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 : 649

MONOPHYLY OF EOMYSTICETIDAE

An important concern of this analysis was to evaluate whether or not the Eomysticetidae actually constitute a monophyletic group. Previous analyses have only included two eomysticetids (although see Marx and Fordyce, 2015): Eomysticetus and Micromysticetus ( Geisler & Sanders, 2003) , and Eomysticetus and T. lophocephalus ( Steeman, 2007; Marx, 2011). The monophyly of a clade containing Eomysticetus and Micromysticetus (Eomysticetoidea; Geisler & Sanders, 2003) or Eomysticetus and T. lophocephalus ( Steeman, 2007; Marx, 2011) was well supported, despite the absence of the holotype skull of T. lophocephalus and the partial nature of the holotype skull of Micromysticetus rothauseni . The inclusion of six nominal eomysticetids in this analysis permits an evaluation of eomysticetid monophyly. This study found moderate to strong support for the monophyly of Eomysticetidae (bootstrap support = 56% under equal weighting, 77% under implied weighting; Fig. 31 ). Eight synapomorphies common to both weighted analyses supported eomysticetid monophyly, including a frontal with anteromedial projection (character 77: 1), postorbital ridge absent (character 84: 1), subvertical nuchal crest partially obscuring temporal wall of braincase (character 107: 1), absence of a supramastoid crest along the entire zygomatic process or squamosal (character 118: 2), zygomatic process of squamosal with parallel medial and lateral margins (character 125: 1), secondary squamosal fossa developed (character 127: 1), discontinuous superior process of periotic with anterior (= anterodorsal angle) and posterior (= posterodorsal angle) apices (character 161: 1), and distinct ventromedial ridge developed on bulla (character 231: 0, reversal). Other synapomorphies were unique to the results from equal or implied weighting.

Strong to moderate support was found for more inclusive clades within Eomysticetidae , including a Tokarahia + Tohoraata clade to the exclusion of Northern Hemisphere eomysticetids (bootstrap support = 81 and 62%, respectively; Fig. 31 ). Six synapomorphies common to both weighting schemes supporting a New Zealand eomysticetid clade include an incisural flange closely appressed to the anteroventral margin of the pars cochlearis of the periotic (character 168: 1), posteroexternal foramen developed as elongate fissure (character 175: 1), dorsal and posterior margins of posterodorsal angle of periotic meeting at ≤ 90° (character 178: 1), concave anterodorsal margin of anteri- or process of the periotic (character 179: 1), anterior portion of internal acoustic meatus of the periotic pinched or roofed over by projections of the meatal rim (character 205: 1), and a crista transversa deeply recessed into the internal acoustic meatus of the periotic (character 219: 1).

Strong to moderate support was also recovered for Tokarahia monophyly (bootstrap support = 79 and 94%, respectively; Fig. 31 ). Tokarahia monophyly was supported by four synapomorphies common to both weighting schemes: exoccipital with bulbous posterior margin (character 114: 1), smooth posterior bullar facet of the periotic (character 173: 0, reversal), clear separation of the stapedial muscle fossa stylomastoid fossa (character 198: 1), and presence of a sharp transverse crest on the dorsal surface of the periotic between the posterodorsal angle and the internal acoustic meatus, and separating the suprameatal and stylomastoid fossae (character 206: 1). A monophyletic group of northern hemisphere Eomysticetidae ( Eomysticetus , Micromysticetus , and Yamatocetus ) was weakly supported under implied weighting only.

Critically, this study follows Geisler & Sanders (2003) in recognizing a clade including Eomysticetus and Micromysticetus rothauseni ( Fig. 31 ). Earlier, Micromysticetus had been placed in the subfamily Cetotheriopsinae by Sanders & Barnes (2002a), which they considered a subfamily of the ‘Cetotheriidae’ s.l. (e.g. Bouetel & Muizon, 2006). The Cetotheriopsinae was subsequently erected to familial status by Geisler & Sanders (2003), who erected the new clade Eomysticetoidea to contain both the Eomysticetidae and Cetotheriopsidae . These actions overemphasized familylevel diversity and underemphasized the close similarity between Eomysticetus and Micromysticetus . Furthermore, Sanders & Barnes (2002a,b) did not differentiate between Eomysticetidae and Cetotheriopsinae , nor did they provide any synapomorphies to diagnose the Cetotheriopsinae . Geisler & Sanders (2003) listed two potential features in their diagnosis to differentiate the Cetotheriopsidae from Eomysticetidae , including an anteroposteriorly shorter intertemporal region and zygomatic processes that do not extend anteriorly beyond the apex of the occipital shield; however, the intertemporal region is relatively short in Tokarahia , and when the squamosal is placed into approximate articulation with the braincase, the occipital shield extends far anteriorly, as in Cetotheriopsis and implied for Micromysticetus rothauseni ( Geisler & Sanders, 2003: 71) ; however, in Micromysticetus rothauseni , the zygomatic processes clearly extend somewhat anterior to the occipital shield ( Sanders & Barnes, 2002a; figs 7, 10), and therefore does not differ from the condition in Eomysticetus and other eomysticetids. Here, Micromysticetus is recognized as an eomysticetid, and Cetotheriopsidae is restricted to the poorly known Cetotheriopsis lintianus , which is here identified as Chaeomysticeti incertae sedis. Although it is possible that Cetotheriopsis is also a member of this clade – which would make Eomysticetidae a junior synonym of Cetotheriopsidae – the fragmentary nature of the skull and absence of a rostrum, tympanoperiotic, and postcrania make Cetotheriopsis lintianus a poor hypodigm for a family. Furthermore, the lack of eomysticetid synapomorphies precludes the recognition of an eomysticetid–cetotheriopsid clade, and precludes the ready diagnosis of the Cetotheriopsidae . Discovery of more complete diagnostic cranial material of Cetotheriopsis lintianus would be required to declare Eomysticetidae as a junior synonym of Cetotheriopsidae .

Figures

Figure 31. Phylogenetic relationships of Tokarahia and the Eomysticetidae. Cladograms shown are strict consensus trees with branch support shown as GC frequency values. A, strict consensus of 37 equally most-parsimonious trees recovered under equal weighting; B, single most-parsimonious tree recovered under implied weighting.