Collaborative Research: Feeding and Diet at the Origin of Whales: Evolution, Function, and Development J. G. Thewissen and M. T. Clementz
Cetaceans (whales, porpoises, and dolphins) originated from land mammals (even-toed ungulates or Artiodactyla) about 50 million years ago. A remarkable series of fossils documents this transition and whale origins has become one of the most celebrated examples of macroevolutionary change in the fossil record. In spite of this, it is not known why whale ancestors took to the water. The objective of this project is to investigate whether diet and feeding played a critical role in the land-to-water, artiodactyl-to-whale transition. This project studies feeding and diet during the artiodactyl-to-whale transition using five approaches. First, the morphology of the molars gives clues to their use, are they used to shear, crush, or grind food. Those food processing methods correlate, in modern mammals, to specific diets, and can thus be used to infer diets in extinct animals. Second, the shape and design of skull and mandible of these early whales shows how the chewing muscles were attached, and clarifies hw the jaws were used in processing food, another feature that differs in animals that eat different food items. Third, dental wear facets show how teeth were used during chewing, and these wear facets are highly unusual in fossil whales, suggesting a very specialized diet. Fourth, since the molecules that make teeth are derived from an animal's diet, study of the chemistry of the teeth (stable isotopes) can answer questions about that diet. Lastly, a study of modern dolphin embryos will tell us how dolphin tooth germ form, and how they are derived from fossil whales. Together, using these five approaches to study feeding across the artiodactyls-whale transition will be used to answer a number of specific questions about the evolution of feeding and diet, such as whether a species is a suction feeder, whether fish dominated in its diet, or whether carnivore-like shearing occurred. Combined with data on the evolution of other organ systems in early whales, we will be able to study several questions: 1, Was diet an important reason why whales went into the water? 2, Was early cetacean evolution characterized by a period of experimentation with diets and feeding strategies or was a fish-diet acquired early in evolution?, 3, Does dental morphology and dental function change hand-in-hand across the artiodactyls-whale transition or are they temporally disjunct? These results integrate information at multiple organizational levels, from genes controlling development, to stable isotopes gauging life history parameters, and to muscle moments controlling jaw closing. This integrated approach is exciting because scientists with very different backgrounds all contribute pieces to the puzzle that allows for a thorough understanding of whale origins. The broader impact of the proposal is that whale origins is a topic of great interest to scientists, educators, and the public-at-large. This proposal includes an outreach program that makes its results accessible through the www. It also includes a detailed program that enriches the science curriculum of local, rural fourth and fifth graders in northeast Ohio. This proposal presents hands-on sessions that present whale research as a springboard to science and research and ties in directly to mandated curricular elements on geology, paleontology, anatomy, and embryology. After fine-tuning, these sessions will be adapted to be available for nationwide use.
