The upper and lower jaws of Duriavenator, illustrated when they were thought to belong to Megalosaurus, in A History of British Fossil Reptiles Vol. II. Image from Wikipedia.

If you have been following the Dinosaur Alphabet series so far, you may have noticed a pattern among the first four entries. At one time or another, all the dinosaurs I’ve selected so far were thought to be different animals. The horned Agujaceratops was originally named as a species of Chasmosaurus, the distinctive high-spines of Becklespinax gave Richard Owen’s dopey Megalosaurus its hump, the sauropod Cetiosaurus was originally envisioned as a giant crocodile, and the armored Dyoplosaurus was lumped in with its cousin Euoplocephalus before being split back out again as a distinct genus. I didn’t intend this trend, but it struck me when I came across  one of the rejected candidate for yesterday’s entry for the letter D. Had it not shared much of its story with Becklespinax, I would have picked Duriavenator:

Megalosaurus was a mess. Even though this Jurassic carnivore has been a prehistoric icon ever since it was named by William Buckland in 1824, it has been one of the most confounding of all dinosaurs. That’s because generations of researchers attributed dozens of fragments and isolated bones to the dinosaur, creating a monstrous composite of animals from different places and times. Dinosaurs were unfamiliar animals–the name itself only coined in 1842–and 19th-century naturalists didn’t have the kind of geologic resolution their intellectual descendants rely on to properly constrain when particular species lived. Sometimes researchers named too many species on the basis of scrappy, non-overlapping material, and other times they applied the same name ad infinitum to roughly similar fossils.

Eventually, though, it became apparent that Megalosaurus was unstable. No one could say what the dinosaur really looked like or what bones could accurately be attributed to the predator.  The situation was so bad that, in 2008, paleontologist Roger Benson and colleagues stripped the name Megalosaurus from everything save for the fragment of jaw originally used to name the animal. Whether the rest of the fossils really belonged to Megalosaurus remained to be seen, and, as Benson demonstrated later the same year, at least one other theropod had been improperly obscured behind the famous name.

In 1883, anatomist Richard Owen described a partial theropod skull found on Dorset, England, as another piece of Megalosaurus “bucklandi.” The sharp-toothed dinosaur was only represented by parts of the upper and lower jaws, but, given how little was known about Megalosaurus to start with, Owen’s assignment was reasonable. Nearly a century later, paleontologist Michael Waldman proposed that these fossils represented a previously unknown species of the dinosaur he called Megalosaurus hesperis. Other researchers weren’t sure that the bones really belonged to Megalosaurus, but it wasn’t until Benson’s reexamination that the fossils were split out as a different dinosaur. While the dinosaur was a close cousin of Megalosaurus bucklandii, Benson was able to pick out subtle anatomical characteristics that distinguished the fragmentary skull. In Benson’s analysis, what once was Megalosaurus took on a new life as Duriavenator hesperis.

Benson’s reconstruction of Megalosaurus, with known elements in white and reconstructed portions in grey. While Duriavenator was older and anatomically distinct, the dinosaur would have been similar in form to Megalosaurus. From Benson, 2010.

Unfortunately, we don’t know very much at all about Duriavenator. The dinosaur lived about 170 million years ago in Jurassic England and was a large carnivore of comparable size to the 20-foot-plus Megalosaurus, but that’s where the evidence gives out. Perhaps other Duriavenator specimens are resting in museum collections, but until the discovery of a nearly complete skeleton allows paleontologists to connect the jaws to a body, the dinosaur will be an enigma. But here Megalosaurus itself gives us reason to hope. The Duriavenator paper was just part of Benson’s effort to rehabilitate Megalosaurus, and in 2010 he published a refined, revised reconstruction of the dinosaur’s skeleton based on material collected from Stonesfield, Oxfordshire–the locality where the original jaw came from. Perhaps, with a little detective work in the lab and in the field, paleontologists might also be able to fill out the form of Duriavenator and other Middle Jurassic mysteries.

References:

Benson, R., Barrett, P., Powell, H., Norman, D. 2008.  The taxonomic status of Megalosaurus bucklandii (Dinosauria, Theropoda) from the Middle Jurassic of Oxfordshire, UK. Palaeontology, 51, 2: 419-424.

Benson, R. 2008.  A redescription of “Megalosaurus” hesperis (Dinosauria, Theropoda) from the Inferior Oolite (Bajocian, Middle Jurassic) of Dorset, United Kingdom. Zootaxa 1931: 57-67

Benson, R. 2010. A description of Megalosaurus bucklandii (Dinosauria: Theropoda) from the Bathonian of the UK and the relationships of Middle Jurassic theropods. Zoological Journal of the Linnean Society 158: 882. doi:10.1111/j.1096-3642.2009.00569.x.

Waldman, M. 1974. Megalosaurids from the Bajocian (Middle Jurassic) of Dorset. Palaeontology 17, 2:325-339.

A mount of Cetiosaurus at the New Walk Museum in Leicester. While the neck of this sauropod is almost completely known, no skull has ever been described. Photo by Flickr user Paul Stainthorp.

Sauropods were magnificent dinosaurs. These long-necked, small-headed titans were unlike anything that has evolved before or since, and they were so strange that paleontologists are still debating the basics of how Apatosaurus and kin actually lived. As iconic as their skeletons are now, though, the first sauropod ever described was initially envisioned as a very different sort of creature. The great Cetiosaurus was originally seen as a gargantuan, plesiosaur-crunching crocodile.

In 1841, the British anatomist Richard Owen described a curious collection of limb bones and vertebrae found at various locations in England. The limb elements reminded Owen of the same bones in crocodiles, and the vertebrae were reminiscent of those in whales. The scattered elements seemed to correspond in structure to aquatic animals, and since function was dictated by skeletal form, Owen believed that Cetiosaurus–the “whale lizard”–must have been a marine predator larger than anything that had been found before.

The following year, in his massive Report on British fossil reptiles, Part II, Owen reassessed the various prehistoric reptiles from his country. This was the landmark monograph in which Owen coined the term “Dinosauria,” but he didn’t include Cetiosaurus within the newly named group. The animal seemed vastly different from Megalosaurus, Iguanodon and Hylaeosaurus. Dinosaurs, in Owen’s view, were terrestrial animals with upright limbs, and he saw Cetiosaurus as a marine carnivore. Owen grouped the poorly known animals with crocodiles, instead.

It wasn’t until 1869 that Cetiosaurus was formally recognized as a dinosaur. Thomas Henry Huxley, Owen’s chief academic rival, proposed that Cetiosaurus was a close relative of Iguanodon, although he later changed his mind and suggested that the puzzling animal was an oddball that didn’t belong with crocodiles or dinosaurs. Other researchers were more confident that Cetiosaurus belonged among the dinosaurs. John Phillips, in an 1871 monograph, proposed that Cetiosaurus was an herbivorous dinosaur, and in 1875 Owen conceded that his creature was a huge, aquatic dinosaur.

Like many other early dinosaur finds, the identity of Cetiosaurus was obscured by a lack of material and the unfamiliarity of the Mesozoic curiosities. When O.C. Marsh, E.D. Cope and other North American paleontologists began to uncover relatively complete skeletons of dinosaurs such as Diplodocus and “Brontosaurus” from the American West during the late 19th century, a more accurate vision of Cetiosaurus as a sauropod started to come into focus. All the same, researchers named multiple species of this dinosaur from various sites of different ages. Cetiosaurus became a taxonomic wastebasket for numerous scrappy sauropods found in England.

Paleontologists Paul Upchurch and John Martin sorted out the mess in 2003. Out of 13 different species named from bones belonging to different kinds of sauropods that lived millions of years apart, Upchurch and Martin recognized only one valid taxon–Cetiosaurus oxoniensis. This sauropod trod Jurassic England around 170 million years ago. And even though our knowledge of this dinosaur’s skeleton isn’t yet complete, discoveries both old and new have helped paleontologists outline what this historically significant dinosaur was like.

In 1868, quarry workers at Bletchingdon Station (near Oxford, England) uncovered a Cetiosaurus bonebed containing a trio of skeletons, one being much larger than the others. These bones formed the basis of Phillips’ study of the dinosaur, and, as Upchurch and Martin noted, “potentially represents one of the best preserved sauropods from the Jurassic of Europe.” A century later, in 1968, workers at Williamson Cliffe Brickworks in Rutland discovered bones in their quarry, and some of the remains were briefly described by M.D. Jones in 1970. Upchurch and Martin reexamined the Rutland material as part of their bigger Cetiosaurus project and found that the individual dinosaur is represented by an almost complete neck, various parts of the spinal column and limb elements, making it one of the best-preserved Cetiosaurus ever found.

Altogether, the bones of Cetiosaurus indicate that the sauropod was medium to large in size, though exactly how big this dinosaur was isn’t clear. (Estimating the length and mass of incompletely-known dinosaurs is a difficult task.) What makes Cetiosaurus of special interest to paleontologists, though, is that it was a relatively archaic form of sauropod. Most of the famous sauropods–Diplodocus, Camarasaurus, Brachiosaurus and their ilk–belong to lineages within a big group called the neosauropoda. Cetiosaurus seems to fall just outside this group, and so the dinosaur might clue paleontologists in to what sauropods were like just before the fantastic radiation of neosauropods during the Late Jurassic. It took three decades to change the animal from a crocodile to a dinosaur, and a century more for the sauropod’s identity to be untangled, but, now that the dinosaur has a definite name and evolutionary identity, paleontologists can start to investigate the biological secrets locked inside Cetiosaurus bones.

Check out previous entries in the Dinosaur Alphabet here.

References:

Naish, D. 2009. The Great Dinosaur Discoveries. Berkeley: University of California Press. pp. 30-31

Upchurch, P., Martin, J. 2003. The Anatomy and Taxonomy of Cetiosaurus (Saurischia, Sauropoda) from the Middle Jurassic of England. Journal of Vertebrate Palaeontology 23 (1): 208–231

Upchurch, P., Martin, J. 2002. The Rutland Cetiosaurus: the anatomy and relationships of a Middle Jurassic British sauropod dinosaur. Palaeontology, 45: 1049–1074.

Wilson, J. 2005. Overview of sauropod phylogeny and evolution, pp. 15-49  in Curry Rogers and Wilson (eds.), The Sauropods: Evolution and Paleobiology, Berkley: University of California Press.

Heterodontosaurs were freaky. If you don’t believe me, check out the time-lapse reconstruction of this Heterodontosaurus head by artist Tyler Keillor. Released earlier this month in conjunction with a massive monograph on these dinosaurs in ZooKeys, the video beautifully demonstrates how our changing understanding of paleobiology is reviving even classic dinosaurs.

Heterodontosaurus was originally described in 1962. This ornithischian was a relatively small dinosaur, only about four feet long, but the creature’s name is a clue to its Jurassic weirdness. Heterodontosaurus, like its close relatives, had a toolkit of different teeth (or a “heterodont dentition) in its mouth that would have allowed the dinosaur to slice meat, insects, and vegetation. The dinosaur’s teeth are a tell-tale indicator that it was an omnivore. Even more recently, a heterodontosaurid from China named Tianyulong showed that these ornithischians –as distantly-related to birds as possible while still being a dinosaur–had manes of feather-like bristles. Put the whole thing together, and you get what Keillor has created–a Mesozoic equivalent of a wild boar, and one of the strangest-looking dinosaurs ever.

[Hat-tip to Thomas Holtz.]

A headless Haplocanthosaurus, laid out at the Utah Field House of Natural History. Photo by the author.

The Morrison Formation is one of the most wonderful slices of prehistoric time found anywhere in the world. Parts of this Late Jurassic record pop up all over the American west, from Montana to Texas, and the sequence harbors wonderful bonebeds such as those at Dinosaur National Monument, Utah, and Bone Cabin Quarry, Wyoming. Yet, while the upper part of the Morrison has yielded splendid specimens of famous dinosaurs such as Apatosaurus, Stegosaurus, Allosaurus and more, the lower part of the formation contains a gaggle of puzzling dinosaurs. Haplocanthosaurus is one of these enigmas.

When discussing any geologic formation, it’s easy to talk about it as if it’s just a narrow slice of time. Yet distinct formations can record many millions of years of evolution and extinction. The Morrison Formation, for one, records about 10 million years of Jurassic history, from about 156 to 146 million years ago. And the dinosaurs paleontologists find near the top are not the same as the ones they found lower down in the formation.

Haplocanthosaurus, one of the long-necked sauropods, was part of the lower Morrison fauna. The 50-foot herbivore trod the Jurassic landscape around 155 million years ago and lived alongside the equally unfamiliar forerunners of famous dinosaurs. The stegosaur Hesperosaurus, the slender Allosaurus “jimmadseni” and hefty Eobrontosaurus also lived during this earlier portion of Morrison time.

Despite the fact that the dinosaur was named in 1903, however, paleontologists are still confounded by Haplocanthosaurus. The mid-sized sauropod appears to have been a close relative of the extremely common, blunt-headed dinosaur Camarasaurus. Frustratingly, though, Haplocanthosaurus is extremely rare, and no one has found the dinosaur’s skull just yet. With a skull, the dinosaur’s relationships and biology would come into sharper focus, but no such luck.

Haplocanthosaurus is a symbol of how much we still have to learn about even long-known dinosaurs. The lower part of the Morrison Formation, in particular, seems to be filled with strange dinosaurs that may offer clues about how the exceptionally rich fauna of the later Morrison–filled with sauropods and knife-toothed predators–evolved. Were Hesperosaurus, Eobrontosaurus, Allosaurus “jimmadseni” and Haplocanthosaurus ancestral to any of the later forms? Or did they fall away as new species migrated into the same habitats from elsewhere? The depths of the Morrison Formation still hold Jurassic mysteries worth investigating.

Dilophosaurus, in a restoration based on an impression found at St. George, Utah. Art by Heather Kyoht Luterman, from Milner et al., 2009.

The Early Jurassic is a mysterious time in dinosaur evolution. In North America, at least, paleontologists have uncovered scores of dinosaur tracks from this critical time when dinosaurs had been handed ecological dominance in the wake of a mass extinction, but body fossils are rare. In the orange sandstone that makes up so much of Arches and Canyonlands national parks in Utah, for example, only a handful of skeletons have ever been found. This formation–called the Glen Canyon, Navajo, Nugget or “Nuggaho” depending on who you ask–preserves immense sand dunes that recorded prehistoric footsteps but rarely bone. The recently described sauropodomorph Seitaad, and a group of as-yet-unnamed coelophysoids, are exceptionally rare finds.

Yet, from Connecticut to Arizona, there is one dinosaur that is constantly presented as an icon of dinosaurs circa 190 million years ago. This is Dilophosaurus–the 20-foot-long, double-crested theropod that gained dubious fame thanks to Jurassic Park. (Contrary to the film, there’s no evidence that this carnivore was a “spitter” with a collapsible neck frill.) At sites where Early Jurassic theropod tracks are found in abundance, Dilophosaurus is invoked as a possible trackmaker. But is this really so?

The remains of what would eventually be named Dilophosaurus were discovered in 1942 by Jesse Williams near Tuba City, Arizona. It took another 12 years before paleontologist Samuel Welles mistakenly attributed the bones to a new species of Megalosaurus –“M.” wetherilli–and the name Dilophosaurus itself wasn’t actually coined until 1970. Despite all this shifting around, though, Dilophosaurus wetherilli became a symbol of top Early Jurassic carnivores. Paleontologists had found plenty of Early Jurassic tracks made by a Dilophosaurus-size dinosaur, and now they finally had a body.

Frustratingly, though, we usually don’t know what dinosaur left a particular trace fossil unless the animal literally died in its tracks. While Dilophosaurus is a good fit for many large-size, Early Jurassic tracks, and may very well have left tracks at places such as St. George, Utah’s megatracksite, there’s no way to know for sure. And it seems unlikely that the same species of dinosaur that left tracks in Early Jurassic Utah also made footprints in the mud of what would become the Connecticut Valley. Who knows how many mid-sized theropods might have stalked lakeshores during this time? We don’t know, and the situation is made all the more irksome since the sediments which preserve tracks often don’t contain body fossils. We know these dinosaurs from the bottom of their feet but little else. Until future discoveries fill out the fauna of North America’s Early Jurassic, Dilophosaurus will remain the most familiar and iconic predator of its epoch.

Reference:

Naish, D. 2009. The Great Dinosaur Discoveries. University of California Press: Berkeley. pp. 94-95

A gliding Stegosaurus. From the Ogden Standard-Examiner, 1920.

Stegosaurus is undoubtedly one of the most perplexing dinosaurs. What was all that iconic armor for? (And how did amorous stegosaurs get around that complication?) Paleontologists have been investigating and debating the function of Stegosaurus ornamentation for decades, but without much consensus. The dinosaur’s spectacular plates were certainly prominent visual signals, but could they also have been used for regulating body temperature? Or might there be some evolutionary impetus we’re not thinking of?

Of course, a few ideas have been tossed in the scientific wastebasket. Despite what 19th and early 20th century paleontologists thought, Stegosaurus plates were not protective armor. And, contrary to numerous restorations I saw as a child, Stegosaurus could not waggle or flap its plates around. But the weirdest idea of all was forwarded by paleontology enthusiast and writer W.H. Ballou in 1920. Stegosaurus plates were not armor, heat regulators, or flashy ornaments, Ballou wrote, but were wings that allowed the dinosaur to glide.

Ballou’s article appeared in the Utah’s Ogden Standard-Examiner. And, fortunately for fans of bizarre fossil ideas, a large illustration of flying Stegosaurus graces the piece. One stegosaur crouches to take off, another perches on a rock, and a third buzzes a prehistoric human. (Ballou pointed out in the article that humans originated after dinosaurs, but apparently the artist decided to take some historical license.) This ungainly and aerodynamically-challenged dinosaur, the paper said, was the “Father of All the Birds.” “Crude aeroplane or glider as the Stegosaur was, the principle of all flight was there in the parallel rows of flaps upon his back,” Ballou wrote, concluding, “Certainly he was the factory in which the first bird was built.”

There wasn’t any scientific evidence behind this. While Ballou mentioned the recent discovery of the lovely Stegosaurus skeleton now on display at Smithsonian’s National Museum of Natural History as the inspiration for the idea, the wild notion seems to have been entirely his. The vision of swooping stegosaurs isn’t attributed to any paleontological authority.

But Ballou did draw from a few references that offer a clue to his bizarre vision of gliding stegosaurs. Ballou pointed out that Stegosaurus was an ornithischian, or “bird-hipped” dinosaur. If Stegosaurus was bird-hipped, he reasoned, it must have been close to avian ancestry. Yet Ballou was confused by terminology. Despite having generally bird-like hips, the ornithischian dinosaurs—the hadrosaurs, ceratopsids, ankylosaurs, stegosaurs and others—were nowhere near the bird lineage. Their hip shape was a red herring, a case of superficial convergence. Ironically, the hips of birds were modified from an earlier “lizard-hipped” saurischian form. Ballou wasn’t the only one to be fooled by ornithischian hips—from the 1870s to the 1960s, some paleontologists thought that birds evolved from an ornithischian root—but he certainly ran with his mistaken assumption as far as he could possibly go.

Ballou wasn’t the only one taken with the dramatic idea. In a comment thread about the strange article at Dave Hone’s Archosaur Musings, paleontologist Mike Taylor points out that science fiction writer Edgar Rice Burroughs later imagined a flying stegosaur in one of his novels. In Burroughs’ world, Stegosaurus was a formidable aerial attacker that used its fearsome, thagomizer-tipped tail as a rudder, and it’s certainly possible that the ludicrous image was inspired by Ballou’s article. Sadly, though, Stegosaurus was less aerodynamic than a brick, so we shouldn’t expect any paleo documentary scenes of angry stegosaurs dive-bombing Allosaurus.

[Hat-tip to Dave Hone, by way of John Hutchinson and Jeff Martz.]

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

The tooth of Ostrafrikasaurus as seen from the front (A), tongue side (B), back (c) and cheek side (d). From Buffetaut, 2011.

There’s a lot we don’t know about spinosaurs. Even though a few of these croc-snouted animals are known from mostly complete skeletons—including Baryonyx and Suchomimus—many spinosaurs are known from only sparse bits and pieces. The large spinosaur Oxalaia from the Cretaceous rock of Brazil is known from two skull fragments, and only a few elements have been found from the newly announced Ichthyovenator. We know even less about another recently proposed spinosaur. Called Ostafrikasaurus, this dinosaur is represented by a pair of teeth.

Paleontologist Eric Buffetaut described the dinosaur teeth in the journal Oryctos. They were found a century ago by the German fossil expeditions to Tanzania. During that time, the field team collected more than 230 teeth attributable to Late Jurassic theropod dinosaurs, predators that lived among sauropods and stegosaurs around 150 million years ago. Determining exactly which dinosaurs these dental tidbits belonged to has been a persistent problem. Mammal teeth, with their various cusps and troughs, are often distinctive enough to identify genera and species, but isolated dinosaur teeth are not usually so informative. Many dinosaur species named from teeth alone have turned out to be synonyms of dinosaurs known from better material. Unless you have a detailed knowledge of the dinosaurs that lived in a particular area at a given time, attributing isolated teeth to particular dinosaurs is a risky proposition. Anatomical context is extremely important in these situations.

No surprise, then, that the teeth Buffetaut described have had a complicated history. German paleontologist Werner Janensch, who did much of the initial descriptive work on the Jurassic dinosaurs of Tanzania, thought that the serrated, ridged and slightly curved teeth probably belonged to a dinosaur O.C. Marsh named from the Jurassic of North America, “Labrosaurus.” (“Labrosaurus” is now considered a synonym of Allosaurus.) More recently, in 2000, paleontologists James Madsen and Samuel Welles suggested that the teeth belonged to a form of Ceratosaurus, a highly ornamented theropod typically found in the Late Jurassic rock of western North America. And in 2008, paleontologist Denver Fowler mentioned that these peculiar teeth from Tanzania might hint at a connection between ceratosaurs and spinosaurs. With this in mind, Buffetaut reexamined the strange teeth and concluded that they represent a hitherto unknown form of early spinosaur.

Buffetaut singled out two possible spinosaur teeth—specimens designated MB.R.1084 and MB.R.1091. Both of these teeth have relatively coarse serrations and a number of prominent vertical ridges along both sides of the teeth, with more on the tongue side than the cheek side. Overall, they look similar to the teeth of Baryonyx, and so Buffetaut created a new genus and species of dinosaur for the two teeth: Ostafrikasaurus crassiserratus.

If Ostafrikasaurus is a spinosaur, it would be the earliest known and could help elucidate what these dinosaurs were like before they became fish-catching specialists. But there’s too little material to be sure. The Ostrafrikasaurus teeth look similar to spinosaur teeth, but as previously recognized by other paleontologists, they also resemble ceratosaur teeth. We need a nice skull set with Ostrafrikasaurus-like teeth to determine what this dinosaur actually was. The same is true of a large claw found in the Late Jurassic strata of North America, currently attributed to Torvosaurus, that has been highlighted as possible evidence of a spinosaur. There may have been spinosaurs in North America, and their history might have stretched back 150 million years to the time of Apatosaurus, but definitive proof remains elusive. Until adequate fossil evidence turns up, the idea of Late Jurassic spinosaurs will be left hanging.

References:

Buffetaut, E. 2011. An early spinosaurid dinosaur from the Late Jurassic of Tendaguru (Tanzania) and the evolution of the spinosaurid dentition. Oryctos. 10, 1-8

The shape of the "Pachysuchus" fossil (in grey) set into a sauropodomorph dinosaur skull. Image from Barrett and Xu, 2012.

Paleontologists are naming new dinosaurs at an extremely rapid pace. This past week alone, we’ve seen the announcement of Philovenator and Ichthyovenator, and the next new dinosaur is undoubtedly only a few days from publication. But we have also lost a few dinosaurs. Some of these, such as Dracorex, Anatotitan and Torosaurus, might get folded into other genera thanks to our changing understanding of how dinosaurs grew up. And as paleontologist Bill Parker pointed out at Chinleana, creatures once thought to be dinosaurs have been recategorized as very different, distantly related sorts of archosauriforms (the major group to which dinosaurs, crocodiles and many related lineages belong). Shuvosaurus, for example, was originally described as a Triassic iteration of the “ostrich mimic” dinosaurs such as Ornithomimus but turned out to be a strange, bipedal creature that was more closely related to crocodiles. And Revueltosaurus, an animal originally cast as a dinosaur because of its teeth, is now known to be more closely related to the well-armored “armadillodile” aetosaurs.

Yet reinterpretations can go the other way. Parker points out that a paper just published in Vertebrata PalAsiatica reports that a fossil thought to represent a superficially crocodile-like animal is actually part of a dinosaur jaw.

In 1947, paleontologist Yang Zhongjian—better known to many by the name C.C. Young—mentioned a fragment of a sauropodomorph dinosaur’s snout discovered in the roughly 195-million-year-old, early Jurassic deposits near Lufeng, China. He referred the specimen to Lufengosaurus, one of the many long-necked, small-skulled dinosaur cousins of the more famous sauropods. A few years later, Young changed his mind. He redescribed the battered fragment as a piece of a phytosaur skull. These archosaurs, found in older Triassic strata, generally resembled crocodiles but were actually a different group. (The easiest way to tell the difference is that the nasal openings of phytosaurs sat far back on their snouts, near their eyes.) Young named the animal Pachysuchus imperfectus, and although heavily damaged, the fragment became an important milestone for phytosaurs. The fossil was discovered in early Jurassic rock, so it lived millions of years after phytosaurs disappeared elsewhere. Young’s phytosaur seemed to represent the last of these trap-jawed aquatic predators.

Not everyone agreed with Young’s conclusion. While some paleontologists followed Young’s phytosaur ID, others said that the fragment was too uninformative to tell exactly what kind of archosaur it belonged to. The specimen was somehow lost in the collections of China’s Institute of Vertebrate Paleontology and Paleoanthropology, hindering efforts to figure out exactly what sort of animal Pachysuchus was.

Paul Barrett and Xu Xing relocated and re-examined Pachysuchus, but they didn’t see a phytosaur. Young was much closer to the mark with his original determination. The damaged skull piece exhibits many traits never seen in phytosaurs but that closely match what paleontologists have documented among sauropodomorph dinosaurs. Exactly what species of dinosaur the jaw belonged to is impossible to say—the appropriate traits for a species identification may be missing—but the best fit is certain some variety of sauropodomorph.

There were no Jurassic phytosaurs in Asia. And the proposed occurrences of Jurassic phytosaurs elsewhere are highly questionable, at best. These creatures, which lived alongside and probably preyed on early dinosaurs, were wiped out at the end of the Triassic, just before dinosaurs rose to global dominance.

Reference:

Barrett, P. M., and X. Xu. 2012. The enigmatic reptile Pachysuchus imperfectus Young, 1951 from the lower Lufeng Formation (Lower Jurassic) of Yunnan, China. Vertebrata PalAsiatica 50:151-159

Camarasaurus, as envisioned by Erwin Christman. From Osborn and Mook, 1921.

Sauropods were swamp monsters. At least, that’s what books, movies, and illustrations taught me when I first encountered the huge dinosaurs. If Diplodocus and Brachiosaurus didn’t actually spend most of their time in the water, then the dinosaurs always stayed close to watery refuges where they could escape from Allosaurus and other predators.

But starting in the 1960s, a renewed scientific interest in dinosaurs overturned this cherished imagery. Sauropods were wholly terrestrial creatures. These giants did not possess any features related to an aquatic or amphibious lifestyle—Apatosaurus and kin were often plunked down into bogs and lakes in reconstructions because that environment seemingly answered nagging questions about the biology of these animals. But early 20th century paleontologists didn’t think that all sauropods were equally adept at life in the water. Rather than take the line that all sauropods were skilled swimmers, paleontologists identified at least one Jurassic sauropod that probably spent more time on land.

In 1920, a trio of American Museum of Natural History scientists published a pair of short papers on the sauropod Camarasaurus. This dinosaur, with a blunt head and spoon-shaped teeth, was one of the better-known members of the classic Morrison Formation fauna, and the AMNH paleontologists had just completed a major reexamination of the dinosaur’s remains. In the first note, Henry Fairfield Osborn and Charles Mook briefly summarized the results of their study, and in a second, accompanying missive, William Gregory outlined the dinosaur’s life habits.

Camarasaurus didn’t seem suited to a life wallowing in a Jurassic lake. While Gregory mentioned that the dinosaur “might well have been an efficient wader,” the dinosaur was also “positively devoid of special adaptations for swimming.” The dinosaurs limbs, shoulders and hips were clearly suited to supporting the animal’s bulk, and Gregory considered the “relatively small and feeble” tail of Camarasaurus to be of no help in swimming. While Gregory did waffle on the habitat the dinosaur preferred, the overall picture was of a relatively straight-limbed dinosaur that carried its body high off the ground. Sauropods did not drag their bellies through the Jurassic mud, as other paleontologists had suggested under the supposition that sauropods were like lizards or crocodiles, writ large.

The following year, when Osborn and Mook published their massive revision of sauropods collected by Edward Drinker Cope, they similarly cast Camarasaurus as a dinosaur that was “terrestrial in gait but adapted to an amphibious life.” And the plates of that paper present some of the restorations and reconstructions previously mentioned in the PNAS papers. A model of Camarasaurus, created by artist Erwin Christman under Gregory’s direction, showed the dinosaur walking on land with slightly bent forelimbs, similar to how the museum mounted its great “Brontosaurus” skeleton years before. Christman and Gregory also collaborated on a pair of skeletal reconstructions—one with the head of Camarasaurus held high, and the other in a droopy pose, with neck and tail slung low.

Osborn, Mook and Gregory’s insistence that Camarasaurus was an amphibious dinosaur, or at least frequently waded, is puzzling. The paleontologists didn’t justify this part of their argument. Sauropods were simply considered synonymous with warm, luxuriant swamps. Contrary to this belief, the experts explicitly pointed out evidence that Camarasaurus walked tall and had a skeleton well-suited to holding up the animal’s weight while walking on land. Even before the “Dinosaur Renaissance” forever changed dinosaurian imagery, early 20th century paleontologists were already cataloging the same evidence. They just saw that evidence differently, in the context of a lazy Mesozoic world filled with shuffling, basking sauropods.

References:

Gregory, W.K. 1920. Restoration of Camarasaurus and life model. PNAS. 6, 16-17

Osborn, H.F., Mook, C.C. 1920. Reconstruction of the skeleton of the sauropod dinosaur Camarasaurus Cope (Morosaurus Marsh). PNAS. 6, 15

Osborn, H.F., Mook, C.C. 1921. Camarasaurus, Amphicoelias, and other sauropods of Cope. Memoirs of the American Museum of Natural History, new series, 3, 247-387 (plates LX-LXXXV).

Taylor, Michael P. 2010. Sauropod dinosaur research: a historical review. pp. 361-386 in: Richard T. J. Moody, Eric Buffetaut, Darren Naish and David M. Martill (eds.), Dinosaurs and Other Extinct Saurians: a Historical Perspective. Geological Society of London, Special Publication 343.

A pair of bristly Fruitadens models on display at the Natural History Museum of Los Angeles. Photo by the author.

When asked to account for why dinosaurs are so popular, psychologist Sheldon White delivered the simple answer: “Big, fierce and extinct.” Our perennial favorites—Tyrannosaurus, Triceratops, Stegosaurus, Diplodocus and so on—were all gigantic and wielded a potential for destruction unlike anything alive today. From the time that dinosaurs were first recognized by science, we have brought them back to life in art and museum reconstructions only to eviscerate each other once more. To borrow a few lines from Tennyson’s In Memoriam, we often see dinosaurs as “dragons of the prime, that tare each other in their slime.”

But a dinosaur’s ferocity lies at the intersection of anatomy and imagination. We cheer Mesozoic conflicts, but dinosaurs did not spend every waking hour trying to eat and avoid being eaten. Nor were all dinosaurs titans. The largest sauropods stretched more than 100 feet in length, but the smallest dinosaur we know of is the bee hummingbird—a minuscule avian that weighs less than two grams and is about two inches long. While not quite that tiny, there were small non-avian dinosaurs, too. One of the smallest—a Jurassic omnivore named Fruitadens haagarorum—has just received a detailed description in PLoS One.

Found in the 150-million-year-old rock of Colorado, Fruitadens lived in the shadow of Jurassic giants. The relatively puny dinosaur was only about three feet long as an adult. But the most remarkable aspect of this dinosaur is its dentition. Fruitadens was a heterodontosaurid—a group of small, bipedal dinosaurs with skulls lined with several different kinds of teeth. In addition to leaf-shaped teeth suited to crushing through vegetation, heterodontosaurids also possessed a set of sharp, piercing teeth at the front of the jaw, including a set that looked like canines. And thanks to a peculiar form called Tianyulong, we know that at least some of these dinosaurs sported a mane of bristly filaments along their backs.

Whether Fruitadens was similarly decorated—as restored in sculptures at the Natural History Museum of Los Angeles—is unknown. The rock in which the little dinosaur was found doesn’t record the intricacies of the feather-like body coverings. All we know of Fruitadens comes from the animal’s bones, and the new paper by paleontologist Richard Butler and colleagues focuses on the dinosaur’s skull.

Fruitadens had the dental armament of an omnivore. The dinosaur’s varied set of teeth looks best suited to gripping and puncturing insects as well as plants. But Butler and co-authors went beyond simply, giving Fruitadens a dental exam. After reconstructing the dinosaur’s musculature, the paleontologists examined how Fruitadens would have bitten into its meals. This dinosaur, the researchers found, was capable of opening its jaws wide and delivering quick bites—a skill set different from that of its larger cousin Heterodontosaurus, which had a more powerful bite at a smaller gape. A weaker, quicker bite, the paleontologists hypothesized, indicates that Fruitadens might have been catching invertebrates as well as crushing plants in its jaws, and this represents a dietary shift from earlier, more herbivorous heterodontosaurids.

When I was introduced to dinosaurs as a child, I was often told that the entire swath of dinosaurian diversity could be divided into carnivores and herbivores. Theropods were the meat eaters, and all other dinosaurs—the sauropods and the whole ornithischian group—chewed plants. Nice and simple. And also wrong. Many theropod lineages, particularly feather-bearing coelurosaurs, shifted from carnivorous to omnivorous and herbivorous diets. And as Fruitadens shows, some ornithischian dinosaurs were probably omnivores that consumed whatever small prey they could catch. The dinosaur diet was not a simply a choice between steak or salad.

For more on Fruitadens, see Andy Farke’s post on the new paper at the official PLoS blog.

References:

Butler, R., Porro, L., Galton, P., & Chiappe, L. (2012). Anatomy and Cranial Functional Morphology of the Small-Bodied Dinosaur Fruitadens haagarorum from the Upper Jurassic of the USA PLoS ONE, 7 (4) DOI: 10.1371/journal.pone.0031556

Gould, S.J. 1991. Bully for Brontosaurus. New York: W.W. Norton & Company. pp. 94-106

A reconstruction of a hypothetical adult Brachiosaurus next to a possible juvenile Brachiosaurus, SMA 0009. From Carbadllido et al., 2012.

Brachiosaurus used to hold the title of biggest dinosaur ever. I remember when, as a young dinosaur fanatic, books and documentaries told me that this long-necked dinosaur was the ultimate prehistoric titan. Then Supersaurus, Argentinosaurus and other super-sized dinosaurs came along and ruined all the fun. Even worse, paleontologists recently realized that we actually know very little about what Brachiosaurus really looked like.

In 1903, paleontologist Elmer Riggs described Brachiosaurus altithorax from fossils discovered in the 150-million-year-old Late Jurassic strata of western Colorado. The dinosaur, which Riggs believed to be the largest known, was represented by a huge humerus and assorted elements of the shoulder girdle, hips, hindlimbs, vertebrae, ribs and a few other miscellaneous parts. Despite the relative smattering of material, though, the proportions of the bones led Riggs to conclude that he had found a previously unknown dinosaur that was significantly larger than Apatosaurus, Diplodocus and other giants which lived at the same time.

Fossils discovered by German expeditions to Tanzania seemed to fill out the form of Brachiosaurus. At the beginning of the 20th century, the Late Jurassic deposits of Africa were believed to be roughly equivalent to those of western North America, and so dinosaurs discovered in Tanzania’s Tendaguru Formation were often assigned to genera known from the Morrison Formation of Colorado, Utah and Wyoming. As a result, paleontologist Werner Janesch described partial skeletons and skulls of a large sauropod dinosaur from Tanzania under the name Brachiosaurus brancai. The fact that the material from Africa was more complete allowed paleontologists to get a better idea of just how big the dinosaur was—Brachiosaurus brancai reached over 80 feet long and may have weighed more than 25 tons.

But there’s a major problem with this approach. Paleontologists recently determined that the brachiosaurs from Africa and North America don’t actually belong to the same genus after all. Artist Gregory S. Paul noted differences between the two brachiosaurs in 1988, and in 2009 sauropod expert Mike Taylor confirmed that the two dinosaurs were different enough to warrant placement in separate genera. Furthermore, a skull fragment tentatively assigned to Brachiosaurus hints that the traditional picture of the dinosaur may have been skewed by reliance on fossils from Tanzania. While the North American form has retained its name, Brachiosaurus altithorax, the dinosaur from Tanzania is now called Giraffatitan brancai. Thanks to a name change, we know significantly less about Brachiosaurus than we thought we did.

Then again, a reevaluation of another Jurassic dinosaur skeleton may provide a rough idea of what Brachiosaurus looked like as a baby. In 2007, Daniela Schwarz-Wings and colleagues described a juvenile sauropod skeleton found in Wyoming’s Howe Stephens Quarry. This Late Jurassic specimen was designated SMA 0009, and was initially thought to be a young diplodocid dinosaur. But in a new paper published in Palaeontology, Schwarz-Wings, José Carballido and colleagues have amended their diagnosis. Additional preparation of the partial skeleton revealed that the dinosaur was not a close relative of Diplodocus and Apatosaurus at all, but was more closely related to Brachiosaurus.

Schwarz-Wings and co-authors refrained from assigning SMA 0009 to a particular dinosaur species. The fact that the animal is a juvenile confounds precise identification attempts—dinosaurs changed significantly as they grew up, and the traits seen in adult dinosaurs may not have been present in juveniles. Likewise, the revised idea that SMA 0009 is a brachiosaur makes comparisons difficult since paleontologists have yet to assemble a complete picture of an adult Brachiosaurus. Still, since the young dinosaur is grouped closely with Brachiosaurus, and Brachiosaurus was the only dinosaur of its kind present in the Morrison Formation, there is a good possibility that SMA 0009 is a young Brachiosaurus. Until someone finds more complete remains of this rare and enigmatic dinosaur, however, Brachiosaurus will remain a dinosaurian enigma.

References:

CARBALLIDO, J., MARPMANN, J., SCHWARZ-WINGS, D., & PABST, B. (2012). New information on a juvenile sauropod specimen from the Morrison Formation and the reassessment of its systematic position Palaeontology DOI: 10.1111/j.1475-4983.2012.01139.x

RIGGS, E.S. (1903). “Brachiosaurus altithorax, the largest known dinosaur.” American Journal of Science (series 4) 15(88): 299-306.

TAYLOR, M.P. (2009). “A Re-evaluation of Brachiosaurus altithorax Riggs 1903 (Dinosauria, Sauropod) and its generic separation from Giraffatitan brancai (Janensh 1914).” Journal of Vertebrate Paleontology, 29(3): 787-806

The known skeleton of Juratyrant (black outline) compared to the dinosaur Guanlong for size. The scale bar is one meter. From Benson, 2008.

Despite belonging to one of the most famous dinosaur groups of all time, few people have heard of Stokesosaurus clevelandi. This predator, named in 1974 by paleontologist James Madsen, Jr., was a tyrannosauroid dinosaur that roamed North America tens of millions of years before Tyrannosaurus rex.

The bones of Stokesosaurus were initially discovered in the fossil-rich Cleveland-Lloyd Dinosaur quarry in eastern Utah. Although dominated by the remains of at least 46 Allosaurus, rarer traces of other theropod dinosaurs have come out of the quarry. (The mid-size carnivore Marshosaurus and possibly a distinct species of Ceratosaurus have also been recognized from bones found here.) In the case of Stokesosaurus, Madsen had identified two portions of the hip and a piece of the upper jaw, the premaxilla, as belonging to this small theropod. The complete animal probably didn’t stretch longer than 12 feet from nose to tail. While Madsen was tentative about this conclusion, the diminutive predator seemed to represent the early days of the tyrant dinosaurs in North America. Since then, one of the hips has been lost and the jaw fragment is thought to have belonged to a different dinosaur, but the primary hip Madsen relied upon for his description still indicates the presence of the tyrants in Jurassic Utah around 150 million years ago.

By now you may be wondering why I opened a post titled “England’s Jurassic Tyrant” with a note about a tyrannosauroid from Utah. The reason is because, until recently, Stokesosaurus was thought to have been present in Jurassic Europe, too. In 2008, paleontologist Roger Benson described a partial skeleton from the Late Jurassic of England that he attributed to a new species of the dinosaur, Stokesosaurus langhami. There was far more of this animal than the North American species, whose anatomy remains largely a mystery. The new species, on the other hand, was represented by numerous vertebrae, the majority of the hips, and most of a hindlimb.

But the dinosaur Benson described probably wasn’t Stokesosaurus, after all. In a paper to be published at Acta Palaeontologica Polonica, Benson and colleague Stephen Brusatte suggest that the more complete material from England represents a distinct genus of dinosaur. The change was spurred by the discovery of additional archaic tyrannosaurs in recent years. These finds indicated that some of the features Benson had used to link Stokesosaurus from Utah and the British form together were widely distributed among the tyrannosauroids and therefore might not reveal clear relationships. The more complete material from England now seems more distinct from Stokesosaurus than previously understood. Brusatte and Benson have renamed the animal Juratyrant.

But we still know very little about Stokesosaurus, Juratyrant and their close relatives. For Stokesosaurus, most of the skeleton is unknown, and significant portions of Juratyrant—such as the skull and forelimbs—have yet to be found. These tyrants are hardly unique in this respect. Other closely related dinosaurs such as Aviatyrannis are known from frustratingly incomplete remains. We know that these dinosaurs were small predators that set the stage for the later rise of more imposing tyrants, but what they looked like and how they lived remains mysterious.

References:

Benson, R. (2008). New information on Stokesosaurus, a tyrannosauroid (Dinosauria: Theropoda) from North America and the United Kingdom Journal of Vertebrate Paleontology, 28 (3), 732-750 DOI: 10.1671/0272-4634(2008)28[732:NIOSAT]2.0.CO;2

Brusatte, S., & Benson, R. (2012). The systematics of Late Jurassic tyrannosauroids (Dinosauria: Theropoda) from Europe and North America Acta Palaeontologica Polonica DOI: 10.4202/app.2011.0141

Madsen, J. 1974. A new theropod dinosaur from the Upper Jurassic of Utah. Journal of Paleontology, 48 (1), 27-31

A parent Massospondylus attends to its hatchlings. Art by Julius Csotonyi.

Two years ago, paleontologist Robert Reisz and colleagues revealed that the Early Jurassic dinosaur Massospondylus started off life as an awkward little thing. An exceptional set of eggs recovered from South Africa in 1976 contained the well-preserved skeletons of these baby dinosaurs, and the infants did not look very much like their parents. A roughly 20-foot-long adult Massospondylus had an extended neck and a long, low skull and it walked on two legs. But a baby of the same dinosaur had a short neck, a big head for its body, and it walked on all fours. The change between baby and adult was fantastic, and now, in a new PNAS paper, Reisz and colleagues provide an even more detailed look at how Massospondylus started life.

In 2006, Reisz and collaborators located the site where the Massospondylus eggs had been discovered in South Africa’s Golden Gate Highlands National Park. They found more eggs and baby dinosaurs, but not just that. About 190 million years ago, this place was a nesting ground that multiple Massospondylus used from one season to the next.

The paleontologists have discovered bones, eggshell fragments and ten egg clutches—the largest has 34 eggs—within a six-and-a-half-foot swath of siltstone. These nest sites were not all found in the same level, demonstrating that this particular place was used multiple times by Massospondylus moms. Despite the fact that this place was a nesting ground, however, there does not appear to be any evidence that the parent dinosaurs made special accommodations for the eggs—no clear sign of bowl-shaped depressions or other hints of nest construction were found.

Exactly how much parental care adult Massospondylus offered their babies is unknown. Crocodylians and many birds—the closest living relatives of dinosaurs—often attend their nests from the time the eggs are laid and guard their offspring for at least a short interval after their babies hatch. Massospondylus may have done the same, and small tracks found in siltstone blocks indicate that hatchling dinosaurs remained in the nesting site after emerging from their eggs. The tiny hind- and fore-foot tracks are about twice the size of what would be expected for a newly-hatched Massospondylus, and so it seems that the babies stayed at the site until they doubled in size, at least.

The setting of the nesting site allowed all these intricate details to be preserved. In the time of Massospondylus, the site was a relatively dry habitat near the margin of a prehistoric lake. Relatively gentle flooding events covered up the nest site with fine-grained sediment, and afterwards the area dried out. This was a regular, seasonal cycle, and the bad timing of some expectant dinosaur parents resulted in the good fortune of the paleontologists.

With this new data point, Reisz, Evans, and co-authors looked at the big picture of dinosaur reproduction to see which traits might be widely shared and which might be specializations. It seems that communal nesting sites that were used over and over again was an old, common aspect of dinosaur behavior. And, regarding sauropodomorphs specifically, the Massospondylus site may provide some insight into the evolution of different reproductive behavior among its larger sauropod cousins. Evidence from some sauropod nesting sites has been taken to suggest that exceptionally large long-necked dinosaurs did little more than lay eggs and leave their offspring to fend for themselves. What the Massospondylus site might indicate is that the “lay ‘em and leave ‘em” strategy was not the ancestral state for these dinosaurs, but instead was a reproductive specialization related to increasing body size.

So far, this is the oldest known dinosaur group nesting site. Similar sites created by hadrosaurs and sauropods are about 100 million years younger—a vast expanse of time. Potentially earlier nest site finds have not been well studied. One such Late Triassic site in Argentina has yielded multiple infant and juvenile specimens of the sauropodomorph Mussaurus. I asked David Evans, a paleontologist at the Royal Ontario Museum and one of the co-authors of the new study, about the possibility that the Mussaurus locality is an even older nesting ground. “[E]vidence of any form of extensive nesting site [at the Mussaurus localities] is very scant,” he said, but noted that “given our luck in South Africa, I would not at all be surprised if there are a bunch of nests similar to what we have [found] at the Mussaurus localities too—someone just needs to look and document.”

References:

Pol, D., & Powell, J. (2007). Skull anatomy of Mussaurus patagonicus (Dinosauria: Sauropodomorpha) from the Late Triassic of Patagonia Historical Biology, 19 (1), 125-144 DOI: 10.1080/08912960601140085

Reisz, R., Evans, D., Roberts, E., Sues, H., & Yates, A. (2012). Oldest known dinosaurian nesting site and reproductive biology of the Early Jurassic sauropodomorph Massospondylus Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1109385109

Ceratosaurus nasicornis at the Smithsonian National Museum of Natural History. Photo by the author.

Eastern Utah’s Cleveland-Lloyd dinosaur quarry is a treasure trove of predatory dinosaurs. In addition to elements from more than 46 individual Allosaurus, this fossil-rich pocket has yielded remains of rarer predators that lived in the region 150 million years ago, including the little-known Marshosaurus and the tyrannosaur Stokesosaurus. The charismatic, well-ornamented predator Ceratosaurus has been uncovered from these deposits, too, but the particular individual found in the Jurassic quarry might belong to a species that was only recently recognized.

Since the late 19th century, the Ceratosaurus genus has been best represented by one species: Ceratosaurus nasicornis. Paleontologist O.C. Marsh included a beautiful reconstruction of this dinosaur in a kangaroo-like pose in his essential 1896 tome The Dinosaurs of North America. In 2000, however, paleontologists James Madsen and Samuel Welles named two additional species in their detailed monograph on the osteology of Ceratosaurus. One, represented by an articulated skeleton found in Colorado’s Fruita Paleontological Area, was named Ceratosaurus magnicornis, and the unusual Cleveland-Lloyd specimen was dubbed Ceratosaurus dentisulcatus.

A reconstruction of Ceratosaurus at the Museum of Ancient Life. Photo by the author.

The Cleveland-Lloyd species was not found all together in a single, articulated skeleton. Work over many years turned up the scattered remains of what Madsen and Welles considered to be a single Ceratosaurus individual. When the isolated parts were viewed together, the paleontologists were struck by the size of the dinosaur. This Ceratosaurus was significantly larger than any found before. (I have seen these fossils myself in the Natural History Museum of Utah collections, and compared to the skeleton on display at the Smithsonian National Museum of Natural History, the Cleveland-Lloyd Ceratosaurus is huge.) What Masen and Welles called Ceratosaurus dentisulcatus also differed in various anatomical aspects such as larger, more recurved teeth and a nasal opening set lower down at the front of the skull. Sadly, the portions of the skull which preserved the dinosaur’s ornaments were not found, so we don’t know how this species might have differed from others in this respect.

It’s difficult to say how large this individual actually was. The Cleveland-Lloyd Ceratosaurus was much larger than the roughly 17.5-foot specimen that formed the basis of previous anatomical descriptions, and informal estimates have placed the larger species at about 28 feet. Yet, given the new interest in dinosaur growth, I have to wonder if Ceratosaurus dentisulcatus really represents a bigger, badder species than Ceratosaurus nasicornis. Ceratosaurus is a relatively rare dinosaur, so much so that we still don’t have a good idea of how individuals varied from one to another, nor do we have a solid understanding of Ceratosaurus growth. Maybe the Cleveland-Lloyd Ceratosaurus is just an older, and therefore larger, individual of Ceratosaurus nasicornis in the same way that the dinosaur often called Saurophaganax might be an older or particularly large variant of Allosaurus. Even though the dinosaurs of the Morrison Formation have been known for a long time and seem familiar, there is much we still don’t know about their biology.

References:

Madsen JH, Welles SP. Ceratosaurus (Dinosauria, Therapoda), a Revised Osteology. Miscellaneous Publication. Utah Geological Survey.