Gigantic Macroraptorial Sperm Whale Tooth (cf. Livyatan) from the Miocene of Orange County, California

Abstract

A fossil tooth from the middle-upper Miocene Monterey or Capistrano Formation in the Orange County Cooper Center Paleontology Collection shows that a gargantuan sperm whale once inhabited the Miocene seas of southern California. Though difficult to diagnose to genus level based on a single, incomplete tooth, comparisons with known Miocene physeteroid whales provide key insight into the affinities of this fossil. Even though the tip is broken, the entire tooth is over 250 mm long and 86 mm in diameter. It has enamel only on the tip of the broken crown and there is no enamel coating over the rest of the tooth. Instead, the tooth consists mostly of layers of cementum over a core of ossified dentin. It is slightly smaller than the largest teeth of the largest known physeteroid, the South American Miocene Livyatan melvillei, a genus that has not been found outside of the Southern Hemisphere besides one record from northern Europe. It is also just slightly smaller than similar gigantic teeth reported from South Africa and Australia from the middle-late Miocene through the early Pliocene. We compared it to other Miocene members of the family such as Hoplocetus, Scaldicetus, and Zygophyseter, but none have teeth as large as this one. It is bigger than all known specimens of all other North American Miocene physeteroid whales, including another whale from the Monterey Formation, Albicetus oxymycterus. This fossil suggests that giant physeteroid whales closely related to Livyatan lived in the North Pacific. It represents a substantial geographic range extension for giant physeteroid whales, previously known only from the Miocene of the Southern Hemisphere and northern Europe.