Chest of an Eocene seacow from Kachchh, India. The left and right ribs are visible on either side of the vertebral column, still embedded in rock. Fieldwork in India is in collaboration with Dr. Sunil Bajpai, Indian Institute of Technology, Roonkee.
Seacows (including manatees and dugongs) and elephants are closely related, and their common ancestor lived more than 55 million years ago in Africa or South Asia. They are also related to the Desmostylia, an extinct group of hippo-like mammals that lived on the shores of the Pacific Ocean. Together, Sirenia (seacows), Proboscidea (elephants), and Desmostylia are referred to as tethytheres.
Ongoing research in the Thewissen Lab focuses on the origin and early divergence of the tethytheres. Fossils of anthracobunids are known from Pakistan and India. Fewer than 50 fossils of members of this family have ever been found, and they played a key role in the early evolution of the tethytheres. It is likely that anthracobunids were ancestral to later sirenians, proboscideans, and/or desmostylians.
Field areas in India and Pakistan have also produced specimens of sirenians of different ages. Eocene sirenians from India show many primitive features not present in the modern forms. Oligocene specimens are closely related to modern dugongs.
All pictures on Dr. Thewissen's pages are public access, although the source must be identified in publication.