Sebecia
Encyclopedia
Sebecia is an extinct clade
of mesoeucrocodylia
n 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 crocodilia
ns, although some later studies have placed it within Neosuchia as a basal
clade. Sebecians were terrestrial crocodyliforms characterized by their deep snouts and ziphodont dentitions. They first appeared in the Late Cretaceous
, survived the Cretaceous-Tertiary extinction event
, and went extinct in the Miocene
epoch.
According to paleontologists Hans Larsson and Hans-Dieter Sues
, who constructed the clade in 2007, Sebecia also includes genera that were once assigned to Baurusuchidae
, namely Pabwehshi
. However, other baurusuchids, namely Baurusuchus
, were placed outside Sebecia. Therefore, Baurusuchidae was considered polyphyletic and thus not a true clade. Below is the cladogram
produced from Larsson and Sues' phylogenetic analysis:
Larsson and Sues defined Sebecidae as all taxa more closely related to Sebecus than to Peirosaurus
or Uberabasuchus
, both of which are peirosaurids. They defined Peirosauridae as all taxa more closely related to Peirosaurus and Uberabasuchus than to Sebecus, which is a sebecid. This definition is problematic, especially in relation to later phylogenetic studies of crocodyliforms. Many of these studies have found sebecids to be derived
members of a clade containing notosuchia
ns, while finding peirosaurids to be basal neosuchians. If the definitions of these two families are applied to later phylogenetic analyses, Sebecidae would include all notosuchians and Peirosauridae would include all neosuchians.
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
of mesoeucrocodylia
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 peirosaurids and sebecids. It was first constructed in 2007 to include Hamadasuchus
Hamadasuchus
Hamadasuchus is an extinct genus of sebecian crocodylomorph. Fossils have been found from the Kem Kem Formation outcropping in southeastern Morocco. These beds date back to the Albian and Cenomanian stages of the Late Cretaceous. It was first assigned to the family Trematochampsidae. Diagnostic...
, Peirosauridae, and 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...
. It was initially considered to be the sister taxon of the clade 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...
, which includes living crocodilia
Crocodilia
Crocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
ns, although some later studies have placed it within Neosuchia as a 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:...
clade. Sebecians were terrestrial crocodyliforms characterized by their deep snouts and ziphodont dentitions. They 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...
, survived the Cretaceous-Tertiary extinction event
Cretaceous-Tertiary extinction event
The Cretaceous–Paleogene extinction event, formerly named and still commonly referred to as the Cretaceous-Tertiary extinction event, occurred approximately 65.5 million years ago at the end of the Maastrichtian age of the Cretaceous period. It was a large-scale mass extinction of animal and plant...
, and went extinct in the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
epoch.
According to paleontologists Hans Larsson and Hans-Dieter Sues
Hans-Dieter Sues
Hans-Dieter Sues is a German-born paleontologist who is Senior Scientist and Curator of Vertebrate Paleontology at the National Museum of Natural History of the Smithsonian Institution in Washington, DC. He received his education at Johannes Gutenberg-Universität Mainz , University of Alberta, and...
, who constructed the clade in 2007, Sebecia also includes genera that were once assigned to 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...
, namely Pabwehshi
Pabwehshi
Pabwehshi is an extinct genus of mesoeucrocodylian. It is based on GSP-UM 2000, a partial snout and corresponding lower jaw elements, with another snout assigned to it...
. However, other baurusuchids, namely Baurusuchus
Baurusuchus
Baurusuchus is an extinct genus of baurusuchid mesoeucrocodylian from the Late Cretaceous of Brazil. It was a terrestrial predator and scavenger, about 3.5 to 4 meters long. Baurusuchus lived during the Turonian to Santonian stages of the Late Cretaceous Period, in Adamantina Formation, Brazil...
, were placed outside Sebecia. Therefore, Baurusuchidae was considered polyphyletic and thus not a true clade. Below is the 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...
produced from Larsson and Sues' phylogenetic analysis:
Larsson and Sues defined Sebecidae as all taxa more closely related to Sebecus than to Peirosaurus
Peirosaurus
Peirosaurus is an extinct genus of peirosaurid crocodylomorph. It is the type genus of the family Peirosauridae. Fossils of the type species P. tormini, first described in 1955, have been found from the Marília Formation in Uberaba, Brazil and date back to the late Maastrichtian stage of the Late...
or Uberabasuchus
Uberabasuchus
Uberabasuchus is an extinct genus of crocodylomorph from the Late Cretaceous of Brazil.-Sources:* - original description of genus...
, both of which are peirosaurids. They defined Peirosauridae as all taxa more closely related to Peirosaurus and Uberabasuchus than to Sebecus, which is a sebecid. This definition is problematic, especially in relation to later phylogenetic studies of crocodyliforms. Many of these studies have found sebecids to be derived
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
members of a clade containing 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 finding peirosaurids to be basal neosuchians. If the definitions of these two families are applied to later phylogenetic analyses, Sebecidae would include all notosuchians and Peirosauridae would include all neosuchians.