[PaleoMammalogy • 2015]
Tokarahia kauaeroa • A New Genus and Species of Eomysticetid (Cetacea: Mysticeti) and A Reinterpretation of ‘Mauicetus’ lophocephalus Marples, 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 ‘Mauicetus’ lophocephalus
(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 ‘Mauicetus’ lophocephalus, 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). ‘Mauicetus’ lophocephalus 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.
DOI: 10.1111/zoj.12297
|
 |
| 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.
DOI: 10.1111/zoj.12297
|
 |
| 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
CHAEOMYSTICETI Mitchell, 1989
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.
DOI: 10.1111/zoj.12297
|
 |
| 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.
DOI: 10.1111/zoj.12297
|
Conclusion
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 ‘Mauicetus’ lophocephalus 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 ‘Mauicetus’ lophocephalus Marples, 1956: Transitional Baleen Whales from the upper Oligocene of New Zealand. Zoological Journal of the Linnean Society. DOI: 10.1111/zoj.12297
Nenhum comentário:
Postar um comentário
Observação: somente um membro deste blog pode postar um comentário.