Middle Triassic archosaur population structure:: interpretation based on Isochirotherium delicatum fossil footprints (Southern Alps, Italy)

Well-preserved archosaur footprints have recently been found on a single bedding plane in the Italian Alps. The tracks are referable to Isochirotherium delicatum Courel and Demathieu 1976, a form that was identified for the first time at the Anisian-Ladinian boundary in the area of Argentiere (Ardeche, France). The Isochirotherium delicatum footprints and trackways from Gampenpass represent a possible social group or 'herd'. Estimating the age of the trackmakers from the examination of the footprints is difficult and complicated by the fact that the sample can be divided into two groups of tracks (distinguishable by the L/W, cross axis and interdigital angle). The diversity of the tracks is here interpreted as an indication of sexual dimorphism. (C) 2002 Elsevier Science B.V. All rights reserved.