Revision of Ichniotherium track-trackmaker correlation and implications for models of diadectid locomotion

Recent excavations at the early Permian Bromacker locality (Thuringian Forest, Germany) yielded body and trace fossil finds that shed new light on diadectid track-trackmaker correlation. A partially articulated skeleton assigned to Diadectes absitus includes a pes – which was absent in the type material of this species – and, in contrast to the expected similarity to North American Diadectes and the track type Ichniotherium cottae, the foot proportions of D. absitus are in better agreement with co-occurring Ichniotheirum sphaerodactylum tracks. Furthermore, despite the differences in bone proportions, the ratio of trunk length (distance between shoulder and hip joints measured along the vertebral column) to foot size was similar in both species, D. absitus and O. pabsti. To infer the likely sequence of footfalls that defines the gait pattern of the track producer, the skeletal proportions of D. absitus and O. pabsti were put in relationship to the footprint proportions and trackway pattern of I. sphaerodactylum. Based on a large sample of I. sphaerodactylum trackways from the Tambach Formation and assuming different degrees of lateral trunk bending and of flesh cover for fitting the autopodia into the footprints, we find that the skeletal proportions of both possible producers support a lateral sequence walk or even a pace gait instead of a common walking trot (the latter was assumed in previous models of O. pabsti as the producer of I. sphaerodactylum). According to our results, the type of gait should be taken into account as a critical variable in future models of diadectid walk.