EOMYSTICETIDAE, Sanders & Barnes, 2002

Boessenecker, Robert W. & Fordyce, R. Ewan, 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 (Zool. J. Linn. Soc.) 175 (3), pp. 607-660 : 654

DENTITION IN EOMYSTICETIDAE

Eomysticetus was initially proposed as the earliest diverging toothless mysticete ( Sanders & Barnes, 2002b), but Meredith et al. (2010) speculated that it (and other stem edentulous mysticetes, and even archaic crown mysticetes) may have retained vestigial teeth. Indeed, the lateral edge of the maxilla and dorsal edge of the mandible of Eomysticetus whitmorei are missing and damaged, respectively. The Yamatocetus canaliculatus holotype is more complete and preserves a series of oval to flattened alveoli within an alveolar groove, but no teeth were recovered during preparation; regardless, Okazaki (2012) inferred these alveoli to have housed teeth at some point during ontogeny. The discovery of a possible tooth consisting of a root (but missing the crown) with OU 22081 ( Tokarahia sp. , cf. T. lophocephalus ) lends substantial support to the hypothesis that eomysticetids retained adult teeth. The tooth bears a linguolabially flattened root, which matches the flattened oval-shaped alveoli of Yamatocetus canaliculatus and other New Zealand eomysticetids (OU 22044); the alveolar morphology of Tokarahia cannot be confirmed because specimens either have a fragmented lateral maxilla (OU 22081) or are incompletely prepared (OU 22235; T. kauaeroa gen. et sp. nov.). Because Tokarahia is a stem mysticete, the retention of teeth does not preclude a single loss of enamelled teeth within mysticetes; at present no extinct crown mysticetes have been recovered with alveoli or associated teeth. The tiny size and peg-like shape of the tooth, restriction of alveoli to the anterior oral cavity in other eomysticetids (OU 22044, Yamatocetus ), and host of bulk filter-feeding adaptations in Tokarahia and other eomysticetids (baleen, unfused mandibular symphysis, lengthened palate, incipient rostral kinesis; see below) suggests that the dentition was nonfunctional. Because Mitchell (1989) defined the Chaeomysticeti as a clade uniting all mysticetes with baleen and lacking a functional dentition, eomysticetids are provisionally retained as the earliest diverging members therein. Peg-like, presumably nonfunctional teeth in Tokarahia and shallow alveoli in other Eomysticetidae thus reflect an additional intermediate stage in the evolution of the mysticete feeding apparatus, spanning the gap between aetiocetids with functional adult dentition and probable baleen and toothless modern baleen whales ( Deméré & Berta, 2008; Deméré et al., 2008).