Sphenosuchia

Sphenosuchians Temporal range: Late Triassic - Late Jurassic, 228–150 Ma PreЄ Є O S D C P T J K Pg N
Life restoration of Hesperosuchus agilis
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	Crocodylomorpha
Informal group:	Sphenosuchia von Huene, 1942
Genera
See below
Synonyms
Pedeticosauria Walker, 1968

Sphenosuchia is a suborder of basal crocodylomorphs that first appeared in the Triassic and occurred into the Late Jurassic. 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 crocodilians.

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) in age.^[1] 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 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).^[2] 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.^[1] 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).^[3] Sphenosuchians are marked by the green bracket.

Crocodylomorpha   CM 73372  Hesperosuchus   Dromicosuchus   Sphenosuchus   Dibothrosuchus   Terrestrisuchus   Litargosuchus   Kayentasuchus   Crocodyliformes   Orthosuchus  Protosuchus  Alligator

Sphenosuchians

Genera

Genus	Status	Age	Location	Unit	Notes	Images
Barberenasuchus	Valid	Late Triassic	Brazil	Santa Maria Formation	A putative sphenosuchid;[4] alternatively, it could be a rauisuchian.[5]
Dibothrosuchus	Valid	Early Jurassic	China	Lower Lufeng Series
Dromicosuchus	Valid	Late Triassic	USA	Newark Supergroup
Dyoplax[6]	Valid	Late Triassic (Carnian)	Germany	Schilfsandstein Formation	A possible sphenosuchian;[6] alternatively, it could be an erpetosuchid.[7]
Hallopus	Valid	Late Jurassic	USA	Morrison Formation	Possible synonym of Macelognathus
Hesperosuchus	Valid	Late Triassic (Carnian)	USA	Chinle Formation
Junggarsuchus	Valid	Middle Jurassic	China	Shishugou Formation
Kayentasuchus	Valid	Early Jurassic (Sinemurian - Pliensbachian)	USA	Kayenta Formation
Litargosuchus	Valid	Early Jurassic	South Africa	Elliot Formation
Macelognathus	Valid	Late Jurassic	USA	Morrison Formation
Parrishia	Nomen dubium	Late Triassic	USA	Dockum Group	An indeterminate sphenosuchian known only from undiagnostic vertebrae[8]
Phyllodontosuchus[9]	Valid	Early Jurassic	China	Lower Lufeng Series
Pseudhesperosuchus	Valid	Late Triassic (Norian)	Argentina	Los Colorados Formation
Redondavenator	Valid	Late Triassic	USA	Redonda Formation
Saltoposuchus	Valid	Late Triassic (Norian)	Germany   Switzerland  UK	Löwenstein Formation Trossingen Formation Lossiemouth Sandstone
Sphenosuchus	Valid	Early Jurassic	South Africa	Elliot Formation
Terrestrisuchus	Valid.	Late Triassic	UK
Trialestes	Valid	Late Triassic	Argentina	Ischigualasto Formation	Known specimens may represent basal crocodylomorphs and dinosaurs[8]

References

1. Clark, J.M., et al. (2004).A Middle Jurassic 'sphenosuchian' from China and the origin of the crocodylian skull Nature 430:1021-1024.
2. Clark, J.M., and Sues, H.-D. (2002). Two new species of basal crocodylomorphs and the status of the Sphenosuchia. Zoological Journal of the Linnean Society 136:77−96.
3. Nesbitt, S.J. (2011). "The early evolution of archosaurs: relationships and the origin of major clades" (PDF). Bulletin of the American Museum of Natural History 352: 1–292. doi:10.1206/352.1.
4. Mattar, L.C.B. 1987. Descrição osteólogica do crânio e segunda vértebrata cervical de Barberenasuchus brasiliensis Mattar, 1987 (Reptilia, Thecodontia) do Mesotriássico do Rio Grande do Sul, Brasil. Anais, Academia Brasileira de Ciências, 61: 319–333.
5. Kischlat, E.-E. (2000). "Tecodôncios: a aurora dos arcossáurios no Triássico". In Holz, M.; and De Ros, L.F. (eds.). Paleontologia do Rio Grande do Sul. Porto Alegre: CIGO/UFRGS. pp. 273–316.
6. Lucas, S. G.; Wild, R.; Hunt, A. P. (1998). "Dyoplax O. Fraas, a Triassic sphenosuchian from Germany". Stuttgarter Beiträge zur Naturkunde, B 263: 1–13.
7. Michael W. Maisch, Andreas T. Matzke, Thomas Rathgeber (2013). "Re-evaluation of the enigmatic archosaur Dyoplax arenaceus O. Fraas, 1867 from the Schilfsandstein (Stuttgart Formation, lower Carnian, Upper Triassic) of Stuttgart, Germany". Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 267 (3): 353–362. doi:10.1127/0077-7749/2013/0317.
8. Clark, J. M.; Sues, H.-D.; Berman, D. S. (2001). "A new specimen of Hesperosuchus agilis from the Upper Triassic of New Mexico and the interrelationships of basal crocodylomorph archosaurs". Journal of Vertebrate Paleontology 20 (4): 683–704. doi:10.1671/0272-4634(2000)020[0683:ANSOHA]2.0.CO;2.
9. Harris, Jerald D.; Lucas, Spencer G.; Estep, J. W.; Jianjun Li (2000). "A new and unusual sphenosuchian (Archosauria: Crocodylomorpha) from the Lower Jurassic Lufeng Formation, People's Republic of China". Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 215 (1): 47–68.