原鲸（学名：Protocetus atavus ）是一种已经灭绝的古代鲸鱼，属于原鲸科。巴基鲸生活在始新世中期，约4500万年前。原鲸身长为2.5公尺。

原鲸是一种相当原始的鲸鱼，仍然拥有后鳍，前鳍则长有脚趾。牠们的长下颚中长有锐利的牙齿。与更原始的巴基鲸不同的是，原鲸可以完全听见水中的声音。

Protocetus atavus ("first whale") is an extinct species of primitive cetacean from Egypt. It lived during the middle Eocene period 45 million years ago.

The first discovered protocetid, Protocetus atavus was described by Fraas 1904 based on a cranium and a number of associated vertebrae and ribs found in middle Lutetian Tethyan marine limestone from Gebel Mokattam near Cairo, Egypt.