Shastasauridae is an extinct

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

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 ...

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 ...

s that includes the genera '' Shastasaurus'', ''

Shonisaurus ''Shonisaurus'' is a very large genus of ichthyosaur. At least 37 incomplete fossil specimens of the marine reptile have been found in the Luning Formation of Nevada, USA. This formation dates to the late Carnian age of the late Triassic period, ...

'' and ''

Himalayasaurus ''Himalayasaurus'' is an extinct genus of ichthyosaur from the Late Triassic Qulonggongba Formation of Tibet. The type species ''Himalayasaurus tibetensis'' was described in 1972 on the basis of fragmentary remains, including teeth, limb bones, ...

''. Many other Triassic ichthyosaurs have been assigned to Shastasauridae in the past, but recent

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 ...

analyses suggest that these species form an

evolutionary grade A grade is a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit. Definition An evolutionary grade is a group of ...

of early ichthyosaurs rather than a true

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

or evolutionary grouping that can be called Shastasauridae. Shastasauridae was named by American paleontologist John Campbell Merriam in 1895 along with the newly described genus ''Shastasaurus''. In 1999, Ryosuke Motani erected the clade Shastasauria to include ''Shastasaurus'', ''Shonisaurus'', and several other traditional shastasaurids, defining it as a stem-based taxon including "all

merriamosauria Merriamosauria is an extinct clade of ichthyosaurs. It was named by Ryosuke Motani in his 1999 analysis of the relationships of ichthyopterygian marine reptiles and was defined in phylogenetic terms as a stem-based taxon including "the last co ...

ns more closely related to '' Shastasaurus pacificus'' than to ''

Ichthyosaurus communis ''Ichthyosaurus'' (derived from Greek ' () meaning 'fish' and ' () meaning 'lizard') is a genus of ichthyosaurs from the Early Jurassic (Hettangian - Pliensbachian), with possible Late Triassic record, from Europe (Belgium, England, Germany, Swi ...

''." He also redefined Shastasauridae as a

node-based taxon Phylogenetic nomenclature is a method of nomenclature for taxa in biology that uses phylogenetic definitions for taxon names as explained below. This contrasts with the traditional approach, in which taxon names are defined by a '' type'', which ...

including "the last common ancestor of ''Shastasaurus pacificus'' and '' Besanosaurus leptorhynchus'', and all its descendants" and Shastasaurinae, which Merriam named in 1908, as a stem taxon including "the last common ancestor of ''Shastasaurus'' and ''Shonisaurus'', and all its descendants." In an alternative classification scheme, paleontologist Michael Maisch restricted Shastasauridae to the genus ''Shastasaurus'' and placed ''Shonisaurus'' and ''Besanosaurus'' in separate families, Shonisauridae and Besanosauridae, respectively. In May 2016, researcher and fossil collector Paul de la Salle discovered a partial jawbone measuring long which was catalogued as BRSMG Cg2488, also referred to as the Lilstock specimen. In 2018, Dean Lomax, de la Salle, Judy Massare, and Ramues Gallois identified the Lilstock specimen as a shastasaurid. While its incompleteness made the size of the animal difficult to suggest, it clearly was very large. Using ''Shonisaurus sikanniensis'' as a model, the researchers estimated the ichthyosaur to have been long, nearly the size of a

blue whale The blue whale (''Balaenoptera musculus'') is a marine mammal and a baleen whale. Reaching a maximum confirmed length of and weighing up to , it is the largest animal known to have ever existed. The blue whale's long and slender body can ...

. Scaling based on ''Besanosaurus'', however, found a shorter length estimate of .

Feeding Habits

Unlike other

s, which fed almost exclusively on

cephalopods A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, an ...

, shastasaurians fed on a variety of

prey Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...

. Evidence for this prey diversity includes gut contents from '' Guizhouichthyosarus tangae,'' ''

popularis,'' and an unnamed specimen from the

Brooks Range The Brooks Range ( Gwich'in: ''Gwazhał'') is a mountain range in far northern North America stretching some from west to east across northern Alaska into Canada's Yukon Territory. Reaching a peak elevation of on Mount Isto, the range is believ ...

Alaska Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., ...

References

Ichthyosaurs Triassic ichthyosaurs Triassic reptiles of North America Triassic California Fossils of the United States Paleontology in California Prehistoric reptile families {{triassic-reptile-stub