Sphenacodontia is a stem-based clade of derived

synapsid Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids, the group that includes rep ...

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

Haptodus garnettensis ''"Haptodus" garnettensis'' is an extinct species of basal (phylogenetics), basal sphenacodont from the Late Carboniferous (Pennsylvanian (geology), Pennsylvanian) of Kansas, USA. Taxonomy The holotype of ''"Haptodus" garnettensis'' is Redpath ...

'' and ''

Sphenacodon ferox ''Sphenacodon'' (meaning "wedge point tooth") is an extinct genus of synapsid that lived from about 300 to about 280 million years ago (Ma) during the Late Carboniferous and Early Permian periods. Like the closely related ''Dimetrodon'', ''Sphena ...

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

Late Pennsylvanian The Pennsylvanian ( , also known as Upper Carboniferous or Late Carboniferous) is, in the ICS geologic timescale, the younger of two subperiods (or upper of two subsystems) of the Carboniferous Period. It lasted from roughly . As with most ot ...

(

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 fo ...

) epoch. From the end of the Carboniferous to the end of the

Permian The Permian ( ) is a geologic period and 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 251.9 Mya. It is the last period of the Pale ...

, most of them remained large, with only some secondarily becoming small in size.

Basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is nec ...

Sphenacodontia constitute a transitional

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

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'' had been used, and pelycosaur was considered an order, but this is now ...

s to ancestral

therapsid Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented mor ...

s (which in turn were the ancestors of more advanced forms and finally the mammals). 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 The maxilla (plural: ''maxillae'' ) in vertebrates 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 ...

visible on its internal surface, above the large front (

caniniform In mammalian oral anatomy, the canine teeth, also called cuspids, dog teeth, or (in the context of the upper jaw) fangs, eye teeth, vampire teeth, or vampire fangs, are the relatively long, pointed teeth. They can appear more flattened however ...

) 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 mammal has ...

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 *

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 f ...

** Sphenacodontia *** †''

Haptodus ''Haptodus'' is an extinct genus of basal sphenacodont, 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, feedin ...

'' *** †''

Hypselohaptodus ''Hypselohaptodus'' is a genus of sphenacodont synapsid from the Cisuralian of England. It contains a single species, ''Hypselohaptodus grandis'', and is known only from a single specimen, a partial left maxilla, which is hosted at the Warwick ...

'' *** 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 subperiod of the Carboniferous in what is now Garnett, Kansas ...

'' **** †''

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. I ...

'' **** † Palaeohatteriidae ****

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 conce ...

***** †

Sphenacodontidae Sphenacodontidae (Greek: "wedge point tooth family") is an extinct family of small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian pelycosaurs. The most recent one, ''Dimetrodon angelensis'', is from the late Kungurian ...

***** Therapsida

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 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 site ...

External links

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

Characteristics

Classification

See also

References

External links