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Askeptosaurus is an extinct genus of aquatic reptile related to the thalattosaurian group. Their remains have been found in Italy and Switzerland.
Description[]
Askeptosaurus was a very thin, elongated creature, that probably swam like an eel. Its tail was very long, accounting for around half of the animal's total length of 2 metres (6.6 ft), and its webbed feet would have been well suited for steering itself through the water. Judging from its long jaws, it primarily ate fish.
Typical features of thalattosaurs are the elongated premaxilla and the relatively large snout, and a small or absent upper temporal fenestra. The cranial reconstruction of Askeptosaurus is consistent with the features previously listed: Askeptosaurus had a very slender and flattened skull. The snout was significantly elongated, the orbits were comparatively large, and the posterior skull table was deeply emarginated. The premaxilla of Askeptosaurus is almost half as long as the skull (maximum length is 26 cm (10.2 inches) among the investigated specimens) and forms more than one-third of the tooth row in the upper jaw. However, Askeptosaurus also had the following traits differ from the non-askeptosauroid thalattosaurs:
1. Lack of a fusion between postorbital and postfrontal.
2. Presence of a homogenous dentition.
3. Absence of a diastema and palatal dentition.
4. Presence of low neural spines.
5. Presence of a slender radius.
According to the research, the vertebrae of Askeptosaurus were amphicoelous with no sign of pachyostosis. Based on observations, Askeptosaurus possessed at least 38 presacral vertebrae, two sacral vertebrae, and more than 60 caudal vertebrae. There is double-headed rib articulation in the cervical region and single-headed articulation in the dorsal area, which gave the estimated number of cervical vertebrae at least 13. Sacral and caudal ribs are all significantly shorter than the dorsal ribs and have holocephalous heads.
The maximum length within the investigated specimens on femur is 13.8 cm (5.4 inches). The distal tarsals have different sizes. The largest element is confirmed to be distal tarsal 4. The latter articulates with metatarsals 4 and 5 distally, while the remaining distal tarsals meet the associated metatarsal. The phalangeal formula of the pes is 2-3-4-4-4.
History of discovery[]
Askeptosaurus and the species Askeptosaurus italicus were first used and described in a 1925 research done by Hungarian paleontologist Franz Nopcsa von Felső-Szilvás. Specific epithet "italicus" is an scientific adjective used to describe "Italian".
The most recent research on A. italicus is done by Dr. Johannes Müller in 2005. He used the fossils preserved by MSNM (Museo di Scienze Naturali Milano, Italy) and PIMUZ (Paläontologisches Institut und Museum der Universität Zürich, Switzerland) to distinguish A. italicus from its sister taxa Anshunsaurus.
Classification[]
Prior to 2005, fossils of Askeptosaurus were rare and the position of Askeptosaurus on the phylogenetic tree had been a heated debate between different research teams. Recent analyses corroborate Renesto's (1992)argument that Endennasaurus is more closely related to Askeptosaurus than to other thalattosaurs. It is now commonly agreed that a monophyletic group is formed by Anshunsaurus and Askeptosaurus. To be more specific, Askeptosaurus belongs to the family Askeptosauridae, a division of the suborder Askeptosauroidea. Within Askeptosauridae, Askeptosaurus is considered to be the sister taxon of Anshunsaurus, from Middle Triassic deposits in Guizhou, China. At present, the Askeptosauroidea is only known from the Alpine Triassic and southern China, and Askeptosaurus represents the oldest record for this clade.
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