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A reconstruction of Irritator. Photo by Kabacchi, image from Wikipedia.

Spinosaurs are often called “fish-eating dinosaurs.” Their long, shallow snouts recall the jaws of crocodiles, and, based on gut contents and fossil geochemistry, it seems that these dinosaurs truly were piscivores. Yet spinosaurs weren’t on a strict fish diet. In 2004, Eric Buffetaut and colleagues described a spinosaur tooth embedded in the fossilized neck vertebrae of an Early Cretaceous pterosaur found in Brazil’s roughly 110-million-year-old Santana Formation. The paleontologists couldn’t say whether the dinosaur caught its prey on the wing or scavenged a fresh carcass, but, based on fossils previously found in the same geologic formation, one spinosaur stood out as the probable culprit–Irritator challengeri.

The spinosaur’s quirky name symbolizes its unconventional back story. As explained in the 1996 description of the dinosaur by David Martill and colleagues, the mostly complete skull of Irritator had been artificially modified by a commercial fossil dealer prior to being purchased and making its way into the collection of Germany’s Stuttgart State Museum of the Natural Sciences. The tip of the snout was made up of bone from elsewhere on the skull, “concealed by blocks of matrix removed from other parts of the specimen and a thick layer of Isopon car body filler.” The fabrication not only deceived the buyers, but was especially difficult to remove from the authentic fossil. Martill and colleagues named the dinosaur Irritator as a tribute to “the feeling the authors felt (understated here) when discovering that the snout had been artificially elongated.”

Martill and collaborators originally proposed that Irritator was a maniraptoran dinosaur–a relative of the feathery deinonychosaurs, oviraptorosaurs, and their kin. That same year, however, paleontologist Andrew Kellner recognized that Irritator was actually a spinosaur–one of the croc-snouted, and often sail-backed, predatory dinosaurs. Kellner also named what he suspected was another spinosaur found in the same geologic formation–”Angaturama limai“–but many researchers suspect that this animal is the same as Irritator, and the so-called “Angaturama” remains may even complete the missing parts of the Irritator skeleton.

But even after Irritator was properly identified, there was still work to be done. Diane Scott undertook the painstaking work of fully cleaning the skull of the encasing matrix, which led to a new description by Hans-Dieter Sues and coauthors in 2002. Irritator is represented by the most complete skull yet known for any spinosaur. Among other new aspects, it was apparent that the back of the skull was significantly deeper among spinosaurs than had previously been thought. And even though Martill and co-authors originally described a prominent crest on the top of the spinosaur’s skull, the fully-prepped fossil showed that this bone did not actually belong to the Irritator skull.

There’s still much we have to learn about spinosaurs. Most of these dinosaurs are only known from bits and pieces. And despite starring in Jurassic Park III, Spinosaurus itself is among the most poorly known dinosaurs of all, and the fragmentary nature of so many of these dinosaurs makes it possible that paleontologists have named too many genera. In their study, Sues and coauthors argue that Suchomimus is really just a different species of Baryonx, and even Irritator might be a distinct species of Spinosaurus. Researchers have only just begun to track the record of these long-snouted dinosaurs, although, hopefully, future finds will not be quite so aggravating as Irritator.

This is the latest post in the Dinosaur Alphabet series.

References:

Buffetaut, E., Martill, D., Escuillie, F. 2004. Pterosaurs as part of a spinosaur diet. Nature. 430: 33

Martill, D., Cruickshank, A., Frey, E., Small, P., Clarke, M. 1996. A new crested maniraptoran dinosaur from the Santana Formation (Lower Cretaceous) of Brazil. Journal of the Geological Society 153: 5-8.

Sues, H., Frey, E., Martill, D., Scott, D. 2002. Irritator challengeri, a spinosaurid (Dinosauria: Theropoda) from the Lower Cretaceous of Brazil. Journal of Vertebrate Paleontology. 22, 3: 535-547

Only hindlimb elements of Alnashetri are known so far, but, based on the dinosaur’s relationships, the tiny theropod probably looked something like this Alvarezsaurus. Photo by FunkMonk, image from Wikipedia.

Many dinosaurs have gained fame thanks to their gargantuan size. A creature in the form of a dipldodocid or tyrannosaur would be wonderful at any scale, but the fact that Apatosaurus was an 80-foot-long fern-sucker and Tyrannosaurus was a 40-foot carnivore make their skeletal frames all the more spectacular. Even as an adult, long after my first encounter with their bones at the American Museum of Natural History in New York City, I still feel tiny when I look up at what’s left of the great dinosaurs.

But not all non-avian dinosaurs were gigantic. There were 100-foot giants, like the sauropod Argentinosaurus, but there were also pigeon-sized theropods such as the strikingly-colored Anchiornis. Indeed, a significant part of how we know dinosaurs really ruled the earth is because they occupied such a wide range of body sizes–from the breathtakingly large to the diminutive. And, earlier this month, Field Museum of Natural History paleontologist Peter Makovicky and colleagues added a previously unknown tiny dinosaur to the ever-growing roster of Mesozoic species.

Named Alnashetri cerropoliciensis, the small dinosaur is mostly a mystery. All that we know of it, Makovicky and coauthors report, are a set of articulated hindlimbs from a single animal found in the roughly 95-million-year-old rock of La Buitrera, Argentina. (The dinosaur’s genus name, the paper says, means “slender thighs” in a dialect of the Tehuelchan language.) Yet those appendages contain enough clues about the dinosaur’s identity that the researchers were able to figure out that the specimen represented a new species of alvarezsaur–one of the small, possibly ant-eating dinosaurs recognizable by their short, stout arms and long skulls set with tiny teeth. While the paleontologists acknowledge that their Alnashetri specimen might be a juvenile, Makovicky and collaborators estimate that the dinosaur was comparable to its relative Shuvuuia in size–about two feet long.

How Alnashetri resembled other alvarezsaurs, and where it departed in form, will have to wait for more complete specimens. Further research is also needed to narrow down when this dinosaur lived, but for the moment, Alnashetri appears to be the oldest alvarezsaur found in South America. If only we knew more of this dinosaur! As Makovicky and coauthors conclude, “continued fieldwork and future discoveries hopefully will provide more information on the anatomy of Alnashetri and allow a more definitive evaluation of its affinities and its significance for understanding biogeography and evolutionary trends such as body size evolution within alvarezsaurids.” At least the enigma has a name.

Reference:

Makovicky, P., Apesteguía, S., Gianechini, F. 2012. A new coelurosaurian theropod from the La Buitrera fossil locality of Rio Negro, Argentina. Fieldiana Life and Earth Sciences, 5: 90-98

The reconstructed skull of Eotriceratops. The actual specimen is not complete, but, based on the recovered elements and the dinosaur’s relationships, we know the dinosaur would have looked similar to Triceratops. Photo by Roland Tanglao, image from Wikipedia.

Triceratops is among the most cherished of dinosaurs. Even that might be a bit of an understatement. Fossil fans threw a conniption when they mistakenly believed that paleontologists were taking the classic “three-horned face” away, after all. But where did the charismatic chasmosaurine come from? Triceratops didn’t simply spring from the earth fully formed–the ceratopsid was the descendant of a long tail of evolutionary forerunners. And in 2007, paleontologist Xiao-chun Wu and collaborators described a 68-million-year-old dinosaur that might represent what one of the close ancestors of Triceratops was like–Eotriceratops.

In 2001, while on an expedition to search the Horseshoe Canyon Formation around the Dry Island Buffalo Jump Provincial Park in Alberta, Canada, Glen Guthrie discovered the partial skeleton of a huge ceratopsid dinosaur. This was the first identifiable dinosaur skeleton found in the top quarter of the formation, and, as Wu and coauthors later argued, the bones represented a new species. They called the animal Eotriceratops xerinsularis.

Paleontological devotees know that “eo” translates to “dawn.” The tiny mammal Eohippus was the “dawn horse” (which Victorian anatomist Thomas Henry Huxley famously characterized for the steed of a tiny “Eohomo“), and there are plenty of dawn dinosaurs such as Eoraptor, Eodromaeus, Eobrontosaurus and Eolambia. The prefix is a kind of honorific, used to indicate the hypothesized beginning of a major lineage or significant change. In the case of Eotriceratops, Wu and colleagues found that the dinosaur was the oldest known member of the evolutionary ceratopsid club containing Triceratops, Torosaurus and Nedoceratops (which, depending on who you ask, may or may not be the same dinosaur).

The individual Guthrie found had fallen apart between death and burial. Aside from some vertebrae, ribs and ossified tendons, the scattered specimen was primarily represented by a dis-articulated skull. When reconstructed, though, the head of Eotriceratops stretched almost ten feet long–about a foot longer than the largest-known Triceratops skull. And while different in some characteristics, Eotriceratops had the same three-horned look of its later relatives Triceratops and Torosaurus.

This isn’t to say that Eotriceratops was directly ancestral to Triceratops, Torosaurus, Nedoceratops or whatever combination of the three paleontologists ultimately settle on. Eotriceratops could be the closest relative of Triceratops to the exclusion of Torosaurus, which would support the idea that those later dinosaurs were separate genera.  Then again, Wu and coauthors pointed out that Eotriceratops might be the most basal member of the subgroup, which would make sense given that it was older than the other three genera. In either case, Eotriceratops can give us a rough idea of the Triceratops and Torosaurus prototype, but we lack the resolution to know if Eotriceratops was ancestral to any later dinosaur. Eotriceratops undoubtedly had some significance in the evolution of the last three-horned dinosaurs, but we need many more fossils to know this little-known dinosaur’s role in the story. Every dinosaur paleontologists find comes with a handful of answers and a myriad of new mysteries.

This post is the latest in the Dinosaur Alphabet series.

Reference:

Wu, X., Brinkman, D., Eberth, D., Braman. 2007. A new ceratopsid dinosaur (Ornithischia) from the uppermost Horseshoe Canyon Formation (upper Maastrichtian), Alberta, Canada. Canadian Journal of Earth Sciences 44: 1243-1265

Fossil teeth, found by Ferdinand Hayden in Montana, which Joseph Leidy attributed to the dinosaur “Trachodon.” From Leidy, 1860, image from Wikipedia.

More than 150 years ago, a young naturalist picked up a collection of isolated teeth and bones weathering out of the ground in what is now northern Montana. These weren’t the remains of any living animals but vestiges of Cretaceous life that naturalists had only just begun to recognize and categorize. Even the young explorer who picked them up, Ferdinand Hayden, didn’t know what they were, and so he sent them back east for identification. As the Philadelphia-based polymath Joseph Leidy later determined, some of Hayden’s scrappy finds were dinosaurs–among the earliest recorded dinosaur discoveries in the American West.

Hayden wasn’t the first person to discover fossils in North America. First Nations peoples were familiar enough with strange fossil bones that the prehistoric remnants inspired their legends, and naturalists such as Thomas Jefferson puzzled over what was left of Ice Age mammals such as mastodons and giant ground sloths. Dinosaurs got a relatively early start, too, although naturalists didn’t always realize what they had found. Even though he misidentified the fossil as part of a giant fish, explorer Meriwether Lewis found part of a dinosaur rib in the vicinity of what is now Billings, Montana, when he passed through the area in 1806 on his famous expedition with William Clark. And starting in the 1830s, the Amherst geologist Edward Hitchcok described scores of Early Jurassic dinosaur tracks, which he attributed to prehistoric birds.

All the same, the bits and pieces Hayden found showed that the wilds of the western territories harbored dinosaurs and were a portent of the “Bone Wars” that would later unfold among the badlands of Montana, Wyoming and Colorado. Now, the Great Falls Tribune reports, paleontologist Kristi Curry Rogers and her geologist husband Ray Rogers believe that they have located the place where Hayden stumbled across the Cretaceous tidbits.

Even though Hayden did not keep detailed field notes, a brief mention in a technical paper of the area in which he found the fossils helped the Rogers team narrow down their search area. From there, they followed game trails and looked for sites that would have produced the kinds of fossils Hayden picked up. They can’t be entirely certain that their site is the very same Hayden sampled, and they are wary of divulging the exact location given how often fossil sites are vandalized, but the Rogers have placed Hayden’s stop somewhere in Montana’s Missouri River Breaks north of Winifred. With assistance from the Bureau of Land Management, they want the area to be placed in the National Register of Historic Places–a testament to Hayden’s lasting contribution to American paleontology.

Not only was Ornithomimus feathered, but the dinosaur’s fluffy coat changed as it aged. Lovely art by Julius Csotonyi.

Another week, another feathery dinosaur. Since the discovery of the fluffy Sinosauropteryx in 1996, paleontologists have discovered direct evidence of fuzz, feather-like bristles and complex plumage on over two dozen dinosaur genera. I love it, and I’m especially excited about a discovery announced today. In the latest issue of Science, University of Calgary paleontologist Darla Zelenitsky adds another enfluffled species to the dinosaurian ranks. Even better, the specimens raise hopes that many more dinosaurs might be preserved with their feathery coats intact.

Zelenitsky’s downy dinosaurs are not newly discovered species. Ornithomimus edmontonicus was initially described by famed bone hunter C.H. Sternberg in 1933, and it is one of the characteristic Late Cretaceous species found in Alberta, Canada’s fossil-rich Horseshoe Canyon Formation. In Sternberg’s time, these dinosaurs were thought to be scaly, but recent finds of so many feathery dinosaurs has raised the likeliehood that the “ostrich mimic” dinosaur was at least coated in some sort of dinofuzz.

A family tree of Saurischian dinosaurs, showing lineages within this group with direct evidence for feathers. From Zelenitsky et al., 2012.

The prediction of fluffy Ornithomimus came from the spread of feathers on the coelurosaur family tree. The Coelurosauria is a major dinosaur group that encompasses tyrannosaurs, compsognathids, ornithomimosaurs, alvarezsaurs, oviraptorosaurs, deinonychosaurs and birds. To date, evidence of feathers has been found in every coelurosaur lineage except one–the ornithomimosaurs. The spread of feathers hinted that some sort of plumage was present in the common ancestor of all coelurosaurs and therefore should have been inherited by the ornithomimosaurs, but, until now, no one had found direct evidence.

A trio of Ornithomimus skeletons have finally confirmed what paleontologists expected. Zelenitsky enthusiastically explained the details to me by phone earlier this week. In 1995, when Zelenitsky was a graduate student, paleontologists uncovered an articulated Ornithomimus with weird marks on its forearms. No one knew what they were. But in 2008 and 2009 a juvenile and an adult Ornithomimus turned up with preserved tufts of filamentous feathers. “When we found these specimens,” Zelenitsky said, “we made the link to the 1995 dinosaur.” All those strange marks on the arms of the previously discovered Ornithomimus, Zelenitsky and colleagues argue, are traces of longer, shafted feathers.

Even though paleontologists expected feathery Ornithomimus, the discovery was still a surprise. “I was in disbelief,” Zelenitsky said. “They’re the first feathered dinosaurs from the Americas, and the first ornithomimosaurs with feathers, as well. It was shocking to say the least.”

But there’s more to the find than simply adding another species of fluffy dinosaurs to the list. The fact that the adult and juvenile animals had different kinds of plumage adds new evidence that coelurosaurs changed their fluffy coats as they aged. “The one juvenile was completely covered in filamentous type feathers,” Zelenitsky said. What the adults looked like comes from the two other specimens. One adult skeleton, lacking forearms, preserves fuzzy feathers, and “the second adult had markings on the forearm.” Together, the specimens indicate that adult Ornithomimus were mostly covered in fuzz but developed more complex arm feathers by adulthood.

Sex is probably behind the plumage change. “We infer that because these wing feathers are not showing up until later in life, they were used for reproductive purposes,” Zelenitsky said. Perhaps adult Ornithomimus used flashy arm feathers to strut their stuff in front of potential mates. Then again, based upon the resting and brooding postures of other theropod dinosaurs, adult Ornithomimus could have used their proto-wings to cover their nests. We don’t know for sure, but the developmental change appears to be another example of dinosaurs undergoing significant changes as they approach sexual maturity. This discovery, and others like it, will undoubtedly play into the ongoing discussion about the role of sexual selection in dinosaur biology and evolution.

Best of all, the new study indicates that paleontologists may soon find more feathered dinosaurs in unexpected places. The Ornithomimus skeletons were found in prehistoric river deposits composed of sandstone. Since almost all feathered non-avian dinosaurs have been found in fine-grained sediment–such as those around Liaoning, China–paleontologists thought that coarser-grained sandstone deposits were too rough to record such fine details. Now we know better. “That’s the really exciting part of it,” Zelenitsky says. If traces of dinosaur feathers can be preserved in sandstone, the twist opens up the possibility that paleontologists might find fluff and feathers with a greater array of dinosaurs–including the tyrannosaurs, deinonychosaurs, therizinosaurs and other coelurosaurs of North America. The trick is recognizing the traces before they’re destroyed during excavation and preparation. Rock saws and airscribes can all too easily obliterate the delicate fossils. A word to researchers–keep your excavation tools sharp, and your eyes sharper.

Reference:

Zelenitsky, D., Therrien, F., Erickson, G., DeBuhr, C., Kobayashi, Y., Eberth, D., Hadfield, F. 2012. Feathered non-avian dinosaurs from North American provide insight into wing origins. Science. 338, 510-514