Bulk-filter feeding is an energetically efficient strategy for resource acquisition and assimilation, and facilitates the maintenance of extreme body size as exemplified by baleen whales (Mysticeti) and multiple lineages of bony and cartilaginous fishes. Among mysticetes, rorqual whales (Balaenopteridae) exhibit an intermittent ram filter feeding mode, lunge feeding, which requires the abandonment of body-streamlining in favor of a high-drag, mouth-open configuration aimed at engulfing a very large amount of prey-laden water. Particularly while lunge feeding on krill (the most widespread prey pmc-status-qastatus 0 pmc-status-live yes pmc-status-embargo no pmc-status-released yes pmc-prop-open-access yes pmc-prop-olf no pmc-prop-manuscript no pmc-prop-legally-suppressed no pmc-prop-has-pdf yes pmc-prop-has-supplement yes pmc-prop-pdf-only no pmc-prop-suppress-copyright no pmc-prop-is-real-version no pmc-prop-is-scanned-article no pmc-prop-preprint no pmc-prop-in-epmc yes pmc-license-ref CC BY Introduction The extreme body size of baleen whales (Mysticeti) is generally attributed to the overall energetic efficiency of bulk filter feeding [1] . Instead of hunting single prey items which is typified by the raptorial and suction feeding strategies in toothed whales (Odontoceti), baleen whales are obligate suspension filter feeders that engulf large quantities of prey-laden water. By processing vast amounts of small prey in bulk, baleen whales are thought to reap the rewards of an abundant resource using a more efficient feeding mechanism [2] , [3] . However, the energetics of foraging in cetaceans has yet to be fully assessed, especially with respect to microphagy in large mysticetes. Considering that some baleen whale species represent the largest animals to have ever lived, exploring the metabolic expenditures of feeding in baleen whales may shed light on the evolution of gigantism as well as the potential energetic limits to body size. Baleen whales exhibit a variety of filter feeding mechanisms, with distinct modes occurring in different mysticete lineages [2] , [4] . Bowhead and right whales (Balaenidae) are continuous ram feeders that exploit patches of copepods at slow and steady speeds [5] , using massive tongues to direct incoming prey-laden water along parallel racks of baleen [6] , [7] . Hydrodynamic modeling of engulfment parameterized with kinematic and morphological data indicates that lunge feeding comes at high energetic costs which are largely incurred from the engulfment and entrainment of a very large amount of water [25] – [27] . Such high energetic expenditures are significant enough to greatly reduce, in comparison with non lunge-feeding whales of similar size, the diving time in which foraging occurs [28] . energy limitation) predictably constrains maximum body size in this lineage of baleen whales. However, it is unknown what limits size in other cetacean lineages, as well as other lineages of other aquatic tetrapods that also exhibited gigantism in the past [67] . Clearly more research is needed to explore what factors limit body size in different taxa not only from an energetics perspective, but also with respect to other life history constraints. Our analyses, including those of the minke whale (a fish- as well as a krill-feeder), also have implications for the lowest body size classes of rorquals, which suggest relatively low power requirements for lunge feeding. This has a significant impact on the ontogeny of rorquals since weaned juveniles reap the advantages of efficiency in a low-cost feeding strategy that will facilitate rapid growth. Such a characteristic, which is exemplified by the large range in intraspecific body size of extant rorqual species, likely played a major role in the evolution of gigantism in balaenopterids. Lower energetic costs associated with engulfment at smaller body sizes may also have implications for how lunge feeding evolved in smaller ancestral baleen whales. Fossil evidence between the late Oligocene and late Miocene indicate that extinct rorquals reached maximum body sizes no larger than extant minke whales (i.e. 10 m long) [79] . These data, together with our minke results ( Figure 11 ), suggest that lunge feeding evolved within a body size range where the cost of engulfment does not appear to be significantly higher than non-feeding swimming (Interestingly, the minke modeling suggests that such costs may be even smaller). We posit that the evolution of baleen in cetaceans [80] at small body size classes [79] generated a mode of feeding that exhibited high energetic efficiency where vast amounts of prey could be captured at a relatively low cost [25] . Future research should further explore the feeding energetics of the smallest baleen whale species, both extinct and extant, to examine how different feeding modes may have evolved and to what extent it promoted extreme body size. Conclusions This paper has shown that the physical requirements of lunge-feeding towards krill, particularly with regards to the rate of energy delivery during engulfment, may present an obstacle to ever increasing body size. This would follow from the allometry of the skull, along with the approach speeds being dictated by the evasion strategies of the prey. But ultimately, and given that most Rorquals prey on both krill and fish, the linkages between food resources, motion energetics, and body size will not be completely resolved until further modeling is carried out on lunge-feeding towards fish. In general, lunging on fish will demand significantly higher prey approach speeds and accelerations by the predator. In most rorqual species such extra effort will be mitigated by the use of smaller gape angles (as with minke whales), as well as by other maneuvering and dynamic adaptations such as vertical lunging without active VGB muscle action. Although these constraints are not unique in yielding equideceleration, they represent a plausible

Herpetocetus Herpetocetus was a genus of cetotheriid whales. It was smaller than modern baleen whales, measured just 3 to 4 meters, and due to its jaw structure, it couldn’t open its mouth as wide as them, which meant it was incapable of doing lunge feeding.[1] Description Herpetocetus morrowi had an elongated snout and a roughly quadrate skull, and also probably did a feeding strategy very similar to that of the gray whale (Eschrichtius robustus).[2] Also, Herpetocetus had a unique shape, making it resemble a dolphin rather than a whale as seen by its elongated and a bit slender body. One young specimen discovered in Hokkaido, Japan includes a partial skull, mandible, vertebrae, and a scapula, and this specimen also exhibits a postglenoid process of the squamosal more transversely compressed than in the genus Nannocetus.[3] Species Herpetocetus has four recognized species: - †Herpetocetus bramblei Whitmore and Barnes, 2008 - †Herpetocetus morrowi El Adli, Deméré, and Boessenecker, 2014 - †Herpetocetus scaldiensis van Beneden, 1872 (type) - †Herpetocetus transatlanticus Whitmore and Barnes, 2008 Related pages References - ↑ Boessnecker, R.W. (2013).

mmons Attribution License http://creativecommons.org/licenses/by/4.0/ , which permits unrestricted use, provided the original author and source are credited. PMC Copyright notice PMCID: PMC5454272  PMID: 28539520 Abstract Vertebrates have evolved to gigantic sizes repeatedly over the past 250 Myr, reaching their extreme in today's baleen whales (Mysticeti). Hypotheses for the evolution of exceptionally large size in mysticetes range from niche partitioning to predator avoidance, but there has been no quantitative examination of body size evolutionary dynamics in this clade and it remains unclear when, why or how gigantism evolved. By fitting phylogenetic macroevolutionary models to a dataset consisting of living and extinct species, we show that mysticetes underwent a clade-wide shift in their mode of body size evolution during the Plio-Pleistocene. This transition, from Brownian motion-like dynamics to a trended random walk towards larger size, is temporally linked to the onset of seasonally intensified upwelling along coastal ecosystems. High prey densities resulting from wind-driven upwelling, rather than abundant resources alone, are the primary determinant of efficient foraging in extant mysticetes and Late Pliocene changes in ocean dynamics may have provided an ecological pathway to gigantism in multiple independent lineages. Keywords: macroevolution, tempo and mode, phylogeny, fossil, body size, trend 1. Introduction Vertebrates have evolved to gigantic sizes repeatedly over the past 250 Myr [ 1 , 2 ], reaching their extreme in today's blue whale, Balaenoptera musculus , which is the largest animal to have ever lived. All living baleen whales (Mysticeti), including the blue whale, are obligate suspension feeders and they possess a complex suite of adaptations that enhance the energetic efficiency of foraging on small-bodied, low trophic-level prey [ 3 – 5 ]. That such large animals should feed on such small prey is not without precedent; the fossil record dem