Captorhinid trackways from mid- to late Permian red beds in Morocco: Implications for locomotion and the palaeobiogeography of northwest Gondwana

Abstract

In this paper, we report a new vertebrate ichnoassemblage from the mid- to late Permian red beds of the Ikakern Formation (Tourbihine Member, T2) from the Argana Basin of Morocco, to improve knowledge of paleobiology and palaeobiogeography. The ichnofossils comprise than 50 footprints organized as four trackways and assigned to the ichnogenus Hyloidichnus. The tetrapod tracks are preserved in convex hyporelief and concave epirelief on upper and lower mud-rich surfaces near the top of fine-grained sandstone units. The trackway pattern and the alternating arrangement of the pes-manus sets suggest a sprawling and symmetrical gait, with the movements of the front and hind limbs being of similar size, and it is likely that the animal moved at slow trot. We infer that the potential trackmaker was a captorhinomorph within the Moradisaurinae. This new fossil discovery helps reconstruct the palaeoenvironments and the palaeogeographic distribution of these Permian organisms, with Morocco acting as a faunal exchange gateway between western Gondwana and western Laurasia. Besides the tetrapod tracks, the red beds contain ubiquitous rain-drop marks, current ripples, plant fossil impressions, invertebrate burrows, tetrapod skin imprints, and a single insect wing that suggest that the strata were deposited in an episodically inundated alluvial plain.