Sphenacodon

Skeletal reconstruction of Sphenacodon ferox in the Natural History Museum of Chicago

• USA

• Sphenacodon ferox Marsh, 1878

Sphenacodon (Greek " spline " ) is an extinct genus of synapsids from the late Carboniferous and early Permian with an age of about 300 to 270 million years. Like its close relative Dimetrodon, Sphenacodon was a carnivorous member of the family of Sphenacodontidae from the clade of Eupelycosauria. Unlike Dimetrodon Sphenacodon had no high back sailing, but a low ridge, which was formed from the elongated spinous processes of the vertebrae. Fossils of Sphenacodon are known from New Mexico and the border region of Utah and Arizona in North America.

Currently two types are scientifically recognized: Sphenacodon ferox ( type species ) and Sphenacodon ferocior. Sphenacodon ferocior could reach a size of up to three meters and was 40 percent larger than Sphenacodon ferox, which could reach a length of about two meters. In addition, the dorsal ( back-side ) projections of Sphenacodon were ferocior proportional up to 45 percent longer than Sphenacodon ferox. With the recent discoveries of a nearly complete skull of Sphenacodon ferox could further distinctions between the two species are elucidated, such as the number of teeth in certain regions of the jaw and the size of the indentation between the upper jaw and the Zwischenkieferbein. Both species appear together in some formations, but Sphenacodon ferox seems to have survived well into the early Permian into it.

Description

The skull of Sphenacodon was very similar to that of Dimetrodon. It was narrow from one side to the other, but wider vertically. At the front of the maxilla of the upper jaw, there was an indentation. Upper and lower jaws were equipped with a range strong teeth, which in sharp incisors ( präcanine ), large, dagger -like fangs ( caniniforme ) and smaller molars ( postcanine ) were formed. The orbit was high and wide rear with a single pace Ralf Rochester behind and partly below the eye as for Synapsids characteristic.

The body proportions are also similar to those of Dimetrodon: Very large head, short neck, robust trunk and relatively short front and hind limbs, and a tapering tail, which accounted for about half the body length of the animal. However Sphenacodon did not have the extremely elongated, cylindrical spines and spinal sailing abgeleiteterer forms of Sphenacodontiden as Dimetrodon. Instead Sphenacodon had only extended slightly, but flattened spinous processes, on which probably muscles were attached, which allowed the robbers to be powerful to pounce on its prey. The sphenacodontide genus Ctenospondylus also did not have extended spinous processes, their dorsal crest was higher than that of Sphenacodon, but as high as that of Dimetrodon.

There is evidence of a pronounced epaxiale muscles along the base of the spinous processes at elevated Sphenacodon. Most likely, these muscles were stiffening and reinforcement of the spine at the Fort movements and the hunting of prey by taking tied meandering movements. A recent study on the structure of the spinous processes of Sphenacodon confirms the assumption that the upper parts of the spinous processes were not surrounded by muscle, but stood out from the muscle layer and a low dorsal crest formed. Findings of specimens, in which post-mortem pathological curvature of the body caused by a superposition of the projections, suggest that these were not connected to each other through hard or particularly resistant fabric. The function of this low, covered with skin back ridge of Sphenacodon is the subject of scientific debate. A thermoregulatory function appears unlikely, although the higher ridge at Sphenacodon is allometrically larger ferocior than Sphenacodon ferox. Recent studies favor a function for the expression behavior for the high sails of Dimetrodon and Edaphosaurus.

In traditional representation of both Sphenacodon as well as Dimetrodon the short limbs of both classes at an angle of 90 degrees were abducted from the body, tail and belly of the animals similar to modern lizards and crocodiles dragged across the floor. Such an attitude is typical of the contemporary skeletal reconstructions of Sphenacodon in museums. Footmarks of Dimetropus et al from Bromacker, which are consistent with the large foot placement Sphenacodontiden and have no tail or belly casts, however, show that the animals were moving themselves by keeping their limbs under the body and had a narrow, semi- erect gait. Such clear evidence for efficient upright position suggest that important details of the anatomy and locomotion of Sphenacodon and other early Pelycosauriern are not yet fully understood. Some well-preserved Dimetropus tracks from the Prehistoric Trackways National Monument in New Mexico fit to the relatively small size of Sphenacodon, which is evidenced by the fossil record in this area. The tracks can also originate by another representative of the Sphenacodonten.

Sphenacodon and Dimetrodon are typical example found in different geographical regions that were separated by the primeval Hueco - sea, which during the early Permian wide areas of the equatorial Pangaea covered ( the southern part of present-day Mexico ). Sphenacodon is known from the western New Mexico, Arizona and Utah, while Dimetrodon can mainly be found from the more eastern former Delta regions of Texas and Oklahoma. The type Dimetrodon occidentalis but was found in New Mexico. Each of the two genera presented probably the terrestrial Spitzenprädator in its ecosystem is and probably captured amphibians, Diadectomorphe, and early synapsids and Diapsiden. Sphenacodon seems to have died out around 280 million years ago during the Wolfcampiums. The genus Dimetrodon survived, however, until about 270 million years. Such large sphenacodontiden robbers were later replaced by the therapsids, that group of synapsids, which included the direct ancestors of mammals.

History of discovery and classification

The American paleontologist Othniel Charles Marsh gave the first description in 1878 of Sphenacodon using a part of a lower jaw bone, which had been found by the fossil collector David Baldwin in the Rotliegend of northern New Mexico. The name " Sphenacodon " consists of ancient Greek σφήνη " wedge", ἀκή, "point" and ὀδούς "tooth" together. In his very brief description of the jawbone Marsh led the compressed crowns of the molars and their " very sharp cutting edges without battlements " and concluded that the animal was about 2 feet long to be had and a carnivore, although the rest of the skeleton was unknown. He also prepared a sketch of the instance. Marsh knew the type species with the epithet ferox (wild) and created the family of Sphenacodontidae, which he put to the primitive reptilian order " Rhynchocephala " ( Rhynchocephalia ). Then he took it together almost all groups earlier reptiles and the extant tuatara.

Other paleontologists gave Marsh's brief mention of Sphenacodon for nearly three decades no attention. Dimetrodon, which was also named in 1878 by Marsh's rival Edward Drinker Cope, became a scientifically important genre that was well documented by many finds. The recognition of Sphenacodon as a carnivorous Pelycosaurier with low back comb, which differed from Dimetrodon, happened during the early 20th century, as more fossils were found in New Mexico. The proposed at this time taxa Elcabrosaurus baldwini ( Case, 1907) and Scoliomus (Williston and Case, 1913) are now regarded as junior synonyms of Sphenacodon ferox.

Alfred Sherwood Romer in 1937 described a second species from New Mexico, which he called Sphenacodon ferocior ( "wild " ) because it was bigger, made a more robust impression and longer spines possessed. Romer and Price (1940 ) provided detailed descriptions of both S. ferox and S. ferocior with skeletal reconstructions.

A third type, Sphenacodon britannicus is sometimes cited in the literature. This was described in 1908 by German paleontologist Friedrich von Huene as Oxyodon britannicus based on a maxilla from England. The genus name Oxyodon ( Baur, 1906), however, was already occupied by a fish species and therefore possessed for the described type not valid. The specimen had been previously identified as a possible Triassic dinosaur, but v. Hühne recognized a Pelycosaurier. In 1974, the species was to the genus Sphenacodon found under the Note that the specimen had approximately the size of Sphenacodon ferox. Recent studies, however, have raised the question of how can be distinguished on the basis of such scanty fossil material between Dimetrodon, Sphenacodon or a separate genus. The kind of " Oxyodon " Britannicus (or Sphenacodon (?) Britannicus ) is now generally classified as incertae sedis Sphenacodontidae.