Pakicetidae

Pakicetidae is an extinct family of early whales, among the earliest known cetaceans in the fossil record. They lived in the early Eocene, around 50 million years ago, and fossils are primarily from what is now Pakistan, indicating a South Asian origin for the group. Pakicetidae are considered stem cetaceans within the broader whaling lineage, representing a transitional stage between terrestrial artiodactyls and later fully aquatic whales.

Anatomy and appearance of pakicetids show a combination of terrestrial and aquatic traits. They possessed elongated skulls and long jaws with sharp teeth, suggesting a diet of fish. Their limbs were robust and adapted for walking on land, indicating a semi-aquatic lifestyle. The auditory region of the skull reveals primitive cetacean features, and while there are signs of enhanced underwater hearing relative to their land-dwelling relatives, pakicetids lack the highly specialized ear structures seen in later whales.

Ecology and behavior are inferred from their morphology and the environments where fossils are found. Pakicetids likely inhabited nearshore or riverine systems and pursued aquatic prey in shallow waters, while still being capable of terrestrial locomotion. This dual lifestyle places them at a key juncture in the whale transition from land to sea.

Taxonomy and significance: Pakicetidae includes the type genus Pakicetus and related forms from early Eocene deposits. They are important as some of the earliest cetaceans, illustrating the initial steps in the evolutionary shift from land-dwelling mammals to aquatic whales, preceding groups such as Ambulocetidae and Protocetidae.