Sebecosuchia is an extinct group of

mesoeucrocodylia Mesoeucrocodylia is the clade that includes Eusuchia and crocodyliforms formerly placed in the paraphyletic group Mesosuchia. The group appeared during the Early Jurassic, and continues to the present day. Diagnosis It was long known that Mes ...

crocodyliform 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 pseu ...

s that includes the families Sebecidae and Baurusuchidae. The group was long thought to have first appeared in the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

with the baurusuchids and become extinct in the Miocene with the last sebecids, but '' Razanandrongobe'' pushes the origin of Sebecosuchia to the Middle Jurassic. Fossils have been found primarily from

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...

but have also been found in

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North Africa North Africa, or Northern Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Mauritania in ...

Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Afric ...

, and the Indian subcontinent.

History and phylogeny

Sebecosuchia was first constructed in 1937 by

George Gaylord Simpson George Gaylord Simpson (June 16, 1902 – October 6, 1984) was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern synthesis, contributing '' Tempo ...

.Simpson, G.G. 1937. "New reptiles from the Eocene of South America". ''American Museum Novitates'' 967: 1-20 In 1946 the concept was again used by

American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...

paleontologist

Edwin Colbert Edwin Harris "Ned" Colbert (September 28, 1905 – November 15, 2001)O'Connor, Anahad ''The New York Times'', November 25, 2001. was a distinguished American vertebrate paleontologist and prolific researcher and author. Born in Clarinda, Iowa, he ...

to include '' Sebecus'' and Baurusuchidae. ''Sebecus'', which had been known from

since 1937, was an unusual crocodyliform with a deep snout and teeth that were ziphodont, or serrated and laterally compressed. The family Baurusuchidae was named the year before and included the newly described ''Baurusuchus'', which was also a South American deep-snouted form. More recently, other crocodyliforms have been assigned to Sebecosuchia that cannot be placed into either family. These include the genera ''

Eremosuchus ''Eremosuchus'' is an extinct genus of sebecosuchian mesoeucrocodylian. Fossils have been found from El Kohol, Algeria of Eocene age. It had serrated, ziphodont teeth. The genus was originally referred to the family Trematochampsidae in 1989. ...

'', named in 1989, and ''

Pehuenchesuchus ''Pehuenchesuchus'' (meaning " Pehuenche crocodile", after the Mapuche name for the region in which it was found) is an extinct genus of sebecosuchian mesoeucrocodylian. It was discovered in rocks of the late Turonian-Coniacian-age Upper Cre ...

'', named in 2005. They are usually considered to be more basal sebecosuchians than the sebecids and baurusuchids. Below is a

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

showing the possible phylogenetic position of Sebecosuchia modified from Turner and Calvo (2005). In this cladogram, Sebecidae is a

paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...

assemblage of basal sebecosuchians while Baurusuchidae is monophyletic and includes the more derived sebecosuchians. In a phylogenetic study of crocodyliforms, Benton and Clark (1988) split up Sebecosuchia, finding baurusuchids to be basal notosuchians while sebecids were basal

neosuchia Neosuchia is a clade within Mesoeucrocodylia that includes all modern extant crocodilians and their closest fossil relatives. It is defined as the most inclusive clade containing all crocodylomorphs more closely related to ''Crocodylus niloticu ...

ns. Since that time, most studies have supported a monophyletic Sebecosuchia. In 2007, however, a phylogenetic study placed baurusuchids as basal metasuchians and sebecids as close relatives to a family of notosuchians called the

Peirosauridae Peirosauridae is a Gondwanan family of mesoeucrocodylians that lived during the Cretaceous period. It was a clade of terrestrial crocodyliforms that evolved a rather dog-like form, and were terrestrial carnivores. It was phylogenetically define ...

. Together, sebecids and peirosaurids made the new clade Sebecia. Below is a cladogram from that study, Larsson and Sues (2007): Two years later, Sereno and Larsson (2009) came to the same conclusion, except they placed baurusuchids as advanced notosuchians. More recently however, Turner and Sertich (2010) found support for Sebecosuchia in their analysis of notosuchian relationships. In their study, Sebecosuchia was a derived clade within Notosuchia. Iori and Carvalho (2011) came to similar conclusions, grouping ''Baurusuchus'' alongside Sebecidae. Below is the cladogram from Turner and Sertich (2010): Diego Pol and Jaime E. Powell (2011) came to the same conclusion, however their analysis couldn't find a

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gr ...

Baurusuchidae within Sebecosuchia. The following cladogram simplified after their analysis, with focus on Sebecosuchia.

Paleobiology

All sebecosuchians were carnivorous and terrestrial. The nares open at the very tip of the snout, suggesting that it lived on land rather than in water (in aquatic crocodyliforms, the nares usually open dorsally on top of the snout). The snout itself is laterally compressed, a feature shared with other terrestrial reptiles such as

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

s. The eye sockets are opened laterally rather than dorsally as in aquatic crocodyliforms. Moreover, there is a prominent fourth trochanter on the

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates ...

for the attachment of muscles that would have aided in upright walking. Although they are now widely accepted to be terrestrial, sebecosuchians were once thought to be semiaquatic, spending part of their time in water. The laterally compressed snout of sebecosuchians may have enabled them to withstand high forces during biting. The teeth are also laterally compressed, pointed, and serrated. Their shape would have allowed them to easily penetrate and slice flesh. The

pterygoid bone The pterygoid is a paired bone forming part of the palate of many vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and ...

in the skull is strongly bent, allowing for a larger jaw adductor muscle to quickly close the jaws and give sebecosuchians a powerful bite.

References

{{Taxonbar, from=Q7442744 Terrestrial crocodylomorphs Late Cretaceous crocodylomorphs Paleogene crocodylomorphs Neogene crocodylomorphs Late Cretaceous first appearances Miocene extinctions