''Nectosaurus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

thalattosaur Thalattosauria (Greek for "sea lizards") is an extinct order of prehistoric marine reptiles that lived in the middle to late Triassic period. Thalattosaurs were diverse in size and shape, and are divided into two superfamilies: Askeptosauroidea an ...

(marine

diapsid Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The group first appeared about three hundred million years a ...

reptiles) which lived during the Late

Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

in what is now

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

. The type and only known

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 ...

, ''Nectosaurus halius'', was found in the

Hosselkus Limestone The Hosselkus Limestone is an Upper Triassic fossiliferous marine micritic limestone formation that outcrops in Plumas and Shasta Counties, California. It is known for its invertebrate fauna, most notably the many species of shelled cephalopod ...

and described by

John C. Merriam John Campbell Merriam (October 20, 1869 – October 30, 1945) was an American paleontologist, educator, and conservationist. The first vertebrate paleontologist on the West Coast of the United States, he is best known for his taxonomy of ver ...

in 1905, making it one of the first thalattosaurians known (along with '' Thalattosaurus'').Sepkoski, J.J. (2002). "A compendium of fossil marine animal genera". ''Bulletins of American Paleontology'' 363: 1-560.

Discovery

''Nectosaurus'' is known from fragmentary remains. 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 sever ...

, UCMP 9124, is an incomplete skeleton including vertebrae, a humerus,

coracoid A coracoid (from Greek κόραξ, ''koraks'', raven) is a paired bone which is part of the shoulder assembly in all vertebrates except therian mammals (marsupials and placentals). In therian mammals (including humans), a coracoid process is prese ...

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

, and partial skull and mandibles. Many isolated bones from other localities were referred to the genus by Merriam in 1908. In addition, a partial skull from the same locality, UCMP 9120, was referred to the genus as ''Nectosaurus sp.'' in 1905. This specimen is much larger than any specimen of ''Nectosaurus halius'' but is otherwise similar to several referred specimens. UCMP 9120 may represent an adult specimen, making the holotype a juvenile specimen, a hypothesis supported by the fact that the holotype has unfused

dermal bone A dermal bone or investing bone or membrane bone is a bony structure derived from intramembranous ossification forming components of the vertebrate skeleton including much of the skull, jaws, gill covers, shoulder girdle and fin spines rays ( le ...

s and incomplete ossification on certain long bones.

Description

Based on the position of the

vomer The vomer (; lat, vomer, lit=ploughshare) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right max ...

s, the general shape of the premaxillae was inferred to be that of a dramatically downward hooking rostrum, descending at a vertical angle. This trait is also known in '' Hescheleria'' as well as a specimen referred to '' Paralonectes'' in 1993.''Nectosaurus'' also had pointed, needle-like teeth (particularly in the front of the maxilla) and a mandible with a very high and pointed coronoid process. Like other thalattosauroids, the vomers and

pterygoid Pterygoid, from the Greek for 'winglike', may refer to: * Pterygoid bone, a bone of the palate of many vertebrates * Pterygoid processes of the sphenoid bone ** Lateral pterygoid plate ** Medial pterygoid plate * Lateral pterygoid muscle * Medi ...

also had teeth.

Classification

''Nectosaurus'' was a member of a group of marine reptiles known as thalattosaurs, characterized by their long, paddle-like tails and short legs with independently movable digits. Most thalattosaurs had extended

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 ...

e, forming a

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * Ros ...

. Thalattosaurs with downward curving, hook-like premaxillae (such as ''Nectosaurus'') are known as thalattosauroids. Although a 2001 analysis considered it a close relative of '' Xinpusaurus'' and ''Paralonectes'' because it was interpreted as having an upward-curving maxilla, further inquiry has shown that this was mistaken.

References

Thalattosaurs Late Triassic reptiles of North America Taxa named by John Campbell Merriam Fossil taxa described in 1905 Prehistoric reptile genera {{paleo-reptile-stub