Helveticosaurus
Encyclopedia
Helveticosaurus is an unusual extinct genus
of diapsid reptile
. Fossil
s have been found from Monte San Giorgio
, Switzerland
, an area well known for its rich record of marine life during the Middle Triassic
.
at the time when much of the continent was part of the Tethys Ocean
. The long, flexible tail is similar to what can be seen in other extinct marine reptiles such as thalattosaur
s, and it probably propelled itself through the water by means of lateral undulation. However, Helveticosaurus also possessed a robust pectoral girdle and forelimbs that were well adapted for paddle like propulsion as a supplementary method of locomotion, as seen in secondarily aquatic tetrapods. This unique combination of undulation and paddling is highly unusual for an aquatic reptile.
The caniniform teeth suggest a predatory lifestyle for Helveticosaurus. Unlike most other marine reptiles which exhibited a lengthening and narrowing of the skull, the head of Helveticosaurus was more robust and boxlike. It is unknown what purpose the shortness of the skull would have had in feeding.
. It was seen as a basal
member of the clade, being representative of a new superfamily
, the Helveticosauroidea. However it is unlikely that Helveticosaurus is a placodont. Only the dorsal vertebrae of Helveticosaurus, which are very similar to those of placodonts, suggest that it is a member of the order; the genus lacks many of the autapomorphies characteristic of sauropterygia
ns and thus evolved from a different ancestor, independently adapting a marine lifestyle.
Its affinities with other diapsids remain largely unknown, as it differs greatly from any other known taxa, with no apparent close relatives. It shares some characteristics with archosauromorphs
, and may be related to the clade if not a member of it.
strata in Spitsbergen
, may share similarities with the pelvic material known from Helveticosaurus. However, this is only if the anterior element of the pelvic girdle in Helveticosaurus is interpreted as the pubis. The pubis of SVT 203 also shares similarities with placodonts, although the ischium differs in lacking constriction. SVT 203 was once referred to the ichthyosaur
Grippia longirostris
, but the pubis, femur
, metatarsals, and phalanges suggest that it is not from an ichthyopterygia
n, therefore making it more probable that it belongs to a taxon related, and possibly ancestral, to Helveticosaurus, although more material is needed to give a definitive confirmation. The small size of material comprising SVT 203 in relation to Helveticosaurus, along with the compression seen on both ends of the femur, may indicate that it is a juvenile form of the species to which it belongs, but both temporal and geographical separation of SVT 203 with Helveticosaurus makes size comparison as a means of determining immaturity unnecessary, as it is possible that Helveticosaurus evolved from an ancestor that was smaller in overall size.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of diapsid reptile
Sauropsida
Sauropsida is a group of amniotes that includes all existing reptiles and birds and their fossil ancestors, including the dinosaurs, the immediate ancestors of birds...
. Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s have been found from Monte San Giorgio
Monte San Giorgio
Monte San Giorgio is a wooded mountain located in the south of canton Ticino in Switzerland. Monte San Giorgio became a UNESCO World Heritage Sites in 2003, because it "is the single best known record of marine life in the Triassic period, and records important remains of life on land as well."...
, Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
, an area well known for its rich record of marine life during the Middle Triassic
Middle Triassic
In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma...
.
Description and paleobiology
Helveticosaurus possessed many features that were adaptations to a marine lifestyle in the shallow-sea environment that existed in EuropeEurope
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
at the time when much of the continent was part of the Tethys Ocean
Tethys Ocean
The Tethys Ocean was an ocean that existed between the continents of Gondwana and Laurasia during the Mesozoic era before the opening of the Indian Ocean.-Modern theory:...
. The long, flexible tail is similar to what can be seen in other extinct marine reptiles such as thalattosaur
Thalattosaur
Thalattosaurs are a group of prehistoric marine reptiles which lived during the mid-late Triassic Period. Some species of thalattosaur grew to over 4 meters in length, including a long, flattened tail used in underwater propulsion...
s, and it probably propelled itself through the water by means of lateral undulation. However, Helveticosaurus also possessed a robust pectoral girdle and forelimbs that were well adapted for paddle like propulsion as a supplementary method of locomotion, as seen in secondarily aquatic tetrapods. This unique combination of undulation and paddling is highly unusual for an aquatic reptile.
The caniniform teeth suggest a predatory lifestyle for Helveticosaurus. Unlike most other marine reptiles which exhibited a lengthening and narrowing of the skull, the head of Helveticosaurus was more robust and boxlike. It is unknown what purpose the shortness of the skull would have had in feeding.
Relationship with other sauropsids
Upon its naming and description in 1955, Helveticosaurus was classified as a member of the order Placodontia, a group of robust, barrel-bodied marine reptiles similar in lifestyle to the extant marine iguanaMarine iguana
The Marine Iguana is an iguana found only on the Galápagos Islands that has the ability, unique among modern lizards, to live and forage in the sea, making it a marine reptile. The Iguana can dive over 30 ft into the water. It has spread to all the islands in the archipelago, and is...
. It was seen as a basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
member of the clade, being representative of a new superfamily
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...
, the Helveticosauroidea. However it is unlikely that Helveticosaurus is a placodont. Only the dorsal vertebrae of Helveticosaurus, which are very similar to those of placodonts, suggest that it is a member of the order; the genus lacks many of the autapomorphies characteristic of sauropterygia
Sauropterygia
Sauropterygia were a group of very successful aquatic reptiles that flourished during the Mesozoic before they became extinct at the end of the era. They were united by a radical adaptation of their shoulder, designed to support powerful flipper strokes...
ns and thus evolved from a different ancestor, independently adapting a marine lifestyle.
Its affinities with other diapsids remain largely unknown, as it differs greatly from any other known taxa, with no apparent close relatives. It shares some characteristics with archosauromorphs
Archosauromorpha
Archosauromorpha is an infraclass of diapsid reptiles that first appeared during the late Permian and became more common during the Triassic. Included in this infraclass are the groups Rhynchosauria, Trilophosauridae, Prolacertiformes, Archosauriformes, and, tentatively, Choristodera...
, and may be related to the clade if not a member of it.
Possible relatives
Pelvic material from SVT 203, found from older Early TriassicEarly Triassic
The Early Triassic is the first of three epochs of the Triassic period of the geologic timescale. It spans the time between 251 ± 0.4 Ma and 245 ± 1.5 Ma . Rocks from this epoch are collectively known as the Lower Triassic, which is a unit in chronostratigraphy...
strata in Spitsbergen
Spitsbergen
Spitsbergen is the largest and only permanently populated island of the Svalbard archipelago in Norway. Constituting the western-most bulk of the archipelago, it borders the Arctic Ocean, the Norwegian Sea and the Greenland Sea...
, may share similarities with the pelvic material known from Helveticosaurus. However, this is only if the anterior element of the pelvic girdle in Helveticosaurus is interpreted as the pubis. The pubis of SVT 203 also shares similarities with placodonts, although the ischium differs in lacking constriction. SVT 203 was once referred to the ichthyosaur
Ichthyosaur
Ichthyosaurs were giant marine reptiles that resembled fish and dolphins...
Grippia longirostris
Grippia
Grippia is a genus of ichthyosaur, an extinct group of reptiles that resembled dolphins. Fossils have been found along the coasts of Greenland, China, Japan, and Canada; of Early Triassic age. These ichthyosaurs were small; they were 1 - 1.5 m in length...
, but the pubis, femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
, metatarsals, and phalanges suggest that it is not from an ichthyopterygia
Ichthyopterygia
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.Basal ichthyopterygians were...
n, therefore making it more probable that it belongs to a taxon related, and possibly ancestral, to Helveticosaurus, although more material is needed to give a definitive confirmation. The small size of material comprising SVT 203 in relation to Helveticosaurus, along with the compression seen on both ends of the femur, may indicate that it is a juvenile form of the species to which it belongs, but both temporal and geographical separation of SVT 203 with Helveticosaurus makes size comparison as a means of determining immaturity unnecessary, as it is possible that Helveticosaurus evolved from an ancestor that was smaller in overall size.
External links
- Helveticosaurus in the Paleobiology DatabasePaleobiology Database' is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms.-History:The Paleobiology Database was founded in 2000. It has been funded by the National Science Foundation and the Australian Research Council...
- Tetrapod Zoology post on Helveticosaurus