| Simosaurus | |
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| Mounted skeleton ofSimosaurus gaillardoti in theState Museum of Natural History Stuttgart | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Superorder: | †Sauropterygia |
| Order: | †Nothosauroidea |
| Family: | †Simosauridae Huene, 1948 |
| Genus: | †Simosaurus Meyer, 1842 |
| Type species | |
| †Simosaurus gaillardoti Meyer, 1842 | |
| Synonyms | |
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Simosaurus is anextinctgenus ofmarine reptile within thesuperorderSauropterygia from theMiddle Triassic of central Europe. Fossils have been found in deposits inFrance andGermany that are roughly 230 million years old. It is usually classified as anothosaur,[1] but has also been considered apachypleurosaur or a more primitive form ofsauropterygia.
Simosaurus grew from 3 to 4 metres (9.8 to 13.1 ft) in length. It has a blunt, flattened head and large openings behind its eyes called upper temporal fossae. These fossae are larger than the eye sockets but not as big as those of other nothosaurs.Simosaurus also differs from other nothosaurs in that it has blunt teeth that were probably used for crushing hard-shelled organisms. The jaw joint is set far back, projecting beyond the main portion of the skull.[2]
Thetype species ofSimosaurus,S. gaillardoti, was named by German paleontologistChristian Erich Hermann von Meyer in 1842.[1] In the same year, von Meyer also namedS. mougeoti. He named a third species,S. guilelmi, in 1855. Oscar Fraas namedS. pusillus in 1881. A year later, however, it was reassigned to its own genus,Neusticosaurus.[3]S. mougeoti andS. guilelmi have more recently been considered junior synonyms ofS. gaillardoti, meaning that they represent the same species.[2]
The first fossils ofSimosaurus, those described by von Meyer, were found inLunéville, France.[1] These were found in the upperMuschelkalk, which dates back to theLadinian stage of the Middle Triassic. Material found in France includes theholotype skull ofS. gaillardoti and a partial mandible referred toS. mougeoti. Both were described by von Meyer. The skull, which served as the basis for the first description ofSimosaurus, has since been lost. Although initially attributed toSimosaurus, the mandible was labeled as "Nothosaurus mougeoti" in one of von Meyer's later papers.
Additional remains ofSimosaurus were found inFranconia andWürttemberg in Germany.Duke William of Württemberg discovered a complete skull and sent it to von Meyer in 1842. Von Meyer namedS. guilelmi on the basis of this skull, noting that it was smaller and narrower than those of the type species. A complete skeleton first referred toS. guilelmi has been designated theneotype ofSimosaurus. Some German fossils have been found in the stratigrafically youngerKeuper deposits, but are very rare.Simosaurus is present in biozones of the Muschelkalk that are distinguished by differentammonite fauna.Simosaurus first appears in thenodosus biozone, where fossils of the ammoniteCeratites nodosus are abundant. Specimens becomescommon in the slightly youngerdorsoplanus biozone, characterized by the ammoniteCeratites dorsoplanus.[2]
Simosaurus has well-developed vertebrae and a dorsoventrally flattened trunk that would have inhibited side-to-side movement. This movement, called lateral undulation, is seen in most other nothosaurs, includingNothosaurus. Thehumerus has well-developed crests and the underside of the pectoral girdle is large, suggesting that the forelimbs had a powerful downstroke and provided most of the thrust required for swimming. Thescapula is relatively small for a reptile that swims with its limbs, indicating that the upstroke ofSimosaurus was weak.Simosaurus was probably a moderately powerful swimmer with a locomotion that was transitional between the lateral undulation of early sauropterygians and the strong flipper-driven swimming of plesiosaurs.[2]
Because it has blunt teeth,Simosaurus is often thought to have beendurophagous, meaning that it ate organisms with hard shells. Durophagous reptiles usually have deep jaws and large adductor muscles that close them, butSimosaurus had long, slender jaws and relatively small adductor muscles. The long jaw ofSimosaurus more closely resembles those of reptiles that have snapping bites. Long jaw muscles attach to the front of the large temporal fossae in the top of the skull and slant down to the back end of the lower jaw. These long, slanted muscles exert a forward pull on the jaw, quickly snapping it shut. Smaller muscles are located farther back in the skull, attaching to the back portion of the temporal fossae. These muscles are shorter because they are angled vertically and the skull is very low along the vertical axis. Their close proximity to the jaw joint, however, allows for more crushing power to be exerted. The combination of muscles that quickly snap the jaw shut and muscles that provide crushing power at the back of the jaw is unique toSimosaurus. It probably fed on moderately hard-shelled organisms such asCeratites andholostean fish.[2]
Authority control databases: National |
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