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Guanlingsaurus (Ichthyosauria) juvenile from Triassic of China



From: Ben Creisler
bcreisler@gmail.com


In the new issue of JVP:



Cheng Ji, Da-Yong Jiang, Ryosuke Motani, Wei-Cheng Hao, Zuo-Yu Sun &
Tao Cai (2013)
A new juvenile specimen of Guanlingsaurus (Ichthyosauria,
Shastasauridae) from the Upper Triassic of southwestern China.
Journal of Vertebrate Paleontology 33 (2):-348
DOI:10.1080/02724634.2013.723082
http://www.tandfonline.com/doi/full/10.1080/02724634.2013.723082


A new nearly complete skeleton from the Wayao Member of the Falang
Formation (lower Carnian, Upper Triassic) of Guizhou, South China, is
described and ascribed as a juvenile individual of Guanlingsaurus
liangae. The new specimen supplies hitherto unknown information on
this species: a complete pelvic girdle shows that the ilium was
misidentified as the ischium by previous authors; complete hyoids show
that their length was overestimated previously; unlike in other
shastasaurids, the obturator foramen on the pubis is widely open as
part of the obturator fossa; and the fibula has a posterior flange,
similar to that of Shonisaurus. Guanlingsaurus liangae was reassigned
to the genus Shastasaurus and was suggested to be a suction feeder due
to its short snout, lack of teeth, and hyoid. However, the new
specimen of Guanlingsaurus described here shows much smaller hyoids
compared with Shonisaurus, which was thought to be a suction-feeding
ichthyosaur. Suction feeding in ichthyopterygians as a whole requires
scrutiny: the group lacks an ossified hyoid corpus that is typically
expanded in suction-feeding cetaceans, which suggests that
ichthyopterygian hyoids were insufficiently robust for suction
feeding. A phylogenetic analysis of Ichthyopterygia based on a revised
data matrix clarifies the shastasaurid affinity of G. liangae as a
sister taxon of Shonisaurus, with Shastasaurus as their sister group,
and Shonisaurus is reestablished as a genus containing Shonisaurus
sikanniensis as traditionally held. It suggests that the assignment of
Guanlingsaurus and Shonisaurus sikanniensis to Shastasaurus
unnecessarily confuses existing taxonomy.