My Favorite Fossil: Maiacetus inuus
Paleontologist Ryan Bebej shares about his favorite fossil—a four-legged aquatic mammal called Maiacetus that lived about 47.5 million years ago.
My favorite fossil is an early, four-legged cetacean known as Maiacetus inuus. This fascinating creature lived on the shores of modern-day Pakistan about 47.5 million years ago and provides valuable information about cetaceans as they became increasingly adapted for life in water.
I became interested in evolution and paleontology as an undergraduate student, especially after I read an article for a class about Philip Gingerich’s work on “walking whales.” I applied to the Ph.D. program in the Department of Ecology and Evolutionary Biology at the University of Michigan so that I could study under Gingerich and research the earliest ancestors of modern whales, dolphins, and porpoises.
It was during my on-campus interview in early 2005 that Gingerich told me about a new type of early whale they had recently discovered (but not yet named or described). I distinctly remember him opening a cabinet in his office and showing me a partial skeleton discovered in Pakistan during fieldwork in 2000. He described the process of uncovering the skeleton in the field and trying to make sense of the odd features he was seeing, only to discover that the specimen was of an adult cetacean with bones from a fetus preserved in the abdominal region.
I was absolutely astounded! He told me that they had also recently recovered a nearly complete skeleton from another individual of the same species during fieldwork in Pakistan in 2004, but that that material was not yet available for study.
Fast-forward six months, and I was a Ph.D. student at Michigan in Gingerich’s lab. I was there in the fossil preparation lab when some of the plaster jackets containing Maiacetus were opened for the first time, revealing the skeleton of one of the most complete fossil cetaceans ever discovered. This specimen included a mostly intact skull, a complete vertebral column (all the way down to the tip of the tail), and complete fore- and hind limbs. I spent quite a bit of time over the next several years studying this specimen. After years of work, this new cetacean was finally named and formally described in February 2009: Maiacetus inuus (maia meaning mother, cetus meaning whale, and inuus for the Roman god of fecundity).
These two specimens are of vital importance to our understanding of cetacean evolution. The preservation of a fetus positioned for headfirst delivery suggests that Maiacetus was still coming back onto land to give birth, even though it was spending most of its time in the water. The virtually complete skeleton known for this species provides a rare opportunity to reconstruct the body and lifestyle of an extinct creature without having to hypothesize about missing elements.
Personally, Maiacetus is still valuable to me in my work. I have continued to utilize elements from this species to help me understand the anatomies of other early cetaceans. It also provides an incredible illustration of the careful and laborious work involved in studying fossils and the immense joy of discovering and studying the array of unique creatures that once roamed our planet.
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