Sphenosuchia

Taxobox
name = Sphenosuchians
fossil_range = Late Triassic - Late Jurassic

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image_width = 250px
image_caption = "Hesperosuchus"
regnum = Animalia
phylum = Chordata
classis = Sauropsida
subclassis = Diapsida
infraclassis = Archosauromorpha
superordo = Crocodylomorpha
subordo = †Sphenosuchia
subordo_authority =
subdivision_ranks = Families
subdivision =
* †Sphenosuchidae

Sphenosuchia is the name of a suborder of basal crocodylomorphs that first appeared in the Triassic and occurred into the Middle Jurassic. Most were small, gracile animals with an erect limb posture.

tratigraphic Range

The earliest known members of the group occur (i.e. "Hesperosuchus") in the Lower Petrified Forest member of the Chinle Formation, these specimens are Carnian in age. 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) in age.Clark, J.M., "et al." (2004). [http://www.nature.com/nature/journal/v430/n7003/full/nature02802.html A Middle Jurassic 'sphenosuchian' from China and the origin of the crocodylian skull] "Nature" 430:1021-1024.] The youngest sphenosuchian, "Macelognathus", is known from the Late Jurassic of North America during the Kimmeridgian, (155 - 150 Ma).

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 argued that the Spenosuchia formed a clade.Clark, J.M., and Sues, H.-D. (2002). [http://www.blackwell-synergy.com/doi/abs/10.1046/j.1096-3642.2002.00026.x Two new species of basal crocodylomorphs and the status of the Sphenosuchia.] "Zoological Journal of the Linnean Society" 136:77−96.] 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.

List of sphenosuchian genera

Because of the current uncertainty surrounding sphenosuchian monophyly, no phylogenetic tree is presented in the article; however, the genera currently classified as sphenosuchians are:

"Barbarenasuchus"
"Dibothrosuchus"
"Dromicosuchus"
"Dyoplax"
"Hallopus"
"Hesperosuchus"
"Junggarsuchus"
"Kayentasuchus"
"Litargosuchus"
"Macelognathus"
"Parrishia"
"Pedeticosaurus"
"Pseudhesperosuchus"
"Redondavenator"
"Saltoposuchus"
"Sphenosuchus"
"Terrestrisuchus"
"Trialestes"

References