Hostname: page-component-7c8c6479df-8mjnm Total loading time: 0 Render date: 2024-03-28T09:30:00.568Z Has data issue: false hasContentIssue false

Evaluating hypotheses for the early diversification of dinosaurs

Published online by Cambridge University Press:  17 May 2011

Randall B. Irmis*
Affiliation:
Utah Museum of Natural History and Department of Geology & Geophysics, University of Utah, 1390 E. Presidents Circle, Salt Lake City, UT 84112–0050, USA Email: irmis@umnh.utah.edu

Abstract

Many hypotheses have been proposed for the rise of dinosaurs, but their early diversification remains poorly understood. This paper examines the occurrences, species diversity and abundance of early dinosaurs at both regional and global scales to determine patterns of their early evolutionary history. Four main patterns are clear: (1) sauropodomorph dinosaurs became abundant during the late Norian–Rhaetian of Gondwana and Europe; (2) Triassic dinosaurs of North America have low species diversity and abundance until the beginning of the Jurassic; (3) sauropodomorphs and ornithischians are absent in the Triassic of North America; and (4) ornithischian dinosaurs maintain low species diversity, relative abundance and small body size until the Early Jurassic. No one hypothesis fully explains these data. There is no evidence for a Carnian–Norian extinction event, but sauropodomorphs did become abundant during the Norian in some assemblages. No clear connection exists between palaeoenvironment and early dinosaur diversity, but environmental stress at the Triassic–Jurassic boundary is consistent with changes in North American dinosaur assemblages. Elevated growth rates in dinosaurs are consistent with the gradual phyletic increase in body size. This study demonstrates that early dinosaur diversification was a complex process that was geographically diachronous and probably had several causes.

Type
Research Article
Copyright
Copyright © Royal Society of Edinburgh 2011

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)