''Nectosaurus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

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

(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 earliest traditionally identified diapsids, the araeosc ...

reptiles Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

) which lived during the Late

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

in what is now

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

. The

type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...

and only known

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

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

Hosselkus Limestone The Hosselkus Limestone is an Upper Triassic fossiliferous marine micrite, micritic limestone Formation (stratigraphy), formation that outcrops in Plumas County, California, Plumas and Shasta County, California, Shasta Counties, California. It is ...

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 ''Thalattosaurus'' (pronounced: , from and ) is an extinct genus of marine reptile in the family Thalattosauroidea. Known exclusively from the Triassic period, it was a long shellfish-eating diapsid with paddle-like limbs and a down-turned ros ...

'').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 (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

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

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

coracoid A coracoid 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 present as part of the scapula, but this is n ...

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

radius In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...

, 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, fin rays ( lepidotrich ...

s and incomplete ossification on certain long bones.

Description

Based on the position of the

vomer The vomer (; ) 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 maxillary bones. The vomer forms ...

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 ''Hescheleria'' is an extinct genus of thalattosaurian marine reptile from the Middle Triassic (247.2 to 235 Ma) of Monte San Giorgio in Switzerland. It is represented by a single type species, ''H. ruebeli'', which was named in 1936. Descript ...

'' as well as a specimen referred to ''

Paralonectes ''Paralonectes'' is an extinct genus of thalattosaurian reptile which lived in the Early or Middle Triassic of what is today British Columbia. The type and only species is ''P. merriami''. The genus name is derived from Ancient Greek and means " ...

'' 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 * Medial ...

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 mammals h ...

e, forming a

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit ** podium * 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 ...

. 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 ''Xinpusaurus'' is an extinct genus of thalattosaur from the Late Triassic of Guanling in Guizhou, China. Several species have been named since 2000: the type species ''X. suni'' along with the species ''X. bamaolinensis'' and ''X. kohi''. A 2013 ...

'' and ''Paralonectes'' because it was interpreted as having an upward-curving maxilla, further inquiry has shown that this was mistaken.

References

{{Taxonbar, from=Q2712533 Thalattosauria Late Triassic reptiles of North America Taxa named by John Campbell Merriam Fossil taxa described in 1905 Prehistoric reptile genera