The Black Peaks Formation in Texas, especially well known from Big Bend National Park, preserves rocks from the end of the Cretaceous into the early Cenozoic, spanning a critical interval near the Cretaceous-Paleogene transition about 66.5 million years ago. Its fossils record changing animal life across one of Earth’s great extinction boundaries. Finds include dinosaur remains attributed to a titanosaurian sauropod and a tyrannosaurid, as well as Quetzalcoatlus northropi. The formation also preserves rays, gar, alligatorids, turtles, and, in later layers, mammals such as multituberculates, barylambdids, and insectivores. Together these remains make it an important geologic and paleontological record in North American history.