Thermosynapsida Founding Form

The founding form of the proposed order Thermosynapsida is recorded in the archive as a small-bodied, cave-associated synapsid occupying the pelycosaur-therapsid transition zone. It is not treated as a direct synonym of Dimetrodon grandis or any named pelycosaur taxon. Instead the restricted registry treats it as a derived relative whose anatomy already reflects sustained fossorial activity, low-light specialization, and a metabolic profile intermediate between surface-active pelycosaurs and later therapsids.

The record remains fragmentary, but the character suite is internally coherent. Robust excavation claws, reduced orbits, enlarged cranial gland impressions, reduced caniniform dentition, and elevated metabolic efficiency all point toward a lineage adapting to geothermal cave life before the better-known therapsid surface radiation reached its Late Permian peak.

Claims

c0001 - Founding-form body size falls at 0.3 to 0.8 m and 0.4 to 3.2 kg

The GDCC Morphology Registry records the founding Thermosynapsida form as a small-bodied synapsid with estimated snout-vent length of 0.3 to 0.8 meters and estimated mass of 0.4 to 3.2 kilograms. The estimate derives from regression equations applied to fragmentary long-bone material and is explicitly carried with uncertainty, but even the upper bound remains far below adult Dimetrodon grandis scale and near the lower range of contemporaneous cynodonts.

c0002 - Manual unguals are broadened, grooved, and mechanically fossorial

The founding form's manual claws are broader and more laterally compressed than the slightly recurved grasping unguals typical of pelycosaurs. A pronounced medial groove and disproportionate forelimb robustness align the material more closely with sustained substrate excavation than with ordinary surface locomotion. In functional terms the hand is built for digging compact cave-adjacent substrate rather than for prey capture on open ground.

c0003 - Orbit-to-skull ratio below 0.18 indicates low-light reallocation

The most complete skull material in the restricted collection yields an orbit-to-skull ratio below 0.18, markedly smaller than the 0.22 to 0.25 range cited for Dimetrodon grandis. The archive interprets this not as full eye reduction but as transitional reallocation of cranial investment away from large visual organs and toward chemosensory, mechanosensory, or gland-bearing structures better suited to regular subterranean use.

c0004 - Cranial gland impressions exceed 8 percent of dorsal skull surface

The founding form preserves bilateral skull-roof depressions whose total area exceeds 8 percent of dorsal skull surface in the best specimen. Periosteal remodeling around the margins implies long-term soft-tissue loading rather than incidental taphonomic damage. The archive reads these impressions as enlarged cutaneous gland complexes and treats them as one of the founding lineage's most consequential derived characters.

c0005 - Dentition is reduced toward peg-like omnivore or insectivore function

Where pelycosaur-grade predators carried pronounced caniniform differentiation, the founding Thermosynapsida form shows reduced or absent caniniform teeth and relatively uniform peg-like postcanines with broad occlusal surfaces. The dental profile is more consistent with omnivory, insectivory, and feeding on small cave-margin resources than with active vertebrate predation.

c0006 - Relative metabolic efficiency rises above the pelycosaur baseline

Isotopic proxy modeling in GDCC Technical Annex 7 places pelycosaur-grade synapsids around 0.55 to 0.65 on the archive's relative metabolic efficiency index, while the founding Thermosynapsida form falls at approximately 0.65 to 0.72 where proxy data are available. The archive interprets the elevation as consistent with the metabolic demands of digging, tunnel maintenance, and repeated movement through thermally variable cave systems.

c0007 - Alternating growth and arrest histology indicates active-torpor cycling

Long-bone sections from the restricted sample reportedly preserve alternating zones of active deposition and arrested growth rather than a uniform low-activity pattern. In archive usage this histology is treated as indirect support for repeated cycling between active periods and metabolically suppressed intervals. The inference is necessarily cautious because sample size remains limited, but it is one of the traits carried into the order-level diagnosis.