Proterosuchidae

Proterosuchidae is an early family of basal archosauriforms whose fossils are known from the Late Permian and the Early Triassic. The highest diversity of genera is known from European Russia, but fossils are also known from South Africa, India, China, Australia, Brazil and possibly Argentina. The name comes from Greek πρότερο- ("first") and σοῦχος ("crocodile").

Description
They were slender, medium-sized (about  long, largest specimens reached ), long-snouted and superficially crocodile-like animals, although they lacked the armoured scutes of true crocodiles, and their skeletal features are much more primitive. The limbs are short and indicate a sprawling posture, like contemporary lizards but unlike most later archosaurs.

Their most characteristic feature is a distinct down-turning of the premaxilla (the front of the upper jaw, which overhangs the lower jaw).

Evolutionary history
The terminal Permian catastrophe, which killed off 95% of all types of life, cleared the world of all large therapsids and allowed the proterosuchids to become the top predators.  Within the space of five million years the proterosuchids had evolved to fill a wide variety of terrestrial and semi-aquatic niches. The proterosuchids represent perhaps the earliest adaptive radiation of the archosaurs. They gave rise to the Erythrosuchidae some time in the Early Triassic.

A 2023 study recovered a majority of proterosuchids outside of Proterosuchus and Sarmatosuchus as belonging to a distinct subfamily, the Chasmatosuchinae, defined as "the most inclusive clade containing Chasmatosuchus rossicus, but not Proterosuchus fergusi, "Chasmatosaurus" yuani, Proterosuchus alexanderi, Proterosuchus goweri, Erythrosuchus africanus, or Alligator mississippiensis (the American alligator)". Chasmatosuchinae contains many Triassic proterosuchids in addition to the only Permian proterosuchid, Archosaurus; this would suggest that an initial taxonomic diversification of the Proterosuchidae (including an initial taxonomic divergence between Proterosuchus and chasmatosuchines) had already occurred in the Permian.

Classification

Phylogeny
Recent studies consider Proterosuchidae to be at least a partially paraphyletic grouping, meaning that it does not form a true clade with a single common ancestor and proterosuchids as its only descendants. Instead, they are a chain of successively basal archosauriforms.Ezcurra, M.D. (2016). The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ, e1778  Proterosuchidae sensu stricto is defined as "all taxa more closely related to Proterosuchus fergusi than to Erythrosuchus africanus, Crocodylus niloticus (the Nile crocodile), or Passer domesticus (the house sparrow). Below is a cladogram from Ezcurra (2016), that reexamined all historical members of the "Proterosuchia" (a polyphyletic historical group including proterosuchids and erythrosuchids). The placement of fragmentary taxa that had to be removed to increase tree resolution are indicated by dashed lines (in the most derived position that they can be confidently assigned to). Taxa that are nomina dubia are indicated by the note "dubium". Bold terminal taxa are collapsed. Ezcurra (2016) recovered a monophyletic Proterosuchidae containing only Archosaurus and the species of Proterosuchus, however some species (e.g. Chasmatosuchus spp, Vonhuenia friedrichi) are too fragmentary to resolve whether they also fall into Proterosuchidae. Tasmaniosaurus, Fugusuchus, Sarmatosuchus, Cuyosuchus and the "Long Reef proterosuchid" (SAM P41754) on the other hand were recovered confidently outside of Proterosuchidae.

The following phylogeny for the Proterosuchidae sensu stricto was recovered by Ezcurra et al (2023):

Genera
 Genus Status Age Location Description ImagesAnkistrodon nomen dubium Early Triassic India  
Archosaurus Valid Late Permian, Changhsingian Russia  200pxBlomosuchus nomen dubium Early Triassic, Induan RussiaChasmatosuchus Valid Early Triassic Russia 200px GamosaurusValidEarly TriassicRussiaJaikosuchusValidEarly TriassicRussiaKoilamasuchusDisputedMiddle - Late TriassicArgentina 
Proterosuchus Valid Early Triassic South Africa 200pxSamsarasuchusValidEarly TriassicIndiaSarmatosuchusDisputedEarly TriassicRussiaframeless|198x198pxTsylmosuchusValidEarly TriassicRussiaVonhuenia Valid Early Triassic, Induan Russia

 References 

Further reading
 Benton, M. J. (2000), Vertebrate Paleontology, 2nd Ed.; (2004) 3rd edition Blackwell Science Ltd
 Carroll, R. L. (1988), Vertebrate Paleontology and Evolution, WH Freeman & Co.

 External links 

 Proterosuchidae  
 Proterosuchidae - list of species (Mikko's Phylogeny Archive)


Category:Prehistoric reptile families
Category:Lopingian first appearances
Category:Early Triassic extinctions
Category:Taxa named by Friedrich von Huene