then, did Aetiocetus feed by bulk-feeding or by bite-and-swallow? If they fed only by selective prey capture, were they simply pre-adapted for the specialized feeding behavior of extant mysticetes? Structurally, Aetiocetus possesses teeth that are quite similar to primitive odontocetes, such as Squalodon. These odontocetes have an inferred bite and tear style of eating with limited mastication. Both primitive and extant odontocetes find their prey through the use of echolocation; however, mysticetes have no evidence in their fossil record of ever evolving or initially possessing the ability to echolocate. Piscivory, or a diet based solely on fish, is likely the primitive condition for Cetacea, and it seems most parsimonious that Aetiocetus fed like an archaeocete, locating fish without the use of echolocation. However, an argument exists that Aetiocetus was in fact a bulk feeder, who fed by gulping and straining prey from the water through their interlocking cusped cheek teeth. This is supported by the presence of a lack of mandibular symphysis, meaning the jaw was loosely articulated, and by the presence of the wide palate. This feeding method has an analog in crab-eater seals. This hypothesis combines the idea of bulk feeding and retention of the dentition. Aetiocetus might have been a functional mysticete. Lending credence to this interpretation is the presence of mandibular kinesis in Aetiocetus, though they lack the rostral kinesis seen in more derived mysticetes. This cranial kinesis, or ability of the skull bones to move relative to one another, permit the mysticete skull to decrease the strain exerted on the skull during bulk feeding. Fitzgerald argued against the model of tooth-aided filter feeding, based on the lack of closely pressed teeth and the presence of simple postcanine crowns. Deméré argues that this assumes a very small prey size (i.e., krill). The distinction here is that Aetiocetus was a bulk feeder, and prey size does not enter into this definition of feeding strategy. There is no reason to assume a priori that all bulk filter-feeders eat small prey, given the large diversity of food items consumed by modern mysticetes. Demere hypothesizes that Aetiocetus’ bulk feeding behavior could have targeted large prey, such as schooling fish or squid. With prey items of this size, Aetiocetus’ teeth would still have served well as a coarse sieve. Geography and endemism At first glance, the fact that species are known from only one locality, and that may suggest that Aetiocetus