Cymbospondylus (meaning "cupped vertebrae") is an extinct genus of large ichthyosaurs, of which it is among the oldest representatives, that lived from the Lower to 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 to the Fossil Hill Member 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.
As an ichthyosaur, Cymbospondylus had flippers for limbs and a fin on the tail. Like other non-parvipelvian ichthyosaurs, Cymbospondylus has a very slender profile, unlike later ichthyosaurs which have a morphology similar to those of dolphins. The different species of Cymbospondylus vary greatly in size, with the smallest reaching around in length. The largest known species, C. youngorum, is estimated over long, making Cymbospondylus one of the largest ichthyosaurs identified to date, but also one of the largest animals known of its time. The animal has a skull with a long, thin snout, proportionally small eye sockets, an elongated trunk, and a less pronounced tail than in later ichthyosaurs. The teeth are conical and pointed, having longitudinal ridges, indicating a diet of fishes and cephalopods, and possibly other marine reptiles for larger species.
Unlike cetaceans, Triassic ichthyosaurs like Cymbospondylus show that they reached large sizes very quickly after their appearance, probably because of the adaptive radiation of their prey, conodonts and ammonites, after the Permian–Triassic extinction. The size of ichthyosaurs began to decrease later, notably due to the increase in the size of their eyes, which were very useful for spotting prey. All established species of Cymbospondylus are known from the fossil records of Nevada and Switzerland, with referred specimens without specific affiliations having nevertheless been discovered in Idaho, the rest of the Alps and Spitsbergen, an island in Norway. The formations where the recognized species were discovered show that Cymbospondylus lived in marine ecosystems alongside molluscs like bivalves and ammonites, bony fishes like Saurichthys and coelacanths, cartilaginous fishes like hybodonts, and marine reptiles like sauropterygians and other ichthyosaurs. The different ichthyosaurs from these localities would have used different feeding strategies to avoid competition.
Research history Discovery and identification
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 holotype of C. piscosus is a block containing five incomplete dorsal vertebrae that was discovered in the New Pass Range, northwest of the city of Austin. Leidy attributes two other specimens to the species, one being a series of eight caudal vertebrae discovered at Star Canyon in the Humboldt Range, and the other being a single vertebra, probably also caudal, discovered in the Toiyabe Range, in the Reese River, northeast of Austin. The second species is C. petrinus, named from five large dorsal vertebrae discovered in the Humboldt Range. 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.
Between 1901 and 1907, the University of California sent ten expeditions across different corners of the United States to recover as many ichthyosaur fossils as possible dating from the Triassic, in order to be analyzed in more detail. These same expeditions were led by Merriam and were almost all financed by Annie Montague Alexander. The research finally collected more than fifty specimens, each preserving a significant portion of their skeletons. Among these fossils are several specimens of excellent quality from C. petrinus, including an almost complete skeleton, cataloged as UCMP 9950, all discovered in the origin locality mentioned by Leidy. Like the other ichthyosaurs mentioned in the work, Merriam describes the taxon in more depth based on new known fossil material. Merriam's anatomical descriptions of C. petrinus are still recognized as viable, and are even used in comparative anatomy in later studies of the genus Cymbospondylus, thus lending validity to the species.
Unlike C. petrinus, no additional fossils of the type species C. piscosus have been discovered. In Merriam's works, the latter recognized C. piscosus as distinct on the basis of its smaller size and by the regularly concave faces of the vertebrae of the holotype specimen. Only later did the validity of C. piscosus begin to be questioned, with authors mentioning the questionable nature of the fossils. In their work published in 2003, Christopher McGowan and Ryosuke Motani assert that the fossil vertebrae attributed to C. piscosus do not present distinctive characteristics to prove its validity. This would therefore pose a taxonomic problem, because if the type species turns out to be a nomen dubium, the genus to which it is classified will also be. To try to resolve this problem, the two authors suggest that the most complete known skeleton of C. petrinus (UCMP 9950) could be designated as a neotype of C. piscosus. However, as no formal ICZN appeal has been established to date, the name C. petrinus for the proposed neotype should be retained until further notice. Therefore, C. piscosus is not included in most descriptions of the genus, although it is still recognized as the type species.
Recognized species In 1927, a partial skeleton of a large ichthyosaur was discovered in the Grenzbitumenzone Member at the Monte San Giorgio fossil site in Switzerland and was mentioned by Bernhard Peyer in 1944. 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.
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. In their description, Fröbisch and his colleagues consider that an almost complete skull attributed to C. petrinus, cataloged as UCMP 9913, could in fact belong to C. nichollsi, because it presents similar characteristics. However, as the specimen has been relatively little described in the scientific literature, the authors do not know whether it would show intraspecific variations within C. petrinus, judging therefore that a more in-depth description is necessary. Subsequent studies carried out on the genus Cymbospondylus nevertheless always refer specimen UCMP 9913 to C. petrinus, but still mentioning some notable differences.
In 2011, a notable new Cymbospondylus fossil was also discovered in the Augusta Mountains, then exhumed three years later in 2014. This discovery was a partial skeleton that was briefly mentioned in a 2013 in a secondary article describing the large contemporary ichthyosaur Thalattoarchon, as well as in a 2018 histological study, where it is among the specimens analyzed. 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.
In 1998, still in the Augusta Mountains, Sander discovered another notable specimen of Cymbospondylus, and exhumed it with his colleagues between 2014 and 2015. After preparation of the fossils, the specimen, cataloged as LACM DI 157871, consists of a large complete skull, some cervical vertebrae, the right humerus as well as fragments of the shoulder girdle. It was in 2021, one year after the identification of C. duelferi, that a new species of the genus was named from this specimen in Science by Sander and his colleagues. This species, C. youngorum, is named in honor of Tom and Bonda Young, these latter having financially supported the fossil exhumation project.
Specimens that may belong to the genus Many other more partial specimens of Cymbospodylus have been discovered in various geological formations in Europe, but their specific attribution cannot be determined, the latter are then referred to under the name Cymbospondylus sp. in the scientific literature. Three of these specimens, including one from Idaho, and two from the Norwegian archipelago of Svalbard, are dated to the Olenekian stage of the Lower Triassic, making them the oldest known representatives of the genus. Below, the list of specimens that could potentially belong to Cymbospondylus:
In 1980, Kuhn-Schnyder described an anterior partial skeleton of an ichthyosaur discovered at Monte Seceda, Italy. The described specimen was first referred by the author to Shastasaurus sp., before being referred to Cymbospondylus in the official description of C. buchseri by Sander in 1989, an attribution which seems to still be recognized today.