Pakicetus inachus, a whale ancestor from the Early Eocene

27 August 2025

This dog-like mammal who lived 50 million years ago in the Early Eocene is actually the ancestor of whales. Though Pakicetus inachus was the size of a large dog, his genus name means “whale found in Pakistan.”

Pakicetus size compared to human (diagram from Wikimedia Commons)

Instead of eating meat, Pakicetus hung out in water and ate fish. His closest living relative is the hippopotamus.

Hippopotamus (photo from Wikimedia Commons)

In 50 million years Pakicetus‘ descendants became more water-oriented and then spent their whole lives in water. Consequently their bodies evolved fish-like features and they became recognizable whales.

Diagram of Pakicetus descendants as they changed into recognizable whales (from Wikimedia Commons)

Find out how paleontologists could tell this “dog” is related to whales in this vintage article:

p.s. Sometimes Pakicetus inachus is drawn with shaggy fur and spots.

Pakicetus inachus, a whale ancestor from the Early Eocene of Pakistan, after Nummelai et al., (2006), pencil drawing, digital coloring