My interests are in the evolution and paleobiology of vertebrates, primarily hoofed mammals (ungulates), but I maintain interests in, and occasionally have published upon, a wide range of topics in vertebrate evolution. These broad interests in vertebrate evolution and functional anatomy are reflected in my contributions to the text book "Vertebrate Life".

My research falls into two main areas (a third, more minor one, is in the systematics of ruminant artiodactyls):

The correlation between skeletal morphology and behavior, and in using the correlations derived from the living animals to determine the probable behavior of extinct taxa.

My initial interest was in the craniodental morphology and feeding behavior in herbivores, but I have become increasingly interested in the evolution of cursorial locomotion in mammals in general.

Patterns of Cenozoic mammalian faunal change, and community evolution in relation to changing vegetation and climate.

I am especially interested in the evolution of the Miocene (around 25-5 million years ago) savanna ecosystem in North America. For the past several years I have been amassing data on Tertiary mammal faunal assemblages, in correlation with my editorial work on a multi-authored book: Evolution of Tertiary Mammals of North America.

These data have been incorporated into a computerized database, and I am currently collaborating with both North American and European researchers on a comparison of evolutionary patterns between North American and New World mammals, in relation to climatic changes.

The fauna of the Sheep Creek Formation, Late early Miocene of Nebraska ~17 million years ago.

These two apparently disparate areas can be related to each other as follows. An understanding of the diversity of feeding and locomotor behaviors (plus range of body sizes) in a mammalian assemblage (living or fossil) is reflective of the structure of the habitat. It is usually held that "The Present is the Key to the Past": yet I am becoming increasingly interested in the possibility of both subtle and more radical differences in even relative recent (past 20 million years) habitats and ecosystems in comparison with those of the present day. For example, the mammalian communities of the supposed savannas of the late Miocene of North America have certain ecomorphological differences to those of present-day East African savannas (absence of pursuit predators, large diversity of grazing horses but no grazing ruminants) that may indicate a precise type of habitat unknown today.

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