The Primary Purpose Of Sails On The Backs Of Pelycosaurs Was Likely To Help The Animals Do What?

Introduction to the Pelycosaurs

Synapsids with mental attitude

The "pelycosaurs" are members of the Synapsida, a major branch of the Amniota. Pelycosaurs are the earliest, most primitive synapsids, a group characterized by a single dermal opening in the skull permitting musculus zipper to the jaw. This ways that the pelycosaurs are non reptiles, since reptiles accept two such openings in their skulls. Like virtually other groups of synapsids, all pelycosaurs are now extinct. In fact, the only currently living synapsids are the mammals. It is believed that the pelycosaurs, like their living mammal relatives, were endothermic, which means that they maintained a constant internal body temperature. This is some other feature that sets pelycosaurs autonomously from the reptiles. If this view is correct, then pelycosaurs are one of the earliest examples of endothermic animals.

In many respects, the pelycosaurs are intermediate betwixt the reptiles and mammals, so they have commonly been referred to as "mammal-similar reptiles". The pelycosaurs indeed resemble large lizards in their overall appearance, but every bit nosotros have seen, this is a misnomer since pelycosaurs are not reptiles. The name "pelycosaur" refers to a paraphyletic group of basal synapsids consisting of 6 separate branches: Caseasauria, Varanopseidae, Ophiacodontidae, Edaphosauridae, "Haptodonts", and Sphenacodontidae. It is currently believed that haptodonts themselves are a paraphyletic group. The Sphenacodontidae are probably the well-nigh closely related to the Therapsida (the group that includes mammals).

Sphenacodonts : Because the pelycosaurs are a paraphyletic group, it should not be surprising that there is considerable diverseness of form in the grouping. Among the pelycosaurs, the sphenacodonts are believed to be the group most closely related to the mammals. These include the famous "finback" Dimetrodon, shown in a higher place at left, which dominated the land fauna of the Permian but went extinct by the end of that period. The sphenacodonts also include the "haptodonts", such equally Haptodus, shown above at correct. (Click on either of the pictures higher up for a larger image).

Pelycosaurs first appeared during the upper Carboniferous (Lower Pennsylvanian) and went extinct by the end of the Permian. With the formation of the supercontinent Pangea in the Permian, continental area exceeded that of oceanic area for the first time in geological history. The result of this new global configuration was the extensive evolution and diversification of Permian terrestrial vertebrate brute including pelycosaurs. Consequently, their fossils are found in multiple localities effectually the globe. However, the majority of pelycosaur fossils have been discovered in Texas and Oklahoma, where they are amid the well-nigh common fossils of the Early Permian. Much of the oil in the two states derives from the Permian period, and the search for this oil is partially responsible for the plethora of pelycosaur fossils institute.

Dimetrodon is the most familiar example of a pelycosaur. A powerful carnivore, Dimetrodon was the top predator of the Permian period. With its large head and numerous large, sharp teeth, information technology fed on other vertebrates, including other pelycosaurs, that shared the swamps where it lived. Dimetrodon was about three-and-a-one-half meters (eleven anxiety) long and probably weighed about 100-150 kg (200-300 pounds). Four short and thick legs supported this massive body.

The physical appearance of Dimetrodon is quite distinct. While its torso was long, it was relatively short. It was built similar a large lizard with ane important exception: a "sail". The bony canvass supports rose well-nigh a meter vertically from its back and were continued by highly vascularized skin. The most popular conjecture regarding the role of the sail is thermoregulation. Such a sail would allow a large area for acquiring or releasing estrus. Studies have shown that the area of the sail is proportional to the volume of the Dimetrodon body, as would be expected if the sail were important for oestrus commutation. While many tetrapods in many lineages have evolved like sail-like structures, Dimetrodon is the best known so the majority of work done exploring the function of the sheet has centered on this pelycosaur.

Still, It must be noted that not all pelycosaurs had sails. Still, almost pelycosaurs were similar to Dimetrodon in that they besides were carnivores with large, powerful jaws, and 2 types of teeth: sharp canines and shearing teeth. Two major exceptions to this meat nutrition were the Caseidae and the Edaphosauridae, who were herbivores. While the Caseids were far more various, the most familiar of the herbivorous pelycosaurs is another sail-dorsum, Edaphosaurus. Edaphosaurus had a smaller skull than Dimetrodon, and had large peg-like teeth for grinding and crushing plants. This adaptation allowed pelycosaurs to flourish, and past the beginning of the Permian, pelycosaur genera account for 70 percent of all the known amniotes, outnumbering the reptiles.

Edaphosaurus : Pelycosaurs include a variety of forms and lifestyles. Not all of them were carnivores; some, like Edaphosaurus, were herbivores. In the image above at left, you can see that in that location are no nasty, pointy teeth filling this pelycosaur's jaw. You lot may besides see the additional knobs sticking out from the dorsal fin bones, which are unique to the Edaphosauridae. At correct, yous can see a fully mounted skeleton from the Permian of Texas. The long tail and sprawling posture are characteristic of the pelycosaurs. These images were taken at the Field Museum of Natural History in Chicago. (Click on either of the pictures to a higher place for a larger image).

Pelycosaurs are an important lineage preserved in the fossil tape. They are the earliest known synapsids, the get-go to evolve specializations that would play an important function in the rise to mammals. They are thus a transitional group in both form and functions. Schad (1994) presents two general rules concerning transitional areas. Firstly, no intermediate class represents a totally intermediate grapheme. This is to say that no evolutionary status has been found in whatever taxon where all characteristics are nowadays of both taxa that the status is intermediate to. Secondly, evolutionary transformation predominates in the extremities, and only subsequently affects the centric system. Bearing in mind these principles, we can begin to empathize the development of mammals from their pelycosaur roots.

The pelycosaurs exhibit the first substantial progress of crawling to running. This evolution in the extremities required a modification of the metabolism in the muscular system to provide the free energy reuired for more strenuous action. The resulting modify in the centric system brought about endothermy. Supporting this idea is the fact that as later pelycosaurs and afterwards synapsids evolved, the surface area of sail to body mass ratio decreased. This shows the tendency of reduced demand for outside thermoregulation, which would require an increased apply of endothermy, an important feature today separating the reptiles and mammals.

Visit the Synapsida pages at the Tree of Life, which includes a full discussion of the autapomorphies of the main clades of synapsids, with a focus on the basal (pelycosaur) groups. Or scan Jack Conrad's pages on Synapsida for additional information.

Images of Edaphosaurus taken by B. Chiliad. Waggoner at the Field Museum of Natural History in Chicago. Image of Haptodus plaque besides past B. K. Waggoner and taken at the Senckenberg Museum in Frankfurt, Germany. Photo of Dimetrodon diorama shot at the Carnegie Museum in Pittsburgh by John R. Hutchinson.

Sources:
Bennet, Southward. Christopher. 1996. Aerodynamics and thermoregulatory function of the dorsal canvas of Edaphosaurus. Paleobiology 22: 496-506.

Carroll, R. Fifty. 1988. Vertebrate Paleontology and Evolution. New York: W. H. Freeman.

Florides, G. A., 50. C. Wrobel, Southward. A. Kalogirou, Due south. A. Tassou. 1999. A thermal model for reptiles and pelycosaurs. Periodical of Thermal Biology 24: 1-3.

Hillenius, Willem J. 1994. Turbinates in the Therapsids: Bear witness for Late Permian origins of mammalian endothermy. Evolution 48: 207-229.

Hopson, James A. 1994. Synapsid evolution and the radiation of not-eutherian mamals. Pp 190-219 in D. R. Prothero & R. M. Schoch (eds.) Major Features of Vertebrate Evolution. Short Courses in Paleontology 7.

Schad, Wolfgang. 1994. Heterochronical patterns of evolution in the transitional stages of vertebrate classes. Acta Biotheoretica 41(iv): 383-389.

Sidor, C. A. & J. A. Hopson. 1998. Ghost lineages and "mammalness": Assessing the temporal pattern of graphic symbol acquisition in the Synapsida. Paleobiology 24: 254-273.