Hyphalosaurus

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Hyphalosaurus is among the most interesting fossil animals found in the Early Cretaceous Yixian Formation in Liaoning Province, China, formed around 130-120 million years ago.

Somehow, the slab and counterslab of the holotype were given to different groups of researchers. Each described the taxon and published their results independently, giving the animal two different names. It was quickly recognized that Sinohydrosaurus and Hyphalosaurus were mirror images of one another and in fact represented the same specimen. Sinohydrosaurus is considered a junior synonym of Hyphalosaurus, because the latter name appeared in publication before the former.

Hyphalosaurus fossils are relatively widespread in the Yixian beds. Entire growth series are known, from embryos in eggs to fully-grown adults. This animal achieved an adult body size of about 0.8 meters.

This animal was clearly aquatic, a lifestyle reflected by its elongate neck and tail and relatively reduced limbs. Superficially, it resembles a small plesiosaur or nothosaur, which were large marine reptiles that existed contemporaneously. This resemblance arose convergently and does not reflect evolutionary relatedness.

Hyphalosaurus belongs to the order Choristodera, and is closely related to the large, crocodile-like champsosaur and the smaller, lizard-like Monjurosuchus. This order of aquatic reptiles survived the end-Cretaceous extinction, only to go extinct around 50 million years ago.

[edit] References

http://news.bbc.co.uk/2/hi/science/nature/6195345.stm Interesting article on a 2 headed juvenile hyphalosaurus. http://www.bbc.co.uk/somerset/so/2004/04/fossil.shtml Another interesting article on a larger ,earlier British Plesiosaur cousin from the Jurassic.