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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

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 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

When I was a young dinosaur fan, Spinosaurus was one of my most favorite dinosaurs. What could be more fantastic than a giant predatory dinosaur equipped with a bizarre sail? But Spinosaurus as I knew it during the 1980s—imagine a fin-backed Allosaurus—looked significantly different from the dinosaur as we know it today. The reason for the big change is largely attributable to the discovery of a different, related dinosaur in England.

In 1986, Alan Charig and Angela Milner described a very strange, crocodile-snouted dinosaur they called Baryonyx. The Cretaceous creature turned out to be the key to identifying what is now one of the most famous dinosaur groups, the spinosaurs. Paleontologists had been finding pieces of spinosaurs for over a century, but often the teeth of these dinosaurs were confused for those of crocodiles, and the original Spinosaurus fossils were destroyed during Allied bombing of Germany in WWII. When Baryonyx was discovered, however, paleontologists began to recognize the similarities between it, older discoveries and similar dinosaurs that were soon found in South America, Africa, Asia and Australia. Some, such as Suchomimus and Spinosaurus from Africa, had sails, while others—including Baryonyx—did not, but the initial discovery formed the basis for the great spinosaur makeover. (Even before new Spinosaurus material was found, the relationship between it and other spinosaurs like Baryonyx was used to restore the predator with heavy-clawed hands and an elongated snout.) In the above video, created by London’s Natural History Museum, paleontologist Angela Milner explains how the dinosaur was discovered and why Baryonyx is so peculiar compared to other predatory dinosaurs.

The underside of the snout fragment representing the spinosaur Oxalaia from Brazil. The holes are the tooth sockets. From Kellner et al., 2011.

Paleontologists have not found much of Oxalaia quilombensis. A fragment of the snout and a portion of the upper jaw are all that is known of this dinosaur. Even so, those two parts are enough to know that Oxalaia was one of the peculiar predatory dinosaurs known as spinosaurs, and a giant one at that.

Just described by Alexander Kellner, Sergio Azevedo and colleagues in Annals of the Brazilian Academy of Sciences, the new dinosaur was found in Late Cretaceous deposits of northeastern Brazil dating back to about 95 million years ago. The portion of the snout alone confirms that it was one of the spinosaurs. Unlike other predatory dinosaurs with heavy, broad heads, the spinosaurs had elongated, crocodile-like jaws, with the upper jaw ending in a spoon-shaped rosette. Oxalaia had the same snout shape, and using this fragment along with skull proportions of better-known spinosaurs, Kellner and co-authors estimate that this dinosaur would have had a skull about four and a half feet long.

Oxalaia would have been a giant among spinosaurs. Compared with the spinosaur fossils previously found in slightly older rock in Brazil—given the names Irritator and Angaturama, though likely representing the same dinosaur—Oxalaia was certainly the biggest type of this dinosaur found in South America. Only spinosaurs from Africa—such as Suchomimus and Spinosaurus—were the same size or larger.

Frustratingly, our knowledge of Oxalaia is so incomplete that it is difficult to know what the entire animal looked like. The fossils recovered so far are most similar to those of Spinosaurus, but there is not yet a way to tell whether the new spinosaur from Brazil had a sail on its back or how it compared to its close relatives. Additional Oxalaia bones may be difficult to find. The site where the two skull fragments were found is dominated by isolated bones that are often quickly destroyed by the elements once exposed. Now that paleontologists know what to look for, though, perhaps researchers will be able to accumulate more bits and pieces of Oxalaia.

References:

KELLNER, A.; AZEVEDO, S.; MACHADO, A.; DE CARVALHO, L.; HENRIQUES, D. (2011). A new dinosaur (Theropoda, Spinosauridae) from the Cretaceous (Cenomanian) Alcântara Formation, Cajual Island, Brazil Anais da Academia Brasileira de Ciências, 83 (1), 99-108