Besanosaurus
| Besanosaurus | ||||||||||||
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Besanosaurus leptorhynchus fossil |
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| Temporal occurrence | ||||||||||||
| Middle Triassic | ||||||||||||
| 235 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Besanosaurus | ||||||||||||
| Dal Sasso , 1996 | ||||||||||||
Besanosaurus is a genus of ichthyosaurs (Ichthyopterygia, Ichthyosauria) from the Central Triassic of Europe, which is part of the Shastasauria . Only one species ( type species ) has been scientifically described , Besanosaurus leptorhynchus .
Find history
The Besano - Monte San Giorgio area in northern Italy near the border with Switzerland is a well-known deposit for fossils from the Central Triassic. The bituminous layers of dolomite and slate contain a large number of fish and aquatic reptiles . The Besano formation is particularly rich in ichthyosaurs, almost all of which belong to the Mixosaurus genus .
During an excavation of the Museo Civico di Storia Naturale di Milano ("Municipal Museum of Natural History of Milan") under the direction of Cristiano Dal Sasso , the fossils of Besanosaurus leptorhynchus were found in the quarry Sasso Caldo northeast of Besano . The skeleton of the so far only specimen ( holotype ) of this species is almost completely preserved and is shown in the Natural History Museum in Milan after several years of excavation and preparation work .
Naming
The genus name is derived from the location Besano and the animal's strikingly narrow snout (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 intermediate jaw bone (premaxilla), the elongated neck region, the nearly circular in cross-section cervical vertebra, the heavy and robust abdominal ribs (Gastralia) and the number of presacral (before the sacrum located) vertebral identify him as a shastasaur.
The total number of vertebrae (60 presacral vertebrae, 2 sacral vertebrae and 139 tail vertebrae) is unusually high. There is no other known Shastasaur with such a high number of tail vertebrae, the tail length makes up 51.5% of the total length. The estimated length of the front fins is 70 centimeters, 10 centimeters longer than that of the hind fins.
The dentition is thecodont and homodont , the conical and serrated teeth are comparatively small, the longest measuring 8 millimeters. Dal Sasso therefore suspects that Besanosaurus ate small cephalopods , which he caught but could not chew.
A radiological examination has shown that there are four embryos in the body of this specimen . In teutophage ichthyosaurs with their narrow rostrum , cannibalism is very unlikely to be the cause of the fossil association, therefore it is assumed that this specimen was a pregnant female and that Besanosaurus , like the other ichthyosaurs, was viviparous .
The described properties justify the introduction of the new genus Besanosaurus with the only known species Besanosaurus leptorhynchus .
Web links
- Besanosaurus in Gigadino (French)
- Stuttgart contributions to natural history (English; PDF; 2.2 MB)
- Model of the Besanosaurus in the Natural History Museum of Milan (Italian)