Sebecosuchia

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Sebecosuchia
Temporal range: Late Cretaceous - Middle Miocene, 90–11Ma
Baurusuchus BW.jpg
Life restoration of Baurusuchus salgadoensis
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Superorder: Crocodylomorpha
Suborder: Notosuchia
Node: Ziphosuchia
Branch: Sebecosuchia
Colbert, 1946

Sebecosuchia is an extinct group of mesoeucrocodylian crocodyliforms that includes the families Sebecidae and Baurusuchidae. The group first appeared in the Late Cretaceous with the baurusuchids and went extinct in the Miocene with the last sebecids. Fossils have been found primarily from South America but have also been found in Europe, North Africa, and Asia. Some recent studies have separated Baurusuchidae and Sebecidae, making Sebecosuchia polyphyletic, but others have retained it as a valid grouping.

History and phylogeny[edit]

Sebecosuchia was first constructed in 1946 by American paleontologist Edwin Colbert to include Sebecus and Baurusuchidae. Sebecus, which had been known from South America 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.[1]

More recently, other crocodyliforms have been assigned to Sebecosuchia that cannot be placed into either family. These include the genera Eremosuchus, named in 1989, and Pehuenchesuchus, named in 2005. They are usually considered to be more basal sebecosuchians than the sebecids and baurusuchids.[1]

Below is a cladogram showing the possible phylogenetic position of Sebecosuchia modified from Turner and Calvo (2005). In this cladogram, Sebecidae is a paraphyletic assemblage of basal sebecosuchians while Baurusuchidae is monophyletic and includes the more derived sebecosuchians.

Crocodyliformes 

Hsisosuchus


 Mesoeucrocodylia 

Thalattosuchia


 Metasuchia 
 Neosuchia 


Araripesuchus




Trematochampsidae




Peirosauridae



Mahajangasuchidae







Atoposauridae




Goniopholididae




Bernissartia



Crocodylia







Libycosuchus




Notosuchia


 Sebecosuchia 

Pehuenchesuchus




Eremosuchus



Sebecus




Iberosuchus



Bretesuchus


 Baurusuchidae 

Baurusuchus



Pabwehshi










In a phylogenetic study of crocodyliforms, Benton and Clark (1988) split up Sebecosuchia, finding baurusuchids to be basal notosuchians while sebecids were basal neosuchians. 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. Together, sebecids and peirosaurids made the new clade Sebecia. Below is a cladogram from that study, Larsson and Sues (2007):[2]

Metasuchia 
 Notosuchia

 Notosuchus



 Malawisuchus





 Araripesuchus





 Baurusuchus 




 Neosuchia


 Sebecia 

 Pabwehshi 



 Sebecidae 

 Sebecus 



 Bretesuchus 




 Peirosauridae









Sebecosuchians
Sebecosuchians

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):[3]

Notosuchia

Anatosuchus




Mahajangasuchidae

Kaprosuchus



Mahajangasuchus



Peirosauridae


Peirosaurus



Lomasuchus





Hamadasuchus




Montealtosuchus



Uberabasuchus








"Araripesuchus" wegeneri




"Araripesuchus" tsangatsangana





Araripesuchus buitreraensis




Araripesuchus patagonicus



Araripesuchus gomesii






Uruguaysuchus


Ziphosuchia


Libycosuchus



Simosuchus





Malawisuchus



Notosuchidae

Notosuchus



Mariliasuchus






Chimaerasuchus




Sphagesaurus huenei



Sphagesaurus montealtensis







Comahuesuchus




Yacarerani




Adamantinasuchus



Armadillosuchus





Sebecosuchia

Baurusuchus



Sebecia














Diego Pol and Jaime E. Powell (2011) came to the same conclusion, however their analysis couldn't find a monophyletic Baurusuchidae within Sebecosuchia. The following cladogram simplified after their analysis, with focus on Sebecosuchia.[4]




Chimaerasuchus



Sphagesaurus



Sebecosuchia

Pehuenchesuchus




Cynodontosuchus


Baurusuchidae


Pabwehshi



Stratiotosuchus





Baurusuchus pachecoi



Baurusuchus salgadoensis





Bergisuchidae

Bergisuchus


Iberosuchidae

Iberosuchus


Sebecidae

Lorosuchus




Barinasuchus





Ayllusuchus



Bretesuchus





Lumbrera form



Langstonia



Sebecus



Zulmasuchus










Paleobiology[edit]

Sahitysuchus skull

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 dinosaurs. The eye sockets are opened laterally rather than dorsally as in aquatic crocodyliforms. Moreover, there is a prominent fourth trochanter on the femur 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 in the skull is strongly bent, allowing for a larger jaw adductor muscle to quickly close the jaws and give sebecosuchians a powerful bite.[5]

References[edit]

  1. ^ a b Turner, A.H.; Calvo, J.O. (2005). "A new sebecosuchian crocodyliform from the Late Cretaceous of Patagonia". Journal of Vertebrate Paleontology 25 (1): 87–98. doi:10.1671/0272-4634(2005)025[0087:ANSCFT]2.0.CO;2. 
  2. ^ Larsson, H. C. E.; Sues, H.-D. (2007). "Cranial osteology and phylogenetic relationships of Hamadasuchus rebouli (Crocodyliformes: Mesoeucrocodylia) from the Cretaceous of Morocco". Zoological Journal of the Linnean Society 149 (4): 533–567. doi:10.1111/j.1096-3642.2007.00271.x. 
  3. ^ Turner, Alan H.; Sertich, Joseph J. W. (2010). "Phylogenetic history of Simosuchus clarki (Crocodyliformes: Notosuchia) from the Late Cretaceous of Madagascar". Journal of Vertebrate Paleontology 30 (6, Memoir 10): 177–236. doi:10.1080/02724634.2010.532348. 
  4. ^ Diego Pol and Jaime E. Powell (2011). "A new sebecid mesoeucrocodylian from the Rio Loro Formation (Palaeocene) of north-western Argentina". Zoological Journal of the Linnean Society 163: S7–S36. doi:10.1111/j.1096-3642.2011.00714.x. 
  5. ^ Carvalho, I.S.; Campos, A.C.A.; Nobre, P.H. (2005). "Baurusuchus salgadoensis, a new Crocodylomorpha from the Bauru Basin (Cretaceous), Brazil". Gondwana Research 8 (1): 11–30. doi:10.1016/S1342-937X(05)70259-8.