Sphenacodontia is the name given to the clade

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...

 that includes the Sphenacodontidae

Sphenacodontidae

Sphenacodontidae is a family of small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian pelycosaurs. Primitive forms were generally small in size , but during the later part of the early Permian these animals grew progressively larger , to become the top predators of their...

 and all their descendants (including mammals). They first appear during the Late Pennsylvanian epoch. The defining characteristics

Synapomorphy

In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...

 include a thickening of the maxilla

Maxilla

The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...

 visible on its internal surface, above the large front (caniniform) teeth; and the premaxilla

Premaxilla

The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....

ry teeth being set in deep sockets. All other (sister group and more primitive) synapsid clades have teeth that are set in shallow sockets.

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:...

 Sphenacodontia constitute a transitional evolution

Evolution

Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

ary series from early pelycosaur

Pelycosaur

The pelycosaurs are an informal grouping composed of basal or primitive Late Paleozoic synapsid amniotes. Some species were quite large and could grow up to 3 meters or more, although most species were much smaller...

s to ancestral therapsids (which in turn were the ancestors of more advanced forms and finally the mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s). One might say that the Sphenacodontians are proto-therapsids.

Taxonomy and Phylogeny

• Class Synapsida
• ORDER PELYCOSAURIA
  Pelycosaur
  The pelycosaurs are an informal grouping composed of basal or primitive Late Paleozoic synapsid amniotes. Some species were quite large and could grow up to 3 meters or more, although most species were much smaller...
  
  
  • Suborder Eupelycosauria
    Eupelycosauria
    The Eupelycosauria originally referred to a suborder of 'pelycosaurs' , but has been redefined to designate a clade of synapsids that includes most pelycosaurs, as well as all therapsids and mammals...
    
    
    • Sphenacodontia (incl. paraphyletic Sphenacodontidae)
      • †Cutleria
      • †Haptodus
        Haptodus
        Haptodus was a small sphenacodont, a clade that includes therapsids and hence, mammals. It was at least in length. It lived from Latest Carboniferous to Early Permian, in the equatorial Pangea. It was a medium-sized predator, feeding on insects and small vertebrates. It is one of the basalmost...
        
        
      • †Palaeohatteria
      • †Pantelosaurus
        • Sphenacodontoidea
          Sphenacodontoidea
          Sphenacodontoidea is the name given to the clade that includes the most recent common ancestor of the Sphenacodontidae and the Therapsida and their descendants...
          
          
          • †Ctenorhynchus
            • Family †Sphenacodontidae
              Sphenacodontidae
              Sphenacodontidae is a family of small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian pelycosaurs. Primitive forms were generally small in size , but during the later part of the early Permian these animals grew progressively larger , to become the top predators of their...
              
              (sensu stricto)
              • †Ctenorhachis
                Ctenorhachis
                Ctenorhachis is an extinct genus of the family Sphenacodontidae. Ctenorhachis was related to Dimetrodon, but did not belong to the same subfamily as Dimetrodon and Sphenacodon, being a more basal member of Sphenacodontidae. Ctenorhachis lived in the Early Permian epoch...
                
                
              • †Ctenospondylus
                Ctenospondylus
                Ctenospondylus, was a pelycosaur that was about 3 meters long. It lived from Latest Carboniferous to Early Permian. Its fossils were found in the U.S. states of Ohio and Texas. It was a carnivore and preyed upon animals close to its size...
                
                
              • †Dimetrodon
                Dimetrodon
                Dimetrodon was a predatory synapsid genus that flourished during the Permian period, living between 280–265 million years ago ....
                
                
              • †Neosaurus
                Neosaurus
                Neosaurus is a little-known pelycosaur of the family Sphenacodontidae. It was related to the well known Dimetrodon, although much smaller and lived during the Early Permian. Its fossils were found in the Jura region of France....
                
                
              • †Secodontosaurus
                Secodontosaurus
                Secodontosaurus was a pelycosaur that lived in Texas during the Early Permian age. Though it had the same body style as other sphenacodontids, it had an unusually low and narrow skull. It had a long neural spines, like Dimetrodon, which Secodontosaurus was related to...
                
                
              • †Sphenacodon
                Sphenacodon
                Sphenacodon was a pelycosaur that was about in length. Sphenacodon belongs to the family Sphenacodontidae, a lineage that was related to the therapsids...
                
                
              • †Steppesaurus
                Steppesaurus
                Steppesaurus is an extinct genus of pelycosaur belonging to the Sphenacodontidae family, related to Dimetrodon and Sphenacodon....
                
                
                • Family †Tetraceratops
                  Tetraceratops
                  Tetraceratops insignis was a lizard-like synapsid. It lived during the Early Permian period. According to a recent, controversial report, T. insignis is the first known therapsid. Other scientists, on the other hand, say that it is a more primitive species of synapsid, possibly an unusual,...
                  
                  idae
                  • ORDER THERAPSIDA
                    • Class Mammalia

External links

• Synapsida: Sphenacodontia