The discovery and description of Deinonychus, “terrible claw,” by John Ostrom (1928–2005) of the Yale Peabody Museum turned out to be the catalyst that changed our perceptions about dinosaurs. In 1964, Deinonychus bones were excavated from the Cloverly formation rocks of the Early Cretaceous period in Montana; Ostrom presented his findings in 1969. The information from these fossils, and other fossil finds related to Deinonychus, increased our knowledge of dromaeosaurids, which may have been the most aggressive and maybe the most intelligent of the theropods.

Based on fossil evidence found during the excavation, Ostrom concluded that these animals may have hunted in packs, indicating a social structure. Also, the animals’ skeletons were light and slender, with a stiffened tail for balance, long clawed arms for grasping, sharp backward-curving teeth for tearing flesh, and a huge sickle-shaped claw on the second toe of the foot for slashing. The animal was built for speed and agility, quite unlike the perception of dinosaurs up until that time. From these findings, Ostrom theorized that Deinonychus may have been warm-blooded. This radical notion invited new thinking about dinosaur physiology and led to the modern ideas of dinosaurs as active, social animals.

But Ostrom’s ideas did not stop there; he was also the paleontologist who almost single-handedly convinced the scientific community that birds are descended from dinosaurs. In addition, his discoveries provided the underpinning for the Jurassic Park books and movies, as well as tons of books about dinosaur evolution.