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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

A restoration of Yutyrannus, with the therizinosaurs Beipiaosaurus in the foreground, by Brian Choo. Caption added by the author.

When I first heard the news that paleontologists had discovered a giant, fuzzy tyrannosaur, I was giddy with excitement. The dinosaur, dubbed Yutyrannus, was a confirmation of an idea that researchers and artists had been cautiously exploring for years. While most of the feathered dinosaurs discovered so far have been very small and often quite bird-like animals, Yutyrannus was a roughly 30-foot-long bruiser which showed that even huge predators might have sported fluffy plumage. And if an imposing predator like Yutyrannus sported a fuzzy coat, the same might be true for the theropod’s notorious cousin, Tyrannosaurus rex. The tyrant king may not have been the wholly scaly monstrosity I grew up knowing, but an apex predator decorated by patches of simple protofeathers.

Not everyone shared my enthusiasm. “Tyrannosaurs were supposed to be scaly,” came the cantankerous cry from die-hard fans of more reptilian dinosaurs. Why are paleontologists so committed to destroying the fantastic imagery Jurassic Park embedded in our cultural landscape? Across the web, tyrannosaur traditionalists registered their displeasure. “Oh, how the mighty have fallen!” mourned one WIRED commenter, and elsewhere, Yutyrannus was presented as a “fuzzball” and “chicken from hell.” And while the outrage was not as great as when people mistakenly believed that paleontologists were trying to kill Triceratops, at least some dinosaur fans lamented the increasingly avian aspect of tyrannosaurs.

Paleo blogger Mark Wildman recently jumped in with a post titled “In Defence of Scaly Dinosaurs.” He was sad to see yet another proud dinosaurian lineage turn fluffy. “Those of us who like our dinosaurs scaly appear to be frowned upon,” Wildman wrote, “as if we don’t know what we are talking about and that we really ought to ‘get with it’ and rejoice that the dinosaurs are covered in fuzz and feathers. Well that isn’t going to happen—certainly not by me and, I am sure, not for many others.” And to dapple Tyrannosaurus with feathers would be the ultimate indignity. Citing the awesomeness of Tyrannosaurus in Dinosaur Revolution, and how silly the feathery Gigantoraptor looked, Wildman challenged readers: “Do you really want the ultimate theropods, the megastars of the dinosaurian world—the tyrannosaurs—displaying colourful yet gaudy feathers and dancing like a demented turkey cock?”

I actually wouldn’t mind a strutting tyrannosaur, even though I admit that Dinosaur Revolution‘s Gigantoraptor sequence was a little over the top. And none of this is to say that Wildman objects to the evidence of feathered dinosaurs. He makes it quite clear that he’s entirely on board with the science. All the same, his post and other comments about how Yutyrannus has somehow ruined tyrannosaurs made me wonder about why it is so fashionable to register cranky displeasure with the way dinosaurs have changed. Some people just don’t like feathery dinosaurs, many wept and wailed at the false assertion of journalists that Triceratops might disappear, and “Brontosaurus” still stirs up strong feelings among those who grew up with the thunder lizard. It’s cool to show contempt for new discoveries in favor of the dinosaurs we grew up with. Before I knew the extent of the evidence, even I felt a little sad that so many of the scabrous, ugly dinosaurs I met as a kid were turned into pretty peacocks.

I can’t explain why this is so any more than I can explain why we adore dinosaurs in the first place. I don’t think anyone has successfully articulated why we’re so enthralled by these creatures. But I think Mike Brown identified one important thread in his book How I Killed Pluto and Why it Had it Coming. When Pluto was officially demoted from planet to dwarf planet, many people objected to the loss of one of our solar system’s icons. Brown recalled:

In the days that followed, I would hear from many people who were sad about Pluto. And I understood. Pluto was part of their mental landscape, the one they had constructed to organize their thinking about the solar system and their own place within it. Pluto seemed like the edge of existence. Ripping Pluto out of that landscape caused what felt like an inconceivably empty hole.

Of course, Pluto didn’t actually go anywhere. Its title simply changed. But the alteration virtually obliterated the cosmic body in people’s minds. Might the same be true for dinosaurs? For those of us who grew up with scaly, swamp-dwelling dinosaurs, the new images of fuzzy dinosaurs are conflicting with the Mesozoic world as we think it should be. A Tyrannosaurus with feathers isn’t really a Tyrannosaurus, but a different sort of creature that doesn’t quite fit what we had in mind for so long. This tension is inevitable. There is so much that remains unknown that any vision of the past is certainly going to change. I have no doubt that, a few decades from now, children who grew up with feathery dinosaurs will lament how future generations of paleontologists are altering the picture of dinosaur lives.

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

A restoration of Ichthyovenator by Michel Fontaine. From Allain et al., 2012.

Spinosaurus was one of my favorite childhood dinosaurs. The carnivore’s enigmatic sail was certainly eye-catching, and that immense billboard set the predator apart from the other huge theropods. But the Spinosaurus I grew up with isn’t around anymore. The creature I knew was based on a partial skeleton discovered by German paleontologist Ernst Stromer in 1912, but was destroyed by an Allied bombing raid during World War II. With only photographs left, paleontologists and artists filled in the missing parts of the spinosaur’s anatomy on the basis of other large, carnivorous dinosaurs. The end result was something like an Allosaurus with a sail.

The blunt-skulled Spinosaurus faded away as paleontologists found new specimens of closely related dinosaurs. The long-snouted Baryonx, discovered in England in 1983, showed that spinosaurs had huge hand claws, crocodile-like skulls. And despite the group’s name, some lacked sails. With this new search image in place, paleontologists began to turn up multiple new spinosaurs from Africa, South America, Australia and now southeast Asia.

Earlier this week, paleontologist Ronan Allain and co-authors described the partial skeleton of a new spinosaur in the journal Naturwissenschaften. The dinosaur, named Ichthyovenator laosensis, appears to be the first definite spinosaur known from Asia. (A few probable spinosaur teeth have been uncovered, hinting that there are skeletons still waiting to be found.) Exactly how long ago this dinosaur roamed Laos is unclear. While Ichthyovenator was discovered in Early Cretaceous rock, the deposits could be anywhere from about 125 to 112 million years old.

If the reconstruction presented by Allain and colleagues is correct, Ichthyovenator was an unusual spinosaur. In other sail-backed forms, such as Spinosaurus and Suchomimus, the great ornament is created by neural spines that rise to a peak and gradually slope downwards. But Icthyovenator might have had a more wavy sail that dipped downwards at the hips before briefly rising again, creating the appearance of two smaller sails.

We still don’t know why spinosaurs had sails to start with, so why Ichthyovenator displayed a different arrangement is doubly perplexing. And equally frustrating is the fact that the skull of Ichthyovenator remains unknown. More than anything else, the distinctive skulls of these dinosaurs set them apart from other theropods, but no skull bones or even teeth were found with this dinosaur. This makes the name Ichthyovenator—”fish hunter”—a hypothesis that has yet to be confirmed by additional evidence. Spinosaurs have often been cast as specialized fish hunters that may have hunted along prehistoric rivers and lakes. Ichthyovenator is expected to have shared this way of life, but we as yet know little of this dinosaur’s biology.

Reference:

Allain, R., Xaisanavong, T., Richir, P., & Khentavong, B. (2012). The first definitive Asian spinosaurid (Dinosauria: Theropoda) from the early cretaceous of Laos Naturwissenschaften DOI: 10.1007/s00114-012-0911-7

Did egg-laying spell doom for non-avian dinosaurs, such as this crispy Troodon at the San Diego Natural History Museum? Photo by the author.

How did dinosaurs come to rule the Mesozoic world? No one knows for sure, but the way dinosaurs reproduced probably had something to do with it. Dinosaurs grew fast, started mating before they hit skeletal maturity, and laid clutches of multiple eggs—a life history that may have allowed dinosaurs to rapidly proliferate and diversify. And egg laying itself may have been critical to why many dinosaurs were able to attain gigantic sizes. By laying clutches of small eggs, dinosaurs may have been able to sidestep biological constraints that have limited the size of mammals.

But there was a catch. Consider a large dinosaur, such as Diplodocus. Infant Diplodocus hatched out of eggs roughly the size of a large grapefruit, and if they were lucky, the dinosaurs grew to be more than 80 feet long as adults. And the little sauropods were not just small copies of adults. Like many other dinosaurs, individual Diplodocus changed drastically during their lives, and young dinosaurs may have preferred different habitats and food sources from those of more mature individuals. As outlined by Daryl Codron and co-authors in a new Biology Letters paper, this peculiar life history may have been a consequence of laying eggs.

Codron’s group created a virtual dinosaur assemblage to see how intensely dinosaurs might have competed with one another as they grew. If all dinosaurs started off relatively small, then the largest species had to pass through a series of size classes and change their ecological role as they matured. This ramped up the pressure on young dinosaurs. Juvenile dinosaurs had to contend with other juveniles as well as dinosaurs that topped out at smaller sizes. In a diverse Late Jurassic ecosystem, for example, young Allosaurus, Torvosaurus and Ceratosaurus not only had to compete with one another, but also with smaller carnivores like Ornitholestes, Coelurus, Marshosaurus and Stokesosaurus. Dinosaurs would have faced the most competition at small size classes, and this may have driven some dinosaur lineages to become large.

The new paper also suggests that dinosaur life history may have played a role in the demise of the non-avian species. Competition at smaller size classes, Codron and colleagues suggest, drove dinosaurs to become bigger and bigger, and this created a lack of species that were small at maturity. Mammals and avian dinosaurs occupied those niches. This could have made dinosaurs more vulnerable to the intense pressures of the end-Cretaceous extinction. If the catastrophe targeted large animals, but was less severe among small animals, then non-avian dinosaurs would have been doomed. The big dinosaurs disappeared, and there were no small non-avian dinosaurs left to quickly proliferate in the aftermath.

As John Hutchinson pointed out in a Nature news story about this research, however, we’re going to need a lot more testing to see if this hypothesis holds up. The conclusion is based on a virtual model of ecosystems that we can’t study directly, and mass extinctions are frustratingly complicated phenomena.

Of course, a new dinosaur extinction scenario is irresistible journalist bait. Various news sources picked up the extinction hook (promoted in the paper’s press release) and pointed to the fact that dinosaurs laid eggs as the seeds of their undoing. But this isn’t quite right. After all, turtles, crocodylians and birds all laid eggs, too, and they survived. And mammals did not survive the end-Cretaceous extinction unscathed—several mammalian lineages disappeared or took major hits during the catastrophe. Likewise, not all dinosaurs alive during the final days of the Cretaceous were huge. Titans like Tyrannosaurus, Triceratops and Edmontosaurus are the most famous end-Cretaceous dinosaurs, but in western North America alone, there were also relatively small ceratopians, oviraptorosaurs and troodontid dinosaurs that topped out at about six feet in length. Were these dinosaurs still too big to survive? Was the threshold even lower? If it was, then the reason why medium-sized animals such as crocodylians survived, and why some mammals disappeared, becomes even more complicated. Why non-avian dinosaurs perished, and why so many other lineages survived, remains a mystery.

References:

Codron, D., Carbone, C., Muller, D., & Clauss, M. (2012). Ontogenetic niche shifts in dinosaurs influenced size, diversity and extinction in terrestrial vertebrates Biology Letters DOI: 10.1098/rsbl.2012.0240