Name: Dimetrodon (species: D. angelensis, D. booneorum, D. dollovianus, D. giganhomogenes, D. grandis, D. limbatus, D. loomisi, D. macrospondylus, D. milleri, D. natalis, D. occidentalis, D. teutonis)
Name Meaning: Two Measures of Teeth
First Described: 1878
Described By: Cope
Classification: Eukaryota, Unikonta, Opisthokonta, Holozoa, Filozoa, Metazoa, Eumetazoa, Bilateria, Deuterostomia, Chordata, Olfactores, Craniata, Vertebrata, Gnathostomata, Eugnathostomata, Teleostomi, Osteichthyes, Sarcopterygii, Rhipidistia, Tetrapodomorpha, Tetrapoda, Reptiliomorpha, Amniota, Synapsida, Pelycosauria, Eupelycosauria, Sphenacodontia, Sphenacodontoidea, Sphenacodontidae, Sphenacodontinae
Dimetrodon was a synapsid from the Sakmarian age of the Early Permian, about 295 to 272 million years ago. It is well known for the large sail on its back, formed by elongated spines from the vertebrae. It was quadrupedal and had a long curved tail and heterodontition in its jaw. Fossils of it have been found in both the USA and in Northern Europe, with the first fossils found by Cope in the Red Beds of Texas. It has also been found in Utah, Texas, Oklahoma, and even Ohio and Illinois (I should go looking for it), as well as Germany. Being a synapsid, it was characterized by having only one temporal fenestra, or hole behind the eye socket. This makes it not a reptile, as reptiles are characterized by having two temporal fenestrae. However, it was an amniote, meaning it probably laid eggs, though egg fossils from the species have not been found.
The animal was up to 4 meters long and a carnivore, with finely serrated teeth and was probably the top predator of its environment. It had two different types of teeth: grabbing teeth, and shearing flesh teeth, allowing it to make short work of its prey. The sail was highly vascularized, though the webbing may not have extended all the way to the tips of the spins. This sail may have been used as camouflage, allowed for more stable side to side movement, or have been thermoregulatory. The evidence for thermoregulation is conflicting at best: the sail grew much faster than was necessary for thermoregulation, and it actually could have evolved for sexual selection, and thus could have been used as a display structure. Dimetrodon may have been sexually dimorphic as well, as there are two slightly different body size classes. It is still mildly unsure though which one is which sex.
This animal lived in a complex, but early land based ecological community, living in vast wetlands and lowland ecosystems of the Permian. It lived alongside amphibians Archeria, Diplocaulus, Eryops, and Trimerorhachis, the reptiliomorph Seymouria, the reptile Captorhinus, and the other synapsids Ophiacodon and Edaphosaurus. There are some juvenile specimens known, though they are a different species from known adult Dimetrodon and juveniles and adults may or may not have lived alongside one another. It is known from many species, but D. grandis was the largest known one. Other species show different morphology in the shape of the sail as well as the size of the sail.
Shout out goes to perilousechidna!