Smithsonian.com

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