Expert: David Prus - 6/10/2009

Question
QUESTION: Hi 1)what was the apex predator in north america 90 mya? 2)what was the apex predator in south america,africa,asia,india 65 mya? 3)if dryptosaurus and appalachiosaurus were primitive tyrannosaurids why did they lived 70 mya when already more advanced tyrannosaurids had evolved (albertosauru,daspletosaurus) did thet competed each other? Thanks

ANSWER: 1) Good question. Much of North America was covered in the inland sea at the time, but there are some dinosaur sites. This was the time of faunal turnover when carnosaurs like Acrocanthosaurus were replaced by tyrannosaurs. No predator fossils are known currently, but there were probably some primitive tyrannosaurs and dromeosaurs acting as predators.

2) South America-Carnotaurus, a horned, heavily built abelisaur
Africa-unknown. The last predators are from 90 mya-Carcharodontosaurus and several abelisaurs. If Africa had a faunal turnover as South America did, then probably the descendants of abelisaurs like Rugops and Kryptops
Asia-Tarbosaurus, Tyrannosaurus' Mongolian sister genus
India-Indosuchus, Rajasaurus, two 30-foot abelisaurs

3) These primitive tyrannosaurs were sheltered from being outcompeted by more advanced species by the inland sea, which prevented their more powerful relatives from taking over. We see this in South America and Africa in the Cretaceous-more primitive ceratosaurs and carnosaurs hold out while the tyrannosaurs take over elsewhere. Even in mammalian times we see this-giant predatory marsupials, crocodiles, and birds were the top predators in islands like South America and Australia. When placental predators(cats, dogs, and humans) appeared, the indigenous species were pushed out.

I hope this helps

---------- FOLLOW-UP ----------

QUESTION: tarbosaurus appeared before tyrannosaurus rex? wikipedia says that in mongolia 70mya there were tyrannosaurids (tarbosaurus),velocitaptorines(velociraptor),hadrosaurids(saurolophus).titanosaurids and the last therizinosaurids(therizinosaurus) but all these species died (except tarbosaurus that you said lived till the end of the cretaceous) before the end of the cretaceous. how tarbosaurus survived? also is there any possibility that by the and of the cretaceous in some places on the world the dinosaurs had already become extinct? sorry for my vocabulary mistakes i'm from greece... thanks

Answer
Actually, all the Mongolian dinosaurs manage to survive until the end of the Cretaceous. The Nemegt formation probably extended to 65 mya, and all of its dinosaurs probably survived until the very end.

It's very hard to determine when dinosaurs began to disappear. Some scientists say they already were in decline, while others say that diversity was constant until the K-T extinction event. Unfortunately, there is not enough evidence to prove either interpretation. Therizinosaurus may have died before, at the same time, or after Triceratops; we just don't know. It's an interesting idea, but it's very hard to prove it with the limited evidence.

I hope this helps