Note

Autapomorphies of the main clades of synapsids

Michel Laurin and Robert R. Reisz

The classification of synapsids may be summarized as follows:

                   =============================================================== Eothyrididae 
     ==Caseasauria=|
     |             =============================================================== Caseidae 
     |
     |                ============================================================ Varanopseidae
     |                |
     |                |   ======================================================== Ophiacodontidae 
     |                |   |
     |                |   |   ==================================================== Edaphosauridae
     |                |   |   |
=====|                |   |   |                =================================== Haptodus garnettensis
     |                |   |   |                |
     ==Eupelycosauria=|   |   |                |   =============================== Palaeohatteria
                      ==A=|   |                |   |
                          ==B=|                |   |   =========================== Pantelosaurus
                              ==Sphenacodontia=|   |   |
                                               ==C=|   |   ======================= Cutleria
                                                   ==D=|   |
                                                       ==E=|                   === Sphenacodontidae
                                                           ==Sphenacodontoidea=|
                                                                               === Therapsida

This classification and the list of apomorphies given below is taken from recent studies by Reisz (1986), Hopson (1991), Reisz et al. (1992), Berman et al. (1995), and Laurin and Reisz (1996), to which the readers should refer for further information.

Caseasauria (eothyridids and caseids) exhibits the following autapomorphies:

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Click on an image to view larger version & data in a new window

Figure 1. Synapsid skulls in lateral view. A, Cotylorhynchus, a Lower Permian caseid. B, Varanosaurus, a Lower Permian ophiacodontid. C, Dimetrodon, a Lower Permian sphenacodontid. D, Titanophoneus, an Upper Permian therapsid. Redrawn from B, Berman et al. (1995); C, Romer and Price (1940), and D, Orlov (1958). Abbreviations: An, angular; Ar, articular; Bc, braincase; D, dentary; E, epipterygoid; F, frontal; J, jugal; L, lacrimal; M, maxilla; N, nasal; P, parietal; Pm, premaxilla; Po, postorbital; Pof, postfrontal; Prf, prefrontal; Pt, pterygoid; Q, quadrate; Qj, quadratojugal; Sa, surangular; Sp, splenial; Sq, squamosal; St, supratemporal; T, tabular. Scale bars equal 1 cm.

The main autapomorphy of Eothyrididae (Eothyris and Casea) is as follows:

Caseidae possesses the following autapomorphies:

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Click on an image to view larger version & data in a new window

Figure 2. Synapsid skulls in dorsal view. A, Cotylorhynchus, a Lower Permian caseid. B, Varanosaurus, a Lower Permian ophiacodontid. C, Dimetrodon, a Lower Permian sphenacodontid. D, Titanophoneus, an Upper Permian therapsid. Redrawn from B, Berman et al. (1995); C, Romer and Price (1940), and D, Orlov (1958). Abbreviations: Bc, braincase; F, frontal; J, jugal; L, lacrimal; M, maxilla; N, nasal; P, parietal; Pa, palatine; Pm, premaxilla; Po, postorbital; Pof, postfrontal; Pp, postparietal; Prf, prefrontal; Qj, quadratojugal; Sq, squamosal; St, supratemporal; T, tabular. Scale bars equal 1 cm.

Autapomorphies of Eupelycosauria:

Autapomorphies of Varanopseidae:

Autapomorphies of the clade including Ophiacodontidae, Edaphosauria, and Sphenacodontia (unnamed clade A in the above classification):

Autapomorphies of Ophiacodontidae include:

Click on an image to view larger version & data in a new window
Click on an image to view larger version & data in a new window

Figure 3. Synapsid skulls in occipital view. A, Cotylorhynchus, a Lower Permian caseid. B, Varanosaurus, a Lower Permian ophiacodontid. C, Dimetrodon, a Lower Permian sphenacodontid. D, Titanophoneus, an Upper Permian therapsid. Redrawn from B, Berman et al. (1995); C, Romer and Price (1940), and D, Orlov (1958). Abbreviations: Bc, braincase; J, jugal; P, parietal; Pp, postparietal; Ps, parasphenoid; Pt, pterygoid; Q, quadrate; Qj, quadratojugal; S, stapes; Sq, squamosal; St, supratemporal; T, tabular. Scale bars equal 1 cm.

Autapomorphies of Unnamed clade B (Edaphosauridae and Sephenacodontia) include:

Autapomorphies of Edaphosauridae include:

These three autapomorphies contribute to the peculiar morphology of the sail of edaphosaurs.

Autapomorphies of Sphenacodontia include:

Autapomorphies of Haptodus garnettensis include:

Autapomorphies of unnamed clade C (Palaeohatteria, Pantelosaurus, Cutleria, and Sphenacodontoidea) include:

Autapomorphies of Palaeohatteria longicaudata include:

Autapomorphies of unnamed clade D (Pantelosaurus, Cutleria, and Sphenacodontoidea) include:

Only one autapomorphy was identified in Pantelosaurus saxonicus:

Autapomorphies of unnamed clade E (Cutleria and Sphenacodontoidea) include:

Autapomorphies of Cutleria wilmarthi include:

Autapomorphies of Sphenacodontoidea include:

Autapomorphies of Sphenacodontidae include:

Autapomorphies of Therapsida include:

This list of autapomorphies takes into consideration the recent discovery of Tetraceratops, the oldest known therapsid (Laurin and Reisz, 1990, 1996). Tetraceratops lacks many derived characters present in other therapsids. Therefore, this list differs from other published lists of autapomorphies of therapsids (Hopson and Barghusen, 1986; Gauthier et al., 1988; Kemp, 1988; Hopson, 1991).

Page last updated March 21, 1997.

References

Berman D. S., R. R. Reisz, J. R. Bolt, and D. Scott. 1995. The cranial anatomy and relationships of the synapsid Varanosaurus (Eupelycosauria: Ophiacodontidae) from the Early Permian of Texas and Oklahoma. Annals of Carnegie Museum 64: 99-133.

Gauthier J., A. G. Kluge, and T. Rowe. 1988. Amniote phylogeny and the importance of fossils. Cladistics 4: 105-209.

Hopson J. A. 1991. Systematics of the nonmammalian Synapsida and implications for patterns of evolution in synapsids. In: H.-P. Schultze and L. Trueb (ed.) Origins of the higher groups of tetrapods-Controversy and Consensus (1): 635-693. Ithaca: Cornell University Press.

Hopson J. A. and H. R. Barghusen. 1986. An Analysis of Therapsid Relationships. In: P. D. M. Nicholas Hotton III, Jan J. Roth, and E. Carol Roth (ed.) The Ecology and Biology of Mammal-like Reptiles 83-106. Washington: Smithsonian Institution Press.

Kemp T. S. 1988. Interrelationships of the Synapsida. In: M. J. Benton (ed.) The Phylogeny and Classification of the Tetrapods (2): 1-22. Oxford: Clarendon Press.

Laurin M. and R. R. Reisz. 1990. Tetraceratops is the oldest known therapsid. Nature 345: 249-250.

Laurin M. and R. R. Reisz. 1996. The osteology and relationships of Tetraceratops insignis, the oldest known therapsid. Journal of Vertebrate Paleontology 16: 95-102.

Orlov Y. A. 1958. Primitive dinocephalians of the Isheeva fauna (Titanosuchi). Transactions of the Palaeontological Institute of the Academy of Sciences of the USSR 72: 1-113.

Reisz R. R. 1986. Pelycosauria. Encyclopedia of Paleoherpetology 17A: 1-102.

Reisz R. R., D. S. Berman, and D. Scott. 1992. The cranial anatomy and relationships of Secodontosaurus, an unusual mammal- like reptile (Pelycosauria: Sphenacodontidae) from the early Permian of Texas. Zoological Journal of the Linnean Society 104: 127-184.

Romer A. S. and L. I. Price. 1940. Review of the Pelycosauria. Vol. 28. Geological Society of America, Special Papers, New York: Arno Press.

About This Page

Michel Laurin
Muséum National d'Histoire Naturelle, Paris, France

Robert R. Reisz
University of Toronto, Mississauga, Ontario, Canada

Page: Tree of Life Autapomorphies of the main clades of synapsids Authored by Michel Laurin and Robert R. Reisz. The TEXT of this page is licensed under the Creative Commons Attribution License - Version 3.0. Note that images and other media featured on this page are each governed by their own license, and they may or may not be available for reuse. Click on an image or a media link to access the media data window, which provides the relevant licensing information. For the general terms and conditions of ToL material reuse and redistribution, please see the Tree of Life Copyright Policies.

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