Sphenosuchidae
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Sphenosuchia is a
suborder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...
of basal
crocodylomorph Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. Extinct crocodylomorphs were considerably mor ...
s 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 Crocodyliformes is a clade of crurotarsan archosaurs, the group often traditionally referred to as "crocodilians". They are the first members of Crocodylomorpha to possess many of the features that define later relatives. They are the only pseudo ...
, 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 ...
s.


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 The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In ...
. Only one sphenosuchian is currently known from the Middle Jurassic, ''
Junggarsuchus ''Junggarsuchus'' () is an extinct genus of sphenosuchian crocodylomorpha, crocodylomorph from the Middle Jurassic, Middle or Late Jurassic period of China. The type species, type and only species is ''J. sloani''. The Genus, generic name of ''Ju ...
'', from the
Junggar Basin The Junggar Basin (), also known as the Dzungarian Basin or Zungarian Basin, is one of the largest sedimentary basins in Northwest China. It is located in Dzungaria in northern Xinjiang, and enclosed by the Tarbagatai Mountains of Kazakhstan in t ...
(
Shishugou Formation The Shishugou Formation ( zh, s=石树沟组, t=石樹溝組, p=Shíshùgōu Zǔ) is a geological formation in Xinjiang, China. Its strata date back to the Late Jurassic period. Dinosaur remains are among the fossils that have been recovered fro ...
) 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 In the geologic timescale, the Callovian is an age and stage in the Middle Jurassic, lasting between 165.3 ± 1.1 Ma (million years ago) and 161.5 ± 1.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the ...
(~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 In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to ...
characterize the clade, including extremely slender limbs, a compact
carpus In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known as the carpal ...
and an elongate
coracoid process The coracoid process (from Greek κόραξ, raven) is a small hook-like structure on the lateral edge of the superior anterior portion of the scapula (hence: coracoid, or "like a raven's beak"). Pointing laterally forward, it, together with the ...
. In 2002, Clark and Sues found a possible sphenosuchian clade of '' Dibothrosuchus'', '' Sphenosuchus'', and possibly '' Hesperosuchus'' and ''
Saltoposuchus ''Saltoposuchus'' is an extinct genus of small (1–1.5 m and 10–15 kg), long-tailed crocodylomorph reptile (Sphenosuchia), from the Norian (Late Triassic) of Europe. The name translated means "leaping foot crocodile". It has been propose ...
'', with several other genera in unresolved positions ('' Kayentasuchus'', ''
Litargosuchus ''Litargosuchus'' is a sphenosuchian crocodylomorph, a basal member of the crocodylomorph clade from the Early Jurassic of South Africa. Its genus name ''Litargosuchus'' is derived from Greek meaning "fast running crocodile" and its species name ...
'', '' Pseudhesperosuchus'', and ''
Terrestrisuchus ''Terrestrisuchus'' is an extinct genus of very small early crocodylomorph that was about long. Fossils have been found in Wales and Southern England and date from near the very end of the Late Triassic during the Rhaetian, and it is known by ty ...
''). 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