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Shastasaurus as suction-feeding ichthyosaur



From: Ben Creisler
bh480@scn.org

New in PLoS ONE:

Sander, P.M., Chen X., Cheng L., Wang X. (2011)
Short-Snouted Toothless Ichthyosaur from China Suggests Late Triassic
Diversification of Suction Feeding Ichthyosaurs. 
PLoS ONE 6(5): e19480. doi:10.1371/journal.pone.0019480
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0019480


ABSTRACT
Background
Ichthyosaurs were an important group of Mesozoic marine reptiles and
existed from the Early Triassic to the early Late Cretaceous. Despite a
great diversity in body shapes and feeding adaptations, all share greatly
enlarged eyes, an elongated rostrum with numerous conical teeth, and a
streamlined body.

Methodology/Principal Findings
Based on new material from China and the restudy of Shastasaurus pacificus,
we here reinterpret the classical large-bodied Late Triassic ichthyosaur
genus Shastasaurus to differ greatly from the standard ichthyosaurian body
plan, indicating much greater morphological diversity and range of feeding
adaptations in ichthyosaurs than previously recognized. Phylogenetic
analysis indicates a monophyletic clade consisting of the giant Shonisaurus
sikanniensis, Guanlingsaurus liangae, and Shastasaurus pacificus to which
the genus name Shastasaurus is applied. Shastasaurus liangae comb. nov. is
from the Late Triassic (Carnian) Xiaowa Formation of Guizhou Province,
southwestern China. The species combines a diminutive head with an entirely
toothless and greatly reduced snout. The species also has by far the
highest vertebral count among ichthyosaurs (86 presacral vertebrae and >110
caudal vertebrae), a count that is also very high for tetrapods in general.
A reduced toothless snout and a diminutive head is also apparently present
in the giant S. sikanniensis and presumably in S. pacificus.

Conclusions/Significance
In analogy to many modern odontocetes, Shastasaurus is interpreted as a
specialized suction feeder on unshelled cephalopods and fish, suggesting a
unique but widespread Late Triassic diversification of toothless,
suction-feeding ichthyosaurs. Suction feeding has not been hypothesized for
any of the other diverse marine reptiles of the Mesozoic before, but in
Shastasaurus may be linked to the Late Triassic minimum in atmospheric
oxygen.



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