Gronausaurus
| Gronausaurus | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Lower Cretaceous ( Berriasium ) | ||||||||||||
| 139.3 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Gronausaurus | ||||||||||||
| Hampe , 2013 | ||||||||||||
| Art | ||||||||||||
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Gronausaurus is a genus of plesiosaurs (Plesiosauria). The approximately 3 m long representatives of their only species , Gronausaurus wegneri , lived in the early Lower Cretaceous (139.3 mya ) in the Lower Saxony basin. The fossil material on which the genus is based comes from the Bückeberg Formation in northwest Germany , where it was found in a brick pit in 1910. The genus was first described in 2013 by Oliver Hampe and placedin the Leptocleididae on the basis of a phylogenetic analysis of the skeletal elements.
features
Gronausaurus wegneri was a relatively small plesiosaur about 3 m long. Its skeleton is distinguished by several diagnostic features. So the sides of the parasphenoid end just before the bulbs at the bottom of the eye sockets . The vertebral bodies of the species are slightly procoel, that is, concave on the front and convex on the back. The second to fourth thoracic vertebrae and the anterior vertebrae have fossae below the lateral vertebral processes . They probably served as a stabilization against the pulling movements of the muscles rotatores et levatores . At its distal end, the humerus has a contact point for a third forearm bone. Overall, all epipodal elements (that is, belonging to the forearm and tibia) are longer than they are wide.
Fossil Material, Distribution, and Stratigraphy
The only fossil specimen of the genus Gronausaurus , a partially preserved skeleton with skull fragments, vertebrae, ribs and parts of the swimming apparatus, was found in 1912 in a brick pit near Gronau . The locality was part of the northwestern Tethys in the early Cretaceous and was located in a shallow shelf sea . Today it is part of the Bückeberg Formation , the age of the find layer is dated to the outgoing Berriasium (139.3 mya ).
ecology
Various shark species ( Hybodus , Egertonodus , Lonchidion , Lissodus ), the bowfin Caturus , the bony fish Lepidotes , the pycnodontiforms Coelodus and Sphaerodus and the Pholidophoriforms Ionoscopus and Callopterus were found in the same locality as Gronausaurus . In addition, the turtle Desmemys bertelsmanni , the dinosaur Hylaeosaurus and a crocodile tooth have come down to us. The presence of Corbula clams in Fuschschicht points to a brackish towards environment.
Systematics
The skeleton found in 1912 initially attracted little attention from paleontologists . Theodor Wegner examined the skeleton and briefly noticed in 1914 that the fossil showed clear differences to the Brancasaurus found at the same time in Gronau , but did not go into detail. Paul Siegfried presented it in 1961 in an investigation into the Brancasaurus , which was also found in Gronau in 1912 ; it subsequently remained in the Geomuseum Münster under the inventory number GMM-A3B.2 . It was only at the beginning of the 21st century that Oliver Hampe had the fossils brought to the Natural History Museum in Berlin and subjected them to an overhaul. Although he recognized a similarity between the specimen and Brancasaurus , he emphasized that the differences in the skeleton made it necessary to place the examined specimen in its own genus. He established the genus Gronausaurus with the species Gronausaurus wegneri for the fossils. The generic name means "Gronau lizard" and refers to the place where it was found, the species name honors Theodor Wegner.
A phylogenetic analysis carried out by Hampe identified Gronausaurus as a sister taxon of Brancasaurus and located both within the Leptocleididae . Accordingly, the genera originate from a late Jurassic radiation of the Cryptoclidia .
swell
literature
- Oliver Hampe: The forgotten remains of a leptocleidid plesiosaur (Sauropterygia: Plesiosauroidea) from the Early Cretaceous of Gronau (Münsterland, Westphalia, Germany). In: Paleontological Journal . Vol. 87, No. 4, 2013, pp. 473-491, doi : 10.1007 / s12542-013-0175-3 .