Evolution of the Cetacean Body Plan: Eocene Whales from India

Northeast Ohio Medical University, Rootstown OH

Investigators

Abstract

Evolution is the process that governs the entire diversity of living organisms on Earth. Evolutionary changes accumulate slowly, and, for most organisms, cannot be studied within the life span of one human observer. The most impressive evolutionary changes involve great modifications in all aspects of the design of an animal, its bodyplan. Such macroevolutionary changes become obvious only after they accumulate over a long time period. Actual examples are rare because the fossil record rarely grant researchers this level of detail. One of the best examples of macroevolutionary changes that are documented in the fossil record is the origin of whales, dolphins, and porpoises. All modern whales, dolphins, and porpoises (together constituting the Cetacea) are fully aquatic mammals, perfectly adapted to their watery environment and unable to survive on land. However, cetaceans have ancestors that lived on land, with a body plan that roughly resembled that of a wolf, and very unlike that of modern cetaceans. In less than 15 million years, this archaic body plan was modified into that of modern cetaceans. The present proposal aims to study these transformations from several points of view. First, PIs will collect cetacean fossils in India that document the land-water transition. Second, they will study the evolution of locomotor and sense organs, as cetaceans passed through this transition. Finally, they will study dolphin embryos in order to relate changes in cetacean embryology to evolutionary changes. The cetacean bodyplan is determined, to a large extent, by the unusual mode of swimming of cetaceans (swinging the horizontal tail fluke through the water). However, fossil cetacean had very different modes of swimming and these can be studied with fossils. The evolution of the cetacean bodyplan can also be studied indirectly, by determining its interaction with the sense organs. The most important sense organ with respect to this is the organ of balance and (associated with it) the organ of hearing. These will be studied using CT-scan methods. Finally, the modern cetacean bodyplan is also influenced, to an unknown degree, by its embryologic development, and this will be studied using embryos of modern dolphins.