page_title: Evolution of cetaceans
section_title: Fossil record
hierarchical_section_title: Evolution of cetaceans / Fossil record
caption_attribution_description: Indohyus major, a herbivorous whale ancestor from the Middle Eocene of Kashmir, pencil drawing, digital coloring
context_page_description: The Cetaceans are mammalian marine descendants of land mammals. Their terrestrial origins are indicated by:
  Their need to breathe air from the surface;
  The bones of their fins, which resemble the limbs of land mammals
  The vertical movement of their spines, characteristic more of a running mammal than of the horizontal movement of fish.
  The question of how land animals evolved into ocean-going leviathans was a mystery until recent discoveries in Pakistan revealed several stages in the transition of cetaceans from land to sea.
context_section_description: Hippo fossils are not found until the Miocene, but whale ancestors have been found from the Eocene. This leaves a gap of nearly 30 million years where no hippo ancestors are found.  The most recent hypothesis is that hippos and whales shared a common semi-aquatic ancestor which branched off from other Artiodactyls around 60 million years ago (mya).  This ancestral group probably split into two branches around 54 mya. One branch evolved into cetaceans, possibly beginning with the proto-whale Pakicetus from 52 mya.  These early cetaceans gradually became adapted to life in the sea. They became the completely aquatic cetaceans.
caption: Reconstruction of Indohyus
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