Aetiocetus, EMLONG, 1966

Deméré, Thomas A. & Berta, Annalisa, 2008, Skull anatomy of the Oligocene toothed mysticete Aetioceus weltoni (Mammalia; Cetacea): implications for mysticete evolution and functional anatomy, Zoological Journal of the Linnean Society 154 (2), pp. 308-352 : 312

GENUS AETIOCETUS EMLONG, 1966

Type species: Aetiocetus cotylalveus Emlong, 1966

Distribution: Late Oligocene of Oregon and Japan

Included species: Aetiocetus cotylalveus Emlong, 1966 , A. polydentatus Sawamura in Barnes et al., 1995, A. tomitai Kimura & Barnes in Barnes et al., 1995, A. weltoni Barnes & Kimura in Barnes et al., 1995.

Definition: The monophyletic group containing the most recent common ancestor of Aetiocetus cotylalveus and A. polydentatus and all of its descendants.

Emended diagnosis: Small toothed mysticetes with three or fewer small and simple anterior and posterior denticles on posterior upper teeth, anterior and postcanine teeth weakly heterodont (synapomorphies of species of Aetiocetus ); triangular anterior extension of parietal–frontal suture, fine vertical enamel ridges only on lingual surface of postcanine teeth, wide diastemata between postcanine teeth, and rostral width at antorbital notch relative to occipital condyle width> 170% (possible synapomorphies of species of Aetiocetus ); lacrimal with large and lobate dorsal exposure, palate window exposing vomer present and formed by maxilla and premaxilla, and distinct internal narial notch formed by palatine, pterygoid and vomer (synapomorphies of Aetiocetus + Chonecetus ); zygomatic process of squamosal expanded near its anterior margin and at its posterior end but narrow in its middle, short overlap of jugal by squamosal, and coronoid process of dentary well developed with concave posterior margin (aetiocetid synapomorphies); mandibular symphysis not sutured, descending process of maxilla developed as an edentulous infraorbital plate, anterior and postcanine teeth moderately to weakly heterodont or absent (apomorphies shared with toothed and edentulous mysticetes); supraorbital processes of frontal elevated and at same level as cranial vertex, distinct intertemporal region, anteriorly placed external narial opening, and retention of adult dentition (plesiomorphies shared with dorudontine archaeocetes).