Superregnum: Eukaryota
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Cladus: Craniata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Superclassis: Tetrapoda
Cladus: Reptiliomorpha
Cladus: Amniota
Classis: Reptilia
Cladus: Eureptilia
Cladus: Romeriida
Subclassis: Diapsida
Ordo: †Ichthyosauria
Familia: †Cymbospondylidae
Genus: †Cymbospondylus
Species: †C. buchseri – †C. duelferi – †C. nichollsi – †C. petrinus – †C. piscosus
Species inquirendae: †C. germanicus – †C. grandis – †C. natans – †C. nevadanus – †C. parvus
Name
Cymbospondylus Leidy, 1868
Type species: Cymbospondylus piscosus
References
Maisch, M.W. 2010. Phylogeny, systematics, and origin of the Ichthyosauria — the state of the art. Palaeodiversity 3: 151–214. PDF ResearchGate Reference page.
Klein, N., Schmitz, L., Wintrich, T. & Sander, P.M. 2020. A new cymbospondylid ichthyosaur (Ichthyosauria) from the Middle Triassic (Anisian) of the Augusta Mountains, Nevada, USA. 2020. Journal of Systematic Palaeontology 18(4): 1–25. DOI: 10.1080/14772019.2020.1748132 ResearchGate Reference page.
Links
Cymbospondylus – Taxon details on Fossilworks.
Vernacular names
日本語: キンボスポンディルス
한국어: 킴보스폰딜루스
ไทย: ซิมโบสปอนไดลัส
Cymbospondylus (a Greek word meaning "boat vertebrae") was a basal early ichthyosaur that lived between the early and middle Triassic period (249-237 million years ago). Previously, the genus was classified as a shastasaurid, however, more recent work finds it to be more basal.[1] Cymbospondylus was a cosmopolitan genus found in Nevada, Europe (Switzerland, Germanic Basin) and Spitsbergen.[2] The largest species of Cymbospondylus may have reached lengths of 17 m (56 ft).
History
Skull illustration of Cymbospondylus petrinus by John C. Merriam (1908)
Cymbospondylus was described from Nevada by Joseph Leidy in 1868 on the basis of several fragmentary vertebrae which he assigned to two different species: C. piscosus (the type species) and C. petrinus.[3] The University of California,under the direction of John C. Merriam and funded by Annie Alexander, conducted extensive fieldwork in the region in the late nineteenth and early twentieth century, following the description of Cymbospondylus, recovering additional fossil material of C. petrinus in particular. The fragmentary nature of the type species however presented itself to be a problem later, as research published in the early 2000s indicated that the remains that form C. piscosus are not diagnostic. Although it has been suggested that a nearly complete specimen of C. petrinus should serve as a neotype in order to preserve the already well-established name, no formal appeal has been made as of yet.[3]
Fossils discovered in Switzerland were described as Cymbospondylus buchseri based on an almost complete anterior skeleton including the skull, pectoral girdle and flippers as well as an uniterupted series of 51 presacral vertebrae with associated ribs by P. Martin Sander.[4] Cymbospondylus nichollsi (after curator Dr Elizabeth L. Nicholls) was named by Fröbisch and colleagues in 2006[3] and Cymbospondylus duelferi (after preparator Olaf Dülfer) was named in 2020 by Nicole Klein and colleagues.[5] In 2021, a new species designated C. youngorum was described by P. Martin Sander and colleagues based on remains discovered in 1998 and excavationed in 2014 and 2015. Previously known by the name Jim 2,[6] its skull is close to 2 meters long with an estimated body length of up to 17 meters, making it the largest member of the genus. The species name "youngorum" was chosen to honor Tom and Bonda Young of Great Basin Brewery, Nevada, for supporting the project financially.[7]
As a historic genus dating to the late 19th century, many species have been assigned to Cymbospondylus only to be declared synonymous with already existing species or altogether undiagnostic. These include C. germanicus, C. parvus, C. nevadanus and C. grandis (originally Chonespondylus).[3] Cymbospondylus natans, originally named by Merriam in 1908, was eventually recovered as a member of Mixosaurus[8] and then synonymized with Phalarodon nordenskioeldii.[9] In a similar fashion, remains from China had been named Cymbospondylus asiaticus in 2002, but were later assigned to the shastasaurid Guizhouichthyosaurus tangae[3]
Description
Cymbospondylus was a medium to large sized animal, some species of the genus reaching enormous proportions. Unlike later groups of ichthyosaurs, Cymbospondylus had an elongated, more cylindrical body. The skull of Cymbospondylus is overall wedge-shaped and tapering evenly towards the tip of the snout. Most of the rostrum is made from the premaxilla and nasal bones, as typical in ichthyosaurs. The robustness varies between the species, with C. youngorum having the most massive. The eyes in Cymbospondylus are relatively small for an ichthyosaur and appear to not have grown in relation to the body size increase observed in the genus. Most species in the genus, with the exception of C. youngorum and C. nichollsi, have a very pronounced sagittal crest. The dentition differs between the species, with C. duelferi possessing less than 21 teeth per each side of the jaw, C. petrinus 30 - 35. C. youngorum possesses the most teeth with over 40 per ramus. However, the teeth of C. youngorum are much smaller and lack the cutting edges of the teeth seen in Thalattoarchon, a similarilly sized ichthyosaura from the same region and exact horizon.[7]The caudal fluke of Cymbospondylus was positioned at a relatively shallow angle, unlike the lunate caudal fin typical for the derived ichthyosaurs of the Jurassic and Cretaceous such as Ophthalmosaurus.[10] It is currently unknown of Cymbospondylus had a dorsal fin similar to those seen in more derived taxa. The earliest occurance of a dorsal fin has been observed in Mixosaurus, commonly recovered as more derived than Cymbospondylus.[7]
Life reconstruction of Cymbospondylus petrinus
Size
C. duelferi and C. buchseri are among the smallest Cymbospondylus species, reaching lengths of 4.3–5 m (14–16 ft)[5][7] and 5.5 m (18 ft)[11] meters respectively. Both C. nichollsi and C. petrinus are notably larger, with estimated total body lengths of 7.6 m (25 ft) and 9.1 m (30 ft).[3] When calculating body length based on the humerus rather than the skull length, C. petrinus may have even reached a length of 12.5 m (41 ft).[7] The largest species is C. youngorum, with the holotype skull of LACMDI 15787 measuring a total of 1.89 m (6.2 ft) (1.97 m (6.5 ft) for the lower jaw length). Based on the size of the humerus (the second largest humerus recorded in any ichthyosaur), C. youngorum may have reached a length of 17.65 m (57.9 ft) with a weight of 44,699 kg (98,544 lb).[7]
Evolution
Of particular interest is the rapid increase in body size undergone by ichthyosaurs early in their evolutionary history. Ichthyosaurs evolved from small (skull length 55 mm) ancestors such as Cartorhynchus to giant forms like C. youngorum in the span of only 2.5 million years. Cetaceans meanwhile, which originated under similar conditions (following the mass extinction at the end of the Cretaceous period eradicating much of marine tetrapod diversity) took notably longer to obtain similar sizes. Between Pakicetus (skull width 127 mm) and Basilosaurus isis (skull width 600 mm) a total of 10 to 14 million years passed, almost five times as much as between Cartorhynchus and Cymbospondylus youngorum. In toothed whales, the size increase likewise took notably longer with around 25 million years passing between the basal Simocetus and the massive Livyatan. In their 2021 study Sander, Griebeler, Schmiz and their colleagues determined that ichthyosaurs underwent rapid size increase early on in their evolutionary history, in particular among Cymbospondylus and early merriamosaurs, while whales obtained great sizes relatively slowly. Even when restricting the analysis to only observe the growth in members of Pelagiceti (fully aquatic whales) to account for the varying degrees of aquatic adaptations, cetaceans still reached large body sizes much slower than ichthyosaurs. Meanwhile, after this intial burst the overall size of ichthyosaurs slowed down significantly, while among crown group whales body sizes increased initially slowly before accelerating rapidly later in their history. Sander et al. (2021) suggests that this rapid increase in body size may have been favored by the swift recovery of conodonts and ammonites following the Permian–Triassic extinction event. They further suggests that the evolution of large eyes, a trait present in many ichthyosaurs, further assisted them in exploiting this food source efficiently.[7][12]
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.[13] However it is agreed upon that Cymbospondylus is a rather basal member of the clade. Early phylogenies placed Cymbospondylus within Shastasauridae.[1] 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).[11] 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.[5] 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. Like in many analyses prior, the type species was not included in the dataset due to its questionable and fragmentary nature. Much like in the analysis by Bindellini and colleagues, shastasaurids and mixosaurids were recovered as more derived ichthyosaurs.[7]
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Palaeobiology
Paleoecology
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.[10] A strikinly 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 it's 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.[11]
Examples of longirostrine ichthyosaurs of the Triassic, E) C. buchseri
For C. youngorum a generalist diet of squid and fish is infered 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.[7]
Cymbospondylus was especially diverse in the Fossil Hill Member of the Favret and Prida formations of Nevada, which preserves a pelagic environment from the middle to late Anisian (ca. 246 - 242 million years ago). The Fossil Hill Member specifically preserves some of the greatest ichthyosaur diversity recorded, with 8 distinct taxa present. This includes 4 species of Cymbospondylus, the early macropredatory Thalattoarchon, the small Phalarodon fraasi and P. callawayi as well as the poorly understood Omphalosaurus. Other animals present in the environment include a single sauropterygian, Augustasaurus hagdorni, halobiid bivalves but only few remains of fish. However this may be due to preservation bias. Despite this abundance of amniote fossils, analysis of the preserved ecosystem indicates that the Fossil Hill Member represents a stable food web largely dominated by said amniotes, occupying niches held by fish in modern marine ecosystems. Furthermore, the analysis conducted by Eva Maria Griebeler in the study of Sander and colleagues indicates the presence of an energy surplus, which may indicate the presence of an as of yet unknown animal in the Fossil Hill fauna or that this energy surplus may have been exploited by animals that evolved later. The ecosystem could have supported another giant marine reptile, assuming it were be a bulk feeder specialised on small prey that's lower in the food chain. Such an animal could have for example been a filter feeder, a nische not yet occupied by any animal in the fauna of the Fossil Hill Member.[7]
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.[11]
Reproduction
The holotype of C. duelferi preserves three small strings of articulated vertebrae located within the trunk region of the specimen.[5] 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.
See also
List of ichthyosaurs
Timeline of ichthyosaur research
References
Motani, R. 1999: Phylogeny of the Ichthyopterygia. Journal of Vertebrate Paleontology. 19 (3): 473 – 496
Sander, P. (1992). "Cymbospondylus (Shastasauridae: Ichthyosauria) from the Middle Triassic of Spitsbergen: filling a paleobiogeographic gap". Journal of Paleontology. 66 (2): 332–337. doi:10.1017/s0022336000033825.
Fröbisch, N.; Sander, P. M.; Rieppel, O. (2006). "A new species of Cymbospondylus (Diapsida, Ichthyosauria) from the Middle Triassic of Nevada and a re-evaluation of the skull osteology of the genus". Zoological Journal of the Linnean Society. 147 (515–538): 515–538. doi:10.1111/j.1096-3642.2006.00225.x.
Sander, P. M. (1989). "The large ichthyosaur Cymbospondylus buchseri, sp. nov., from the Middle Triassic of Monte San Giorgio (Switzerland), with a survey of the genus in Europe". Journal of Vertebrate Paleontology. 9 (2): 163–173. doi:10.1080/02724634.1989.10011750.
Nicole Klein; Lars Schmitz; Tanja Wintrich; P. Martin Sander (2020). "A new cymbospondylid ichthyosaur (Ichthyosauria) from the Middle Triassic (Anisian) of the Augusta Mountains, Nevada, USA". Journal of Systematic Palaeontology. 18 (14): 1167–1191. doi:10.1080/14772019.2020.1748132. S2CID 219078178.
"Ichthyosaur: New Discoveries". National History Museum Los Angeles County. Retrieved 10 January 2022. "... While dinosaurs dominated land during the Mesozoic Era (252-66 million years ago), marine reptiles like this giant ichthyosaur—nicknamed Jim 2—ruled the sea. Come see the complete skull on display for the very first time. ...'"
Sander, P.M.; Griebeler, E.M.; Klein, N.; Juarbe, J.V.; Wintrich, T.; Revell, L.J.; Schmitz, L. (2021). "Early giant reveals faster evolution of large body size in ichthyosaurs than in cetaceans". Science. 374 (6575): eabf5787. doi:10.1126/science.abf5787. PMID 34941418. S2CID 245444783.
Sander, P.M.; Bucher, H. (1990). "On the presence of Mixosaurus (Ichthyopterygia: Reptilia) in the Middle Triassic of Nevada". Journal of Paleontology. 64 (1): 161–164. doi:10.1017/S0022336000042396.
Callway, C.M. (1997). Ancient Marine Reptiles Chapter2: A New Look at Mixosaurus. Academic Press. pp. 45–59. doi:10.1016/B978-012155210-7/50005-3. ISBN 9780121552107.
Massare, J.A.; Callaway, JM (1990). "The affinities and ecology of Triassic ichthyosaurs". Geological Society of America Bulletin. 102 (4): 409–416. doi:10.1130/0016-7606(1990)102<0409:TAAEOT>2.3.CO;2.
Bindellini, G.; Wolniewicz, A.S.; Miedema, F.; Scheyer, T.M.; Dal Sasso, C. (2021). "Cranial anatomy of Besanosaurus leptorhynchus Dal Sasso & Pinna, 1996 (Reptilia: Ichthyosauria) from the Middle Triassic Besano Formation of Monte San Giorgio, Italy/Switzerland: taxonomic and palaeobiological implications". PeerJ. 9: e11179. doi:10.7717/peerj.11179. PMC 8106916. PMID 33996277.
Delsett, L. L.; Pyenson, N. D. (2021). "Early and fast rise of Mesozoic ocean giants". Science. 374 (6575): 1554–1555. doi:10.1126/science.abm3751. PMID 34941421. S2CID 245456946.
Michael W. Maisch (2010). "Phylogeny, systematics, and origin of the Ichthyosauria – the state of the art" (PDF). Palaeodiversity. 3: 151–214.
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