Catching a Titanosaur By a Tooth

Sauropods are Mesozoic puzzles. These long-necked, large-bodied dinosaurs pushed evolutionary innovation to the extreme, and even the simplest aspects of their biology are confounding, oft-debated subjects. For one thing, how could these dinosaurs occupy such a range of body sizes – over 100 feet long among the largest – with tiny, peg-like teeth? These dinosaurs couldn’t chew at all, but must have horfed down vast quantities of greens to fuel their fast-growing bodies. The distinctive, simple teeth of sauropods underscore how strange these animals truly were, and an isolated tooth found in Argentina hints at the presence of what may be an unknown, unusual sauropod.

Universidad Nacional de Río Negro paleontologist Rodolfo García describes the simple, cylindrical tooth in an in-press Cretaceous Research paper. Ranging in the neighborhood of 86 to 70 million years old, the isolated sauropod piece was found in the Cretaceous rock of Salitral de Santa Rosa, Río Negro, Argentina. There is no way of knowing exactly what species of dinosaur the tooth belonged to, but, as García points out, the tooth is likely from a particular form of sauropod called a titanosaur. The question is whether this dinosaur was a hefty herbivore or a weirdo with an oversized head.

At almost three inches long, the specimen is larger than any other titanosaur tooth yet found. In particular, García notes, the petrified peg is about 32% longer than the longest tooth in the titanosaur Nemegtosaurus, and about twice as long as the biggest tooth in the jaws of the bizarre, beaked Bonitasaura. Does this mean that the tooth is a small sign of what may the biggest dinosaur ever? Probably not.

García doesn’t offer any body size estimates for the mystery dinosaur in the new study. That’s a wise move given how little we know about many titanosaurs. Nemegtosaurus, for example, is principally known from a skull, while the most gargantuan titanosaurs – 100-foot-plus giants such as Argentinosaurus and Futalognkosaurus – lack skull material. Without bits of jaw, we don’t know how big the teeth of truly enormous titanosaurs were.

There’s a little more of Bonitasaura to work with. Paleontologist Sebastián Apesteguía estimated that this relatively short-necked, stout sauropod was about 30 feet long. The tooth García describes obviously came from a larger animal, but, given the vagaries of scaling and proportion, it’s hard to say just how much bigger. Still, if the mystery tooth belonged to a sauropod a bit more than twice as big as Bonitasaura – let’s be generous and say 75 feet or so, just for the hell of it – that still doesn’t come close to the size of the biggest sauropods. The current contenders for the Biggest Dinosaur EVER superlative are all estimated to be in excess of 100 feet, and, maddeningly, they universally lack heads.

And, as García hypothesizes, it’s possible that the hidden sauropod might have been a big-headed animal with a goofy grin of oversized teeth. The isolated tooth looks large compared to those of other titanosaurs found in the same formation – Bonatitan, Rocasaurus, and Aeolosaurus – but doesn’t tell us anything about the skull or exact size of the rest of the animal. Indeed, whether the tooth even belongs to a new species or represents a large individual of a previously-named sauropod isn’t clear. For now, the tooth is a hint of what remains to be discovered.

References:

Apesteguía, S. 2004. Bonitasaura salgadoi gen. et sp. nov.: a beaked sauropod from the Late Cretaceous of PatagoniaBonitasaura salgadoi gen. et sp. nov.: a beaked sauropod from the Late Cretaceous of Patagonia. Naturwissenschaften. 91, 10: 493-497

García, R. 2012. A giant tooth from the Late Cretaceous (middle Campanian-lower Maastrichtian) of Patagonia, Argentina: An enormous titanosaur or a large toothed titanosaur? Cretaceous Research. http://dx.doi.org/10.1016/j.cretres.2012.10.004

Wilson, J. 2005. Redescription of the Mongolian sauropod Nemegtosaurus mongoliensis Nowinski (Dinosauria: Saurischia) and comments on Late Cretaceous sauropod diversityRedescription of the Mongolian sauropod Nemegtosaurus mongoliensis Nowinski (Dinosauria: Saurischia) and comments on Late Cretaceous sauropod diversityRedescription of the Mongolian sauropod Nemegtosaurus mongoliensis Nowinski (Dinosauria: Saurischia) and comments on Late Cretaceous sauropod diversity. Journal of Systematic Palaeontology. 3,3: 283-318