| Edgarosaurus | |
|---|---|
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| Type specimen ofEdgarosaurus muddi on display in the Museum of the Rockies | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | †Sauropterygia |
| Order: | †Plesiosauria |
| Superfamily: | †Plesiosauroidea |
| Family: | †Polycotylidae |
| Genus: | †Edgarosaurus Druckenmiller, 2002 |
| Species: | †E. muddi |
| Binomial name | |
| †Edgarosaurus muddi Druckenmiller, 2002 | |
Edgarosaurus is agenus ofpolycotylidplesiosaur from theThermopolis Shale, containing onespecies,E. muddi.[1] The type specimen was found inEarly Cretaceous (lateAlbian) rocks in the state ofMontana in the United States.[1] At the time, this location was covered by part of theWestern Interior Seaway.Edgarosaurus was one of the first polycotylids that evolved to become native to the Western Interior Seaway.
Theholotype (which is currently the only known specimen) consists of the skull, neck, parts of thespine and the left front flipper.[1]
The well-preserved holotype specimen ofEdgarosaurus (MOR 751) was found in the Shell CreekMember, the uppermost of the three members of theThermopolis Shale, during the spring of 1993. The specimen's skull is complete and was preserved in articulation with a series 25cervical (neck) vertebrae. An additional cervical vertebra, three pectoral (shoulder) vertebrae, and two dorsal (back) vertebrae were found isolated at the site, but articulate to form a series with the other 25 cervical vertebrae. Three other dorsal vertebrae were also recovered, though they do not seem to belong to this string of vertebrae. An almost complete front paddle is also known.Edgarosaurus muddi was named in 2002 by Pat S. Druckenmiller. Thegeneric name refers to the nearby location ofEdgar, Montana, while thespecific name honors Kevin Mudd.[1]
Druckenmiller estimated the total length ofEdgarosaurus to be roughly 3.2–3.7 meters (10–12 ft), a figure derived from the proportions ofDolichorhynchops andPeloneustes. The cranium of the holotype specimen ofEdgarosaurus is 47.5 centimetres (1.56 ft) long. Eachpremaxilla (front upper tooth bearing bone) contains either six or seven teeth. The top of skull ofEdgarosaurus possesses a small opening towards its back known as apineal foramen. The back of the skull is vertical, rather than sloping. Each side of thebraincase is perforated by a circular hole. The front ends of each half of themandible are fused together to form a mandibular symphysis. There are six tooth pairs situated on the symphysis, a low number for apolycotylid.Edgarosaurus has large, fang-like teeth.[1]
The neck ofEdgarosaurus is short for a plesiosaur, containing a total of 26 vertebrae. The neck and skull together were estimated by Druckenmiller to comprise up to 45% of the animal's length. The lower arm bones ofEdgarosaurus are very short and wide. The first digit of its forelimb consists of seven bones, the second eleven, and the third ten, while the fourth and fifth bear nine.[1]
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