Mounted skeleton of Edaphosaurus at the Field Museum of Natural History, Chicago, photographed by Jason Cross.

Belongs within: Reptiliomorpha.
Contains: Sphenacodontidae.

The Synapsida are the total group for mammals—that is, mammals and all fossil animals more closely related to mammals than to reptiles. The most basal synapsids, the Permian 'pelycosaurs', were still fairly 'reptilian' in their general appearance, and include such well-known exemplars as the carnivorous Dimetrodon and the herbivorous Edaphosaurus. The Caseidae were a group of sometimes massive herbivores with barrel-shaped bodies and relatively small heads.

Synapomorphies (from Kemp 1988): Temporal fenestra bounded above by squamosal and postorbital; occipital plate broad and tilted forwards; post-temporal fenestra small; postparietal single and median; septomaxilla with broad base and dorsal process; medial process of jugal sutured to pterygoid, ectopterygoid primitively present.

<==Synapsida [Edaphosauria, Ophiacodontia, Pelycosauria, Sphenacodontia, Theromorpha, Theropsida]
    |--+--Eothyris LR95 [Eothyrididae K88]
    |  `--Caseidae K88
    |       |--Casea Williston 1910 D07
    |       |    |--C. broilli D07
    |       |    `--C. rutena D07
    |       `--Cotylorhynchus Stovall 1937 D07
    |            |--C. hancocki D07
    |            `--C. romeri D07
    `--+--Varanopseidae K88
       |    |--Basicranodon fortsillensis M06
       |    |--Archaeovenator hamiltonensis D-SMS06
       |    |--Mesenosaurus romeri D-SMS06
       |    |--Elliotsmithia longiceps MS01
       |    |--Aerosaurus GKR88
       |    `--Varanops Williston 1914 D07
       |         `--V. brevirostris N85
       `--+--Ophiacodontidae K88
          |    |--Ophiacodon Marsh 1878 D07
          |    |    |--O. major D07
          |    |    |--O. mirus D07
          |    |    |--O. navajovicus D07
          |    |    |--O. retroversus D07
          |    |    |--O. tranguala D07
          |    |    |--O. uniformis D07
          |    |    `--O. watsoni D07
          |    `--Varanosaurus Broili 1904 R61, C07
          |         `--*V. acutirostris Broili 1904 C07
          `--+--Sphenacodontidae K88
             `--Edaphosaurus Cope 1882 C07 [incl. Naosaurus Cope 1886 C07; Edaphosauridae K88, Naosaurinae]
                  |--*E. pogonias Cope 1882 C07
                  |--E. bonaerges D07
                  |--E. cruciger (Cope 1878) [=Dimetrodon cruciger, *Naosaurus cruciger] C07
                  |--E. claviger (Cope 1886) [=Naosaurus claviger] C07
                  |--E. microdus Cope 1884 [=Naosaurus microdus] C07
                  `--‘Naosaurus’ mirabilis Fritsch 1883 C07

Synapsida incertae sedis:
  Protoclepsydrops LR95
  Mycterosaurus longiceps M06
  Archaeothyris florensis M06
  Oedaleops GKR88
  Pariotichidae C07
    |--Pariotichus brachiops C07
    `--Ectocynodon ordinatus C07
  Poliosauridae C07
    |--Archaeobelus vellicatus Cope 1877 C07
    |--Pleuristion brachycoelous Case 1902–1903 C07
    |--Callibrachion gaudryi Boule & Glengeaud 1893 C07
    |--Stereorachis dominans Gaudry 1880 C07
    |--Poliosaurus Case 1907 [Poliosauridae] C07
    |    `--*P. uniformis (Cope 1878) [=Theropleura uniformis] C07
    |--Elcabrosaurus Case 1907 C07
    |    `--*E. baldwini Case 1907 C07
    |--Anomosaurus v. Huene 1902 C07
    |    `--A. strunzi v. Huene 1905 C07
    `--Theropleura [incl. Diopeus Cope 1892] C07
         |--*T. retroversa Cope 1878 (see below for synonymy) C07
         `--T. grandis Case 1907 C07
  Clepsydropidae [Clepsydropinae] C07
    |--Embolophorus fritillus Cope 1878 C07
    |--Metamosaurus fossatus Cope 1878 C07
    |--Bathygnathus borealis Leidy 1854 C07
    |--Tomicosaurus Case 1907 C07
    |--Ctenosaurus koeneni v. Huene 1902 C07
    `--Clepsydrops Cope 1875 [Clepsydropinae] C07
         |--*C. colletti Cope 1875 (n. d.) C07
         |--C. natalis Cope 1878 C07
         |--C. pedunculatus Cope 1877 (n. d.) C07
         `--C. vinslovii Cope 1877 (n. d.) C07
  Tetraceratops Matthew 1908 D07
    `--T. insignis D07

*Theropleura retroversa Cope 1878 [incl. Clepsydrops leptocephalus Cope 1884, *Diopeus leptocephalus, Theropleura triangulata Cope 1878] C07

*Type species of generic name indicated


[C07] Case, E. C. 1907. Revision of the Pelycosauria of North America. Carnegie Institute of Washington Publication 55: 1–176, 35 pls.

[D-SMS06] Dias-da-Silva, S., S. P. Modesto & C. L. Schultz. 2006. New material of Procolophon (Parareptilia: Procolophonoidea) from the Lower Triassic of Brazil, with remarks on the ages of the Sanga do Cabral and Buena Vista formations of South America. Canadian Journal of Earth Sciences 43: 1685–1693.

[D07] Dixon, D. 2007. The Complete Illustrated Encyclopedia of Dinosaurs & Prehistoric Creatures. Hermes House: London.

[GKR88] Gauthier, J. A., A. G. Kluge & T. Rowe. 1988. The early evolution of the Amniota. In: Benton, M. J. (ed.) The Phylogeny and Classification of the Tetrapods vol. 1. Amphibians, Reptiles, Birds pp. 103–155. Clarendon Press: Oxford.

[K88] Kemp, T. S. 1988. Interrelationships of the Synapsida. In: Benton, M. J. (ed.) The Phylogeny and Classification of the Tetrapods vol. 2. Mammals pp. 1–22. Clarendon Press: Oxford.

[LR95] Laurin, M., & R. R. Reisz. 1995. A reevaluation of early amniote phylogeny. Zoological Journal of the Linnean Society 113: 165–223.

[M06] Modesto, S. P. 2006. The cranial skeleton of the Early Permian aquatic reptile Mesosaurus tenuidens: implications for relationships and palaeobiology. Zoological Journal of the Linnean Society 146: 345–368.

[MS01] Modesto, S. P., & R. M. H. Smith. 2001. A new Late Permian captorhinid reptile: a first record from the South African Karoo. Journal of Vertebrate Paleontology 21 (3): 405–409.

[N85] Norman, D. 1985 (reprinted 2000). The Illustrated Encyclopedia of Dinosaurs. Salamander Books: London.

[R61] Romer, A. S. 1961. Synapsid evolution and dentition. In: Vandebroek, G. (ed.) International Colloquium on the Evolution of Lower and Non Specialized Mammals. Koninklijke Vlaames Academie voor Wetenschappen, Letteren en Schone Kunsten van Belgie—Klasse der Wetenschapen 1961 (1): 9–56.

Last updated: 27 August 2018.

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