Sphenosuchia is a suborder of basal crocodylomorphs that first appeared in the

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

and occurred into the

Middle Jurassic The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 161.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relativel ...

. Most were small, gracile animals with an erect limb posture. They are now thought to be ancestral to crocodyliforms, a group which includes all living

crocodilian Crocodilia () is an Order (biology), order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorp ...

Stratigraphic range

The earliest known members of the group (i.e. '' Hesperosuchus'') are early

Norian The Norian is a division of the Triassic geological period, Period. It has the rank of an age (geology), age (geochronology) or stage (stratigraphy), stage (chronostratigraphy). It lasted from ~227.3 to Mya (unit), million years ago. It was prec ...

in age, found in the Blue Mesa Member of the Chinle Formation. Only one sphenosuchian is currently known from the Middle Jurassic, '' Junggarsuchus'', from the Junggar Basin ( Shishugou Formation) of China during either the

Bathonian In the geologic timescale the Bathonian is an age (geology), age and stage (stratigraphy), stage of the Middle Jurassic. It lasted from approximately 168.2 ±1.2 annum, Ma to around 165.3 ±1.1 Ma (million years ago). The Bathonian Age succeeds ...

or the Callovian (~165 Ma) age,Clark, J.M., ''et al.'' (2004
A Middle Jurassic 'sphenosuchian' from China and the origin of the crocodylian skull
''Nature'' 430:1021-1024. and the Hallopodidae are known from the Late Jurassic of North America.

Phylogeny

The

monophyly In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent comm ...

of the group is debated, although several synapomorphies characterize the clade, including extremely slender limbs, a compact carpus and an elongate coracoid process. In 2002, Clark and Sues found a possible sphenosuchian clade of '' Dibothrosuchus'', '' Sphenosuchus'', and possibly '' Hesperosuchus'' and '' Saltoposuchus'', with several other genera in unresolved positions ('' Kayentasuchus'', '' Litargosuchus'', '' Pseudhesperosuchus'', and '' Terrestrisuchus''). More recently, however, Clark ''et al.'' (2004) argued for the paraphyly of the group, contending that morphological characters were secondarily lost in more highly derived crocodylomorphs. Further analysis and study is required before the group's monophyly is resolved with certainty — a perfect phylogenetic analysis is, at present, impossible due to a paucity of fossil remains demonstrating phylogenetically informative characters. Below is a

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

modified from Nesbitt (2011). Sphenosuchians are marked by the green bracket.

Genera

References

{{Taxonbar, from=Q132746 Terrestrial crocodylomorphs Triassic crocodylomorpha Jurassic crocodylomorphs Paraphyletic groups