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Diandongosaurus, new Triassic eosauropterygian



From: Ben Creisler
bh480@scn.org

Also in the new Vertebrata Palasiatica:


SHANG Qing-Hua, WU Xiao-Chun, & LI Chun (2011). 
A new eosauropterygian from Middle Triassic of eastern Yunnan Province,
southwestern China.
Vertebrata Palasiatica 49(2): 155-171
http://www.ivpp.cas.cn/cbw/gjzdwxb/xbwzxz/201105/P020110530511087154324.pdf

A new eosauropterygian, Diandongosaurus acutidentatus gen. et sp. nov., is
described based on a skeleton from the Upper Member of Guanling Formation
(Middle Anisian) of Luoping County, Yunnan Province, southwestern China.
This new species displays a combination of traits seen in nothosauroids
(Simosaurus and nothosaurians) and pachypleurosaurs (Dactylosaurus,
Anarosaurus, Serpianosaurus, and Neusticosaurus). It has an unconstricted
snout, preorbital region longer than the postorbital region, and a
supratemporal fenestra smaller than the orbit, as in the pachypleurosaurs.
On the other hand, it bears enlarged and procumbent teeth in the premaxilla
and the anterior dentary, and one or two fang-like maxillary teeth, as in
the nothosaurs. In this new species, the frontals and the parietals are
fused, the posterolateral process of the frontal extends posteriorly over
the anterior margin of the supratemporal fenestra, the postorbital is
excluded from the infratemporal fenestra by the jugal-squamosal contact,
the quadratojugal is present, the clavicle has an anterolateral projection,
and the three sacral and anterior caudal ribs are distally pinched off but
not constricted. Unlike in most of other stem eusauropterygians, the
prefrontal and the postfrontal meets each other along the dorsal margin of
the orbit, the descending ramus of the squamosal reaches the articular
condyle of the quadrate, caudal ribs 3 to 8 are elongate and longer than
sacral ribs, and the ungual phalanxes of the pes are extremely
dorsoventrally expanded. Our phylogenetic analysis suggests that
Diandongosaurus is neither a pachypleurosaur nor a nothosauroid; it might
be the sister group of the clade consisting of Wumengosaurus, the
nothosauroids and those taxa traditionally considered as pachypleurosaurs.


Another recent marine reptile article:

Erin E. Maxwell and Patrick S. Druckenmiller (2011)
A small ichthyosaur from the Clearwater Formation (Alberta, Canada) and a
discussion of the taxonomic utility of the pectoral girdle. 
Paläontologische Zeitschrift (advance online publication)
DOI: 10.1007/s12542-011-0106-0 
http://www.springerlink.com/content/35g647092k7x5440/

Albian sedimentary successions of northwestern Canada have yielded a
diverse assemblage of Mesozoic marine vertebrates, and ichthyosaurs form an
important component of these faunas. Here, we describe a partial
postcranial skeleton of a small (estimated at less than 3 m total body
length) ichthyosaur from the Wabiskaw Member of the Clearwater Formation
(lowermost Albian). The semi-articulated specimen includes much of the
presacral vertebral column, dorsal ribs and gastralia. Most significantly,
it possesses an articulated pectoral girdle and humerus, and also preserves
the pelvic girdle, allowing new insights into girdle evolution in
ichthyosaurs. Whereas both sets of girdles are thought to exhibit large
amounts of intraspecific variation, the pectoral girdle of ophthalmosaurids
appears to evolve very slowly, remaining essentially unchanged from the
Middle Jurassic onwards. In contrast, the pelvic girdle shows taxonomically
informative changes within Ophthalmosauridae. The variable and poorly known
nature of girdle morphology in Cretaceous ichthyosaurs precludes generic
referral of the specimen. 




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