Tyrannosaurs were not the only large reptilian predators prowling through North America in the Late Cretaceous Epoch. Crocodilians made rivers and lakes dangerous places to linger, even for small dinosaurs. Unlike today, with American alligators and crocodiles found only in the Southeast, during the Late Cretaceous crocodilians lived all over North America.
These five teeth belong to a species of extinct crocodilian called Borealosuchus sternbergii. They were collected in the Hell Creek Formation of Montana by the late fossil hunter Harley Garbani and donated to the Western Science Center by his wife, Mary Garbani. At about 67 million years old, Borealosuchus shared its habitat with giant dinosaurs such as Tyrannosaurus,Edmontosaurus, and Triceratops. Other Fossil Friday subjects also lived alongside Borealosuchus, including the freshwater ray Myledaphus (https://valleyofthemastodon.wordpress.com/2018/02/02/fossil-friday-ray-tooth/#more-1560) and the large carnivorous lizard Palaeosaniwa (https://valleyofthemastodon.wordpress.com/2018/02/16/fossil-friday-lizard-vertebra/#more-1570).
The skull and body of Borealosuchus resembled those of living crocodilians, suggesting that it too lived as a semi-aquatic ambush predator.