Helveticosaurus
| Helveticosaurus Temporal range: Middle Triassic | |
|---|---|
 | |
| Fossil at Paleontology Museum of Zurich | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauromorpha (?) |
| Genus: | †Helveticosaurus Peyer, 1955 |
| Type species | |
| †Helveticosaurus zollingeri Peyer, 1955 (type) | |
Helveticosaurus is an unusual extinct genus of diapsid reptile. Fossils have been found from Monte San Giorgio, Switzerland, an area well known for its rich record of marine life during the Middle Triassic.
Description and paleobiology
Helveticosaurus was about 2 meters long from snout to tail.[1] It possessed many features that were adaptations to a marine lifestyle in the shallow-sea environment that existed in Europe 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 thalattosaurs, 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.[2]
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 iguana. It was seen as a basal member of the clade, being representative of a new superfamily, the Helveticosauroidea.[3] However it is unlikely that Helveticosaurus is a placodont.[4] 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 sauropterygians 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.
Possible relatives
Pelvic material from SVT 203, found from older Early Triassic strata in Spitsbergen, may share similarities with the pelvic material known from Helveticosaurus.[5] 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,[6] but the pubis, femur, metatarsals, and phalanges suggest that it is not from an ichthyopterygian, 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.
References
- ↑ http://palaeos.com/vertebrates/archosauromorpha/helveticosauridae.html
- ↑ Naish, D. (2008). "One of so many bizarre Triassic marine reptiles." Weblog entry. Tetrapod Zoology. 13 September 2008. Accessed 24 July 2009.
- ↑ Peyer, B. (1955). Die Triasfauna der Tessiner Kalkalpen. XVIII. Helveticosaurus zollingeri, n.g. n.sp. Schweizerische Paläontologische Abhandlungen 72:3-50.
- ↑ Rieppel, O. (1989). Helveticosaurus zollingeri Peyer (Reptilia, Diapsida): skeletal paedomorphosis; functional anatomy and systematic affinities. Palaeontographica A 208:123-152.
- ↑ Motani, R. (2000). Skull of Grippia longirostris: no contradiction with a diapsid affinity for the Ichthyopterygia. Palaeontology 43:1-14.
- ↑ Mazin, J.-M. (1981). Grippia longirostris Wiman, 1929, un Ichthyopterygia primitif du Trias inférieur du Spitsberg. Bulletin du Muséum National d’Histoire Naturelle 4:317–340.
External links
- Helveticosaurus in the Paleobiology Database
- Tetrapod Zoology post on Helveticosaurus