November 27, 2012
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.
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
November 21, 2012
Last week, I wrote about attempts by paleontologist Phil Bell and colleagues to extract biological secrets from fossilized traces of dinosaur skin. Among the questions the study might help answer is why so many hadrosaurs are found with remnants of their soft tissue intact. Specimens from almost every dinosaur subgroup have been found with some kind of soft tissue preservation, yet, out of all these, the shovel-beaked hadrosaurs of the Late Cretaceous are found with skin impressions and casts most often. Why?
Yale University graduate student Matt Davis has taken a stab at the mystery in an in-press Acta Paleontologica Polonica paper. Previously researchers have proposed that the abundance of hadrosaur skin remnants is attributable to large hadrosaur populations (the more hadrosaurs there were, the more likely their skin might be preserved), the habits of the dinosaurs (perhaps they lived in environments where fine-resolution fossilization was more likely) or some internal factor that made their skin more resilient after burial. to examine these ideas, Davis compiled a database of dinosaur skin traces to see if there was any pattern consistent with these ideas.
According to Davis, the large collection of hadrosaur skin fossils isn’t attributable to their population sizes or to death in a particular kind of environment. The horned ceratopsid dinosaurs–namely Triceratops–were even more numerous on the latest Cretaceous landscape, yet we don’t have as many skin fossils from them. And hadrosaur skin impressions have been found in several different kinds of rock, meaning that the intricate fossilization occurred in multiple types of settings and not just sandy river channels. While Davis doesn’t speculate about what made hadrosaurs so different, he proposes that their skin might have been thicker or otherwise more resistant than that of other dinosaurs. A sturdy hide might have offered the dinosaurs protection from injury in life and survived into the fossil record after death.
Still, I have to wonder if there was something about the behavior or ecology of hadrosaurs that drew them to environments where there was a greater chance of rapid burial (regardless of whether the sediment was sandy, silty or muddy). And the trouble with ceratopsids is that they have historically been head-hunted. Is it possible that we’ve missed a number of ceratopsid skin traces because paleontologists have often collected skulls rather than whole skeletons? The few ceratopsid skin fossils found so far indicate that they, too, had thick hides ornamented with large, scale-like structures. Were such tough-looking dinosaur hides really weaker than they appear, or is something else at play? Hadrosaurs may very well have had extra-sturdy skin, but the trick is testing whether that characteristic really accounts for the many hadrosaur skin patches resting in museum collections.
Davis, M. 2012. Census of dinosaur skin reveals lithology may not be the most important factor in increased preservation of hadrosaurid skin. Acta Paleontologica Polonica http://dx.doi.org/10.4202/app.2012.0077
Osborn, H. 1916. Integument of the iguanodon dinosaur Trachodon. Memoirs of the American Museum of Natural History. 1, 2: 33-54
Sternberg, C.M. 1925. Integument of Chasmosaurus belli. The Canadian Field Naturalist. XXXIX, 5: 108-110
November 20, 2012
Dinosaur giants are among the most famous Mesozoic celebrities. Yet the dinosaur growth spurt didn’t start just as soon as Eoraptor and kin evolved. For most of the Triassic, the first act in their story, dinosaurs were small and gracile creatures, with the first relatively large dinosaurs being the sauropodomorphs of the Late Triassic. Even then, Plateosaurus and kin didn’t come close to the truly enormous sizes of their later relatives–such as Diplodocus and Futalognkosaurus. Discerning when dinosaurs started to bulk up is difficult, however, and made all the more complicated by a set of enigmatic bones found in England.
The fossils at the heart of the in-press Acta Palaeontologica Polonica study, as described by University of Cape Town paleontologist Ragna Redelstorff and coauthors, have been known to researchers for a long time. During the mid-19th century, naturalists described at least five large, incomplete shafts found in the Late Triassic rock of southwest England’s Aust Cliff. Two of these fossils were later destroyed, but, drawing from the surviving specimens and illustrations of the lost bones, paleontologist Peter Galton proposed in 2005 that they came from large dinosaurs that lived over 200 million years ago. In particular, two of the bones resembled stegosaur bones, which would have extended the origin of the armored dinosaurs further back than previously thought.
Not everyone agreed with Galton’s proposal. The bone shafts could be from as-yet-unknown sauropods, some paleontologists argued, while other researchers pointed out that the lack of distinctive features on the bones were unidentifiable beyond the level of “tetrapod” (the major group of vertebrates descended from fish with limbs, similar to Tiktaalik). The bones came from big creatures–possibly more than 20 feet long, based on comparisons to other fossils–but the identity of the Aust Cliff animals is unknown.
Since the outside of the bone shafts provide so little information about their identity, Redelstorff and collaborators looked to the microstructure of two specimens for new clues. While the histological evidence appears to show that the sampled bones belonged to the same species, the authors argue, each individual shows different growth strategies. One bone shaft came from a slightly bigger, rapidly growing individual, while the smaller bone represents an older animal that regularly experienced temporary halts in growth (visible as lines called LAGs in the bone). Why this should be so isn’t clear, but Redelstorff and coauthors suggest individual variation, differences between the sexes or ecological factors as possible causes.
But what sort of animals were the Aust Cliff creatures? When the researchers compared their sample with three kinds of dinosaurs–sauropods, archaic sauropodomorphs and stegosaurs–and Triassic croc cousins called pseudosuchians, the pseudosuchians seemed to be the closest match. Indeed, while the researchers concluded that the “Aust Cliff bones simply do not offer a good match with any previously described histologies,” the specimens appeared to share more in common with those of croc-line archosaurs than with dinosaurs.
This isn’t to say that the Aust Cliff animals were definitely large psuedosuchians, like the recently named Smok. As the researchers point out, the specimens contained a type of bone tissue not previously seen in pseudosuchians–either these animals were not pseudosuchians, or these pseudosuchians were a previously unknown histology. And, Redelstorff and collaborators point out, the bones might be attributable to a sauropodomorph named Camelotia that is found in the same deposits. Studying the bone microstructure of Smok and Camelotia for comparison would be a logical next step in efforts to narrow down the identity of the Aust Cliff animals. Until then, this early “experiment” in gigantism–as Redelstorff and colleagues call it–remains an unresolved puzzle.
Still, the study highlights the importance of building a deep database of paleohistological samples. Had the researchers sampled just one bone, they may have come to the conclusion that all bones of that type would exhibit the same life history–either rapid, continuous growth or a stop-and-go pattern, depending on which they studied. Together, the bones show variations in the natural history of what is presumably the same species, which brings up the question of how quirks of environment, biology and natural history are recorded in bone. If we are going to understand the biology of dinosaurs and other prehistoric animals, we need to cut into as many bones as we can to understand how variable and biologically flexible the creatures truly were.
Redelstorff , R., Sander, P., Galton, P. 2012. Unique bone histology in partial large bone shafts from Aust Cliff (England, Upper Triassic): an early independent experiment in gigantism. Acta Palaeontologica Polonica http://dx.doi.org/10.4202/app.2012.0073
November 19, 2012
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.
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
November 16, 2012
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.
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