''Shonisaurus'' is a genus of very large

ichthyosaurs Ichthyosauria is an taxonomy (biology), order of large extinction, extinct marine reptiles sometimes referred to as "ichthyosaurs", although the term is also used for wider clades in which the order resides. Ichthyosaurians thrived during much of ...

. At least 37 incomplete fossil specimens of the

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

, ''Shonisaurus popularis'', have been found in the Luning Formation of

Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...

, USA. This formation dates to the late

Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227.3 ...

-early

Norian The Norian is a division of the Triassic geological period, Period. It has the rank of an age (geology), age (geochronology) or stage (stratigraphy), stage (chronostratigraphy). It lasted from ~227.3 to Mya (unit), million years ago. It was prec ...

age of the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

, around 227 million years ago. Other possible species of ''Shonisaurus'' have been discovered from the middle

deposits of

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

and

Alaska Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the north ...

Description

left, Size of ''S. popularis'' (green) and '' Shastasaurus sikanniensis'' (red) compared with a human (blue) Shonisaurus-LasVegas

''Shonisaurus'' lived during the late

stages of the

. With a large skull about long, ''S. popularis'' measured around in length and in body mass. ''S. sikanniensis'' was one of the largest marine reptiles of all time, measuring long and weighing . ''Shonisaurus'' had a long snout, and its flippers were much longer and narrower than in other ichthyosaurs. While ''Shonisaurus'' was initially reported to have had socketed teeth (rather than teeth set in a groove as in more advanced forms), these were present only at the jaw tips, and only in the very smallest, juvenile specimens. All of these features suggest that ''Shonisaurus'' may be a relatively specialised offshoot of the main ichthyosaur evolutionary line. More recent finds however indicate that ''Shonisaurus'' possessed teeth in all ontogenetic stages. Robust sectorial teeth and gut contents indicate that ''Shonisaurus'' was a macrophagous raptorial predator which fed on vertebrates and shelled mollusks like cephalopods, possibly even large-bodied prey. Additionally, ''Shonisaurus'' was historically depicted with a rather rotund body, but studies of its body shape since the early 1990s have shown that the body was much more slender than traditionally thought, and had a relatively deep body compared with related marine reptiles.

History of discovery

Fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

s of ''Shonisaurus'' were first found in a large deposit in

in 1920. Thirty years later, they were excavated, uncovering the remains of 37 very large ichthyosaurs. These were named ''Shonisaurus'', which means "lizard from the Shoshone Mountains", after the formation where the fossils were found. ''S. popularis'', was adopted as the

state fossil Most states in the US have designated a state fossil, many during the 1980s. It is common to designate a fossilized species, rather than a single specimen or a category of fossils. State fossils are distinct from other state emblems like state d ...

of Nevada in 1984. Excavations, begun in 1954 under the direction of Charles Camp and Samuel Welles of the

University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California), is a Public university, public Land-grant university, land-grant research university in Berkeley, California, United States. Founded in 1868 and named after t ...

, were continued by Camp throughout the 1960s. It was named by Charles Camp in 1976. The Nevada fossil sites can currently be viewed at the Berlin-Ichthyosaur State Park. A second species from the Pardonet Formation of

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

was named ''Shonisaurus sikanniensis'' in 2004. However, a

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

study by Sander and colleagues in 2011 later showed ''S. sikanniensis'' to be a species of '' Shastasaurus'' rather than ''Shonisaurus''. A subsequent study by Ji and colleagues published in 2013 reasserted the original classification, finding it more closely related to ''Shonisaurus'' than to ''Shastasaurus''. Support for both hypotheses has been found in later studies, with some authors classifying the species in ''Shonisaurus'' and others in ''Shastasaurus''. Specimens belonging to ''S. sikanniensis'' have been found in the Pardonet Formation

, dating to the middle

age. An isolated humerus from a smaller individual (TMP 94.381.4) and a postorbital region (TMP 98.75.9) from a juvenile were also reported from the same formation and were referred to as ''Shonisaurus'' sp. Other fossils from this formation include the ichthyosaurs '' Macgowania'' and '' Callawayia'', coelacanths '' Whiteia banffensis'' and possibly '' Garnbergia'', and various genera of molluscs including ammonites and bivalves. Large ichthyosaur remains found in Alaska have also been identified as ''Shonisaurus'' sp.

Notes

References

* Dixon, Dougal. "The Complete Book of Dinosaurs." Hermes House, 2006. * * Camp, C.L. 1981. Child of the rocks, the story of Berlin-Ichthyosaur State Park. Nevada Bureau of Mines and Geology special publication 5. * Cowen, R. 1995. History of life. Cambridge, Massachusetts: Blackwell Scientific. * * *

External links

Nevada Division of State Parks

{{Taxonbar, from=Q132554 Triassic ichthyosaurs Late Triassic ichthyosaurs of North America Triassic geology of Nevada Fossils_of_British_Columbia Fossils of Nevada Taxa named by Charles Lewis Camp Ichthyosauromorph genera Symbols of Nevada Paleontology in Alberta

Description

History of discovery

See also

Notes

References

External links