Erythrosuchidae

Erythrosuchidae (meaning "red crocodiles") are a family of large basal archosauriform carnivores that lived from the later Early Triassic (Olenekian) to the early Middle Triassic (Anisian).

Erythrosuchids Temporal range: Early - Middle Triassic, 249.7–237 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Skull of Erythrosuchus.
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Archosauriformes
Family:	†Erythrosuchidae Watson, 1917
Genera
see below

Naming

A family Erythrosuchidae was named by David Meredith Seares Watson in 1917.[1]

Description

They were the apex predators of their day, with lengths of 2.5 to over 5 meters. Their fossil remains are known to date from South Africa (Beaufort Group of the Karoo Basin), China, and European Russia, from the Early to Middle Triassic.

Erythrosuchids were unusually large and robust archosauromorphs. Several features set them apart from other archosauriformes and are also seen in later, more derived archosaurs. For example, they lack teeth on the palate, which are found in other early archosauriformes, such as Doswellia and euparkeriids. In erythrosuchids, the centra (central parts of vertebrae) are deeply indented on either side, differing considerably from the usual cylindrical shape of the centra in early archosauriformes, but similar to later archosaurs.[2]

The heads of erythrosuchids are generally large and deep. In all erythrosuchids, the lower margin of the premaxilla, the bone at the tip of the upper jaw, is lower than the lower margin of the maxilla, the bone behind the premaxilla. This forms a characteristic "step" that makes erythrosuchids easily distinguishable from all other early archosauriformes, which have smooth jaw margins that are either straight or gradually curved.[2]

Erythrosuchids are notable for being the first archosauriforms to have a triradiate pelvic girdle with three projecting areas formed from three bones: an illium and an elongated pubis and ischium.[3] Although it is small, the fourth trochanter, a ridge on the femur that serves as a muscle attachment in archosaurs, first appears in erythrosuchids. The triradiate pelvis and fourth trochanter are both features which indicate that erythrosuchids had an erect stance similar to later archosaurs. More basal archosauriforms such as proterosuchids lacked these features and probably had a more sprawling posture.[4]

Classification

Erythrosuchids were formerly classified as thecodonts of the suborder Proterosuchia. This classification is no longer used by paleontologists, who now employ a cladistic approach. In this, erythrosuchids constitute an Archosauriformes clade that is an outgroup to the Archosauria proper. The presence of certain archosaurian features, such as the triradiate pelvic girdle, the fourth trochanter, and the third metatarsal longer than the fourth, indicate that erythrosuchids are closer to the true archosaurs than the Proterosuchidae, which lack these features. Thus the Erythrosuchidae occupy a transitional evolutionary position between the most primitive archisauriformes and more advanced Triassic archosaurs.

Genera

Genus[5]	Status	Age	Location	Description	Images
Chalishevia	Valid	Middle Triassic	European Russia
Erythrosuchus	Valid	Early Triassic	South Africa
Garjainia	Valid	Early Triassic	European Russia and South Africa
Guchengosuchus	Valid	Early Triassic	China
Shansisuchus	Valid	Middle Triassic	China
Uralosaurus	Valid	Middle Triassic	European Russia
?Vjushkovisaurus[6]	Valid	Middle Triassic	European Russia

Phylogeny

Cladogram from Parrish (1992):[2]

Archosauriformes	Proterosuchus      Erythrosuchidae      Garjainia       Erythrosuchus       Shansisuchus     Vjushkovia           Fugusuchus       Other archosauriformes

Below is a cladogram from Ezcurra (2016) that reexamined all historical members of the "Proterosuchia" (a polyphyletic historical group including proterosuchids and erythrosuchids). The placement of fragmentary taxa that had to be removed to increase tree resolution is indicated by dashed lines (in the most derived position that they can be confidently assigned to). Taxa that are nomina dubia are indicated by the note "dubium". Bold terminal taxa are collapsed. Ezcurra (2016) recovered a monophyletic Erythrosuchidae, although the relationship of the Long Reef form (SAM P41754) and Uralosaurus remain unknown within the family.[5]

Prolacertidae       SAM-PK-591     "Ankistrodon indicus" (dubium)     "Blomosuchus georgii" (dubium)     Tasmaniosaurus triassicus    Archosauriformes   Chasmatosuchus    Chasmatosuchus magnus     Chasmatosuchus rossicus     Gamosaurus lozovskii       Chasmatosuchus vjushkovi     Vonhuenia friedrichi     Proterosuchidae       Eorasaurus olsoni     Kalisuchus rewanensis     Fugusuchus hejiapanensis       Sarmatosuchus otschevi       Cuyosuchus huenei      Erythrosuchidae    SAM P41754     Uralosaurus magnus     Guchengosuchus shiguaiensis         GHG 7433MI     Garjainia madiba     Garjainia prima         Erythrosuchus africanus       Chalishevia cothurnata     Shansisuchus kuyeheensis     Shansisuchus shansisuchus             Eucrocopoda (=other archosauriformes)

Paleobiology

The large contemporary kannemeyeriid dicynodonts doubtless constituted much of erythrosuchids' prey. However, the first erythrosuchids appear in the fossil record slightly earlier than the kannemeyeriids, so it must be assumed that they fed on other animals as well.

References

1. D.M.S. Watson. 1917. "A sketch classification of the Pre-Jurassic tetrapod vertebrates". Proceedings of the Zoological Society of London 1917: 167-186
2. Parrish, J.M. (1992). "Phylogeny of the Erythrosuchidae". Journal of Vertebrate Paleontology. 12 (1): 93–102. doi:10.1080/02724634.1992.10011434.
3. "Erythrosuchidae". Palaeos. Archived from the original on 9 April 2005. Retrieved 1 July 2010.
4. Sues, H.-D.; Fraser, N.C. (2010). "Early and early Middle Triassic in Gondwana". Triassic Life on Land: The Great Transition. New York: Columbia University Press. pp. 19–36. ISBN 9780231135221. ISBN 0-231-13522-X
5. Ezcurra, M.D. (2016). The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ, e1778
6. Sterling J. Nesbitt (2009). "The early evolution of archosaurs: Relationships and the origin of major clades". Columbia University (open access dissertation): 1–632.

Sources

• Benton, M. J. (2000), Vertebrate Paleontology, 2nd Ed. Blackwell Science Ltd (2004) 3rd edition
• Carroll, R. L. (1988), Vertebrate Paleontology and Evolution, WH Freeman & Co.

External links

• Erythrosuchidae
• Erythrosuchidae - list of species (Mikko's Phylogeny Archive)