Helveticosaurus
| Helveticosaurus | ||||||||||
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The holotype of Helveticosaurus-Zollingeri in the Paleontological Museum Zurich |
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| Temporal occurrence | ||||||||||
| Middle Triassic ( Anisium to Ladinium ) | ||||||||||
| 242 million years | ||||||||||
| Locations | ||||||||||
| Systematics | ||||||||||
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| Scientific name | ||||||||||
| Helveticosaurus | ||||||||||
| Peyer , 1955 | ||||||||||
| Art | ||||||||||
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Helveticosaurus is a fossil genus of aquatic reptiles . Helveticosaurus was a short-snouted reptile with long, pointed teeth and an elongated body. All finds come from the bitumen layers of the Swiss Monte San Giorgio , whichare dated tothe Central Triassic Anisian or Ladinian and are therefore around 242 million years old. Helveticosaurus inhabited a shallow shelf sea, where it possibly preyed on fish and mollusks . His body was adapted to life in the water, but also made it possible to go ashore.
The only species in the genus, Helveticosaurus Zollingeri , was discovered in the 1930s in Ticino , Switzerland and described by Bernhard Peyer in 1955 . He assigned them to the Placodont animals , but meanwhile Helveticosaurus is considered to be an archosauromorph with unclear family relationships.
features
Helveticosaurus zoellingeri was approximately 2 m long. The species had a short skull that looked compressed by its high snout. The lower jaw, which probably corresponded in length to the entire skull, measured around 21.5 cm. The jaws were set with long, slightly curved teeth. The teeth were blunt at the tip and had no sharp edges. In the front part of the upper jaw, H. zollingeri had a clearly elongated tooth that is reminiscent of the canine teeth of predators . The teeth were changed from the outside to the inside, a variant that is rather the exception among reptiles and is otherwise only known from ichthyosaurs , snakes and crocodiles . Helveticosaurus Zollingeri had at least 40 vertebrae lying in front of the sacrum . The ribs of the chest increased in size from front to back, the tail had ribs at least at the base. No reliable statements can be made about the robust shoulder girdle of the species, as it has not been handed down in the fossils found so far, or only in very fragmented form. Comparisons with Placodus gigas made earlier are probably not sustainable. The interclaviculum was about 130 mm wide, the collarbones were about the same length. The shoulder blades were arranged approximately at right angles to the interclaviculum and about 190 mm high. The hip bones were not particularly strong for an animal of this size. The tarsus and wrist were severely reduced. Both the front and the rear feet reported additional phalanges ( Hyperphalangie ) to: The Phalangenformel the forefeet was at least 2-3-4-6-3, so they had over the original Phalangenformel the Archosauromorpha (2-3-4-5- 4) at least one additional link. The hyperphalangia was even more pronounced in the hind feet, here the second toe had at least five, the four outermost toes together at least 19 limbs, which means three or more additional limbs compared to the original formula. The feet were probably transformed into fins.
Locations and stratigraphy
All Helveticosaurus finds come from the Besano Formation of Monte San Giorgio on the southern shore of Lake Lugano . This layer, also known as the border bitumen zone, originates from the transition between the ending anisium and the beginning Ladinium and is estimated to be around 242 million years old. Bernhard Peyer ruled out a spread beyond this location, since localities of similar age and facies are rare worldwide and finds elsewhere are unlikely for this reason.
Way of life
The development of additional toes in Helveticosaurus is typical of aquatic tetrapods and indicates an aquatic way of life and locomotion of Helveticosaurus . Its habitat was a shelf sea of Tethys . Since the skeleton showed neither a particular adaptation to rowing nor to undulating movements, Helveticosaurus probably moved with a mixture of both types. The robust shoulder girdle indicates that the species occasionally went ashore, where the front extremities in particular carried the weight of the body. Strong muscles, especially in the neck, enabled the animals to lift their heads above the ground on land. Bernhard Peyer suspected that Helveticosaurus went ashore to lay eggs. He interpreted his tooth shape as an adaptation to a predatory diet. Sharks and cartilaginous organoids , but above all mollusks such as belemnites, came into question as prey .
Taxonomy and research history
Find history and description
From helveticosaurus previous three fossils were discovered. The first specimen was found in 1933 in the Arnaldo gallery in the Cava Tre Fontane , where the bitumen from the found layer was then industrially mined. This first fossil comprised a relatively complete but highly fragmented skeleton of Helveticosaurus . The disorder under the fossil bones mainly arose before the sedimentation of the carcass through decomposition processes. Later tectonic and strata pressure forces contributed to further deformation after fossilization. The carrier rock of the fossils - dolomite - proved to be difficult to prepare, which is why the scientific description of the find dragged on. Two years later, another fossil was found in the same place, which was far better preserved: the bone arrangement was largely intact, but the skull was shattered and the rear end of the animal's tail was missing. The Swiss paleontologist Bernhard Peyer chose this fossil as the holotype for his first description , but had to revise it again when a snout fragment of the same species came to light during an excavation in 1937. After a complex preparation, a piece of the maxillary bone with a number of teeth could be reconstructed.
In 1955 the first description of the genus Helveticosaurus and the type species Helveticosaurus zoellingeri appeared under the title The Triassic Fauna of the Ticino Limestone Alps. XVIII. Helveticosaurus zoellingeri ngn sp. A year later it was also published in volume 72 of the Swiss Palaeontological Treatises . Peyer chose Helveticosaurus as a generic name to express the Swiss origin of the reptile ( Helvetia ). The specific epithet Zollingeri honors Walter Zollinger, the President of the Board of Trustees of the Georges-and-Antonia-Claraz Donation, which had contributed significantly to the scientific exploration of Monte San Giorgio since 1924.
Systematics
Bernhard Peyer classified Helveticosaurus in his first description as a very basic (original) representative of the Placodontia , a group within the fin lizard (Sauropterygia). Peyer established a new subordination within the Placodontia, the "Helveticosauroidea", which Helveticosaurus contained as the only representative. Current studies come to the conclusion that this genus is unlikely to be assigned to the placodontia. Instead, it could be an early and unusual representative of the Archosauromorpha .
Sources and References
literature
- Roland Mundil, József Pálfy, Paul R. Renne, Peter Brack: The Triassic Time Scale: New Constraints and a Review of Geochronological Data. In: Spencer G. Lucas (Ed.): The Triassic Timescale (= The Geological Society, London. Special Publication. No. 334.) Geological Society, London 2010, ISBN 978-1-86239-296-0 , doi : 10.1144 /SP334.3 , pp. 41-60.
- Darren Naish: Fossils Explained 48: Placodonts. In: Geology Today. Vol. 20, No. 4, July-August 2004, doi : 10.1111 / j.1365-2451.2004.00470.x , pp. 153-158.
- Bernhard Peyer : The Triassic Fauna of the Ticino Limestone Alps. XVIII. Helveticosaurus Zollingeri, ngnsp. In: Swiss palaeontological treatises. Vol. 72, 1956, pp. 3-50.
- Olivier Rieppel : Helveticosaurus Zollingeri Peyer (Reptilia, Diapsida): Skeletal Paedomorphosis, Functional Anatomy and Systematic Affinities. In: Palaeontographica. Department A: Paleozoology, Stratigraphy. Vol. 208, Lfg. 4/6, 1989, ISSN 0375-0442 , pp. 123-152.
Web links
- Helveticosaurus Zollingeri is weird on scienceblogs.com
Individual evidence
- ↑ Peyer 1955 , p. 46.
- ↑ Peyer 1955 , p. 41.
- ↑ Rieppel 1989 , pp. 123-138.
- ↑ Peyer 1955 , p. 47.
- ↑ Mundil et al. 2010 , p. 52.
- ↑ Peyer 1955 , pp. 47-48.
- ↑ Rieppel 1989 , pp. 143-147.
- ↑ Peyer 1955 , p. 48.
- ↑ Peyer 1955 , p. 31.
- ↑ Peyer 1955 , pp. 4-37.
- ↑ Peyer 1955 , pp. 3-4.
- ↑ Naish 2004 , p. 158.