I is for Irritator

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

Riley Black | | READ MORE

Riley Black is the author of The Last Days of the Dinosaurs and many other books. She is a science correspondent for Smithsonian magazine covering fossils and natural history, and she writes about the prehistoric past for a variety of publications.