Aetiocetidae, Emlong, 1966

Marx, Felix G., Hocking, David P., Park, Travis, Ziegler, Tim, Evans, Alistair R. & Fitzgerald, Erich M. G., 2016, Suction feeding preceded filtering in baleen whale evolution, Memoirs of Museum Victoria 75, pp. 71-82 : 72

Comparisons with Aetiocetidae and other marine mammals

The pattern and intensity of tooth wear in NMV P252567 is unique among Aetiocetidae . Besides the present material, tooth wear has been described in some detail for three aetiocetids, namely, Aetiocetus cotylalveus , A. weltoni and Fucaia buelli ( Deméré and Berta, 2008; Emlong, 1966; Marx et al., 2015). In addition, teeth are preserved but have not been properly figured in A. polydentatus and Morawanocetus yabukii ( Barnes et al., 1995) . The enamel covering the crowns in all of these species lacks the heavy abrasion characteristic of NMV P252567. Several of the premolars and molars in the holotypes of A. cotylalveus (USNM 25210) and A. weltoni (UCMP 122900) instead show attritional wear, which has removed much or all of the accessory denticles ( Deméré and Berta, 2008; Emlong, 1966). In addition, relatively minor apical abrasion is evident along at least the anterior portion of the tooth row in A. weltoni , and on both the premolars and molars of A. cotylalveus .

Tooth wear in A. polydentatus has not been described in detail, but (presumably attritional) wear facets seemingly occur at least on the posteriormost mandibular teeth ( Deméré and Berta, 2008). Both attrition and apical abrasion also occur in Fucaia buelli , with extensive attritional wear facets occurring on the lingual surfaces of the upper premolars and molars of the type specimen (UWBM 84024; Marx et al., 2015). Too little is known about Morawanocetus to be sure about wear patterns in this species. Nevertheless, based on photographs, at least one of the posterior molars preserved with the holotype (AMP 01) displays strong apical and, possibly, attritional wear.

In general, the dental wear of NMV P252567 most closely resembles that of the bizarre-looking archaic mysticete Mammalodon colliveri and the extant walrus, Odobenus rosmarus , both of which show lingual abrasion and (microscopic) striations, and are considered to be benthic suction feeders ( Fitzgerald, 2010; Gordon, 1984). Unlike NMV P252567, however, M. colliveri has small, peg-like incisors displaying heavy abrasion, and its dentition is generally even more heavily worn ( Fitzgerald, 2010). Other marine mammals known to show heavy dental wear include the killer whale Orcinus orca , the beluga Delphinapterus leucas , the porpoises Phocoena phocoena and Semirostrum ceruttii , and the archaic beaked whale Ninoziphius platyrostris . However, in orcas such wear generally consists of severe apical abrasion, possibly as a result of preying on sharks ( Ford et al., 2011), while in belugas direct tooth-on-tooth occlusion results in a predominance of attrition ( Fitzgerald, 2010; Struthers, 1895). By contrast, heavy wear in phocoenids and N. platyrostris may primarily reflect benthic foraging and the frequent ingestion of abrasive sediment ( Lambert et al., 2013; Racicot et al., 2014), although more recent studies suggest that stem ziphiids may have foraged on epipelagic prey ( Lambert et al., 2015).