Sphenacodontia is a stem-based

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

of derived

synapsid Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant rept ...

s. It was defined by Amson and Laurin (2011) as "the largest clade that includes ''

Haptodus baylei ''Haptodus'' is an extinct genus of basal sphenacodonts, a member of the clade that includes therapsids and hence, mammals. It was at least in length. It lived in present-day France during the Early Permian. It was a medium-sized predator, fe ...

'', ''

Haptodus garnettensis ''Haptodus'' is an extinct genus of basal sphenacodonts, a member of the clade that includes therapsids and hence, mammals. It was at least in length. It lived in present-day France during the Early Permian. It was a medium-sized predator, fe ...

'' and '' Sphenacodon ferox'', but not '' Edaphosaurus pogonias''". They first appear during the

Late Pennsylvanian The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, on the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period (or the upper of two subsystems of the Carboniferous System). It laste ...

(

Upper Carboniferous Upper may refer to: * Shoe upper or ''vamp'', the part of a shoe on the top of the foot * Stimulant, drugs which induce temporary improvements in either mental or physical function or both * ''Upper'', the original film title for the 2013 found f ...

) epoch. From the end of the

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

to the end of the

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

, most of them remained large, with only some secondarily becoming small in size. Basal Sphenacodontia constitute a transitional

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

ary series from early

pelycosaur Pelycosaur ( ) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term mammal-like reptile was used, and Pelycosauria was considered an order, but this is now thoug ...

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

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s). One might say that the sphenacodontians are proto-therapsids (even though there is almost a 30-million-years gap between the separation of the ancestors of therapsids from other sphenacodontians and the first appearance of therapsids in the fossil record).

Characteristics

The defining characteristics include a thickening of the

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

visible on its internal surface, above the large front (

caniniform In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, eye teeth, vampire teeth, or fangs, are the relatively long, pointed tooth, teeth. In the context of the upper jaw, they are also known as ''fangs''. They can appear mo ...

) teeth; and the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...

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

Classification

The following taxonomy follows Fröbisch ''et al.'' (2011), Benson (2012) and Spinder (2016) unless otherwise noted. Class

Synapsida Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant rep ...

Eupelycosauria Eupelycosauria is a large clade of animals characterized by the unique shape of their skull, encompassing all mammals and their closest extinct relatives. They first appeared 308million years ago during the Early Pennsylvanian epoch, with the fo ...

** Sphenacodontia *** †''

Haptodus ''Haptodus'' is an extinct genus of basal sphenacodonts, a member of the clade that includes therapsids and hence, mammals. It was at least in length. It lived in present-day France during the Early Permian. It was a medium-sized predator, fe ...

'' *** †'' Hypselohaptodus'' *** †''

Ianthodon ''Ianthodon'' is an extinct genus of basal haptodontiform synapsids from the Late Carboniferous about 304 million years ago. The taxon was discovered and named by Kissel & Reisz in 2004.Kissel, R. A. & Reisz, R. R. ''Synapsid fauna of the Upper ...

'' *** Pantherapsida **** †''

Kenomagnathus ''Kenomagnathus'' (meaning "gap jaw", in reference to the diastema in its upper tooth row) is a genus of synapsid belonging to the Sphenacodontia, which lived during the Pennsylvanian (geology), Pennsylvanian subperiod of the Carboniferous in wha ...

'' **** †''

Tetraceratops ''Tetraceratops insignis'' ("four-horned face emblem") is an extinct synapsid from the Early Permian that was formerly considered the earliest known representative of Therapsida, a group that includes mammals and their close extinct relatives. It ...

'' **** †

Palaeohatteriidae Palaeohatteriidae is an extinct family of basal sphenacodonts known from the Early Permian period ( Asselian- Sakmarian stages) of Saxony, Germany.Spindler, F. 2016. Morphological description and taxonomic status of (Synapsida: Sphenacodontia). ...

****

Sphenacodontoidea Sphenacodontoidea is a node-based clade that is defined to include the most recent common ancestor of Sphenacodontidae and Therapsida and its descendants (including mammals). Sphenacodontoids are characterised by a number of synapomorphies co ...

***** †'' Shashajaia'' ***** †

Sphenacodontidae Sphenacodontidae (Greek: "wedge point tooth family") is an extinct family (biology), family of sphenacodontoidea, sphenacodontoid synapsids. Small to large, advanced, carnivore, carnivorous, Late Pennsylvanian to Guadalupian, middle Permian "pelyc ...

*****

Therapsida Therapsida is a clade comprising a major group of eupelycosaurian synapsids that includes mammals and their ancestors and close relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including l ...

Phylogeny

Sphenacodontia in a

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

after Fröbisch ''et al''., 2011:

References

* Laurin, M. and Reisz, R. R., 1997
Autapomorphies of the main clades of synapsids
-

Tree of Life Web Project The Tree of Life Web Project (ToL) is an Internet project providing information about the diversity and phylogeny of life on Earth. This collaborative peer reviewed project began in 1995, and is written by biologists from around the world. The s ...

External links

Synapsida: Sphenacodontia
{{Taxonbar, from=Q930410 Extant Pennsylvanian first appearances Taxa named by Llewellyn Ivor Price Taxa named by Alfred Romer

Characteristics

Classification

Phylogeny

See also

References

External links