Paleobiota
The formation has produced impressive assemblages of invertebrates, plants, mammals, fish, reptiles (including the lizard Obamadon), and amphibians. Notable dinosaur finds include Tyrannosaurus and Triceratops. The most complete Hadrosaurid dinosaur ever found was retrieved in 2000 from the Hell Creek Formation and widely publicised in a National Geographic documentary aired in December 2007. A few bird, mammal, and pterosaur fossils have also been found. Teeth of sharks and rays are sometimes found in the riverine Hell Creek Formation, suggesting that some of these taxa were tolerant of fresh water then as now.
Read more about this topic: Hell Creek Formation