Collaborative Research: Cetacean Phylogeny: A Reconciliation of Fossil and Neontological Data and the Importance of Taxonomic Sampling

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9985847Gatesy Biologists hypothesize that cetaceans (whales) evolved from terrestrial land mammals as many as 60 million years ago or more. This evolutionary transformation is one of the most remarkable known because it involved dramatic changes in size and shape. If we can understand this evolutionary transition it may serve as a model problem describing how evolutionary novelties appear. Fossils, like Ambulocetus, are excellent evidence that whales once had legs and walked on land. During their long evolutionary history whales have, however, lost their hind limbs and hair, developed specialized skulls to feed and hear underwater, and in some cases exceeded the largest dinosaur in body size relative to their ancestors of over 50 million years ago. In order to understand the details of how, why and when this evolutionary transformation occurred, it is important to develop a well-corroborated phylogenetic tree (family history) for whales and their close relatives. Ideally it would be of interest to study the anatomy and molecular biology of all species that are closely related to whales. These include living and extinct groups: Artiodactyla, or even-toed hoofed mammals (camels, pigs, ruminants, hippopotamids and relatives), Perissodactyla, or odd-toed hoofed mammals (horses, rhinos, tapirs and relatives), as well as Procreodi, Condylarthra and Mesonychia, completely extinct groups of hoofed mammals. In particular among the extinct groups, Mesonychia may be very closely related to cetaceans. Most of the taxa ( 90%) that make up the group of interest outlined above are extinct. As a result, scientists trying to generate a phylogenetic tree for whales are forced to work with only part of the data whether they study living animals or extinct animals. Those working on living animals (neontologists) draw on very detailed biological characters (e.g., all of the organisms' anatomy, molecular biology, histology, etc) but only in one instant of time: the present. Those working on extinct species (paleontologists) draw on fossil evidence which almost exclusively comprises skeletal data. However, these data can be scored for many more species, some of which may more closely approximate the ancestral condition of the earliest whales. Here we propose to integrate neontological and paleontological data, to better examine the phylogenetic tree of cetaceans. This is critical to do at this time because scientists working on different data types continue to find different answers as to who is the closest relative of whales: living taxa indicate that it is the hippopotamus and extinct taxa indicate that it is mesonychians. We aim 1) to increase the taxon and character sampling for both extinct and living whales and relatives, and 2) to examine how and why certain biological attributes (e.g., molecules, morphology) have evolutionary histories that do not appear to match the overall family tree. We aim to make the results of our morphological work as standardized as possible with published illustrations. The data collection aspect of this project is large and we will use this as an opportunity to mentor high school and undergraduate students who may be interested in research in evolution and systematics and who can be taught laboratory, computer, and data analysis skills as well as evolutionary theory.