The Hell Creek Formation in what's now the Dakotas, Montana, and Wyoming was once home to some of the world's most beloved dinosaurs, like Triceratops and Tyrannosaurus rex (including SUE, one of the ...

The three fossil specimens (from left to right), Avisaurus darwini, Avisaurus sp., and Magnusavis ekalakaensis, all of which are represented by a tarsometatarsus. They are all shown to scale with one ...

Clive Thompson is a trustee of the Discovery Wilderness Trust, a non-profit organization that supports environmental conservation and the fostering of tracking skills. Charles Helm does not work for, ...

The complete absence of these creatures in later strata suggests they might have vanished in a mass-extinction event that ...