Showing posts with label Mesozoic. Show all posts
Showing posts with label Mesozoic. Show all posts

Friday, May 27, 2011

Suction-Feeding Ichthyosaurs

Photograph and drawing of skull of YGMIR SPCV03107. (A) in left lateral view. Note the greatly abbreviated rostrum, the complete lack of teeth, the large foramina in the maxillary and lacrimal bones, and the dorsally convex coronoid region of the dentary (arrow). (B) in dorsal view. Note the nasals extending to the tip of the rostrum. Abbreviations: a, angular; ar, articular; d, dentary; en, external nares; f, frontal; if, internasal foramen; j, jugal; l, lacrimal; mx, maxilla; pa, parietal; pf, postfrontal; pm, premaxilla; po, postorbital; prf, prefrontal; qj, quadratojugal; sa, surangular; sq, squamosal; st, supratemporal; uto, upper temporal opening.
Ichthyosaurs were important in Mesozoic marine ecosystems and lived 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.

Now, P. Martin Sander and colleagues have examined new material from China and taken a second look at Shastasaurus pacificus, and discovered 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. The Shastasaurus liangae 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 more than 110 caudal vertebrae), a count that is also very high for tetrapods in general. A reduced toothless snout and a diminutive head is also present in the giant S. sikanniensis and presumably in S. pacificus.They concluded that Shastasaurus is a specialized suction feeder, that fed 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 the behavior may be linked to the Late Triassic minimum in atmospheric oxygen.

Citation
Sander PM, 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