How did the albertosaurus become extinct?

Answer 1

The last Allosaurus died because it was redundant. Allosaurs as a whole didn't die off completely until somewhere in the middle cretaceous period, and they did very well up until that point. Thus, a more appropriote question might be "What did Allosaurus evolve into?" Another Allosaurid that we can't exactly pinpoint is the answer to that. There is an early cretaceous true allosaurid that was living on Australia/Antarctica, but last I heard it had not been completely identified as a new species. Of course, an American theropod like Allosaurus somehow evolving into a dwarf species in Antarctica sounds a little iffy, but Allosaurus most certainly evolved into a more specialized form in the millions of years following the end of the Jurassic.

Allosaurs as a whole (and that is including the Early Cretaceous carcharodontosaurs) went extinct due to pressure from even more specialized predators like the Tyrannosaurs and Abelisaurs (Carnotaurus and the like).

Answer 2

With the rapid warming increasing at a higher rate, Allosaurus could not tolerate this and slowly died out and was dethroned by Tyrannosaurus Rex 85 million years later

Answer 3

Albertosaurus went extinct at the same time as T-rex, about 65.5 million years ago at the K-T event.