| Orcinus paleorca | |
|---|---|
 | |
| O. paleorcaholotype, front view (left) and side view (right). Dotted lines indicate inferred dimensions. | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Suborder: | Whippomorpha |
| Infraorder: | Cetacea |
| Family: | Delphinidae |
| Genus: | Orcinus |
| Species: | †O. paleorca |
| Binomial name | |
| †Orcinus paleorca Matsumoto, 1937 | |
Orcinus paleorca is a fossil species ofOrcinus, the genus ofkiller whales (orca), dated to theMiddle Pleistocene.
Theholotype specimen, a tooth fragment, was found by G. Natsume in theSanuki Formation in theKazusa Province ofHonshu, Japan–an area dating back to theMiddle Pleistocene–anddescribed in 1937 by Japanese paleontologistHikoshichiro Matsumoto.Orcinus paleorca could represent the ancestor of the modernkiller whale (Orcinus orca). Matsumoto noted that the teeth ofO. paleorca are much larger and have more similar dimensions to the modern killer whale than those of the PlioceneO. citoniensis.[2]
The tooth is conical and belonged to the upper right or lower left jaw of an adult individual. The tooth fragment is 5 cm (2.0 in) in height–though the actual height may have been double that–2.25 cm (0.89 in) longitudinally–from the side facing the tongue to the side facing the lip–and 2.95 cm (1.16 in) transversely–from the left side of the tooth to the right.[2] In comparison, the modern killer whale has teeth around 8 cm (3.1 in) in height and 2.5 cm (0.98 in) in diameter.[3] Like the modern killer whale, the tooth lacks a coat ofcementum. However, unlike the modern killer whale,O. paleorca had a circular tooth root as opposed to an oval, and thepulp extended more towards the back than the front.[2]
Orcinus species, like many other predatory marine lineages, may have fished up the food chain, with the apparently more primitiveO. citoniensis able to hunt large fish, and the modern killer whale's ability to hunt large whales.[4]
The Middle Pleistocene deposits indicate a warmtemperate climate, and temperate forests of land. The marine mammal diversity comprisesO. paleorca, an undetermined species ofOrcinus, the baleen whaleMizuhoptera, an unidentifiedoceanic dolphin, the fossil false killer whalePseudorca yokoyamai, the fossil walrusOdobenus mandanoensis, an undetermined species ofEumetopias sea lion, and the recently extinctSteller's sea cow (Hydrodamalis gigas).[5][6] Sharks present were thegreat white shark (Carcharodon carcharias) and the extinctbroad-toothed mako (Cosmopolitodus hastalis).[2][7][8]