Sebecosuchia
Encyclopedia
Sebecosuchia is an extinct group of mesoeucrocodylia
n 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.
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.
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.
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.
In a phylogenetic study of crocodyliforms, Benton and Clark (1988) split up Sebecosuchia, finding baurusuchids to be basal notosuchia
ns while sebecids were basal neosuchia
ns. Since that time, most studies have supported a monophyletic Sebecosuchia. In 2007, however, a phylogenetic study placed baurusuchids as basal metasuchia
ns 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):
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):
s. 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.
Sebecosuchians may have had laterally compressed snouts in order 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.
Mesoeucrocodylia
Mesoeucrocodylia is the name of the clade that includes Eusuchia and the paraphyletic group Mesosuchia. The group appeared during the Early Jurassic, and continues to the present day....
n crocodyliforms that includes the families Sebecidae
Sebecidae
Sebecidae is an extinct family of prehistoric crocodylomorphs. They lived mostly in Argentina.This group included many medium and large - sized genera, from Sebecus to a giant indeterminate unnamed species from the Miocene.-Phylogeny:...
and Baurusuchidae
Baurusuchidae
Baurusuchidae is a Gondwanan family of mesoeucrocodylians that lived during the Late Cretaceous. It is a group of terrestrial hypercarnivorous crocodilians from South America and possibly Pakistan. Baurusuchidae has been defined as a clade containing the most recent common ancestor of Baurusuchus...
. The group first appeared in the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
with the baurusuchids and went extinct in the Miocene with the last sebecids. Fossils have been found primarily from South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
but have also been found in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, North Africa
North Africa
North Africa or Northern Africa is the northernmost region of the African continent, linked by the Sahara to Sub-Saharan Africa. Geopolitically, the United Nations definition of Northern Africa includes eight countries or territories; Algeria, Egypt, Libya, Morocco, South Sudan, Sudan, Tunisia, and...
, and Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
. Some recent studies have separated Baurusuchidae and Sebecidae, making Sebecosuchia polyphyletic, but others have retained it as a valid grouping.
History and phylogeny
Sebecosuchia was first constructed in 1946 by AmericanUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
paleontologist Edwin Colbert to include Sebecus
Sebecus
Sebecus is an extinct genus of sebecid crocodylomorph from the Eocene of South America. Fossils have been found in Patagonia. Like other sebecosuchians, it was entirely terrestrial and carnivorous. The genus is currently represented by a single species, the type S. icaeorhinus...
and Baurusuchidae. Sebecus, which had been known from South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
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
Eremosuchus is an extinct genus of sebecosuchian mesoeucrocodylian. Fossils have been found from El Kohol, Algeria of Eocene age. It had serrated, ziphodont teeth....
, named in 1989, and Pehuenchesuchus
Pehuenchesuchus
Pehuenchesuchus is an extinct genus of sebecosuchian mesoeucrocodylian. It was discovered in rocks of the late Turonian-Coniacian-age Upper Cretaceous Río Neuquén Formation Pehuenchesuchus (meaning "Pehuenche crocodile", after the Mapuche name for the region in which it was found) is an extinct...
, named in 2005. They are usually considered to be more basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
sebecosuchians than the sebecids and baurusuchids.
Below is a cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
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.
In a phylogenetic study of crocodyliforms, Benton and Clark (1988) split up Sebecosuchia, finding baurusuchids to be basal notosuchia
Notosuchia
Notosuchia is a suborder of primarily Gondwanan mesoeucrocodylian crocodylomorphs that lived during the Cretaceous. Fossils have been found from South America, Africa, and Asia...
ns while sebecids were basal neosuchia
Neosuchia
Neosuchia is an unranked 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 niloticus than to Notosuchus terrestris...
ns. Since that time, most studies have supported a monophyletic Sebecosuchia. In 2007, however, a phylogenetic study placed baurusuchids as basal metasuchia
Metasuchia
Metasuchia is a major clade within the superorder Crocodylomorpha. It is split into two main groups, Notosuchia and Neosuchia. Notosuchia is an extinct group that contains primarily small-bodied Cretaceous taxa with heterodont dentitions. Neosuchia includes extant crocodylians and basal taxa such...
ns and sebecids as close relatives to a family of notosuchians called the Peirosauridae
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 defined in 2004 as the most recent common ancestor of...
. Together, sebecids and peirosaurids made the new clade Sebecia
Sebecia
Sebecia is an extinct clade of mesoeucrocodylian crocodyliforms that includes peirosaurids and sebecids. It was first constructed in 2007 to include Hamadasuchus, Peirosauridae, and Sebecus. It was initially considered to be the sister taxon of the clade Neosuchia, which includes living...
. 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):
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 dinosaurDinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
s. The eye sockets are opened laterally rather than dorsally as in aquatic crocodyliforms. Moreover, there is a prominent fourth trochanter
Fourth trochanter
The fourth trochanter is a shared characteristic common to archosaurs. It is a knob-like feature on the medial side of the femur that serves as a muscle attachment....
on the femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
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.
Sebecosuchians may have had laterally compressed snouts in order 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
Adduction
Adduction is a movement which brings a part of the anatomy closer to the middle sagittal plane of the body. It is opposed to abduction.-Upper limb:* of arm at shoulder ** Subscapularis** Teres major** Pectoralis major** Infraspinatus...
muscle to quickly close the jaws and give sebecosuchians a powerful bite.