologist Lucas Ernesto Fiorelli has reported on a collection of Cretaceous crocodile bones that may be theropod dinosaur table scraps.

The crocodile in question, described in 1991 but not yet named, was found on the campus of the University of Comahue in Neuquén, Argentina. There was not very much of it left. A few pieces of skull, some vertebrae, a smattering of limb fragments and a nearly complete tail were all that remained. Based on the geology of the area, this animal lived along rivers or streams that skirted along huge sand dunes in a hot, seasonal environment, and its anatomy shows that it belonged to a group of extinct crocs called the peirosaurid crocodyliforms. These animals were more slender than their modern cousins and adapted to a more terrestrial lifestyle.

As described by Fiorelli, there are about 70 punctures and bite marks on the preserved remains of the animal, present on almost every skeletal element except the skull. Particularly noteworthy is the distribution of bitemarks along the preserved tail of the animal, which appears to have been crushed by the powerful bite of a large predator. The question is what left the bite marks.

Fiorelli rejects the hypothesis that this animal was the victim of aggression by another crocodile. When competing for dominance, modern crocodylians display and bite each other, but the amount of trauma indicated by the bite marks on this individual is inconsistent with such behavior. Additionally, while the crocodile was about 10 to 12 feet long, the animal that left the bitemarks appears to have been considerably larger, suggesting that the injuries were probably not caused by a member of the same species.

The idea that the injuries were caused by other crocodile species that have been found from the same deposits were also ruled out by Fiorelli. One, Notosuchus, may have been primarily herbivorous, and Fiorelli states that its contemporary Comahuesuchus just didn’t have the jaw power to do the kind of damage seen on the other crocodile bones. Likewise, even though two other genera of prehistoric crocodiles called baurusuchids were certainly predators, the pattern of bite marks on the victim’s skeleton indicate an animal with a much larger skull. As hypothesized by Fiorelli, a large theropod dinosaur is the most likely culprit, though the specific species of this predator cannot be ascertained. Both abelisaurids and carcharodontosaurids—two groups of diverse theropods common in the Cretaceous of South America—have been found from the geologic formation the crocodile skeleton came from, but so far, no teeth or other remains have been found in proximity to the skeleton to conclusively close the case.

References:

Lucas Ernesto Fiorelli (2010). Predation bite-marks on a peirosaurid crocodyliform from the Upper Cretaceous of Neuquén Province, Argentina Ameghiniana, 47 (3)

One of many dinosaur eggs discovered at the Sanagasta site. From the Nature Communications paper.

Even though they grew to be some of the largest animals ever to walk the earth, sauropod dinosaurs started off small. From numerous nesting sites found all over the world it appears that gravid female sauropods, rather than putting all their effort into laying a few enormous eggs, created large nests of numerous, relatively small eggs. But why they selected particular nesting sites has long been a mystery. Now, in the journal Nature Communications, paleontologists Gerald Grellet-Tinner and Lucas Fiorelli provide evidence that nesting female sauropods picked at least one site based upon its natural heat.

In northwestern Argentina’s La Rioja Province lies a bed of white Cretaceous rock called the Los Llanos Formation. Within that formation, paleontologists have found numerous clutches of eggs at Sanagasta. The eggs are very similar to those of sauropod dinosaurs found elsewhere in Argentina, but the focus of the new study is not so much the eggs as the environment they were deposited in. In one particular area, designated sub-site E, the egg clutches are found dispersed three to ten feet away from geysers, vents, and other hydrothermal features which were active between 134 and 110 million years ago—that is, the eggs were laid in a naturally-heated nursery incubated between 140 and 212 degrees Fahrenheit. During the time the dinosaurs occupied this site, it must have looked somewhat reminiscent of some areas of Yellowstone National Park, but with sauropods wandering among the hot springs instead of elk and bison.

Although this is a wonderful discovery, the fact that these dinosaurs came back to the hydrothermally-active site again and again is not unusual. Some ground-nesting birds, such as the Polynesian megapode, seek out sites warmed by volcanic activity to create their nests, and so it seems that sauropod dinosaurs, too, were very selective about where they created their nests. With this in mind, paleontologists can take a closer look at other nesting sites around the world for clues as to why certain sites were “hot spots” for dinosaur nests.

For more on this discovery, see Not Exactly Rocket Science and Nature News.

Gerald Grellet-Tinner & Lucas E. Fiorelli (2010). A new Argentinean nesting site showing neosauropod dinosaur reproduction in a Cretaceous hydrothermal environment. Nature Communications, 1-8 : 10.1038/ncomms1031