RUI/SG: Phylogenetic Relationships of Archaic "Ungulates" and Their Implications for the Timing and Rate of Divergence of Placental Mammal Clades

Rowan University, Glassboro NJ

Investigators

Abstract

"Condylarths" are a collection of different families of fossil mammals that lived during the first 20 million years or so after the extinction of the dinosaurs. Different kinds of condylarths have been considered to be ancestors or close relatives of certain early lineages of mammals, especially the various groups of hoofed mammals. Recent studies using DNA from living mammals have given us a better understanding of how the different lineages of living mammals evolved, but they have also made the relationships of the condylarths less clear. This research aims to clarify how condylarths are related to other mammals, particularly those lineages that have survived to the present. Because they lived during a time when the various lineages of living mammals appeared in the fossil record, understanding the evolutionary relationships of condylarths to living mammals will help us better understand the origins of different mammal lineages. This will help resolve a longstanding issue as to whether most mammal lineages diversified after the dinosaurs went extinct or well before the dinosaur extinction (as some DNA studies of mammals have proposed). As a result, it will help us understand the reasons why mammals diversified into so many forms that we see today, including our own species. This study will focus specifically on four topics: 1) the phylogenetic affinities of condylarth taxa to extant mammalian lineages; 2) whether any condylarth families form natural (monophyletic) groups; 3) whether ungulates (hoofed mammals) are a natural group; and 4) how condylarth evolution affects the interpretation of divergence times for various mammal lineages. Data from the skeletal anatomy of condylarths will be combined with morphological and molecular data for a broad range of extant and extinct placental mammals. Parsimony, likelihood, and Bayesian methods will be used to evaluate the phylogenetic positions of condylarths, and several new approaches and methods will be used to estimate divergence times. The results will assess the phylogenetic position and taxonomy of condylarth taxa, re-evaluate the significance of condylarths for the origins of placental mammal lineages, and re-evaluate divergence times of extant placental lineages based on condylarth phylogeny.