Selection towards larger body size in both herbivorous and carnivorous synapsids during the Carboniferous

Body size is among the most important characteristics of an organism, impacting on a variety of other traits. As such, a great deal of effort has been put into examining its evolution. One controversial topic of discussion has been the supposed trend towards larger body size in herbivores. In this paper we compare body size evolution in two closely related lineages during the earliest establishment of terrestrial ecosystems during the Carboniferous, more than 300 million years ago. The first of these two groups, Edaphosauridae, include some of the most diverse and abundant herbivores of their time, while the second, Sphenacodontia, were the largest and most abundant top predators. These groups include the famous “sail-back” reptiles Edaphosaurus and Dimetrodon. Using statistical analyses of evolution, it was shown that both edaphosaurids and sphenacodontians show significant increases in body size. However these were not gradual trends, but instead a single rapid increase is found early on in the history of both. The increase that coincides with the evolution of herbivory in edaphosaurids is larger and occurs earlier in time, so it is suggested that the selection towards larger body size in sphenacodontians was caused by the new range of large herbivorous prey available to them.

Read the full paper — Selection towards larger body size in both herbivorous and carnivorous synapsids during the Carboniferous by Neil Brocklehurst and Kirstin S. Brink on the FACETS website.