Cymbospondylus

Discovery and identification block of C. piscosus. In 1868, American paleontologist Joseph Leidy described two new genera of ichthyosaurs dating from the Middle Triassic on the basis of fossil vertebrae discovered in several localities in Nevada, United States, all of which were transmitted through the geologist Josiah Dwight Whitney. One of the two genera he named is Cymbospondylus, to which he assigned two species. The first one is C. piscosus, which Leidy named on the basis of several more or less complete vertebrae having been discovered in different mountain ranges of the state. The genus name Cymbospondylus derives from the Ancient Greek words κύμβη (kymbē, "cup") and σπόνδυλος (spondylos, "vertebra"), all taken together literally meaning cupped vertebrae, in reference to the rather obvious shape of this part of the skeleton. As no type species was designated in the 1868 article, it was not until 1902 that John Campbell Merriam assigned C. piscosus to this title, the latter being the first named in Leidy's official description of the genus. Twenty years later, in 1964, published a photo of this same specimen and suggested that it shared affinities with Cymbospondylus, then only known from North America at that time. The specimen in question, cataloged as PIMUZ T 4351, was formally described for the first time in 1989 under the name C. buchseri by , thus confirming the presence of the genus in Europe. The specific epithet buchseri is named in honor of Fritz Buchser, a member of the Museum of Paleontology at the University of Zurich, the latter having prepared the holotype skeleton in 1931 as his first major professional achievement. , Chicago While C. petrinus was for a time seen as the only valid species of the genus known from Nevada, it was not until the early 21st century that later discoveries contradicted this assertion. In 2006, Nadia Fröbisch and colleagues described the species C. nichollsi based on an incomplete skeleton, cataloged as FMNH PR 2251, which was discovered in the Augusta Mountains. The fossil was originally exhumed in the hope of finding a new specimen of C. petrinus, but the number of significant anatomical differences led researchers to establish a separate species. The species in question is named in honor to Elizabeth Nicholls, an American-Canadian paleontologist specializing in Triassic marine reptiles, who made a major contribution to the ichthyosaurs that lived during this period. However, it was only later that the specimen, cataloged as LACM DI 158109, was formally designated a holotype for the species C. duelferi by Nicole Klein and colleagues in 2020. The species name duelferi was chosen in honor of Olaf Dülfer, fossil preparer who made many practical contributions to research on Mesozoic marine reptiles. before being referred to Cymbospondylus in the official description of C. buchseri by Sander in 1989, • In 1994, Judy A. Massare and Jack M. Callaway referred to a number of Cymbospondylus fossils discovered in 1985 by H. Gregory McDonald in the Platy Siltstone Member of the Thaynes Formation, in Idaho, United States. • In 2001, Olivier Rieppel and Fabio Marco Dalla Vecchia listed a set of fossils of marine reptiles from the Triassic and having been discovered in the comune of Forni di Sotto, in Italy, including two that they attributed with doubt to Cymbospondylus. The first of these collections consists of a single vertebra, a neural spine and three rib fragments, while the second consists of two isolated vertebrae. • In 2012, Balini and Renesto described four more or less partial vertebrae attributed to Cymbospondylus which were discovered in the comune of Piazza Brembana, in Italy, being cataloged MCSNB 11689 A, B, C, and D. • In 2013 and 2018, numerous genus-assigned vertebrae were identified in the Vendomdalen Member of the Vikinghøgda Formation, Svalbard. Formerly assigned species Although many valid and distinct species have been assigned to Cymbospondylus throughout its taxonomic history, some of these have been reassigned to different genera or are considered synonymous or even doubtful. In 1902, the Russian paleontologist Nikolai Nikolajewitch Yakowlew moved the species within the genus Shastasaurus, referring an isolated vertebra to this taxon. In 1908, Merriam in turn moved this species into the genus Cymbospondylus, under the name C. (?) polaris. Merriam still expresses some hesitation about this attribution, asserting that the true generic identity cannot be determined for this species due to the few known fossils. In 1910, the species was moved to the newly erected genus Pessosaurus by Carl Wiman, as P. polaris, to which it has always been referred by this name ever since. Although this taxon is declared as a nomen dubium according to studies published at the end of the 20th century, it is seen as a species inquirenda according to McGowan and Motani in 2003, i.e. a taxon under investigation, as numerous fossils that have since been referred to P. polaris could make it once again as valid. Still in his 1908 work, Merriam erects two new species of the genus, coming from the same locality from which C. petrinus is known. The first is C. nevadanus, named from fossils constituting a hind limb. Merriam distinguishes this species from C. petrinus on the basis of its larger size and the different proportions of some bones. However, the C. nevadanus material is not sufficiently diagnostic to support the validity of this species, and is considered a species inquireda according to McGowan and Motani in 2003. For much of the 20th century, M (?) natans was recognized as a valid species of Mixosaurus until 1999, when it was synonymized with M. nordenskioeldii. Although M. nordenskioeldii itself has been considered a nomen dubium since 2005, the fossil material concerned remains attributed to the family Mixosauridae and is no longer attributable to Cymbospondylus. Immediately afterwards, the validity of C. germanicus was questioned the same year by Ferdinand Broili, the latter citing that the fossils concerned did not present notable features to be recognized as distinct. In 2002, paleontologists Chun Li and Hai-Lu You named a new species as C. asiaticus based on a complete skull discovered in the Xiaowa Formation, located in Guizhou Province, China, and it was considered as the most recent known representative of the genus. In the official description of C. nichollsi published in 2006, the authors are doubtful regarding the attribution of this species to Cymbospondylus. They mention that the latter does not share any notable commonalities with the three then recognized species of the genus at the time, namely C. petrinus, C. buchseri and C. nichollsi, and suggest that it would in fact be a junior synonym of Guizhouichthyosaurus tangae. This synonymy was contested the following year, in 2010, in which Michael W. Maisch provisionally reclassified Guizhouichthyosaurus as a distinct genus. In 2011, Sander and his colleagues considered that Guizhouichthyosaurus was distinct, while a 2013 study by Shang and Li still synonymizes it with Shastasaurus. However, numerous phylogenetic and morphological analyzes subsequently published consider Guizhouichthyosaurus to be distinct genus from Shastasaurus. ==Description==

Cymbospondylus, like other ichthyosaurs, had a long, thin snout, large eye sockets, and a tail fluke that was supported by vertebrae in the lower half. Ichthyosaurs were superficially similar to dolphins and had flippers rather than legs, but the oldest representatives (with the exception of the parvipelvians, more advanced) do not have dorsal fins, or would have one but relatively poorly developed. Like most Triassic ichthyosaurs, Cymbospondylus has a more slender anatomy, possessing an elongated trunk and a long, poorly pronounced tail, giving it a body more similar in appearance to that of an eel. Although the colour of Cymbospondylus is unknown, at least some ichthyosaurs may have been uniformly dark-coloured in life, which is evidenced by the discovery of high concentrations of eumelanin pigments in the preserved skin of an early ichthyosaur fossil. Size and size comparison of a C. youngorum with a human The size and weight of Cymbospondylus varies greatly between recognized species. The antiquity as well as such an imposing size for an animal dating from the beginning of the Middle Triassic makes C. youngorum qualify as "the first aquatic giant" according to Lene Liebe Delsett and Nicholas David Pyenson. C. duelferi has a subthecodont type of dentition, meaning that its teeth are implanted in shallow sockets. C. youngorum has a thick base of the bone attaching to the teeth, a trait not seen in other ichthyosaurs. The teeth are homodont, that is to say they share an identical shape, being conical, ridged and pointed. The teeth also have longitudinal ridges that extend from the base of the crown to the apical third. The total number of teeth in the different species of Cymbospondylus is difficult to determine, because the state of preservation of certain fossils prevents formal evaluations from being obtained, being poorly preserved in C. buchseri, and totally unknown in C. nichollsi. Only three species were able to have a more or less clear estimate of their number of teeth: C. duelferi having a number greater than 21 teeth known in the upper jaw, but unknown in the lower jaw; C. petrinus with between 30 and 35 teeth in the upper and lower jaws; and C. youngorum having 43 teeth in the upper jaw and more than 31 teeth in the lower jaw. ==Classification==

Phylogeny The exact placement of Cymbospondylus within Ichthyosauria is poorly understood with its position varying between different studies, sometimes being recovered as more and sometimes as less derived than mixosaurids. However it is agreed upon that Cymbospondylus is a rather basal member of the clade. Early phylogenies placed Cymbospondylus within Shastasauridae. In the analysis of Bindellini et al. (2021), Cymbospondylus is placed at the very base of Ichthyosauria, outside the more derived members of Hueneosauria (including Mixosauridae and Shastasauridae). In the publication describing C. duelferi, Klein and colleagues recovered that all species from the Fossil Hill Member in Nevada form a clade with one another. The description of C. youngorum further supports this Nevadan clade, recovering C. youngorum as its most derived member while C. buchseri from Europe sits at the base of the genus. Much like in the analysis by Bindellini and colleagues, shastasaurids and mixosaurids were recovered as more derived ichthyosaurs. Like in many analyses prior, the type species was not included in the dataset due to its questionable and fragmentary nature. This causes Cymbospondylus to have a very convoluted taxonomy, with it being suggested that the type species should be neglected. The 2020 study reviewed the skull morphology of C. nichollsi and found the species to be valid, as the skull morphology accords with that of C. petrinus but is distinct enough to be separate, such as the upper temporal fenestra shape being oval in C. nichollsi but triangular in C. petrinus. In their phylogenetic analysis the authors did not recover a definite placement for C. buchseri, leading them to state that further study was needed to determine whether the Swiss species belonged to the genus. The following cladogram shows the position of Cymbospondylus within the Ichthyosauria after Sander et al., (2021): }} Evolution Ichthyosaurs form one of the major groups of marine reptiles that flourished during a large part of the Mesozoic, between approximately 248 and 90 million years ago, i.e. during the end of the Lower Triassic until approximately the beginning of the Upper Cretaceous. Appearing in the early temporal stages of this group, Cymbospondylus is therefore one of the oldest representatives to have been identified to date. However, despite its age, the genus shows that certain ichthyosaurs adopted a rapid increase in size throughout their evolution. Indeed, the oldest known representatives of ichthyosauriforms (a group that includes ichthyosaurs, their ancestors and related lineages), such as Cartorhynchus, have a skull measuring long, while the largest known species of Cymbospondylus, C. youngorum, has a skull up to about long, and yet these two taxa are only separated by about 2.5 million years. To compare with the evolution of a group of similar tetrapods, namely the cetaceans, between Pakicetus, which has a skull width of , and Basilosaurus, to which the latter has a skull width of , between 10 and 14 million years ago. A similar case is also observed in the subgroup of odontocetes, because between Simocetus, which has a skull wide of , and Livyatan, which has a skull wide of approximately , approximately more than 25 million years ago. This rapid increase in size among ichthyosaurs could have been favored by the rapid diversification of conodonts and ammonites after the Permian–Triassic extinction event. The evolution of large eyes would subsequently have considerably reduced the large measurements in ichthyosaurs, because they helped better identify their source of food. ==Palaeobiology==

Massare & Callaway (1990) propose that many Triassic ichthyosaurs including Cymbospondylus may have been ambush predators. They argue that the long neck and torso would create drag in water while the laterally-flattened tail lacking the lunate fluke of later ichthyosaur taxa was more suited for an undulating swimming style. In their research they suggest that the elongated flexible bodies of early ichthyosaurs were built to support an undulating swimming style while the powerful tail would provide bursts of speed, both of which they cite as being possible adaptations to ambush prey. Massare & Callaway put this in contrast with Jurassic taxa, known for their compact, dolphin-like bodies adapted for more continuous swimming favorable to pursuit predators. A strikingly similar bauplan was later obtained by two other large bodied marine amniote groups, mosasaurs and archaeocete whales. Direct evidence for its diet exists for the medium-sized Cymbospondylus buchseri from Switzerland, which was found with its stomach contents exclusively consisting of hooks belonging to soft-bodied coleoid cephalopods. However, this does not exclude the possibility that C. buchseri could have taken larger prey, as its last meal may not reflect its typical diet accurately. Bindellini and colleagues suggest that C. buchseri may have employed a more forceful feeding strategy with a slower feeding cycle and a higher biteforce, supported by the animal's robust rostrum. In the Besano Formation, Cymbospondylus would have coexisted with two other smaller ichthyosaurs, the more gracile skulled Besanosaurus and small mixosaurs. Whether or not C. buchseri would have gone after large vertebrate prey, all three taxa display clear adaptations for different hunting strategies and prey preferences, however the details of their ecologies are not yet fully understood. For C. youngorum a generalist diet of squid and fish is inferred based on the blunt and conical teeth in combination with the elongated rostrum. However, as with C. buchseri, Sander et al. entertain the possibility that C. youngorum could have fed on large-bodied vertebrates as well, including the other Cymbospondylus species of the region. Bindellini and colleagues notes that shastasaurid diversity may have profited from the extinction of Cymbospondylus, such as the Carnian of China, known to have supported three ecologically different shastasaurids but no examples of cymbospondylids, which had gone extinct by that time. Reproduction The holotype of C. duelferi preserves three small strings of articulated vertebrae located within the trunk region of the specimen. These vertebrae, which are only a third the size of the adult specimen, have been interpreted to represent the remains of three fetuses, with one specimen specifically facing towards the rear end of the putative mother. Following this interpretation, Cymbospondylus would have given live birth to a minimum of three offspring. ==Paleoecology==

North America '' All North American species of Cymbospondylus are known from fossils found in two geologic formations in the Star Peak Group, located in Nevada. C. petrinus, C. nichollsi, C. duelferi and C. youngorum are known from the Favret Formation, but the first named species is the only known representative of the genus who have been identified in the Prida Formation. while among the sarcopterygians, numerous specimens of indeterminate coelacanthids are known. The most abundant marine reptiles of the Fossil Hill Member are the ichthyosaurs, including Cymbospondylus itself, Omphalosaurus, Phalarodon and the large Thalattoarchon. Few other marine reptiles are known from the Fossil Hill Member, the only clearly identified being the sauropterygian Augustasaurus. Europe . The only currently known specimen of C. buschseri is recorded from the Besano Formation, also known as the Grenzbitumenzone in Switzerland. This formation is located in the Alps and extends from southern Switzerland to northern Italy, containing numerous fossils dating from between the end of the Anisian and the beginning of the Ladinian. However, water circulation within the lagoon was poor, resulting in typically anoxic water at the bottom, deprived of oxygen. Many gastropods are known from the Besano Formation; predominantly those that could have lived as plankton or on algae. Many bony fish have been recorded in this formation, with actinopterygians being quite diverse, including abundant small species as well as larger representatives like Saurichthys. Unlike the Fossil Hill Member in Nevada, ichthyosaurs do not represent the most diverse marine reptiles in the Besano Formation, the latter being limited only to Besanosaurus, C. buchseri, Phalarodon and Mixosaurus, their abundance in the middle part of this zone correlating with the time when the lagoon was deepest. as well as pachypleurosaurs and nothosaurids. The pachypleurosaur Odoiporosaurus is known from the middle Besano Formation, while the particularly abundant Serpianosaurus did not appear until the upper portion of the formation, where ichthyosaurs are becoming rarer. Nothosaurids include the genera Silvestrosaurus and Nothosaurus, the latter notably including N. giganteus and possibly N. juvenilis. While rare, N. giganteus may have been an apex predator like C. buschseri. and the thalattosaurians Askeptosaurus, Clarazia and Hescheleria. Niche partitioning In both the Fossil Hill Member and the Besano Formation, Cymbospondylus is one of a variety of ichthyosaurs. The different species known would have had different feeding strategies to avoid competition. Due to its large and sharp teeth, Thalattoarchon would probably have been the only apex predator with which Cymbospondylus was contemporary, probably attacking smaller marine reptiles, or even juveniles. Besanosaurus would likely have specialized in feeding on coleoids, based on the shape and small size of its teeth. The stomach contents of Mixosaurus cornalianus show the remains of small coleoids and fish, suggesting that it would have gone after smaller prey than its larger relatives. The rarer mixosaurids Mixosaurus kuhnschnyderi and Phalarodon both possess broad crushing teeth. M. kuhnschnyderi is understood to have consumed coleoids, while the larger teeth of Phalarodon may have been suited for crushing prey items with external shells. Omphalosaurus was probably a bulk feeder specialized in grinding up ammonites. ==Extinction==

In 2021, Gabriele Bindellini and colleagues note that shastasaurid diversity may have benefited from the extinction of Cymbospondylus, as shown in the Carnian fossil record of China, known to have three ecologically different shastasaurids, but no examples of cymbospondylids, being extinct at this time. ==Notable appearances in media==

A Cymbospondylus is present in the 2003 BBC docufiction Sea Monsters, and more precisely in a sequence featuring various marine reptiles of the Triassic. In the only scene in which it appears, the latter grabs by surprise a torn tail of a Tanystropheus, until then held by Nigel Marven, before the animal appears threatening towards the presenter. ==See also==