May 30, 2012
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.]
May 24, 2012
Some dinosaur lineages are more famous than others. I can say “tyrannosaur” and most anyone immediately knows what I’m talking about: a big-headed, small-armed predator similar to the notorious Tyrannosaurus rex. The same goes for “stegosaur,” and of course it helps that Stegosaurus itself is the famous emblem of this bizarre group. But public understanding hasn’t kept up with new discoveries. In the past two decades, paleontologists have identified various dinosaur lineages vastly different from the classic types that gained their fame during the Bone Wars era of the late 19th century. One of those relatively obscure groups is the abelisaurids: large theropod dinosaurs such as Carnotaurus with high, short skulls and ridiculously stubby arms that make T. rex look like Trogdor the Burninator. And paleontologists Diego Pol and Oliver Rauhut have just described an animal close to the beginning of this group of supreme predators—a dinosaur from the dawn of the abelisaurid reign.
Pol and Rauhut named the dinosaur Eoabelisaurus mefi. Discovered in roughly 170-million-year-old Jurassic rock near Chubut, Argentina, the mostly complete dinosaur skeleton is about 40 million year older than the next oldest abelisaurid skeleton. Eoabelisaurus, placed in context with other theropod dinosaurs of the same era, represents a time when predatory dinosaurs were undergoing a major radiation. Early members of many terrifying Cretaceous predators such as the tyrannosaurs and abelisaurids had already appeared by the Middle to Late Jurassic.
Not all of these Jurassic predators looked quite like their later Cretaceous counterparts. Jurassic tyrannosaurs such as Juratyrant and Stokesosaurus were relatively small predators, unlike their bulky, titanic relatives from the Late Cretaceous. Eoabelisaurus was a little closer to what was to come.
Despite being many tens of millions of years older than relatives such as Carnotaurus and Majungasaurus, the newly described dinosaur displays some tell-tale features that characterize the group. While a significant portion of the dinosaur’s skull is missing, the head of Eoabelisaurus had the short, deep profile seen among other abelisaurids. And this dinosaur already had distinct forelimbs. Much like its later relatives, Eoabelisaurus had a strange combination of heavy shoulder blades but wimpy forelimbs, with a long upper arm compared to the lower part of the arm. The dinosaur’s condition was not as extreme as in Carnotaurus—a dinosaur whose lower forelimbs were so strange that we have no idea what, if anything, Carnotaurus was doing with its arms—but they were still comparatively small and tipped with little fingers good for wiggling but probably useless in capturing prey.
And with a 40-million-year gap between Eoabelisaurus and its closest kin, there are plenty of other abelisaurids to find. The question is where they are. Is their record so poor that very few were preserved? Or are they waiting in relatively unexplored places? Now that the history of these blunt-skulled predators has been pushed back, paleontologists can target places to look for the carnivores.
Pol, D., Rauhut, O. (2012). A Middle Jurassic abelisaurid from Patagonia and the early diversification of theropod dinosaurs. Proceedings of the Royal Society B, 1-6 : 10.1098/rspb.2012.0660
April 30, 2012
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.
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
April 26, 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.
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
April 17, 2012
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.
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.