Zygorhiza ("Yoke-Root") is an extinct genus of basilosaurid early whale known from the Late Eocene (Priabonian, 38–34 Ma) of Louisiana, Alabama, and Mississippi, United States, and the Bartonian (43–37 Ma on the New Zealand geologic time scale) to the late Eocene of New Zealand (43 to 33.9 million years ago).

[3] Reichenbach (1847) erected Basilosaurus kochii for the posterior skull fragment MB Ma.43248, found in the Late Eocene (middle-late Priabonian) Ocala Limestone of Clarksville, Louisiana.

In the late 19th century there was a debate whether large and small specimens attributed to Zeuglodon brachyspondylus (declared a nomen dubium by Uhen 2005) were separate species or not.

[6] Seeley 1876 named and described the species Zeuglodon wanklyni based on a skull collected by Dr. Arthur Wanklyn from the Barton Clays in southern England.

[8] Köhler & Fordyce 1997 described an incomplete skull, four vertebrae, two teeth, and small fragments in early Bartonian sediments in New Zealand which they tentatively identified as Zygorhiza sp.

[11] Like other dorundontines, Zygorhiza had a body similar to modern cetaceans with flipper-like forelimbs, rudimentary hind limbs, a vertebral column adapted for oscillatory swimming, and a tail fluke.

Using CT scans, they estimated the brain weight to 738.2 g (26.04 oz), resulting in an EQ value of 0.26 (compared to 0.54 for a modern cetacean such as Cuvier's beaked whale.

P2–M2 have two widely separated roots, accessory denticles on the anterior and posterior cutting edges, and anastomosing striae on the enamel.

This is very unusual in modern mammals and contrasts to extant toothed whales that only develop a single set of teeth.