Sphenosuchia is a grouping of basal crocodylomorphs that first appeared in the Triassic and persisted into the Jurassic. Most were small, gracile animals with an erect limb posture. Although sometimes recovered as a monophyletic group, they are now generally thought to represent various early offshoots of the lineage leading to Crocodyliformes, with some sphenosuchians more closely related to crocodyliforms than to other "sphenosuchians", rendering the group paraphyletic.
Stratigraphic range
The earliest known members of the group (i.e. Hesperosuchus) are early Norian 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 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 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 modified from Nesbitt (2011). Sphenosuchians are marked by the green bracket.
Genera Genus Status Age Location Unit Notes Images Dibothrosuchus Valid Early Jurassic Lower Lufeng Series Dromicosuchus Valid Late Triassic Newark Supergroup Dyoplax Valid Late Triassic (Carnian) Schilfsandstein Formation A possible sphenosuchian; alternatively, it could be an erpetosuchid. Hesperosuchus Valid Late Triassic (Carnian) Chinle Formation Junggarsuchus Valid Middle Jurassic Shishugou Formation Kayentasuchus Valid Early Jurassic (Sinemurian - Pliensbachian) Kayenta Formation Litargosuchus Valid Early Jurassic Elliot Formation Parrishia Nomen dubium Late Triassic Dockum Group An indeterminate sphenosuchian known only from undiagnostic vertebraePhyllodontosuchus Valid Early Jurassic Lower Lufeng Series Pseudhesperosuchus Valid Late Triassic (Norian) Los Colorados Formation Redondavenator Valid Late Triassic Redonda Formation Saltoposuchus Valid Late Triassic (Norian) Löwenstein Formation Trossingen Formation Lossiemouth Sandstone Sphenosuchus Valid Early Jurassic Elliot Formation Terrestrisuchus Valid. Late Triassic Trialestes Valid Late Triassic Ischigualasto Formation
References