Edaphosaurus

Julius T. Csotonyi Artwork

***Edaphosaurus*** (/ˌɛdəfɵˈsɔrəs/}; meaning "pavement lizard" for dense clusters of teeth) is a genus of extinct edaphosaurid synapsid that lived around 300 to 280 million years ago, during the late Carboniferous to early Permian periods. The American paleontologist Edward Drinker Cope first described Edaphosaurus in 1882, naming it for the "dental pavement" on both the upper and lower jaws, from the Greek edaphos/εδαφος ("ground"; also "pavement") and σαυρος/sauros ("lizard").

*Edaphosaurus* is important as one of the earliest known large plant-eating (herbivorous) amniote tetrapods (four-legged land-living vertebrates). In addition to the large tooth plates in its jaws, the most characteristic feature of *Edaphosaurus* is a sail on its back. A number of other synapsids from the same time period also have tall dorsal sails, most famously the large apex predator *Dimetrodon*. However, the sail on *Edaphosaurus* is different in shape and morphology. The first fossils of *Edaphosaurus* came from Texas in North America, with later finds in New Mexico, Oklahoma, and West Virginia. Fragmentary fossils attributed to *Edaphosaurus* also have been found in the Czech Republic and in Germany in Central Europe.

## Etymology

The name *Edaphosaurus*, meant as "pavement lizard", is often translated inaccurately as "earth lizard", "ground lizard", or "foundation lizard" based on other meanings for the Greek edaphos, such as "soil, earth, ground, land, base" used in Neo-Latin scientific nomenclature (edaphology). However, older names in paleontology, such as Edaphodon Buckland, 1838 "pavement tooth" (a fossil fish), match Cope's clearly intended meaning "pavement" for Greek edaphos in reference to the animal's teeth.

## Description and paleobiology

*Edaphosaurus* species measured from 0.5 metres (1.6 ft) to almost 3.5 metres (11.5 ft) in length and weighed over 300 kilograms (660 lb). In keeping with the tiny head, the cervical vertebrae are reduced in length, while the dorsal 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 indigestable plant material. Like its more famous relative *Dimetrodon*, *Edaphosaurus* had a sail-like fin that was supported by bones of the vertebral column. *Edaphosaurus* differs from *Dimetrodon* in having cross-bars on the spines that supported its fin.

### Skull

The head of *Edaphosaurus* was short, relatively broad, triangular in outline, and remarkably small compared to its body size. The deep lower jaw likely had powerful muscles and the marginal teeth along the front and sides of its jaws had serrated tips, helping *Edaphosaurus* to crop bite-sized pieces from tough terrestrial plants. Back parts of the roof of the mouth and the inside of the lower jaw held dense batteries of peglike teeth, forming a broad crushing and grinding surface on each side above and below. Its jaw movements were propalinal (front to back). Early descriptions suggested that Edaphosaurus fed on invertebrates such as mollusks, which it would have crushed with its tooth plates. However, paleontologists now think that *Edaphosaurus* ate plants, although tooth-on-tooth wear between its upper and lower tooth plates, indicates only "limited processing of food" compared to other early plant-eaters such as Diadectes, a large non-amniote reptiliomorph (Diadectidae) that lived at the same time. Early members of the Edaphosauridae such as Ianthasaurus lacked tooth plates and ate insects.

### Sail

The sail along the back of *Edaphosaurus* was supported by hugely elongated neural spines from neck to lumbar region, connected by tissue in life. When compared with the sail of Dimetrodon, the vertebral spines are shorter and heavier, and bear numerous small crossbars. *Edaphosaurus* and other members of the Edaphosauridae evolved tall dorsal sails independently of sail-back members of the Sphenacodontidae such as *Dimetrodon* and *Secodontosaurus* that lived at the same time, an unusual example of parallel evolution. The function(s) of the sail in both groups is still debated. Researchers have suggested that such sails could have provided camouflage, wind-powered sailing over water, anchoring for extra muscle support and rigidity for the backbone, protection against predator attacks, fat storage areas, body temperature control surfaces, or sexual display and species recognition. The height of the sail, curvature of the spines, and shape of the crossbars are distinct in each of the described species of *Edaphosaurus* and show a trend for larger and more elaborate (but fewer) projecting processes over time. Romer and Price suggested that the projections on the spines of *Edaphosaurus* might have been embedded in tissue under the skin and might have supported food-storage or fat similar to the hump of a camel. Bennett argued that the bony projections on *Edaphosaurus* spines were exposed and could create air turbulence for more efficient cooling over the surface of the sail to regulate body temperature. Recent research that examined the microscopic bone structure of the tall neural spines in edaphosaurids has raised doubts about a thermoregulatory role for the sail and suggests a display function is more plausible.

## Discovery and classification

Edward Drinker Cope named and described *Edaphosaurus* ("pavement lizard") in 1882, based on a crushed skull and a left lower jaw from Texas. He noted in particular the "dense body of teeth" on both the upper and lower jaws, and used the term "dental pavement" in a table in his description. The type species name pogonias means "bearded" in Greek, referring to the enlarged inward sloping chin on the lower jaw. Cope classified *Edaphosaurus* as a member of his Pelycosauria and created the new family Edaphosauridae. The type material did not include any of the post-cranial skeleton apart from an axis vertebra and Cope was unaware of the animal’s large sail, a feature then known only for *Dimetrodon*.

In 1886, Cope erected the new genus *Naosaurus* "ship lizard" (from Greek naos "ship") for skeletal remains similar to those of the long-spined *Dimetrodon* but with distinctive "transverse processes or branches which resemble the yardarms of a ship's mast". He speculated that "the yardarms were connected by membranes with the neural spine or mast, thus serving the animal as a sail with which he navigated the waters of the Permian lakes". He recognized three species: *Naosaurus claviger* "club-bearer" (for the projections on its spines; now considered a synonym of *Edaphosaurus pogonias*); *Naosaurus cruciger* "cross-bearer" (for the projections on its spines; first described by Cope as *Dimetrodon cruciger* in 1878; now *Edaphosaurus cruciger*, the largest species in size); and *Naosaurus microdus* "small tooth" (first described as *Edaphosaurus microdus* in 1884). Cope noted some incomplete skull material found associated with the specimens of *N. claviger* and *N. microdus*, but thought *Naosaurus* was distinct from *Edaphosaurus*. He later decided that *Naosaurus* must have had a large carnivorous skull similar to *Dimetrodon*, although he had no direct fossil proof.

In 1907, the American paleontologist Ermine Cowles Case suggested that the skull of *Edaphosaurus* might belong with skeletons called *Naosaurus*, based on a specimen found in 1906 that appeared to associate elements of both. In 1913, Samuel Wendell Williston and Case described the new species *Edaphosaurus novomexicanus* from a fairly complete specimen unearthed in New Mexico in 1910, in which a sailbacked *Naosaurus*-type skeleton was found with a small *Edaphosaurus*-type skull. The older generic name *Edaphosaurus* Cope, 1882 became the valid one.

In 1940, paleontologists Alfred Sherwood Romer and Llewellyn Ivor Price named the new species *Edaphosaurus boanerges* ("thunderous orator")--an ironic reference to the remarkably small size of the holotype lower jaw on a composite skeleton originally mounted in the Museum of Comparative Zoology (Harvard University) with the head restored based on the larger species *Edaphosaurus cruciger.*

In 1979, paleontologist David Berman erected *Edaphosaurus colohistion* ("stunted sail") for an early species with a relatively small sail, based on fossils from West Virginia.

Other proposed species of *Edaphosaurus* have been based on more fragmentary material that cannot be rigorously diagnosed to a genus/species level, but which may nonetheless represent edaphosaurids.

## Appearance in other media

### *Jurassic Park*

* Edaphosaurus appeared in the video game Jurassic World: Alive.

### *The Land Before Time*

* in *The Land Before Time: Preschool Adventure*, it appeared in the four-legged creature valley of 'Cera's Creature Categories' minigame.