Shastasauridae

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Shastasauridae
Temporal range: Triassic
Royal Tyrell Shonisaurus.jpg
Skeleton of Shastasaurus sikanniensis
Shonisaurus scale mmartyniuk.png
Scale diagram of Shonisaurus
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Ichthyosauria
Node: Merriamosauria
Motani, 1999
Family: Shastasauridae
Merriam, 1895
Genera

Shastasauridae is an extinct family of Triassic ichthyosaurs. [1] The family contains the largest known species of ichthyosaurs, which include some of and possibly the largest known marine reptiles. [2]

Contents

Taxonomy

Shastasauridae indet. from China Zigong Dinosaur Museum Shastasauridae indet.jpg
Shastasauridae indet. from China

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 merriamosaurians more closely related to Shastasaurus pacificus than to Ichthyosaurus communis ." He also redefined Shastasauridae as a node-based taxon 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." [3] 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. [4] [5] In various studies, the grouping of Shastasauridae has been variously found to be either monophyletic or paraphyletic. Studies that have recovered the group as monophyletic generally include Shastasaurus, Besanosaurus, Guanlingsaurus , Guizhouichthyosaurus , Shonisaurus and ‘Callawayiawolonggangense within the group. [6]

Description

Life restoration of Guanlingsaurus Guanlingsaurus restoration.jpg
Life restoration of Guanlingsaurus
Shonisaurus popularis Shonisaurus popularisDB.jpg
Shonisaurus popularis

Shastasaurids as typically defined have elongate bodies, with over 55 presacral vertebrae. [6] They were the largest ichthyosaurs, with even some of the smaller species like Guanlingsaurus measuring over 8 metres (26 ft) in length. [7] One of the largest specimens was discovered in England in May 2016, [8] when researcher and fossil collector Paul de la Salle discovered a partial jawbone measuring 96 centimeters (3.15 ft) 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 26 meters (85 ft) long, nearly the size of a blue whale. Scaling based on Besanosaurus, however, found a shorter length estimate of 22 meters (72 ft). [9] In 2024, the Lilstock specimen was referred to the newly described species Ichthyotitan , with a length estimate of up to 25 meters (82 ft). [2]

Feeding habits

Unlike other Triassic ichthyosaurs, which fed almost exclusively on cephalopods, [10] shastasaurians fed on a variety of prey. [11] Evidence for this prey diversity includes gut contents from Guizhouichthyosarus tangae, Shonisaurus popularis, and an unnamed specimen from the Brooks Range of Alaska. [11]

Although older studies have suggested that shastasaurids were suction-feeders, current research indicates that the jaws of shastasaurid ichthyosaurs do not fit the suction-feeding profile, since their short and narrow hyoid bones are unsuitable to withstand impact forces for such kind of feeding, [12] and since some species like Shonisaurus had robust sectorial teeth with gut contents of mollusk shells and vertebrates. [13] [11]

Related Research Articles

<span class="mw-page-title-main">Ichthyosauria</span> Extinct order of large marine reptiles

Ichthyosauria is an order of large extinct marine reptiles sometimes referred to as "ichthyosaurs", although the term is also used for wider clades in which the order resides.

<span class="mw-page-title-main">Ichthyopterygia</span> Extinct order of reptiles

Ichthyopterygia was a designation introduced by Sir Richard Owen in 1840 to designate the Jurassic ichthyosaurs that were known at the time, but the term is now used more often for both true Ichthyosauria and their more primitive early and middle Triassic ancestors.

<i>Shonisaurus</i> Extinct genus of reptiles

Shonisaurus is a genus of very large ichthyosaurs. 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, about 237–227 million years ago.

<i>Ophthalmosaurus</i> Extinct genus of reptiles

Ophthalmosaurus is a genus of ichthyosaur known from the Middle-Late Jurassic. Possible remains from the earliest Cretaceous, around 145 million years ago, are also known. It was a relatively medium-sized ichthyosaur, measuring 4 m (13 ft) long and weighing 940 kg (2,070 lb). Named for its extremely large eyes, it had a jaw containing many small but robust teeth. Major fossil finds of this genus have been recorded in Europe with a second species possibly being found in North America.

<i>Cymbospondylus</i> Extinct genus of reptiles

Cymbospondylus is an extinct genus of large ichthyosaurs, of which it is among the oldest representatives, that lived during the Anisian stage of the Middle Triassic in what are now North America and Europe. The first known fossils of this taxon are a set of more or less complete vertebrae which were discovered in the 19th century in various mountain ranges of Nevada, in the United States, before being named and described by Joseph Leidy in 1868. It is in the beginning of the 20th century that more complete fossils were discovered through several expeditions launched by the University of California, and described in more detail by John Campbell Merriam in 1908, thus visualizing the overall anatomy of the animal. While many species have been assigned to the genus, only five are recognized as valid, the others being considered synonymous, doubtful or belonging to other genera. Cymbospondylus was formerly classified as a representative of the Shastasauridae, but more recent studies consider it to be more basal, view as the type genus of the Cymbospondylidae.

<i>Mixosaurus</i> Extinct genus of reptiles

Mixosaurus is an extinct genus of Middle Triassic ichthyosaur. Its fossils have been found near the Italy–Switzerland border and in South China.

<i>Shastasaurus</i> Extinct genus of ichthyosaur reptile

Shastasaurus is an extinct genus of ichthyosaur from the Late Triassic. Specimens have been found in the United States, Canada, and China.

The Westbury Formation is a geological formation in England, one of the Penarth Group. It dates back to the Rhaetian. The formation is named after the village of Westbury-on-Severn in Gloucestershire. The remains of a giant shastasaurid and dinosaurs are known from the formation.

<i>Besanosaurus</i> Genus of Triassic ichthyosaur

Besanosaurus is a genus of Middle Triassic ichthyosaur from Monte San Giorgio of Italy and Switzerland, containing the single species B. leptorhynchus. Besanosaurus was named by Cristiano Dal Sasso and Giovanni Pinna in 1996, based on the nearly complete flattened skeleton BES SC 999, the holotype specimen. This skeleton is preserved across multiple thin rock slabs spanning 3.5 by 4 metres when assembled and took thousands of hours to prepare. Additional specimens from Monte San Giorgio that have previously been considered separate genera, including a partial skull named Mikadocephalus and a well-preserved, largely complete skeleton, have been reinterpreted as additional specimens of Besanosaurus.

Callawayia is an extinct genus of ichthyosaur. It contains the species Callawayia neoscapularis.

<i>Guizhouichthyosaurus</i> Extinct genus of reptiles

Guizhouichthyosaurus is an extinct genus of ichthyosaur which is known primarily from the Xiaowa Formation of the lower Carnian stage of the Late Triassic in southwest China. The type species of this genus is Guizhouichthyosaurus tangae, of which multiple skeletons are known. It has been reassigned as a species of the genus Shastasaurus in the past, though it has since been considered distinct. The ichthyosaurs Cymbospondylus asiaticus, named in 2002, and Panjiangsaurus epicharis, named in 2003, are junior synonyms of G. tangae. The genus is also known from the Ladinian-aged Middle Triassic Zhuganpo Formation; additionally, the species "Callawayia" wollongangense may belong to Guizhouichthyosaurus.

Wimanius is a genus of ichthyosaur from the Middle Triassic of Switzerland, containing a single species, Wimanius odontopalatus. It was described by Michael Maisch and Andreas Matzke in 1998 based on an incomplete skull from Monte San Giorgio, a mountain on the Swiss-Italian border. Wimanius possesses teeth on its palate, though whether they were located on the palatine or pterygoid is disputed. Other features of Wimanius include a large orbit and jugals with two rami of similar lengths. Different phylogenetic placements of Wimanius have been recovered by different studies, including it being a mixosaurid relative or a merriamosaur, and a monotypic family, Wimaniidae has been named for it. However, its validity has also been questioned, and synonymy with various other genera has been proposed. The only specimen of Wimanius come from the Besano Formation. During the Anisian, this region was a lagoon populated by a wide variety of marine life, including a variety of other ichthyosaurs.

Mixosauridae was an early group of ichthyosaurs, living between 247.2 and 235 million years ago, during the Triassic period. Fossils of mixosaurs have been found all over the world: China, Timor, Indonesia, Italy, Germany, Spitsbergen, Switzerland, Svalbard, Canada, Alaska, and Nevada.

Guanlingsaurus is an extinct genus of shastasaurid ichthyosaur from the Late Triassic of China. It grew up to 8.3 metres (27 ft) in length and has a wide, triangular skull with a short and toothless snout.

<span class="mw-page-title-main">Cymbospondylidae</span> Extinct family of reptiles

Cymbospondylidae is an extinct family of Hueneosaurian Ichthyosaurs known from the Middle Triassic of Europe, North America, and Asia.

<i>Cartorhynchus</i> Extinct genus of reptiles

Cartorhynchus is an extinct genus of early ichthyosauriform marine reptile that lived during the Early Triassic epoch, about 248 million years ago. The genus contains a single species, Cartorhynchus lenticarpus, named in 2014 by Ryosuke Motani and colleagues from a single nearly-complete skeleton found near Chaohu, Anhui Province, China. Along with its close relative Sclerocormus, Cartorhynchus was part of a diversification of marine reptiles that occurred suddenly during the Spathian substage, soon after the devastating Permian-Triassic extinction event, but they were subsequently driven to extinction by volcanism and sea level changes by the Middle Triassic.

<span class="mw-page-title-main">Timeline of ichthyosaur research</span>

This timeline of ichthyosaur research is a chronological listing of events in the history of paleontology focused on the ichthyosauromorphs, a group of secondarily aquatic marine reptiles whose later members superficially resembled dolphins, sharks, or swordfish. Scientists have documented ichthyosaur fossils at least as far back as the late 17th century. At that time, a scholar named Edward Lhuyd published a book on British fossils that misattributed some ichthyosaur vertebrae to actual fishes; their true nature was not recognized until the 19th century. In 1811, a boy named Joseph Anning discovered the first ichthyosaur fossils that would come to be scientifically recognized as such. His sister Mary would later find the rest of its skeleton and would go on to become a respected fossil collector and paleontologist in her own right.

<i>Ichthyotitan</i> Genus of giant ichthyosaurs

Ichthyotitan is an extinct genus of giant ichthyosaur from the Late Triassic (Rhaetian), known from the Westbury Mudstone Formation in Somerset, England. It is believed to be a shastasaurid, extending the family's range by 13 million years up to the latest Triassic. The discovery of Ichthyotitan has been considered evidence that shastasaurids were still thriving until their disappearance in the Triassic–Jurassic extinction event.

References

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