Dimetrodon is the most famous early synapsid. Indeed it is likely the only one which most people would recognize. Despite appearing alongside dinosaurs in works of fiction and cheap plastic toys, it died out millions of years before they evolved. Although sometimes called ‘mammal-like reptiles’, Dimetrodon and its relatives aren’t actually reptiles either. It did look reptilian, however, with scaly skin, sprawling legs, a thick tail, and a spectacular sail running along its spine.
The sail's purpose remains hotly debated. The leading theory suggests it regulated body temperature, capturing morning sunlight and managing heat throughout the day. Other hypotheses propose it served for sexual display, rival intimidation, or spinal stabilization during rapid movement. The apparently conspicuous sail might have actually provided camouflage by mimicking the silhouettes of plants or harmless herbivores. Rather than the commonly depicted thin membrane, the sail could have been a fleshy hump storing fat and fluids for lean periods. More outlandish theories include it functioning as a sensory organ for detecting wind and air vibrations, or even acting as an actual sail when swimming!
As one of its era's biggest land animals, Dimetrodon was an apex predator. Later species grew even larger with proportionally bigger sails. Though favoring wetland habitats, these adaptable beasts could survive in arid environments as well.
Dimetrodon
ST 16; DX 11; IQ 2; HT 13.
HP 16; Will 12; Per 10; FP 13; Speed 5.00; Dodge 8; Move 4.
SM +2 (4 hexes), 500 lbs.
Bite (13): 1d+1 cutting.
Traits: Bad Sight (Low Resolution); Born Biter 2; Cold-Blooded (50°); Discriminatory Smell; DR 2; Enhanced Move 1 (Ground Speed 8; Costs Fatigue, 1 FP/second); Quadruped; Wild Animal.
Skills: Brawling-14; Survival (Swampland)-14; Swimming-13.
This profile suits the later and larger species such as D. angelensis or D. grandis. Earlier species such as D. natalis (60 lbs.) could have ST and HP as low as 8 (bite damage 1d−3) and DR 1.