Friday, September 11, 2015

[PaleoMammalogy • 2015] Tokarahia kauaeroa • A New Genus and Species of Eomysticetid (Cetacea: Mysticeti) and A Reinterpretation of ‘MauicetuslophocephalusMarples, 1956: Transitional Baleen Whales from the upper Oligocene of New Zealand

Tokarahia kauaeroa  Boessenecker & Fordyce, 2015
Life restoration of Tokarahia kauaeroa gen. et sp. nov.
Artwork by Christopher Gaskin || DOI: 10.1111/zoj.12297

The early evolution of toothless baleen whales (Chaeomysticeti) remains elusive, despite a robust record of Eocene–Oligocene archaeocetes and toothed mysticetes. Eomysticetids, a group of archaic longirostrine and putatively toothless baleen whales, fill in a crucial morphological gap between well-known toothed mysticetes and more crownward Neogene Mysticeti. A historically important but perplexing cetacean is ‘Mauicetuslophocephalus (upper Oligocene South Island, New Zealand). The discovery of new skulls and skeletons of eomysticetids from the Oligocene Kokoamu Greensand and Otekaike Limestone permit a redescription and modern reinterpretation of ‘Mauicetuslophocephalus, and indicating that this species may have retained adult teeth. Tokarahia kauaeroa gen. et sp. nov. is erected on the basis of a well-preserved subadult to adult skull with mandibles, tympanoperiotics, and cervical and thoracic vertebrae, ribs, sternum, and forelimbs from the Otekaike Limestone (> 25.2 Mya). ‘Mauicetuslophocephalus is relatively similar and recombined as Tokarahia lophocephalus. Phylogenetic analysis supports the inclusion of Tokarahia within the Eomysticetidae, alongside Eomysticetus, Micromysticetus, Yamatocetus, and Tohoraata, and strongly supports the monophyly of Eomysticetidae. Tokarahia lacked extreme rostral kinesis of extant Mysticeti, and primitively retained a delicate archaeocete-like posterior mandible and synovial temporomandibular joint, suggesting that Tokarahia was capable of, at most, limited lunge feeding in contrast to extant Balaenopteridae, and used an alternative as-yet unspecified feeding strategy.

Keywords: Baleen whales; Oligocene; cetacea; Mysticeti; Eomysticetidae

Figure 2. Excavation of the Tokarahia kauaeroa gen. et sp. nov. holotype skull and skeleton:
  A, exposure of the skull and mandibles in a ventral-up position; B, removal of the large jacket containing the skull.

Figure 4. Holotype (OU 22235) skull, mandibles, vertebrae, and sternum of Tokarahia kauaeroa gen. et sp. nov.
A, orthogonal image derived from photogrammetry. B, interpretive line drawing.

Figure 34. Life restoration of Tokarahia kauaeroa gen. et sp. nov.
Artwork by Christopher Gaskin, ©Geology Museum, University of Otago.

Systematic Palaeontology
CETACEA Brisson, 1872
MYSTICETI Gray, 1864

Family EOMYSTICETIDAE Sanders & Barnes, 2002b

Type species: Eomysticetus whitmorei.

Included genera: Eomysticetus, Micromysticetus, Tohoraata, Tokarahia, and Yamatocetus.

TOKARAHIA new genus

Etymology: Named after the Tokarahi township, located near Island Cliff, North Otago, the type locality of T. kauaeroa gen. et sp. nov., meaning large (or panoramic) rock, referring to a mesa-like geographic feature. From the Māori ‘toka’ (rock) plus ‘rahi’ (large). Pronunciation: To-kah-rah-hi-ah, with o as in English ‘toe’, a as in ‘far’, and i as in ‘we’.

Type species: Tokarahia kauaeroa gen. et sp. nov.
Included species: Tokarahia kauaeroa gen. et sp. nov. and Tokarahia lophocephalus Marples, 1956.

TOKARAHIA KAUAEROA gen. et sp. nov.
Etymology: Kauaeroa, meaning long jaw (referring to the elongate, delicate mandibles and rostrum of the holotype), from the Māori ‘kauae’ (jaw) and ‘roa’ (long). Pronunciation: Kau-ae-roa, with au as in English ‘hoe’, ae as in ‘I’, o as in ‘toe’, and a as in ‘far’.

Figure 3. Silhouetted skeletal reconstructions of the three primary specimens of Tokarahia described in this study, with a human figure shown for scale. Skeletal reconstruction based in part on Eomysticetus whitmorei and Yamatocetus canaliculatus.

Figure 33. Comparison of skeletal reconstructions, crania, and tympanic bullae of the protocetid Georgiacetus vogtlensis, the basilosaurid Dorudon atrox, the aetiocetid Aetiocetus weltoni, Tokarahia kauaeroa, and extant Balaenoptera edeni.
Sources for illustrations include Emlong (1966), Barnes et al. (1995), Hulbert et al. (1998), Uhen (2004), Deméré & Berta (2008), and photographs courtesy F.G. Marx and C.H. Tsai.

New fossil material, including a well-preserved skull, tympanoperiotics, mandibles, and postcrania, is described as a new genus and species T. kauaeroa gen. et sp. nov. within the archaic chaeomysticete family Eomysticetidae. The problematic taxon ‘Mauicetuslophocephalus is transferred to this new genus and recombined as T. lophocephalus, resolving decades of uncertainty regarding the taxonomic affinities and phylogenetic significance of this historically puzzling taxon. Referred material suggests that both species existed at the same time from at least 27.3–25.2 Mya, and were perhaps sympatric. Phylogenetic analysis using a large and exhaustive data set of extant and extinct Mysticeti places both species of Tokarahia within Eomysticetidae, and robustly confirms the monophyly of Eomysticetidae. Micromysticetus is also confirmed as an eomysticetid and removed from the Cetotheriopsidae, which is not possible to diagnose and at present is restricted to the holotype of Cetotheriopsis lintianus. Incipient rostral fusion and a delicate and synovial tempromandibular joint seem to preclude lunge feeding in Tokarahia and other eomysticetids, but the uniquely elongate rostrum and comparatively enormous temporal fossae and crests for temporalis attachment suggest an uncertain but highly specialized adaptation for an as-yet unidentified feeding strategy.

Robert W. Boessenecker and R. Ewan Fordyce. 2015. A New Genus and Species of Eomysticetid (Cetacea: Mysticeti) and A Reinterpretation of ‘Mauicetuslophocephalus Marples, 1956: Transitional Baleen Whales from the upper Oligocene of New Zealand. Zoological Journal of the Linnean Society. DOI: 10.1111/zoj.12297