Author's note: these pages were written some years ago. I am not planning to update them. For a more current coverage, see the link to palaeos com Palaeos website (to which many links on these pages point to anyway. More info here

family Sphenacodontidae


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 

Genus list



Adult Length: from 60cm upto 1.5 meters
Adult Mass: 3 to 30 kg
Duration: Latest Carboniferous to Early Permian
Region: equatorial Pangea
Province: Edaphosaurid-Nectridean Empire
Ecological Niche: medium sized terrestrial predator
Habitat: lowlands, floodplains, near watercourses.
Food: smaller vertebrates, arthropods, whatever it could catch
Main predators: in the case of adults, probably none

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)

Haptodus garnettensis Currie 1977
Haptodus garnettensis

Length: about 60 cm
Mass: about 3 kg
Duration: link to palaeos com Kasimovian (Late Carboniferous)
Fossil remains: skeleton and skull elements

Notes: The most primitive known member of the Sphenacodontian lineage

Haptodus longicaudatus (Credner 1888)
Haptodus longicaudatus

Length: about 60 cm (juveniles)
Mass: about 3 kg
Duration: link to palaeos com Sakmarian (Early Permian)
Fossil remains: numerous remains, mostly of juveniles, from Niederhässlich, near Dresden, Germany.

Notes: Also known under the generic name Palaeohatteria.

Haptodus saxonicus (Von Huene 1925)
Haptodus saxonicus

Adult Length: upto 140 cm
Adult Mass: about 30 kg
Duration: link to palaeos com Asselian (Early Permian)
Fossil remains: six nearly complete remains, from the Döhlen Basin, near Dresden, Germany (Cuseler Stufe, lower Rotliegende).

Notes:Also known under the generic name Pantelosaurus

Haptodus wilmarthi (Lewis and Vaugn 1965)
Duration: Early Permian
Fossil remains: from the Cutler Formation of the Placerville area, Colorado, USA

Notes: Synonym: Cutleria wilmarthi (Lewis and Vaugn 1965)


SphenacodonDuration: Early Permian
Region: equatorial Euramerica
Ecological Niche: large terrestrial predator
Habitat: lowlands, floodplains, near watercourses.
Food: smaller vertebrates, whatever it could catch
Main predators: none (top of food chain)

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.

Sphenacodon ferox
Sphenacodon ferox

Adult Length: 177 cm
Adult Mass: 52 kg
Duration: link to palaeos com Sakmarian
Fossil remains: from the Abo/Cutler Formation, New Mexico, USA

Notes:Distinguished from the contemporary S. ferocior by smaller size, more slender build, and less neural spine development.

Sphenacodon ferocior
Sphenacodon ferocior

Adult Length: 225 cm
Adult Mass: 129 kg
Duration: link to palaeos com Sakmarian
Fossil remains: from the Abo/Cutler Formation, New Mexico, USA

Notes:A larger and less common contemporary of S. ferox, distinguished by more robust proportions and greater neural spine development.


Meaning of name: "two-measures tooth" (referring to the fact that unlike conventional reptiles the teeth differ in size)
Adult Length: upto three metres or more (varies according to species)
Adult Mass: around 150 kg (varies according to species)
Duration: early to mid Permian
Region: a localised area in western equatorial Euramerica (known only from Oklahoma and Texas) - West Edaphosaurid-Nectridean Empire - "Dimetrodon sub-province"
Habitat: lowlands, floodplains, pond and river margins.
Food: all other vertebrates, whatever it could catch
Main predators: none (top of the food chain)
Evolutionary relationships: An advanced member of the Sphenacodontid family.  May have evolved from an early Spheenacodon-like form (e.g. Sphenacodon ferox) during the latest Carboniferous or earliets Permian (Gzelian-Asselian) time.

Notes:  Perhaps the most well-known prehistoric non-dinosaur reptile, Dimetrodon was a common large carnivorous pelycosaur of the early Permian of North America, immediately recognisable by the "fin" or "sail" of elongate vertebral spines running along its back, upto a metre in length, and in life covered with a layer of skin and blood vessels and serving as a heat-exchange mechanism.  In size and build it was comparable to a modern-day alligator, except that it was a fully terrestrial (land-living) creature.  Dimetrodon was the dominant predator in its environment for some twenty-five million years, during which time it evolved through about a dozen species, become steadily larger as time progressed (an example of "Cope's Law"). Dimetrodon legs, although strong, were short, so it may have hunted through ambushing its prey, the sail on the back also no doubt serving to help camoflague the creature when it hid among stands of bamboo-like Calamite plants.

The largest, most specialised and most spectacular of the pelycosaur carnivores, Dimetrodon remained the dominant carnivore in its environment for some twenty-five million years, before being ousted by the up and coming eotitanosuchian and dinocephalian theraspids during the Ufimian age.  Curiously, despite its obvious adaptions, Dimetrodons remained confined to a limited geographical region (fossils are known only from the Witchita, Clear Fork and San Angelo beds of the Texas-Oklahoma region, and some fragments of a small early species from New Mexico).  This limited area (the actual extent being unknown due to the fact that only in a few places are there fossil deposits) is here termed the "Dimetrodon sub-province".

In skull and general body form, Dimetrodon was very similar to contemporary types like Sphenacodon and Ctenospondylus. However, these latter two have blade-like (narrow/flattened in cross section) neural spines supporting the sail, whereas Dimetrodon has greatly elongated spines that are rounded in cross-section section.

Dimetrodon is such a well-known creature it's even featured in most popular books on dinosaurs (even though it is not a dinosaur, and not even related).  There are also several webpages dedicated to it.   I've listed a few technical references under each species.

Known species:

well represented:

D. milleri Romer 1937 - Sakmarian
D. natalis (Cope 187 - Sakmarian
D. limbatus (Cope 1877) - Sakmarian and Artinskian
D. booneorum Romer 1937 - Artinskian
D. gigashomognes Case 1907 - Kungurian
D. grandis (Case, 1907) - early Kungurian
D. loomisi Romer 1937 - Kungurian
D. angelensis Olson 1962 - early Ufimian

known only from fragmentary material

D. dollovianus (Cope, 1888) - Artinskian
D. macrospondylus (Cope 1884) - Artinskian
D. occidentalis Berman 1977 - the only member of the genus from the Abo Foration, New Mexico

too fragmentary to tell what it is:

D. kempae Romer 1937 - Kungurian

Dimetrodon grandis
Dimetrodon grandis

Adult Length: 3.2 metres
Adult Mass: around 250 kg
Duration: Early link to palaeos com Kungurian

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.

under construction

Web links Dimetrodon on the web Web links

here are a few sites:

web page Dimetrodon - American Museum of Natural History - a good non-technical essay:

web pagePermain PeriodIncludes Dimetrodon images

web pageDimetrodon plaque - replica of skeleton preserved in rock

web pageDimetrodon bear - a little strange


under construction

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


Ctenospondylus casei
Ctenospondylus casei, shown here, is known from the Petrolia formation, (circa  271 - 272 million years ago)
(photo from Fossilnet Gallery)

some printed references some Links and References Web links

web pagesmall photographsBiology 356 - Major Features of Vertebrate Evolution - Permo-Carboniferous Synapsids - by Dr. Robert Reisz, University of Toronto

web pagecladogramdrawingsAutapomorphies of the main clades of synapsids - Michel Laurin and Robert R. Reisz - gives detailed information on Haptodine sphenacodonts and other basal synapsid foms

cladogramEupelycosauria (cladogram)

monograph Romer, A.S. and Price, L.I. Review of the Pelycosauria, Geological Society of America Special Papers,. no.28,

monographRobert R. Reisz, Pelycosauria, Encylopedia of Paleoherpetology, Part 17A, 1986, Gustav Fischer Verlag, Stuttgart and New York

Pelycosauria index page

images not loading? | error messages? | broken links? | suggestions? | criticism?

contact me

page history

page uploaded 17 June 1998
revised 31 October
and again 26 March 1999
converted to css format 18 July 2000, links updated 16 January 2010

text content by M.Alan Kazlev