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Ichthyosaur were not suction feeders



From: Ben Creisler
bcreisler@gmail.com

New in PLoS ONE:


Ryosuke Motani, Cheng Ji, Taketeru Tomita, Neil Kelley, Erin Maxwell,
Da-yong Jiang & Paul Martin Sander (2013)
Absence of Suction Feeding Ichthyosaurs and Its Implications for
Triassic Mesopelagic Paleoecology.
PLoS ONE 8(12): e66075.
doi:10.1371/journal.pone.0066075
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0066075


Mesozoic marine reptiles and modern marine mammals are often
considered ecological analogs, but the extent of their similarity is
largely unknown. Particularly important is the presence/absence of
deep-diving suction feeders among Mesozoic marine reptiles because
this would indicate the establishment of mesopelagic cephalopod and
fish communities in the Mesozoic. A recent study suggested that
diverse suction feeders, resembling the extant beaked whales, evolved
among ichthyosaurs in the Triassic. However, this hypothesis has not
been tested quantitatively. We examined four osteological features of
jawed vertebrates that are closely linked to the mechanism of suction
feeding, namely hyoid corpus ossification/calcification, hyobranchial
apparatus robustness, mandibular bluntness, and mandibular pressure
concentration index. Measurements were taken from 18 species of
Triassic and Early Jurassic ichthyosaurs, including the presumed
suction feeders. Statistical comparisons with extant sharks and marine
mammals of known diets suggest that ichthyosaurian hyobranchial bones
are significantly more slender than in suction-feeding sharks or
cetaceans but similar to those of ram-feeding sharks. Most
importantly, an ossified hyoid corpus to which hyoid retractor muscles
attach is unknown in all but one ichthyosaur, whereas a strong
integration of the ossified corpus and cornua of the hyobranchial
apparatus has been identified in the literature as an important
feature of suction feeders. Also, ichthyosaurian mandibles do not
narrow rapidly to allow high suction pressure concentration within the
oral cavity, unlike in beaked whales or sperm whales. In conclusion,
it is most likely that Triassic and Early Jurassic ichthyosaurs were
‘ram-feeders’, without any beaked-whale-like suction feeder among
them. When combined with the inferred inability for dim-light vision
in relevant Triassic ichthyosaurs, the fossil record of ichthyosaurs
does not suggest the establishment of modern-style mesopelagic animal
communities in the Triassic. This new interpretation matches the
fossil record of coleoids, which indicates the absence of soft-bodied
deepwater species in the Triassic.