Reply to comment by Kienle et al . 2017

Abstract

Kienle et al. [1] suggest amendments to our framework for feeding in predatory aquatic mammals [2]. Below we reply to their suggestions and demonstrate that they are fundamentally flawed from both a mechanical (feeding cycle, strategies) and an evolutionary perspective. They do, however, inspire an important addition to the range and structuring of capture behaviours encoded in our framework.Feeding cycle. Our framework groups feeding behaviours with similar functions, such as capture and processing, and thus clarifies how different species perform similar tasks during feeding. Kienle et al.[1] suggest that these groupings should be broken up, with capture, 'external' processing and manipulation behaviours instead being clustered into a single 'ingestion' stage. We question the biological justification for lumping behaviours as disparate as chasing, killing and dismembering. Capturing prey is unrelated to, and need not be followed by, processing. By contrast, 'external' and intraoral processing behaviours are functionally akin, with both aiming to dismember prey to start the digestive process. Lumping capture and processing furthermore deviates from the most recent conceptualization of the tetrapod feeding cycle by Schwenk & Rubega [3], which, contra [1], both explicitly includes a separate capture/subjugation stage ( p. 12) and specifically associates 'external' with intraoral processing ( p. 21).Besides the inclusion of water removal, our model differs from [3] only in not recognizing a separate 'ingestion' stage. This is because we view ingestion as a moment in time-namely, when food enters the mouth [4]-that can occur during multiple stages, and be achieved and reversed several times during feeding. By contrast, capture, manipulation and processing reflect periods of time over which specific behaviours are performed.

Wonky whales: the evolution of cranial asymmetry in cetaceans

“…Whales appear in the fossil record approximately 52.5 million years ago (Mya), with the two extant cetacean suborders, mysticetes (baleen whales) and odontocetes (toothed whales), diverging around 39 million years ago (Mya) [ 3 ]. Mysticetes evolved large body sizes and specialisations for bulk filter feeding whilst odontocetes evolved echolocation (biosonar) [ 4 – 6 ] and employ various raptorial and/or suction feeding strategies [ 7 , 8 ]. Cetaceans have undergone extensive morphological changes to adapt to a fully aquatic lifestyle [ 9 , 10 ] and show extremely divergent morphologies compared to their terrestrial artiodactyl relatives.…”

Mystacodon selenensis, the earliest known toothed mysticete (Cetacea, Mammalia) from the late Eocene of Peru: anatomy, phylogeny, and feeding adaptations

“…Furthermore, Hocking et al (2017b) also challenged the capacity of dental filter feeding in Coronodon, proposed by Geisler et al (2017), suggesting in contrast a mix of raptorial and suction feeding in the latter; they also concluded that suction feeding may have preceded the emergence of baleen. Therefore, both the evolutionary history and the feeding ecology of early mysticetes currently remain unclear and a matter of debate (Kienle et al 2017;Hocking et al 2017c).…”

Clawed forelimbs allow northern seals to eat like their ancient ancestors

“…This is made possible by their relatively primitive forelimb morphology, including flexible digits and strong claws. Semi-aquatic feeding behaviours, where prey is captured underwater before being brought to the surface for processing, were likely important when pinnipeds first began the transition from feeding on land to feeding in water [ 5 , 6 ]. Unlike more specialized aquatic feeding strategies common in living pinnipeds (e.g.…”

“…Meanwhile, all of this is further complicated by the need to dramatically modify their body form to increase streamlining and to adapt their limbs for generating propulsion when swimming [ 4 ]. In response to these challenges, marine mammals have adopted a myriad of aquatic feeding strategies, involving behaviours which are often so highly specialized that they would be impossible to use on land [ 5 , 6 ].…”

“…Echoes of this transition can be seen in living semi-aquatic mammals like river otters, which typically capture prey underwater using their teeth and forelimbs, before bringing it on to land for processing [ 7 ]. Land-based processing helps these mammals avoid some of the main challenges of fully aquatic foraging, as seawater simply drains off their prey and it allows them to breathe freely during lengthy bouts of prey processing [ 5 , 6 ]. Semi-aquatic feeding, where prey is captured underwater but processed in air, therefore plausibly assists in smoothing the evolutionary transition between terrestrial and fully aquatic feeding.…”