Research Training Program

Andrew Rominger
Stanford University
Stanford, California

Douglas Erwin, Ph.D.
Supervising Scientist
Department of Paleobiology

Peter Wagner, Ph.D.
Supervising Scientist
Department of Paleobiology

Diversification of the Wellerellinae brachiopods during the West Texan
Permian: A combined phylogenetic and morphometric approach

Darwin gave us the theory of evolution by natural selection with which we could begin to understand the mechanisms that produce new species and consequently new and novel kinds of organisms. We saw a unique opportunity to study such mechanisms in the highly species diverse West Texan Permian fossil record of brachiopods. Brachiopods are bivalves, as are for example, clams and mussels; recall that West Texas was a shallow sea 300 million years ago. The Wellerellinae reached their peak diversity in the middle of the Permian, approximately 265 million years ago, with two branches of the phylogenetic tree reaching a peak diversity of 12 species having started with just one species several million years earlier. Interestingly, in the later Permian a new group appears and grows in diversity. This group, which is related to other brachiopods found all around the world, most likely immigrated into this area, as opposed to evolving here. This demonstrates another important force in the diversification of species colonization from other areas. These brachiopods exhibit interesting shell morphology, actually changing the rate at which they grow several times through their lifetimes. This change through life, termed developmental change, is important in understanding how the organisms interact with their watery environment, as size and shape are very important in determining mobility, feeding ability and ultimately survival in a fluid medium. As such, this developmental change will be very important in thinking about whether similar species can coexist.

This research was supported by a grant
from the National Science Foundation, Award EAR 0451802.