Evolution Diary

The discovery of a dog-size T. rex ancestor may rewrite dinosaur evolutionary history, a new study says.

Measuring about 6 feet (180 centimeters) long–tail included–the 215-million-year-old Tawa hallae was found by hikers who noticed some small bits of bone at New Mexico’s fossil-rich Ghost Ranch.

The dinosaur bears a mix of characteristics, such as air sacs, that link Tawa to older dinosaur species found in South America, researchers say.

The connection boosts the theory that–at a time when the continents were still linked as a single supercontinent, Pangaea–the earliest dinosaurs arose in what is now South America, according to the study, which was funded in part by the National Geographic Society’s Committee for Research and Exploration and will be published December 11 in the journal Science.

The dinosaurs then diversified into three lineages and migrated out to the rest of the world, scientists say.

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