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The Smithsonian Stegosaurus sculpture, on display in 1904.

Like many fossils fans, I quite enjoy picking apart bad restorations of dinosaurs, but I must admit that I have a soft spot for the 20th century image of drab, slow, stupid dinosaurs. Those were the dinosaurs I first encountered at museums and school libraries—just before the “Dinosaur Renaissance” hit the mainstream of public consciousness—and so I was delighted when I came across this old photograph of a Stegosaurus created by the Smithsonian Institution.

Printed in a companion volume to the 1904 World’s Fair in St. Louis, Missouri, the photo shows a vintage dinosaur. Strangely, though, the plaster dinosaur was not mentioned by name in the image caption, which merely described it as “an armored dinosaur, a huge reptilian creature that once roamed the plains of what are now Wyoming, Colorado and Kansas, distinguished among others of its species by a small head, large projecting plates on the back, and stout spines on the tail.” Still, any dinosaur aficionado would immediately recognize the creature as Stegosaurus, and the 1904 model looked little different from depictions of the same animal I saw just before images of 20th century dinosaurs were swept away.

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The AMNH Allosaurus, standing over the bones of its prey. Image from Wikipedia.

I feel a little sorry that I said Allosaurus had one of the dullest names in paleontology yesterday. It’s not the dinosaur’s fault that Othniel Charles Marsh gave it the unimaginative title of “different reptile.” Had Marsh seen the complete skeleton when he coined the name, perhaps he would have come up with a more fearsome moniker. Seeing the American Museum of Natural History mount of Allosaurus crouched over the tooth-scored bones of a sauropod certainly captured my imagination.

Put on display in 1908, the AMNH’s iconic Allosaurus had actually been collected decades before. In 1879, just two years after the dinosaur was named, a man by the name of F.F. Hubbell discovered the skeleton at the Jurassic locality of Como Bluff, Wyoming. Hubbell was a collector for Edward Drinker Cope—Marsh’s personal and academic rival—and the specimen he found was far more complete than the bits of broken bone Marsh had described.

Strangely, however, it seems that Cope did not appreciate the exquisite Allosaurus. He may not have even known what he really had. Some of the bones Hubbell had previously collected were mere scraps, and Cope may have assumed that the boxes from Como Bluff held only specimens of trifling importance.

The dinosaur remained crated up for decades was sold to the AMNH after Cope’s death as part of the paleontologist’s massive collection of fossils. Thought to contain a nearly worthless collection of fragments, the crates from Hubbell were the last to be opened by the museum’s paleontologists, around 1903. They were astounded by what they found.

According to the AMNH paleontologist William Diller Matthew, the skeleton was a “treasure.” Recounting the backstory of the specimen, he wrote in the American Museum Journal:

Although collected by the crude methods of early days, [the Allosaurus] consisted of the greater part of the skeleton of a single individual, with the bones in wonderfully fine preservation, considering that they had been buried for say eight million years. They were dense black, hard and uncrushed, even better preserved and somewhat more complete than the two fine skeletons of Allosaurus from Bone-Cabin Quarry, the greatest treasures that this famous quarry had supplied.

Comparison to the other known Allosaurus specimens and the bones of smaller theropod dinosaurs were needed to fill in some of the gaps, but soon Matthew and his colleagues were able to assemble a complete skeleton of the predator. Fortuitously, an AMNH expedition in 1897 had collected a the partial remains of a “Brontosaurus” that had clearly been damaged by a theropod dinosaur, and the discovery of broken Allosaurus teeth around the bones confirmed the connection between the two. The decision was made to put the two specimens together, with the Allosaurus taking on a threatening posture to drive away any smaller scavengers that might come by. A snapshot of a past age, Matthew described the exhibit’s intent this way:

As now exhibited in the Dinosaur Hall, this group gives to the imaginative observer a most vivid picture of a characteristic scene of that bygone age, millions of years ago, when reptiles were the lords of creation, when “Nature, red in tooth and claw” had lost none of her primitive savagery, and the era of brute force and ferocity showed little sign of the gradual amelioration, which was to come to pass in future ages through the predominance of superior intelligence.

A restoration of Acrocanthosaurus (top) and a line drawing of the skull from Oklahoma. Illustrated by Emily McGrew and from Eddy and Clarke, 2011.

Allosaurus has one of the dullest names in all of paleontology. The famous dinosaur’s moniker simply means “different reptile”—a bit of a letdown for one of the top predators of Jurassic North America. Early on, the name fit well—Allosaurus was a very unusual dinosaur compared to other large, predatory species—but since 1878 bone hunters have found a slew of closely related dinosaurs whose relationships are still being worked out by paleontologists.

Among the most puzzling of the allosauroids has been the high-spined Acrocanthrosaurus from the Early Cretaceous of North America. Looking like a larger, beefier version of Allosaurus, with a raised ridge of spines along its back, this dinosaur was considered to be the closet relative of Allosaurus until discoveries in South America and Africa started turning up remains of similar creatures. Called carcharodontosaurids, these giant predators were clearly related to Allosaurus and its closest kin. Where Acrocanthosaurus fit among these two lineages has been a matter of debate, but a paper just published by Drew Eddy and Julia Clarke in PLoS One seeks to resolve the issue.

In 2000, paleontologists Ken Carpenter and Phil Currie described the almost entirely intact skull of an Acrocanthrosaurus from Oklahoma. The skull was still partially encased in rock when initially studied, though. Now that the specimen has been completely prepared, Eddy and Clarke decided to give it another look. By comparing this exceptional Acrocanthrosaurus skull to those of other allosauroids and more distantly related theropod dinosaurs, they hoped to determine where the high-spined dinosaur fit among similar species.

The new paper by Eddy and Clarke serves as a minutely detailed guidebook to the Acrocanthosaurus skull, and the scientists were able to draw a few conclusions from their in-depth study. Eddy and Clarke confirmed that Acrocanthrosaurus was a carcharodontosaurid, being particularly close to Eocarcharia from Niger. This means that Allosaurus and Acrocanthrosaurus were only cousins that belonged to separate lineages within the larger group Allosauroidea.

A simplified evolutionary tree showing the relationships of allosauroids. Allosaurus is underlined in blue, and Acrocanthosaurus in underlined in red. Modified from Eddy and Clarke, 2011.

Allosaurus and Acrocanthosaurus shared a common ancestor at a distant point in time, and this recognition can tell us something about how dinosaurs moved around the world. Around 143 to 134 million years ago, Eddy and Clarke state, dinosaurs could have moved from prehistoric Europe to North America by way of land connections including Greenland and island chains. Since the dinosaur Neovenator—identified as an early carcharodontosaurid in the new study—was present in Europe just after this time, the scientists propose that carcharodontosaurids could have radiated out of Europe into Africa, Asia and North America through the various pathways open around that time. Members of the dispersals would have been adapted in different ways on each continent, with Acrocanthosaurus being unique to North America.

But we are really only just beginning to understand the origin and evolution of this group of dinosaurs. For a long time Allosaurus and Acrocanthosaurus seemed like North American oddballs—predators unlike carnivorous dinosaurs elsewhere—but new discoveries are allowing scientists to slowly piece together their relationships and history. There are probably many allosauroid dinosaurs waiting to be discovered, and the recognition of these yet-unknown dinosaurs will further flesh out the story of some of the biggest predators to have ever lived.

References:

Eddy, D., & Clarke, J. (2011). New Information on the Cranial Anatomy of Acrocanthosaurus atokensis and Its Implications for the Phylogeny of Allosauroidea (Dinosauria: Theropoda) PLoS ONE, 6 (3) DOI: 10.1371/journal.pone.0017932

The underside of the snout fragment representing the spinosaur Oxalaia from Brazil. The holes are the tooth sockets. From Kellner et al., 2011.

Paleontologists have not found much of Oxalaia quilombensis. A fragment of the snout and a portion of the upper jaw are all that is known of this dinosaur. Even so, those two parts are enough to know that Oxalaia was one of the peculiar predatory dinosaurs known as spinosaurs, and a giant one at that.

Just described by Alexander Kellner, Sergio Azevedo and colleagues in Annals of the Brazilian Academy of Sciences, the new dinosaur was found in Late Cretaceous deposits of northeastern Brazil dating back to about 95 million years ago. The portion of the snout alone confirms that it was one of the spinosaurs. Unlike other predatory dinosaurs with heavy, broad heads, the spinosaurs had elongated, crocodile-like jaws, with the upper jaw ending in a spoon-shaped rosette. Oxalaia had the same snout shape, and using this fragment along with skull proportions of better-known spinosaurs, Kellner and co-authors estimate that this dinosaur would have had a skull about four and a half feet long.

Oxalaia would have been a giant among spinosaurs. Compared with the spinosaur fossils previously found in slightly older rock in Brazil—given the names Irritator and Angaturama, though likely representing the same dinosaur—Oxalaia was certainly the biggest type of this dinosaur found in South America. Only spinosaurs from Africa—such as Suchomimus and Spinosaurus—were the same size or larger.

Frustratingly, our knowledge of Oxalaia is so incomplete that it is difficult to know what the entire animal looked like. The fossils recovered so far are most similar to those of Spinosaurus, but there is not yet a way to tell whether the new spinosaur from Brazil had a sail on its back or how it compared to its close relatives. Additional Oxalaia bones may be difficult to find. The site where the two skull fragments were found is dominated by isolated bones that are often quickly destroyed by the elements once exposed. Now that paleontologists know what to look for, though, perhaps researchers will be able to accumulate more bits and pieces of Oxalaia.

References:

KELLNER, A.; AZEVEDO, S.; MACHADO, A.; DE CARVALHO, L.; HENRIQUES, D. (2011). A new dinosaur (Theropoda, Spinosauridae) from the Cretaceous (Cenomanian) Alcântara Formation, Cajual Island, Brazil Anais da Academia Brasileira de Ciências, 83 (1), 99-108

A restoration of Platypterygius specimen SAM P14508 showing the location of the injuries on the lower jaw. From Zammit and Kear, 2011.

The prehistoric world was intensely violent. So I believed when I was a kid, anyway. Almost every book I read or movie I saw about now-fossilized creatures showed them as ferocious monsters that were constantly biting and clawing at each other. I spent hours with plastic toys and mud puddles reenacting these scenes myself, never thinking about whether there were any fossil traces of such epic battles.

Finding fossil evidence of ancient conflicts is very difficult. A predator might leave behind traces of feeding—such as toothmarks on bone or undigested muscle tissue in their fossilized dung—but the signs of prehistoric fights are very rare. Sometimes, as in the case of the holes in the frill of the horned dinosaur Nedoceratops, what were thought to be injuries inflicted by fighting with animal turn out to be a different kind of pathology or a strange bone growth pattern. Nevertheless, a few signs of prehistoric conflicts have been found.

A little more than 100 million years ago, the large ichthyosaur Platypterygius australis swam the seas of Cretaceous Australia. It was not a dinosaur—not even close—but a marine reptile belonging to a lineage that had returned to the sea many millions of years before. Thanks to new fossil evidence reported by Maria Zammit and Benjamin Kear in an in-press Acta Palaeontologica Polonica paper, we now have evidence that one of these ichthyosaurs may have had a painful run-in with one of its own kind. SAM P14508, a Platypterygius found in South Australia, has a distinctive set of healed wounds on its lower jaw that were most likely made by another ichthyosaur.

The key to the Platyptergius puzzle was the fact that the animal survived its injuries. Had a predator been feeding on the carcass, Zammit and Kear would have found distinctive toothmarks without any signs of healing. Since the injured bone had grown and remodeled after being damaged, though, the ichthyosaur clearly lived for quite some time after being attacked. The bones were scored rather than deeply punctured or broken; while painful, the injuries would not have debilitated the ichthyosaur.

Naturally, predators aren’t always successful and might injure an animal without killing it, but the pattern of the wounds lead Zammit and Kear to propose the marks were made by another Platyptergius. The only other large predators in the area at the time were the enormous pliosaur Kronosaurus and large sharks, both of which would have left very different bite marks and probably would have attacked part of the body containing vital organs rather than the snout. Zammit and Kear are tentative about their conclusions—without a time machine and some scuba gear, we can’t know for sure what happened—but the wounds on the specimen are consistent with the damage another Platyptergius could have inflicted. “[I]t is tempting to reconstruct the positioning of the marks on the ventral side of the mandible as the result of a restraining bite,” they write, “delivered when another ichthyosaur approached SAM P14508 from below and attempted to neutralize the threat of a counter attack by clamping onto and forcing aside its elongate jaws.”

References:

Zammit, M. and Kear, B.J. (2011). Healed bite marks on a Cretaceous ichthyosaur Acta Palaeontologica Polonica, 5 : 10.4202/app.2010.0117