Plesiosuchus
| Plesiosuchus | ||||||||||||
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Holotype of Plesiosuchus in side view |
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| Temporal occurrence | ||||||||||||
| Upper Jurassic (Upper Kimmeridgian to Lower Tithonian ) | ||||||||||||
| 154.7 to 147.7 million years | ||||||||||||
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| Scientific name | ||||||||||||
| Plesiosuchus | ||||||||||||
| Owen , 1884 | ||||||||||||
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Plesiosuchus ( Greek plesios = "near" and Suchos = " Sobek ") was a genus of large metriorhynchids from the Upper Jurassic of Western Europe .
The holotype consists of an incomplete skull with an isolated right joint leg . Other fossils are parts of the lower jaw , isolated teeth , a humerus and a large number of ribs and vertebrae .
description
Plesiosuchus resembled other metriorhynchids, also known as "sea crocodiles". They had developed paddle-shaped limbs and a caudal fin . Furthermore, they were the only crocodylomorpha that completely adapted to life in the sea .
The skull of Plesiosuchus is only preserved in fragments, the skull, the rostrum and the lower jaw are present. The snout was long and narrow, there are a total of six teeth on the premaxillary , 13 on the maxilla and 14 teeth on the lower jaw . The largest specimen has an estimated skull length of 125.5 cm and was probably just under seven meters long. Thus it reached similar dimensions as the pliosaur Liopleurodon ferox , a top predator from the English Oxford Clay Formation .
According to Delfino and Dal Sasso (2006), in Thalattosuchia (and other Crocodylomorpha) it is possible to determine whether an animal was already fully grown by merging the cervical vertebrae. However, since the vertebrae of Plesiosuchus are too poorly preserved to see this merger, it cannot be determined whether the fossils belonged to an adult or subadult animal.
Systematics
Plesiosuchus fossils have been assigned to different genera throughout history, including Steneosaurus and Dakosaurus .
Young et al. (2012) showed through a phylogenetic analysis and a more precise description of the fossils that Plesiosuchus is to be regarded as an independent genus and belongs to the subfamily Geosaurinae together with Dakosaurus , Torvoneustes and Geosaurus . In the most recent analyzes, Plesiosuchus is the sister genus of Suchodus . Together they form the subtribe Plesiosuchia.
Abbreviated cladogram according to Foffa et al . (2017)
| Metriorhynchidae |
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Paleoecology and Nutrition
Plesiosuchus shared its habitat with other large marine reptiles, especially the geosaurine Dakosaurus maximus . Although closely related to each other, the two species differ in terms of the structure of the skull and a consequent diet. Dakosaurus maximus is characterized by a robust snout, which was adapted to the stress of turning and bending, the teeth at the base of the tooth crown were also adapted to high pressure , the tips are often broken or splintered. Plesiosuchus manselii, on the other hand, was larger overall and had a less robust snout with mostly intact tooth crowns. The "optimum gape" (the angle of the open mouth at which the prey comes into contact with most of the teeth) in P. manselii was 24 ° larger than that of D. maximus (19 °).
Young et al. deduce from this that D. maximus was a generalist who suckled smaller prey, but whose mouth was also designed to eat larger prey by tearing off smaller pieces of their body, while P. manselii specialized in prey that was its "optimum." gape "corresponded. Due to the high "optimum gape" and the overall larger body, the prey of Plesiosuchus were probably larger on average than those of Dakosaurus maximus . The authors compare these results with the feeding behavior of North Atlantic killer whales . Here, too, two types of "freshening" are known. The first is smaller and feeds by sucking up fish, and occasionally seals. Type 2 is larger and specializes in eating other whales .
Other carnivorous marine reptiles from the former habitat of Plesiosuchus were the similarly large ichthyosaur Brachypterygius and the giant Pliosaurus macromerus . The different adaptations in feeding behavior and prey spectrum made it possible that these different large predators could coexist in the same habitat.
Find history
The holotype of Plesiosuchus comes from the bay of Kimmeridge , a village in the English county of Dorset . It was found there in the 1860s by John Clavell Mansel-Pleydell in a reef after it was exposed by low tide . Mansel-Pleydell gave the fossils to the British Museum in 1866 .
literature
- Mark T. Young, Stephen L. Brusatte, Marco Brandalise de Andrade, Julia B. Desojo, Brian L. Beatty, Lorna Steel, Marta S. Fernández, Manabu Sakamoto, Jose Ignacio Ruiz-Omeñaca, Rainer R. Schoch : The Cranial Osteology and Feeding Ecology of the Metriorhynchid Crocodylomorph Genera Dakosaurus and Plesiosuchus from the Late Jurassic of Europe. In: PLoS ONE . Vol. 7, No. 9, 2012, e44985, doi : 10.1371 / journal.pone.0044985 .
Web links
Individual evidence
- ↑ Foffa, D., Young, MT, Brusatte, SL, Graham, MR, & Steel, L. (2017). A new metriorhynchid crocodylomorph from the Oxford Clay Formation (Middle Jurassic) of England, with implications for the origin and diversification of Geosaurini. Journal of Systematic Palaeontology, 1-21, doi : 10.1080 / 14772019.2017.1367730