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
May 24, 2012
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.
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
October 14, 2011
This week, dinosaur fans got a sneak preview of one of the most beautiful theropod dinosaur skeletons yet discovered. Depending on what the critter turns out to be, the specimen may alter our understanding of how widespread partial coats of fuzzy feathers were among dinosaurs.
Originally reported in the German newspaper Der Spiegel and later mentioned by the Nature news blog, the new specimen is a nearly complete juvenile theropod dinosaur. Even better, traces of skin and possible feathers can be seen on the fossil. Contrary to those reports, though, the specimen is geologically older than the 135 million years attributed to it in the press. The geological and preservational qualities of the fossil look identical to those from the famous Jurassic limestones that have yielded so many other exceptional fossils. I contacted Oliver Rauhut, paleontologist and conservator of Bavaria’s state paleontological and geological collections and one of the researchers currently studying the specimen, and asked about the animal’s geologic context. He replied: “The theropod is indeed from the Jurassic, from the unit underlying the Solnhofen Formation, and thus 145 to 150 million years old rather than the 135 given in the press release.”
That is nearly all that has been publicly released, but the specimen was also featured in a talk titled “New Information on Late Jurassic Theropod Dinosaurs from Southern Germany” given by Rauhut and paleontologist Christian Foth at the recent Latin American Conference of Vertebrate Paleontology in San Juan, Argentina. Scuttlebutt from that conference has already started fueling speculation about how important this new dinosaur might be. Of course, we will have to wait for all the published results to find out the essential details, but the presence of simple feather traces on this specimen could have important consequences for our understanding of dinosaurs.
So far, all the theropod dinosaurs definitively known to have possessed feathers belonged to a subgroup called coelurosaurs. (The question of whether the non-coelurosaurian theropod Concavenator had feather-like bristles on its arms remains unresolved.) That includes another, roughly 151-million-year-old theropod from Germany with preserved feather traces called Juravenator. If the new specimen turns out to be a coelurosaur, then we will gain a little more resolution about how common feathers were among this group and possibly details of the development of those feathers as coelurosaurs matured. But what if it turns out to be something else? If the new dinosaur is something other than a coelurosaur, then the fact that it was at least partially covered in simple feathers would indicate that either: 1) such structures evolved multiple times among dinosaurs, or 2) the forerunners of feathers were inherited from an even older common ancestor. In either case, simple feathers or feather-like structures may have been more widespread among theropods than previously understood.
In fact, we already know that dinosaurs other than coelurosaurian theropods had feather-like structures on their bodies. The ornithischian dinosaurs Tianyulong and Psittacosaurus—two genera very, very, very distant from the theropod dinosaurs—were partially covered by bristles that were structurally similar to feathers. The presence of these coverings on dinosaurs so distantly related to coelurosaurs has already raised the possibility that other dinosaurs shared this feature. What we lack are the exceptionally preserved fossils to test the ideas about how widely feather-like body coverings evolved and how widely they were shared. Perhaps the new dinosaur and the work by Rauhut and Foth will help paleontologists broaden their understanding of what dinosaurs looked like and how feathers evolved. Regardless of what subgroup the animal is eventually assigned to, the unnamed dinosaur is a wonderful specimen. I cannot wait to find out more.