Abstract
Abstract. Among odontocetes, members of the family Kogiidae (pygmy and dwarf sperm whales) are known as small-sized and in many respects enigmatic relatives of the great sperm whale Physeter macrocephalus. Most of the still scanty fossil record of Kogiidae is represented by isolated skulls and ear bones from Neogene deposits of the Northern Hemisphere, with the significant exception of Scaphokogia, a highly autapomorphic genus from late Miocene deposits of the Pisco Formation exposed along the southern coast of Peru. Here we report on a new fossil kogiid from Aguada de Lomas, a site where the late Miocene beds of the Pisco Formation are exposed. This specimen consists of an almost complete cranium representing a new taxon of Kogiidae: Koristocetus pescei gen. et sp. nov. Koristocetus mainly differs from extant Kogia spp. by displaying a larger temporal fossa and well-individualized dental alveoli on the upper jaws. Coupled with a relatively elongated rostrum, these characters suggest that Koristocetus retained some degree of raptorial feeding abilities, contrasting with the strong suction feeding specialization seen in Recent kogiids. Our phylogenetic analysis recognizes Koristocetus as the earliest branching member of the subfamily Kogiinae. Interestingly, Koristocetus shared the southern coast of present-day Peru with members of the genus Scaphokogia, whose unique convex rostrum and unusual neurocranial morphology seemingly indicate a peculiar foraging specialization that has still to be understood. In conclusion, Koristocetus evokes a long history of high diversity, morphological disparity, and sympatric habits in fossil kogiids, thus suggesting that our comprehension of the evolutionary history of pygmy and dwarf sperm whales is still far from being exhaustive.
Highlights
Among extant odontocetes, members of the currently monotypic family Kogiidae (Kogia breviceps and K. sima, pygmy and dwarf sperm whales) are known as small-sized and in many respects enigmatic relatives of the great sperm whale, Physeter macrocephalus
Most of the still scanty fossil record of Kogiidae is represented by isolated skulls and ear bones from Neogene deposits of the Northern Hemisphere, with the significant exception of Scaphokogia, a highly autapomorphic genus from late Miocene deposits of the Pisco Formation exposed along the southern coast of Peru
The still scanty fossil record of Kogiidae is mostly represented by isolated skulls and ear bones from Neogene deposits of the Northern Hemisphere (e.g., Barnes, 1973, 1998; Pilleri, 1987; Whitmore, 1994; Bianucci, 1996, 1997; Cigala Fulgosi, 1996; Luo and Marsh, 1996; Bianucci et al, 1998, 2011; Bianucci and Landini, 1999; Lambert, 2008; Whitmore and Kaltenbach, 2008; Velez-Juarbe et al, 2015, 2016), with the significant exception of Scaphokogia, a highly autapomorphic genus from the late Miocene marine deposits of the Pisco Formation exposed along the southern coast of Peru
Summary
Members of the currently monotypic family Kogiidae (Kogia breviceps and K. sima, pygmy and dwarf sperm whales) are known as small-sized and in many respects enigmatic relatives of the great sperm whale, Physeter macrocephalus. In spite of their wide geographic distribution, the natural history of pygmy and dwarf sperm whales remains largely speculative, and most of our knowledge about them comes from the study of stranded individuals (e.g., Nagorsen, 1985; McAlpine, 2002; Bloodworth and Odell, 2008; Taylor et al, 2012a, b, and references therein). Nov.: urn:lsid:zoobank.org:act:790FADA0-A6C5-4345-95AE7CD5CF00149D, record created by Alberto Collareta on 30 October 2017). Nov.: urn:lsid:zoobank.org:act:805D6750-10CF-4FB0-ABDB30160400A8D6, record created by Alberto Collareta on 30 October 2017) (ZooBank LSID for Koristocetus pescei sp. nov.: urn:lsid:zoobank.org:act:805D6750-10CF-4FB0-ABDB30160400A8D6, record created by Alberto Collareta on 30 October 2017)
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