Besanosaurus

Fossil of Besanosaurus leptorhynchus

• Besano (Italy )

Besanosaurus is a genus of ichthyosaur ( Ichthyopterygia, Ichthyosauria ) from the Middle Triassic of Europe, which will be provided to Shastasauria. There was only one type ( type species ) scientifically described Besanosaurus leptorhynchus.

Fund history

The Besano Monte San Giorgio area in northern Italy near the border with Switzerland is a known deposit of fossils from the Middle Triassic. The bituminous dolomite and shale layers involve a variety of fish and aquatic reptiles. The Besano lineup is particularly rich in ichthyosaurs, almost all belong to the genus Mixosaurus.

During an excavation of the Museo Civico di Storia Naturale di Milano ( " Urban Natural History Museum of Milan" ), headed by Cristiano Dal Sasso Sasso Caldo were in the quarry north-east of Besano 1993 found the fossils of Besanosaurus leptorhynchus. The skeleton of the previously single specimen ( holotype ) of this kind is almost unchanged and will be shown after several years of excavation and preparation work in the Natural History Museum in Milan.

Naming

The genus name is derived from the locality Besano and the strikingly narrow snout of the animal from (Greek: leptos narrow, rhynchos = snout ).

Features of the holotype

The holotype has a length of 5.80 meters. The other skeletal structures, in particular the shape of the upper jaw ( maxilla ) and the premaxillary bone ( premaxilla ), the extended neck region, the nearly circular in cross-section cervical vertebrae, the heavy and robust belly ribs ( Gastralia ) and the number of presacral ( located in front of the sacrum) vortex show him to be Shastasaurier.

The total number of vertebrae ( 60 Präsakralwirbel, 2 sacral vertebrae and tail vertebrae 139 ) is unusually high. There is no other Shastasaurier with such a high number of caudal vertebrae known, the tail length makes 51.5 % of the total length of. The estimated length of the front fins is 70 centimeters by 10 centimeters longer than that of the rear fins.

The dentition is thekodont and homodont, the cone-shaped and grooved teeth are comparatively small, the longest measures 8 millimeters. Dal Sasso presumed, therefore, that Besanosaurus of small cephalopods malnourished, but he grabbed could not chew.

A radiological examination showed that in the body of this specimen are four embryos. In teutophagen ichthyosaurs with its narrow rostrum Cannibalism as the cause of the fossil association very unlikely, therefore, it is assumed that it has acted in this specimen to a pregnant female and Besanosaurus as the other ichthyosaurs, has been viviparous.

The properties described leptorhynchus justify the introduction of the new genus Besanosaurus with the so far only known type Besanosaurus.