A previously unknown species of carnivorous dinosaur, revealed recently in the journal Science, is providing new insight into the early evolution of dinosaurs. Tawa hallae (after the Hopi Indian name for their sun god) is one of the oldest dinosaur species ever found in North America. Scientists studying the find say it demonstrates that carnivorous dinosaurs began evolving early and quickly began spreading across Pangaea, the supercontinent of the late Triassic period.
Fossils of the small-sized carnivore (about the size of a Great Dane), including a complete skeleton of a juvenile Tawa, were found at the world-renowned paleontological site at Ghost Ranch in northern New Mexico beginning in 2005. The Tawa featured feathers, a long neck and tail, and carnivore teeth and claws. It belongs to a group of dinosaurs known as theropods, which includes the Tyranosaurus Rex and Velociraptor.
The team of paleontologists studying the Tawa began developing their new insights into early carnivorous dinosaur evolution when they compared their find with a similar species discovered in Argentina in the 1960s, Herrerasaurus ischigualastensis. While Herrerasaurus featured some traits found in therapods – such as carnivore teeth and large claws – it was missing some other therapod features, such as the hollow areas in the neck vertebrae, which link the theropod to modern birds. These inconsistencies resulted in debates among paleontologists as to whether the Herrerasaurus was an early theropod or from an entirely separate evolutionary tree.
With the recent discovery of the Tawa, the team of paleontologists found that it shared a range of characteristics with both the Herrerasaurus and established therapod dinosaurs. Therefore, say the scientists, this demonstrates that the Herrerasaurus traits didn’t arise independently – as many paleontologists had thought – and that it is in fact, like the Tawa, an early theropod.
In turn, this has helped scientists to develop a clearer picture of the early diversification of dinosaurs across the Pangaea supercontinent, as well as showing that the characteristic bone structures of later therapods and modern birds were evolved much earlier than previously thought.