Palaeos Vertebrates 390.300 Synapsida: Ophiacodontidae & Edaphosauridae

*Palæos:*		Unit 390: Synapsida
*The Vertebrates*		300: Ophiacodontidae & Edaphosauridae

Page Back	Unit Back	Unit Home	Unit References	Unit Cladogram	Glossary	Taxon Index
Page Next	Unit Next	Vertebrates Home	Vertebrate References	Vertebrate Cladograms	Bones	Time

Synapsida: Ophiacodontidae & Edaphosauridae

Taxa on This Page

Ophiacodontidae

Ophiacodontids include small to very large carnivorous pelycosaurs distinguished by certain specialized cranial features. These were possibly semi-aquatic or fully aquatic animals, appearing early in the Carboniferous coal swamps.

There is a curious tendency to increase in the skull to trunk ratio, larger taxa having unusually large, awkward looking, elongate skulls. These animals also have relatively large, massive shoulder girdles, possibly to provide muscle attachment to support the weight of the huge head.

The modern cladistic paradigm unites ophiacodontids, edaphosaurids, and sphenacodontids by the possession of certain specialized features of the skull. However this is also the oldest family of pelycosaurs, and indeed of Synapsids/Theropsids, with the oldest known pelycosaurs - Protoclepsydrops and Archaeothyris - being included in this family (the former tentatively, the latter definitely).

From an ophiacodont stem, pelycosaurs evolved in two directions. One line of pelycosaurian development led to large aggressive, land-living carnivores, the sphenacodontids, the other to large plant- eating forms, the edaphosaurs. The ophaicodonts and edaphosaurs died out with the drying out of their swamp and pond-margin environments during the middle Permian, the sphenacodontids continued on a bit longer. (MAK 000720)

Characters: Semi-aquatic piscivores (per Romer. Reisz disagrees, based on the awkward length and height of the skull). Up to 4m. Head long & slender; deep jaw; numerous (40+) small teeth; well-developed lateral mandibular fenestra in notch of dentary; posterodorsal processes of premaxillae are long, thin & separated at midline by anterior process of nasal; angular with well developed ventral keel; lingual maxillary buttress above canines; $ antorbital skull at least twice as long as postorbital skull; $ nasal longer than frontal (at least twice as long as parietal); lacrimal elongated; orbit high on skull; ventral edge of skull concave postorbitally & includes jugal; relatively low skull table; braincase elements less fused than in other eupelycosaurs; $ paroccipital process short, not extending to the cheek long tail; tabular with large medial process; pectoral girdles large and massive; particularly broad anterior of scapulocoracoid; carpals & tarsals poorly ossified; claws blunted? absent?. Includes oldest known synapsid (Protoclepsydrops).

Range: Pennsylvanian (Kasimovian, possibly Moscovian) of North America (Nova Scotia) [TH04]

Introduction: Protoclepsydrops from the Middle Pennsylvanian of Joggins, Nova Scotia has been placed within the Ophiacodontidae, but its identity and taxonomic status is uncertain, partly because the known skeletal remains are fragmentary. Archaeothyris, from slightly younger sediments near Florence, Nova Scotia, is the oldest known diagnosable ophiacodontid. This was a more advanced animal than the contemporary protorothyrid captorhinomorphs. Its jaws were strong, and could be opened wide and snapped shut. Although its teeth were all the same shape - sharp and pointed - they were of different sizes, including a large pair of canines at the front of the jaws. Such teeth suggest a varied, carnivorous diet, and area distinguishing mark of the carnivorous pelycosaurs. MAK

Introduction: Ophiacodon, a large Permian synapsid commonly 1.5 to 2.5 meters in length, was a specialized member of the ophaicodontid lineage. It is also the best known member of the family, represented by an extensive fossil record in North America, that has been subdivided, somewhat arbitrarily (based largely on stratigraphic position and size) into six species. The skull was very deep, with long jaws, these being provided with many sharp teeth. It has often been suggested that Ophiacodon was a fish-eating animal that lived largely along the shores of streams and ponds, although the high narrow skull would seem to mitigate against such a lifestyle. MAK

Introduction: An important evolutionary line of early synapsids springing from an ophiacodontid- varanopseid ancestry were the edaphosaurs. These animals were quite different from their contemporaries, the sphenacodontids. Unlike most basal synapsids, the edaphosaurs were herbivores, as is shown by the structure of the skull and teeth. In fact, together with the diadectomorphs, they were among the first tetrapod animals to adopt a herbivorous lifestyle.

Like their carnivorous sphenacodontid cousins, edaphosaurs were often equipped with a large sail along the back, formed by a great elongation of the neural spines of the vertebrae. This striking features, exhibited by several early synapsid lineages, functioned as a temperature control device and perhaps also for sexual display

Edaphosaurus and Ianthasaurus are the only pelycosaurs that can be placed with confidence in this family, but a number of other less well known forms, like Luperosaurus and Nitosauruus, may belong here as well. Apart from the poorly known Nitosaurus, all are characterized by the presence of greatly elongated neural spines that are rounded in traverse section. In the case of Edaphosaurus and Ianthasaurus, the neural spines also bear well-developed lateral tubercles or crossbars, like mast of an old-fashioned square-rigged sailing ship. The arrangement of these tubercles along the height of the spines is similar in the two taxa, as is the loss of contact between the postorbital and supratemporal bones of the skull. MAK

Despite superficial differences, edaphosaurs and sphenacodonts also share a large number of cranial features, and it seems that these two groups may have descended from a common ophaicodont or varanopseid ancestor.

Characters: Herbivorous pelycosaurs with "sails." Small head; skull short and broad; teeth uniform, short and peg-like; large, toothed pterygoid and facing teeth on internal lower jaw; jaw short, but broad and massive; "reflected" lamina of angular (characteristic of sphenacodonts and therapsids) not present; massive supraorbital shelf (bony "eyebrow"); subtemporal arch from jugal & squamosal; anterior process of quadratojugal reduced; posterior process of postorbital reduced, with loss of contact between postorbital and supratemporal; body barrel-shaped; dorsal vertebrae with elongated neural spines bearing multiple short transverse cross-bars; neural spines circular in cross section distal to laterally compressed proximal section; cervical neural spines lean anteriorly & posterior spines lean posteriorly; neural spines presumably supported presumed "sails" (independently derived from sphenacodonts?) with possible thermoregulatory function; limbs short. May have evolved from insectivores; often said to have inhabited swampy or marsh areas.

Introduction: Ianthasaurus is a small edaphosaur from the Late Pennsylvanian that lacks many of the spectacular specializations seen in Edaphosaurus. For example, the marginal dentition of Ianthasaurus is similar to that of insectivorous reptiles, with slender conical teeth which are slightly recurved at the tips, and there is a slight development of a caniniform region. The palatal and mandibular dentition is unspecialized, and there are no batteries of teeth for crushing of plant materials. Also unlike Edaphosaurus, Ianthasaurus was lightly built and was probably quite agile. Ianthasaurus also shows many similarities in its cranial morphology to the small, primitive sphenacodont Haptodus. MAK

Introduction: Edaphosaurus possesses a combination of features that clearly indicate that this animal was a heavy, slow herbivore.

The skull of Edaphosaurus was remarkably small as compared with the size of the body. It is also short and rather shallow, as contrasted with the elongated skull of the sphenacodonts. Also unlike sphenacodonts and ophaicodonts, the teeth in the edaphosaurs are quite uniform, making an unbroken series around margins of the jaws. In addition to the marginal teeth, there is a massive array of closely packed teeth that ground against a similar set of teeth on the medial surface of the mandible. Clearly these extensive clusters of teeth added to the efficiency in grinding up plant material.

In keeping with the tiny head the cervical (neck) vertebrae are reduced in length, while the dorsal (back) vertebrae are massive, the tail is deep, the limbs are short and robust and the ribs form a wide ribcage. Like most herbivores, Edaphosaurus would have had a capacious gut and symbiotic bacteria to aid in the breakdown of cellulose and other indigestible plant material

Edaphosaurus was characterized by an elongation of the vertebral spines, but the spines are heavier than they were in other forms like Echinerpeton, Lupeosaurus, and the sphenacodontids like Dimetrodon. Moreover, they were ornamented with numerous short lateral projections, tubercles, or crossbars arranged irregularly along their length, rather like the yardarms on the mast of an old sailing ship. The benefits of such an adaptation are unclear, but inasmuch as Edaphosaurus was a successful and wide-ranging animal they surely served some purpose. One possibility is that they may have served as protection against predators, by strengthening the neural spines. The front and rear spines are tilted forwards and backwards respectively, perhaps provided protection in the neck and thigh region, respectively.

Nine species of Edaphosaurus have been described, ranging in size from small (only about half a meter or less) to very large, bulky animals (over three meters long). The largest species, Edaphosaurus cruciger and Edaphosaurus pogonias (see above) have modified their cervical and anterior thoracic spines into massive club-like processes. It is quite likely that Edaphosaurus evolved from a small insectivorous form like Ianthasaurus. MAK

Synapsida: Ophiacodontidae & Edaphosauridae

Abbreviated Cladogram

Contents

Taxa on This Page

Ophiacodontidae