left, 220px, '' Pachypleurosaurus'' Pachypleurosauria is an extinct clade of primitive

sauropterygia Sauropterygia ("lizard flippers") is an extinct taxon of diverse, aquatic reptiles that developed from terrestrial ancestors soon after the end-Permian extinction and flourished during the Triassic before all except for the Plesiosauria became ...

n reptiles that vaguely resembled aquatic lizards, and were limited to the

Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

period. They were elongate animals, ranging in size from , with small heads, long necks, paddle-like limbs, and long, deep tails. The limb girdles are greatly reduced, so it is unlikely these animals could move about on land. The widely spaced peg-like teeth project at the front of the jaws, indicating that these animals fed on

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...

. In the species ''

Prosantosaurus ''Prosantosaurus'' is a monotypic genus of pachypleurosaurian sauropterygian containing the single species ''Prosantosaurus scheffoldi'' discovered in Canton Grison of Switzerland. The genus is named after the Prosanto Formation near the Duc ...

'', it was observed that they fed on small fishes and crustaceans which they devoured entirely and that its teeth regrew after they broke off. This was the first observation of tooth replacement in a European pachypleurosaur, the only other discovery of such an event was made in China.

Classification

Pachypleurosaurs were originally and are often still included within the Nothosauroidea (Carroll 1988, Benton 2004). In some more recent

cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

classifications, however, (Rieppel 2000), they are considered the sister group to the Eosauropterygia, the clade that includes the

nothosaur Nothosaurs (order Nothosauroidea) were Triassic marine sauropterygian reptiles that may have lived like seals of today, catching food in water but coming ashore on rocks and beaches. They averaged about in length, with a long body and tail.F. ...

s and plesiosaurs. In the 2023

description Description is the pattern of narrative development that aims to make vivid a place, object, character, or group. Description is one of four rhetorical modes (also known as ''modes of discourse''), along with exposition, argumentation, and narra ...

of ''

Luopingosaurus ''Luopingosaurus'' (meaning "Luoping lizard") is an extinct genus of pachypleurosaurid sauropterygian from the Middle Triassic Guanling Formation of Yunnan Province, China. The genus contains a single species, ''L. imparilis'', known from a wel ...

'', Xu ''et al''. found support for a similar hypothesis, recovering Pachypleurosauroidea as the sister taxon to the

Eusauropterygia Sauropterygia ("lizard flippers") is an extinct taxon of diverse, aquatic reptiles that developed from terrestrial ancestors soon after the end-Permian extinction and flourished during the Triassic before all except for the Plesiosauria became ...

, a clade which contains both Nothosauroidea and

Pistosauroidea Pistosauroidea is a group of marine reptiles within the superorder Sauropterygia that first appeared in the latter part of the Early Triassic and were the ancestors of plesiosaurs. Pistosauroids are rare in Triassic marine assemblages, and are re ...

. The results of their

phylogenetic analyses In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

are shown in the

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

below:

Sources

* Benton, M. J. (2004), ''Vertebrate Paleontology'', 3rd ed. Blackwell Science Ltd * Carroll, R.L. (1988), ''Vertebrate Paleontology and Evolution'', WH Freeman & Co. * Rieppel, O., (2000), Sauropterygia I, placodontia, pachypleurosauria, nothosauroidea, pistosauroidea: In: Handbuch der Palaoherpetologie, part 12A, 134pp. Verlag Dr. Friedrich Pfei
Table of contents

References

External links

- Palaeos Triassic sauropterygians {{paleo-reptile-stub