Dinosaurs Arose in S. America Fossil of T. rex cousin helps fill in the puzzle By John Johnson, Newser Staff Posted Dec 10, 2009 7:59 PM CST 13 comments Comments Meet Tawa hallae, a cousin of T-Rex. (AP Photo/Artwork by Jorge Gonzalez) (Newser) – The fossil of a feisty little ancestor of T. rex lends credence to the theory that dinosaurs emerged in South America. More precisely, they likely arose about 230 million years ago in Pangaea, which was then the single joined continent of the Americas. The development follow the discovery of a dog-sized dino christened Tawa hallae, reports National Geographic. Hikers found Tawa in New Mexico, and it can be traced to earlier dinosaurs found in what is now South America. If scientists are correct, a single species of dinosaur appeared in Pangaea, diverged into three lines—theropods, sauropods, and ornithischians—and migrated to the rest of the world. Tawa and the much larger T. rex fall into the theropod family.