''Edgarosaurus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

polycotylid Polycotylidae is a family of plesiosaurs from the Cretaceous, a sister group to Leptocleididae. Polycotylids first appeared during the Albian stage of the Early Cretaceous, before becoming abundant and widespread during the early Late Cretaceous. ...

plesiosaur The Plesiosauria (; Greek: πλησίος, ''plesios'', meaning "near to" and ''sauros'', meaning "lizard") or plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared ...

from the Thermopolis Shale, containing one

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

, ''E. muddi''.Druckenmiller, PS, 2002. "Osteology of a new plesiosaur from the lower Cretaceous (Albian) Thermopolis Shale of Montana". ''Journal of Vertebrate Paleontology'' 22: 29-42. (Abstract) The type specimen was found in

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

(late

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± 0.9 M ...

) rocks in the state of

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...

in the United States. At the time, this location was covered by part of the

Western Interior Seaway The Western Interior Seaway (also called the Cretaceous Seaway, the Niobraran Sea, the North American Inland Sea, and the Western Interior Sea) was a large inland sea that split the continent of North America into two landmasses. The ancient sea, ...

. ''Edgarosaurus'' was one of the first polycotylids that evolved to become native to the Western Interior Seaway. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

(which is currently the only known specimen) consists of the skull, neck, parts of the

spine Spine or spinal may refer to: Science Biology * Vertebral column, also known as the backbone * Dendritic spine, a small membranous protrusion from a neuron's dendrite * Thorns, spines, and prickles, needle-like structures in plants * Spine (zoolog ...

and the left front flipper.

History of study

The well-preserved holotype specimen of ''Edgarosaurus'' (

MOR Mor or MOR may refer to: Names and titles * Mór (given name), a list of people named Mór or Mor * Mor (surname), a list of people named Mor or Mór * Mor (honorific), or Mar, in Syriac Radio and television * Middle of the road (music) genre * ...

751) was found in the Shell Creek

Member Member may refer to: * Military jury, referred to as "Members" in military jargon * Element (mathematics), an object that belongs to a mathematical set * In object-oriented programming, a member of a class ** Field (computer science), entries in ...

, the uppermost of the three members of the Thermopolis Shale, during the spring of 1993. The specimen's skull is complete and was preserved in articulation with a series 25 cervical (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. The generic name refers to the nearby location of

Edgar, Montana Edgar is a census-designated place and unincorporated community in Carbon County, Montana, United States. As of the 2010 census it had a population of 114. Edgar has a post office with a ZIP code 59026. The post office was established May 28, 1 ...

, while the

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

honors Kevin Mudd.

Description

Druckenmiller estimated the total length of ''Edgarosaurus'' to be roughly , a figure derived from the proportions of ''

Dolichorhynchops ''Dolichorhynchops'' is an extinct genus of polycotylid plesiosaur from the Late Cretaceous (early Turonian to late Campanian stage) of North America, containing three species, ''D. osborni'', ''D. bonneri'' and ''D. tropicensis'', as well as a ...

'' and ''

Peloneustes ''Peloneustes'' (meaning "mud swimmer") is a genus of pliosaurid plesiosaur from the Middle Jurassic of England. Its remains are known from the Peterborough Member of the Oxford Clay Formation, which is Callovian in age. It was originally descri ...

''. The cranium of the holotype specimen of ''Edgarosaurus'' is long. Each

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

(front upper tooth bearing bone) contains either six or seven teeth. The top of skull of ''Edgarosaurus'' possesses a small opening towards its back known as a

pineal foramen A parietal eye, also known as a third eye or pineal eye, is a part of the epithalamus present in some vertebrates. The eye is located at the top of the head, is photoreceptive and is associated with the pineal gland, regulating circadian rhythm ...

. The back of the skull is vertical, rather than sloping. Each side of the

braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria or skul ...

is perforated by a circular hole. The front ends of each half of the

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

are fused together to form a mandibular symphysis. There are six tooth pairs situated on the symphysis, a low number for a

. ''Edgarosaurus'' has large, fang-like teeth. The neck of ''Edgarosaurus'' 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 of ''Edgarosaurus'' 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.

Sources

{{Taxonbar, from=Q3719104 Early Cretaceous plesiosaurs of North America Polycotylids Fossil taxa described in 2002 Sauropterygian genera

History of study

Description

See also

Sources