Ankylorhiza (meaning “fused roots”; in reference to the type of dentition seen in early toothed whales) is an extinct genus of dolphin that lived in what is now the United States during the Oligocene epoch, between 29 and 23.5 million years ago. The type and only known species is A. tiedemani, though two fossil skeletons may represent an additional, second species within the genus. Ankylorhiza was about 4.8 meters (16 ft) long, with a long, robust skull bearing conical teeth that were angled forwards at the tip of the snout.
Ankylorhiza is the largest known Oligocene toothed whale and represents one of the most completely known early members of this group, with characteristics intermediate between basal and derived cetaceans. Ankylorhiza would have had powerful jaw musculature and probably fed on large prey by seizing it and puncturing it with its robust teeth. The animal likely occupied a similar niche as a fast-swimming predator to that of living orcas.