Closely related tetrapods from the early Permian of North America and Germany had different life history traits

A wealth of studies show that the paleoecosystem recovered from the early Permian Bromacker locality of central Germany was unique and differed from coeval North American (NA) fossil assemblages. The latter mostly represented lowland environments with perennial rivers and tetrapod communities of aquatic to terrestrial taxa dominated by large carnivores. On the contrary, Bromacker paleoclimate was highly seasonal with ephemeral water bodies. Its tetrapod fauna was exclusively terrestrial, with abundant herbivores, but scarce and small predators.

Environmental conditions are expected to impact the growth strategies and lifestyle adaptations of tetrapods. However, this has rarely been reported for early Permian tetrapod communities. Here we investigate, for the first time, the long bone histology of the six largest tetrapod species recovered from Bromacker (i.e. Seymouria sanjuanensis, Diadectes absitus, Orobates pabsti, Dimetrodon teutonis, Martensius bromackerensis, Tambacarnifex unguifalcatus), with the aim to infer their life history traits and compare them to NA relatives.

Preliminary observations reveal that most specimens found at Bromacker consist in subadult to adult individuals, with few young juveniles. Unlike all other investigated species, Bromacker diadectids exhibit highly remodeled long bone cortices; a feature potentially related to fossorial adaptations. D. teutonis shows nearly avascular and thin bone walls, differing from the well vascularized and thicker cortices of its diminutive NA counterpart, D. natalis. Overall, Bromacker species show relatively slower growth rate than their NA relatives. Local environmental conditions might explain these contrasting growth strategies.