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Orcinus Temporal range: Miocene–Holocene
The killer whale (O. orca) is the only extant member of the genus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Infraorder:	Cetacea
Family:	Delphinidae
Subfamily:	Orcininae
Genus:	Orcinus Fitzinger, 1860
Type species
Delphinus orca Linnaeus, 1758
Species
†Orcinus paleorca †Orcinus citoniensis †Orcinus meyeri Orcinus orca
Synonyms
Gladiator Gray, 1870 Ophesia Gray, 1868 Ophysia Gray, 1868 Orca Gray, 1846 Phocaena Gray, 1846 Grampus Iredale & Troughton (not Gray), 1933

Orcinus is a genus of Delphinidae, the family of carnivorous marine mammals known as dolphins. It includes the largest delphinid species, Orcinus orca, known as the orca or killer whale. Three extinct species are proposed, Orcinus paleorca, O. citoniensis and O. meyeri, describing fossilised remains of the genus.

Taxonomy

The genus Orcinus was published by Leopold Fitzinger in 1860, its type species is the killer whale (orca) named by Linnaeus in 1758 as Delphinus orca. Taxonomic arrangements of delphinids published by workers before and after Fitzinger, such as John Edward Gray as Orca in 1846 and Orca (Gladiator) in 1870, are recognised as synonyms of Orcinus. The descriptions of species as Orcinus glacialis Berzin and Vladimirov, 1983 and Orcinus nanus Mikhalev and Ivashin, 1981 are considered synonyms of Orcinus orca, the existing species of killer whales.

The published names for the genus and their relationship to other delphinids combined epithets such as Orca, Grampus, Gladiator and Orcinus throughout the nineteenth century. This uncertain synonomy was complicated by the repetition of mistakes, a lack of specimens, and contradictory descriptions, especially by J. E. Gray. The beaching of whales in Eastern Australia (a female and male Grampus griseus) prompted a taxonomic revision in 1933, the authors Tom Iredale and Ellis Troughton proposed that the extensive use of "Grampus" be conserved as the generic name of killer whales (Orcinus orca) and that a new genus named Grampidelphis be established for Rissos dolphin (Grampus); the general stability of current species names emerged after the publication of the Philip Hershkovitz's Catalog of Living Whales (US National Museum, 1966).

The type of the genus is Delphinus orca, as described by Linnaeus in the 10th edition of Systema Naturae. The type locality was named as "Oceano Europaeo".

Description

A genus of carnivorous marine mammals, cetaceans of the delphinid family, with teeth in the upper and lower jaws. The possess a large brain which is informed by sophisticated auditory and echolocation techniques. The existing population, known as orca or killer whale, are a well known apex predator readily distinguished by their great size, 7 to 10 metres long, and mostly black and white coloring. These are highly intelligent and gregarious animals, able to communicate, educate, and cooperate in hunting the largest marine animals. The ecotypes within this species complex may coexist in a region, with sometimes resident and transient pods, but these are known to be genetically isolated. Distinctions within the living Orcinus population are often observed in unique social behaviours, their cultures, which provided a significant evolutionary advantage in moving from cephlapods and fish to mammalian species.

The fossil remains of Orcinus species are frequently teeth, deposited during the Pliocene, especially in Italy. Orcinus citoniensis is known by a well preserved skull and jaw. This specimen was an animal smaller than the killer whale, around 4 metres in length, and possessed a greater number of proportionally smaller teeth.

The diet of modern orca is wide ranging, although some ecotypes may be specialist fishers in a local range. Most delphinids feed on cephlapods, squid and octopuses, and earlier Orcinus species are thought to have also exploited this resource. The great size of orcas may have been the result of feeding 'up the foodchain', but the ability to prey on other mammals and the largest whales is proposed instead to be the result of exaptation. The social structure of orcas involves strategems that allow a pod to overcome animals greater in size than the individuals, whereas other great marine predators, such as Carcharodon megalodon, likely exceeded the size of their targets.

Distribution

A world wide distribution in a wide range of habitats, deep oceans, continental shelves, arctic seas and coastal regions of every continent, including Antarctica. The modern orca is considered, after humans and their domestic animals, to be the most widely distributed mammal on the planet. They are not a common animal, but population density increases in favourable habitats of temperate and colder waters with residents and transients.

Fossil evidence of Orcinus species occur in a temporal range up to 3.6 million years ago, which includes subfossil material at more recently dated deposits. The extinct species Orcinus meyeri refers to fossils of a partial jaw and teeth located at the early Miocene horizon of a site near Stockach in Germany.

Classification

The classification of Orcinus within subfamilies of delphinids may be summarised as:

• Delphinidae
  • Delphininae
  • Lissodelphininae
  • Globicephalinae
  • Orcininae
    • Orcinus
      • Orcinus citoniensis Capellini, 1883.
      • Orcinus meyeri J. F. Brandt, 1873.
      • Orcinus orca = Delphinus orca L. 1758, the existing population, a complex predicted to include cryptic species and subspecies
      • Orcinus paleorca
  • Subfamily incertae sedis (Lagenorhynchus albirostris, Leucopleurus acutus)

The extant population is considered as a single species, although previously recognised diversity of killer whale populations suggests a number of cryptic species and species may be recognised.

Other members of Orcininae were moved to Globicephalinae, and the relation of Orcinus with other dolphins is unknown.

References

1. "Orcinus Fitzinger, 1860". Integrated Taxonomic Information System. Retrieved 29 August 2017.
2. ^ "Orcinus". Paleobiology Database. Retrieved 29 August 2017.
3. L. J. Fitzinger. 1860. Wissenschaftlich-populäre Naturgeschichte der Säugethiere in ihren sämmtlichen Hauptformen. Nebst einer Einleitung in die Naturgeschichte überhaupt und in die Lehre von den Thieren insbesondere. VI. Band
4. Iredale, Tom; Troughton, Ellis Le G. (1933). "The correct generic names for the Grampus or Killer Whale, and the so called Grampus or Risso's Dolphin". Records of the Australian Museum. 19 (1): 28–36.
5. ^ Hershkovitz, P. 1966. Catalog of living whales. Bulletin of the United States National Museum 246: viii 1–259 [81]. doi:10.5479/si.03629236.246.
6. https://biodiversity.org.au/afd/taxa/Orcinus
7. Barrett-Lennard, L. G; Heise, K. A. (2006). "The Natural History and Ecology of Killer Whales". In Estes, J. A. (ed.). Whales, Whaling and Ocean Ecosystems. Berkeley, CA: University of California Press. pp. 163–173.
8. Croll, D. A.; Kudela, R.; Tershy, B. R. (2006). "Evolutionary patterns in Cetacea". In Estes, J. A. (ed.). Whales, Whaling and Ocean Ecosystems. Berkeley, CA: University of California Press. pp. 76–77.
9. von Brandt, J. F. (1873). "Untersuchungen über die Fossilen und Subfossilen Cetaceen Europa's" [Research on the Fossil and Subfossil Cetaceans of Europe]. Commissionnaires de l'Académie Impériale des Sciences (in German): 227–228.
10. H. Matsumoto. 1937. A new species of orc from the basal Calabrian at Naganuma, Minato Town, Province of Kazusa, Japan. Zoological Magazine 49(8):191-193 citing fossilworks
11. ^ Cunha, H. A.; Moraes, L. C.; Medeiros, B. V.; Lailson-Brito, Jr, J.; da Silva, V. M. F.; Solé-Cava, A. M.; Schrago, C. G. (2011). "Phylogenetic Status and Timescale for the Diversification of Steno and Sotalia Dolphins". PLOS ONE. 6 (12): e28297. doi:10.1371/journal.pone.0028297. PMC 3233566. PMID 22163290.

• Cetaceans
• Cetacean genera
• Oceanic dolphins
• Taxa named by Leopold Fitzinger
• Mammal genera with one living species