Sphenacodontoidea Explained

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).^[1] Sphenacodontoids are characterised by a number of synapomorphies concerning proportions of the bones of the skull and the teeth.^{[2] [3]}

The sphenacodontoids evolved from earlier sphenacodonts such as Haptodus and Ianthodon via a number of transitional stages of small, 1-10 kg, faunivore animals.^[1] The possible common ancestor of sphenacodontids and therapsids was a carnivorous synapsid that reached moderate or large size and more closely resembled the land-dominant Early Permian sphenacodontids than the small Haptodus.^[2] The first predators among Sphenacodontoidea, like Shashajaia, appeared in the tropical western part of Pangea in the Late Carboniferous.^[1] Later, in Permian, sphenacodontoids gave rise to the dominant terrestrial carnivores in both sphenacodontid and therapsid groups.^[2]

Classification

The following taxonomy follows Fröbisch et al. (2011) and Benson (2012) unless otherwise noted.^{[4] [5]}

Class Synapsida

• Sphenacodontoidea
  • Family †Sphenacodontidae
  • Therapsida

Phylogeny

Sphenacodontoidea in a cladogram modified from Huttenlocker et al. (2021):^[1]

See also

• Evolution of mammals

Further reading

• Laurin, M. and Reisz, R. R., 1997, Autapomorphies of the main clades of synapsids - Tree of Life Web Project

External links

• Web site: Synapsida. Mikko's Phylogeny Archive. https://web.archive.org/web/20070903075607/http://www.fmnh.helsinki.fi/users/haaramo/Metazoa/deuterostoma/chordata/Synapsida/synapsida_1.htm#Sphenacodontidae. September 3, 2007. dead.

Notes and References

1. Huttenlocker. A. K.. Singh. S. A.. Henrici. A. C.. Sumida. S. S.. 2021. A Carboniferous synapsid with caniniform teeth and a reappraisal of mandibular size-shape heterodonty in the origin of mammals. Royal Society Open Science. 8. 12. 211237. 10.1098/rsos.211237. 34925870. 8672069. 2021RSOS....811237H.
2. R. R. Reisz, David S Berman, Diane Scott. 1992. The cranial anatomy and relationships of Secodontosaurus, an unusual mammal-like reptile (Synapsida: Sphenacodontidae) from the Early Permian of Texas. Zoological Journal of the Linnean Society. 104. 2. 127-184. 10.1111/j.1096-3642.1992.tb00920.x.
3. Web site: Autapomorphies of the main clades of synapsids. Tolweb. https://web.archive.org/web/20231027063241/http://tolweb.org/notes/?note_id=466. October 27, 2023. live.
4. Jörg Fröbisch . Rainer R. Schoch . Johannes Müller . Thomas Schindler . Dieter Schweiss . 2011 . A new basal sphenacodontid synapsid from the Late Carboniferous of the Saar-Nahe Basin, Germany . Acta Palaeontologica Polonica . 56 . 1 . 113–120 . 10.4202/app.2010.0039. free .
5. Benson . R.J. . 2012 . Interrelationships of basal synapsids: cranial and postcranial morphological partitions suggest different topologies . Journal of Systematic Palaeontology . 10 . 4 . 601–624 . 10.1080/14772019.2011.631042 . 84706899 .