Pampadromaeus: Brazil’s Triassic Plains Runner

A reconstruction of Pampadromaeus. From Cabreira et al., 2011.

November has been a good month for sauropodomorph fans. Earlier this week I wrote about Leyesaurus, a newly named dinosaur that was part of a diverse cast of creatures preceding the mighty, long-necked sauropods. Now paleontologist Sergio Cabreira and colleagues have named another, even older relative of this peculiar group: Pampadromaeus barberenai. This animal may provide some hints about what the ancestral dinosaur might have been like.

Attendees at the 71st annual Society of Vertebrate Paleontology meeting got a preview of Pampadromaeus courtesy of study author Max Langer a few weeks ago. The study published in Naturwissenschaften goes into more detail. The newly described dinosaur is remarkable for both the location of its discovery and its placement in the dinosaur evolutionary tree. While many of the earliest known dinosaurs, such as Eoraptor and Panphagia, have been found in the Late Triassic strata of Argentina, Pampadromaeus was excavated from roughly 230- to 228-million-year-old, Late Triassic deposits in southern Brazil. Most of the skeleton was found, including the majority of the skull.

But what truly makes Pampadromaeus stand out is the dinosaur’s intermediate place between some of the earliest known dinosaurs and the later, more specialized sauropodomorphs such as Leyesaurus and Plateosaurus. While the skull of Pampadromaeus is long, low and generally resembles those of sauropodomorphs, the newly described dinosaur had different kinds of teeth in the jaw. Leaf-shaped teeth thought to correspond to herbivory were set in the front, while an array of short, recurved teeth often associated with carnivory followed toward the back of the mouth. Perhaps Pampadromaeus was an omnivorous dinosaur not yet fully committed to a life of chewing on plants. The anatomy of the rest of the dinosaur’s approximately four-foot-long body is consistent with a unique and varied lifestyle. Pampadromaeus had long legs and comparatively short arms, which hint that the dinosaur was an obligate biped. It seems unlikely that Pampadromaeus switched between walking on two legs and all fours as in later sauropodomorphs.

Taken together, the skeletal traits may indicate that Pampadromaeus retained features of what is thought to be the ancestral dinosaur archetype: a bipedal carnivore or omnivore similar to Eoraptor. Exactly where the dinosaur fits in relation to sauropodomorphs is difficult to ascertain, however. Several analyses in the new study place Pampadromaeus just outside the sauropodomorph group, which may indicate that the dinosaur represents a “stem” lineage from which the true sauropodomorphs evolved. Further discoveries and analyses are required to provide the context necessary to understand where Pampadromaeus belongs in relation to these dinosaurs. Still, Pampadromaeus is more closely related to the early sauropodomorphs than to the forerunners of theropod dinosaurs. By comparing the anatomy of such a creature to theropod foreunners such as Herrerasaurus and Staurikosaurus, perhaps paleontologists will be better able to understand what the common ancestor of the sauropods and theropods was like and reconstruct one of the great splits in the evolutionary history of dinosaurs.

References:

Cabreira, S., Schultz, C., Bittencourt, J., Soares, M., Fortier, D., Silva, L., & Langer, M. (2011). New stem-sauropodomorph (Dinosauria, Saurischia) from the Triassic of Brazil Naturwissenschaften