Hyphalosaurus

Taxobox
name = "Hyphalosaurus"
fossil_range = Early Cretaceous

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image_width = 200px
regnum = Animalia
phylum = Chordata
classis = Sauropsida
ordo = Choristodera
familia = Hyphalosauridae Gao and Fox 2005
genus = "Hyphalosaurus"
genus_authority = Gao, et al. 1999
subdivision_ranks = Species
subdivision =
*"H. lingyuanensis" (type)
*"H. baitaigouensis"

"Hyphalosaurus" is an extinct genus from the Order Choristodera, found in the Early Cretaceous Jehol group in China (around 130-120 million years ago). It contains two species, "H. lingyuanensis" from the Yixian Formation, and "H. baitaigouensis" from the Jiufotang Formation.

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 a junior synonym of "Hyphalosaurus", as 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 aquatic, a lifestyle reflected by its elongate neck and tail and relatively reduced limbs. Superficially, it resembles a small nothosaur. This resemblance arose convergently and does not reflect evolutionary relatedness.

"Hyphalosaurus" is related to the large, crocodile-like "Champsosaurus" and the smaller, lizard-like "Monjurosuchus". Its closest relative was the similarly built species, "Shokawa ikoi", from the Early Cretaceous of Japan. The choristoderes were a clade of aquatic reptiles that survived the end-Cretaceous extinction along with crocodilians, turtles, lizards and snakes. The choristoderes became extinct by the Miocene.

A fossil of "Hyphalosaurus" dating 120 million years ago was found in 2007 with two heads [Buffetaut et al. (2006) "A two-headed reptile from the Cretaceous of China" Biology Letters [http://journals.royalsociety.org/content/08427xp462431367/fulltext.html Early Online] (DOI: 10.1098/rsbl.2006.0580)] , marking the oldest known case of polycephaly.

Gallery

References