DINOSAUR PALEOBIOGEOGRAPHY AND ITS IMPLICATIONS FOR STEGOSAUR EXTINCTION

Stegosaurs are a well-known group of mid to large sized, herbivorous thyreophoran dinosaurs with distinctive rows of elaborate plates and spikes running down their backs and tails. They were the predominant ornithischian group during the Late Jurassic, but declined and became extinct by the end of the Early Cretaceous while other dinosaur groups were increasing in diversity. This study is an attempt to use paleobiogeographic data from the Paleobiology Database (PBDB) to evaluate the distribution of stegosaurs through their stratigraphic range. By mapping the distribution of various dinosaur and plant fossil collections throughout the Jurassic and Cretaceous, we assess the potential roles competition from advanced herbivorous dinosaurs, the arrival of new predatory theropod dinosaurs, or the rise and radiation of angiosperms could have played in the stegosaurs’ demise. Stegosaur abundance declines dramatically in the early Cretaceous, in contrast to other herbivorous dinosaurs, particularly the ankylosaurs. This parallels the decline of cycads, conifers and equisetales in the Cretaceous, bolstering the suggestion that angiosperms replacing older plant groups, such as cycads, may have been the driving force of stegosaur extinction. The arrival of new predators (dromaeosaurs and tyrannosaurs) may have intensified the escalation between the stegosaurs and the ankylosaurs for the same ecological niche as armored low browsers. However, the maps are limited in detail because they do not show the trend of each dinosaur or plant group at the stage level. Also, there appears to be a bias in the plant fossil record because most of the Cretaceous plant collections recorded in the PBDB are mostly North American and other parts of the world are either poorly represented or the collections have not been recorded to the PBDB yet.