Climate, ecosystem delayed success.

• Position: Dinosaurs

Climate and plant community instability may have hampered the success of dinosaurs in the tropics during the Late Triassic Period (235,000,000 to 201,000,000 years ago), according to a study in the Proceedings of the National Academy of Sciences. This finding was reached by coauthor Alan H. Turner, associate professor in the Department of Anatomical Sciences at Stony Brook (N.Y.) University, and an international team of scientists by examining the sedimentary rocks and fossil record preserved in the Chinle Formation in northern New Mexico to investigate the environment in tropical latitudes during the Late Triassic.

Dinosaurs first evolved during the Late Triassic nearly 230,000,000 years ago. Although dinosaurs ecologically dominated high latitudes at least 15,000,000 years before the end of the Triassic, they were rare in tropical latitudes, with only a few meat-eating species present for up to 30,000,000 years after their origin. The results detailed in the study suggest that the fluctuations, associated with high atmospheric carbon dioxide, may have prevented the establishment of a diverse community of fast-growing, warm-blooded large dinosaurs such as sauropods and their close relatives.

These dinosaurs likely required a productive and stable environment to thrive, conditions not present in equatorial North America until the beginning of the Jurassic Period around 200,000,000 years ago.

The team...