October 31, 2016:

Highlights

Synapsids adopted walking, half-bounding, skipping, and running since the Jurassic.

The trackmaker of B. elusivum was a Mammaliamorpha, with a semi-erect leg posture.

B. elusivum is crucial for investigating aspects of locomotion in Mesozoic synapsids.

B. elusivum fills a lack on evolution of bipedal saltatory gait in the Mesozoic synapsids.

B. elusivum remarks the association of bipedal saltatory gait with erg settings.

Abstract

Synapsids were able to adopt different gaits, including half–bounding and bipedal skipping, since the Early Jurassic, as indicated by a large record of fossil footprints, found in hyper-arid erg–dominated paleonvironments from South and North America. The mammaliamorph origin of these footprints is corroborated by their shape, stance, and gait, in a large number of trackway specimens from the Paraná Basin (Botucatu Formation) of Brazil. This record is interpreted as the _expression_ of the locomotor skills of a single trackmaker population, and might be grouped together under a pre-existing ichnotaxonomic label, Brasilichnium elusivum Leonardi, 1981, including one of the few unambiguous Mesozoic records of bipedal saltatory gait in synapsids. This bipedal saltatory gait is associated with desert paleoenvironments, and more specifically with sand dunes with little or no vegetation cover. Decades of collecting has resulted in one of the largest records of synapsid footprints worldwide, and ichnology has proven fundamental to investigate elusive aspects of their natural history.