John Harold Ostrom was an American paleontologist who revolutionized the modern understanding of dinosaurs. Ostrom's work inspired what his pupil Robert T. Bakker has termed a "dinosaur renaissance".
John Ostrom and Deinonychus skeleton cast. Photo courtesy Yale University.
John Ostrom
Skeleton of the hadrosaur Anatosaurus (now E. annectens) paratype YPM 2182 at the Yale University Museum showing its upright posture.
Ostromia crassipes, previously known as the Haarlem Archaeopteryx
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is a subject of active research. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201.3 mya and their dominance continued throughout the Jurassic and Cretaceous periods. The fossil record shows that birds are feathered dinosaurs, having evolved from earlier theropods during the Late Jurassic epoch, and are the only dinosaur lineage known to have survived the Cretaceous–Paleogene extinction event approximately 66 mya. Dinosaurs can therefore be divided into avian dinosaurs—birds—and the extinct non-avian dinosaurs, which are all dinosaurs other than birds.
Image: Stegosaurus ungulatus
Image: Frenguellisaurus ischigualastensis DSC 6185
Image: Triceratops Specimen at the Houston Museum of Natural Science
Image: Louisae