The Late Triassic archosaur ichnogenus Brachychirotherium: first complete step cycles from Morocco, North Africa, with implications for trackmaker identification and ichnotaxonomy

Abstract

© 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group. Complete trackways of the Late Triassic archosaur ichnogenus Brachychirotherium are extremely rare and thus far mostly known from North America, though isolated imprints are abundant. Complete step cycles have been found on the upper and lower bedding surfaces in laminated mudstones and fine-grained sandstones of the lowermost part of the Machraa Abbass Member of the Oued Oum Er Rbiaa Formation (Late Triassic). This is the first complete trackway of the ichnogenus in North Africa. The tetrapod footprints are assigned to B. parvum and B. thuringiacum, based on the presence of diagnostic features of these ichnospecies, such as the orientation of pedal digit V. Supposed trackmakers are archosaurs of the crocodile stem-group (Crurotarsi) that were widely spread over the Triassic Pangea. Associated tetrapod ichnofauna from the unit consists of small-sized Rhynchosauroides (archosauromorph/lepidosauromorph) tracks.