The sphenacodontids were large carnivores Dimetrodon, Sphenacodon, Ctenospondylus, and Secodontosaurus (Reisz, Berman and Scott 1992). These reptiles were the dominant predators of their time, and their fossil record extends from the Latest Carboniferous through to the early Middle Permian.
All the sphenacodonts had a deep, narrow skull with massive jaws and a formidable array of teeth - long canines, daggerlike incisors and small, cutting cheek teeth. The name of the most well-known sphenacodontid, Dimetrodon, actually refers to this adaptation, it means "two measure teeth". The sphenacodonts were the first animals to develop such a specialized set of teeth, and were the first large terrestrial carnivores to evolve (all earlier large carnivores were eitehr fully or semi-aquatic).
Many of these forms (Dimetrodon, Sphenacodon, Secodontosaurus, and Ctenospondylus) are all large to very large predators that have tall neural spines that in life doubtless supporting a large "sail" or fin on the animal's back. This strange structure most certainly served as a thermoregulatory device. In the cool morning the creature would turn side on to the morning rays, thus soaking up heat and becoming more active before its rivals or prey did. During the middle of the day, or whenever the creature was in danger of overheating, it could turn head on to the sun, thus shading the fin and allowing excess heat to dissipate.
These animals had long limbs making them relatively agile, fast moving animals, especially when compared to their slower, bulkier herbivorous relatives. The later and larger types like Dimetrodon, Sphenacodon, and Ctenospondylus all have similarly constructed, massive skulls with extremely large anterior incisors and canines.
Not only were these animals of great ecological significance during their long reign, but they also have an important position on the evolutionary tree, being ancestral to primitive therapsids and ultimately to mammlas and man.
|?- Bathygnathus |?- Macrornerion |?- Neosaurus |-- Haptodus garnettensis `--+-- Haptodus (Palaeohatteria) longicaudatus `--+-- Haptodus (Pantelosaurus) saxonicus `--+-- Haptodus (Cutleria) wilmarthi `--o SPHENACODONTINEA |--o Sphenacodon | `--o Dimetrodon |?- Ctenospondylus | |?- Secodontosaurus | `-- THERAPSIDA
Notes:Haptodus is a relatively small pelycosaur that probably constiututes the basal or primitive ancestral type of the family. It shares many structural features of the skull and skeleton with the more specialised sphenacodontids, indicating they are closely related. Haptodus is known from the Late Pennsylvanian (Latest Carboniferous) and Early Permian of North America and Europe. Both small and medium sized individuals are known. These animals were clearly effective predators, like contemporary large tropical lizards, feeding on both arthropods and small vertebrates. Haptodus lacked the spectacular sail that characterised the bigger Sphenacodontids like Dimetrodon, Ctenospondylus, and Secodontosaurus. It is also more common in Europe (central equatorial Pangea), whilst the other forms are primarily American (west equatorial Pangea)
Notes: The most primitive known member of the Sphenacodontian lineage
Notes: Also known under the generic name Palaeohatteria.
Haptodus saxonicus (Von Huene 1925)
Notes:Also known under the generic name Pantelosaurus
Notes: Synonym: Cutleria wilmarthi (Lewis and Vaugn 1965)
Notes: The vertebral spines of Sphenacodon's backbone were long, and probably acted as attachment points for massive back muscles, allowing the animal to lunge powerfully at its prey. Sphenacodon did not have the elongate spines and distinctive "sail" of other advanced sphenacodontids.
Notes:Distinguished from the contemporary S. ferocior by smaller size, more slender build, and less neural spine development.
Notes:A larger and less common contemporary of S. ferox, distinguished by more robust proportions and greater neural spine development.
known only from fragmentary material
too fragmentary to tell what it is:
Notes: The last and largest of the long-skulled, stocky-bodied lineage of Dimetrodons. Apart from D. angelensis this was the largest species of Dimetrodon.
|Dimetrodon on the web|
Dimetrodon - American Museum of Natural History - a good non-technical essay:
Permain PeriodIncludes Dimetrodon images
Dimetrodon plaque - replica of skeleton preserved in rock
Dimetrodon bear - a little strange
Secodontosaurus is an unusual form that, although similiar in body, differs in the shape of the head from other sphenacodonts. The skull is low and narrow, although the neural spine morphology (of the "sail" backbone) is similiar to that of Dimetrodon. The cranial modifications of Secodontosaurus indicates an adaptation to specialised feeding strategies, perhaps preying upon burrowing animals, or perhaps aquatic feeding habits
|some Links and References|
Biology 356 - Major Features of Vertebrate Evolution - Permo-Carboniferous Synapsids - by Dr. Robert Reisz, University of Toronto
Autapomorphies of the main clades of synapsids - Michel Laurin and Robert R. Reisz - gives detailed information on Haptodine sphenacodonts and other basal synapsid foms
Romer, A.S. and Price, L.I. Review of the Pelycosauria, Geological Society of America Special Papers,. no.28,
Robert R. Reisz, Pelycosauria, Encylopedia of Paleoherpetology, Part 17A, 1986, Gustav Fischer Verlag, Stuttgart and New York
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