late Carboniferous to later Early Permian Period
lowland terrestrial/semi-aquatic herbivores
An important evolutionary line of advanced Pelycosaurs springing from an ophiacodontid-varanopseid ancestry were the Edaphosaurs. These animals were quite different to their contemporaies the sphenacodontids. Unlike most pelycosaurs the edaphosaurs were inoffensive herbivores, as is shown by the structure of the skull and teeth. In fact, together with the diadectid amphibians, they were among the first tetrapod animals to adopt a herbivorous lifestyle.
Like their carnivorous contemporaries the sphenacodontids they 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 pelycosaurian lineages functioned as a temnperature 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, and in the case of Edaphosaurus and Ianthasaurus by the presence of well-developed lateral tubercles. 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.
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.
Edaphosauridae - list of genera
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 lanthasaurus 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.
Edaphosaurus possesses a combination of features that clearly indicate that this animal was a heavy, slow herbivor.
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 efficency 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 celluouse and other indigestable 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 or 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 is unclear, but inasmuch as Edaphosaurus was a succesful and wideranging 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 massice club-like processes. It is quite likely that Edaphosaurus evolved from a small insectivorous form like Ianthasaurus.
|some Links and References|
Biology 356 - Major Features of Vertebrate Evolution - Permo-Carboniferous Synapsids - by Dr. Robert Reisz, University of Toronto
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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