Science, Tech, Math › Animals & Nature Pakicetus Facts and Figures Share Flipboard Email Print Kevin Guertin/Wikimedia Commons/CC BY 2.0 Animals & Nature Dinosaurs Prehistoric Mammals Basics Paleontologists Carnivores Dinosaurs & Birds Herbivores Marine Reptiles Amphibians Birds Habitat Profiles Mammals Reptiles Wildlife Conservation Insects Marine Life Forestry Evolution View More By Bob Strauss Science Writer B.S., Cornell University Bob Strauss is a science writer and the author of several books, including "The Big Book of What, How and Why" and "A Field Guide to the Dinosaurs of North America." our editorial process Bob Strauss Updated November 01, 2019 Name: Pakicetus (Greek for "Pakistan whale"); pronounced PACK-ih-SEE-tussHabitat: Shores of Pakistan and IndiaHistorical Epoch: Early Eocene (50 million years ago)Size and Weight: About three feet long and 50 poundsDiet: FishDistinguishing Characteristics: Small size; dog-like appearance; terrestrial lifestyle About Pakicetus If you happened to stumble across the small, dog-sized Pakicetus 50 million years ago, you'd never have guessed that its descendants would one day include giant sperm whales and gray whales. As far as paleontologists can tell, this was the earliest of all the prehistoric whales, a tiny, terrestrial, four-footed mammal that ventured only occasionally into the water to nab fish. Perhaps because even trained scientists have a hard time accepting a fully terrestrial mammal as the ancestor of all whales, for a while after its discovery in 1983, Pakicetus was described as having a semi-aquatic lifestyle. The discovery of a more complete skeleton in 2001 prompted a reconsideration, and today Pakicetus is deemed to have been fully terrestrial; in the words of one paleontologist, "no more amphibious than a tapir." It was only over the course of the Eocene epoch that the descendants of Pakicetus began to evolve toward a semi-aquatic, and then fully aquatic, lifestyle, complete with flippers and thick, insulating layers of fat. One of the odd things about Pakicetus is that its "type fossil" was discovered in Pakistan, not normally a hotbed of paleontology. In fact, thanks to the vagaries of the fossilization process, most of what we know about early whale evolution derives from animals discovered on or near the Indian subcontinent; other examples include Ambulocetus (aka the "walking whale") and Indohyus.