''Shonisaurus'' is a very large genus of

ichthyosaur Ichthyosaurs (Ancient Greek for "fish lizard" – and ) are large extinct marine reptiles. Ichthyosaurs belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' – a designation introduced by Sir Richard Owen in 1842, altho ...

. At least 37 incomplete fossil specimens of the marine reptile have been found in the Luning Formation of

Nevada Nevada ( ; ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. N ...

, USA. This formation dates to the late

Carnian The Carnian (less commonly, Karnian) is the lowermost stage of the Upper Triassic Series (or earliest age of the Late Triassic Epoch). It lasted from 237 to 227 million years ago (Ma). The Carnian is preceded by the Ladinian and is followed by t ...

age of the late

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

period, about 237–227 million years ago.

Description

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

''Shonisaurus'' lived during the

stage of the late

period. ''S. popularis'' measured around in length and in body mass. A second species from

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, ...

was named ''Shonisaurus sikanniensis'' in 2004. ''S. sikanniensis'' was one of the largest marine reptiles of all time, measuring and weighing . However,

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

studies later showed ''S. sikanniensis'' to be a species of ''

Shastasaurus ''Shastasaurus'' ("Mount Shasta lizard") is a very large extinct genus of ichthyosaur from the middle and late Triassic, and is the largest known marine reptile.Hilton, Richard P., ''Dinosaurs and Other Mesozoic Animals of California'', Universit ...

'' rather than ''Shonisaurus''. A new study published in 2013 reasserted the original classification, finding it more closely related to ''Shonisaurus'' than to ''Shastasaurus''. In the 2019 study, ''S. sikanniensis'' was pertained within the genus ''Shastasaurus''. In the 2021 analysis, ''S. sikanniensis'' forms a clade with ''Shonisaurus'', indicating that it is closer to ''Shonisaurus'' than to ''Shastasaurus''. Specimens belonging to ''S. sikanniensis'' have been found in the

Pardonet Formation The Schooler Creek Group is a Stratigraphy, stratigraphic unit of Middle Triassic, Middle to Late Triassic (Ladinian to Norian) Geochronology, age in the Western Canadian Sedimentary Basin. It is present in northeastern British Columbia. It was nam ...

, dating to the middle

Norian The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic defi ...

age (about 210 million years ago). ''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. It 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. ''S. popularis'' had a relatively deep body compared with related marine reptiles. Although it is not known if ''Shonisaurus'' had one, a more basal ichthyosaur ''

Mixosaurus ''Mixosaurus'' is an extinct genus of Middle Triassic (Anisian to Ladinian, about 250-240 Mya) ichthyosaur. Its fossils have been found near the Italy–Switzerland border and in South China. The genus was named in 1887 by George H. Baur. The ...

'' had a

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...

History

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 preserved ...

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 The Shoshone Mountains, in west central Nevada, make up one of the longest mountain ranges in the state. The range runs in a general north-south direction in Nye and Lander counties. The range has a length of about and a width of about with ...

", after the formation where the fossils were found. ''S. popularis'', was adopted as the

state fossil Most American states have made a state fossil designation, in many cases during the 1980s. It is common to designate one species in which fossilization has occurred, rather than a single specimen, or a category of fossils not limited to a single ...

of Nevada in 1984. Excavations, begun in 1954 under the direction of

Charles Camp Charles Lewis Camp (March 12, 1893 Jamestown, North Dakota – August 14, 1975 San Jose, California) was a palaeontologist and zoologist, working from the University of California, Berkeley. He took part in excavations at the 'Placerias Quarry', in ...

and Samuel Welles of the

University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant u ...

, 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.

Paleoenvironment

Taphonomy

The Nevada bonebed represents a large assemblage of ''Shonisaurus'' which died at varying times and became preserved on the sea floor in a curiously regular arrangement of bones. The lack of fossil invertebrates encrusting the remains indicates that the carcasses sank in relatively deep water poor in oxygen.

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 Nevada Taxa named by Charles Lewis Camp Ichthyosauromorph genera