Ecology of earliest reptiles inferred from basal Pennsylvanian trackways

摘要

Trackways representing the earliest evidence for the origin of reptiles (amniotes) are reported from the basal Pennsylvanian Grande Anse Formation, New Brunswick, Canada. Amniote characters include pentadactyl manus and pes, slender digits whose relative lengths approximate a phalangeal formula of 23453 (manus) and 23454 (pes), narrow digit splay (40–63°), putative transverse scale impressions on digit pads, and straight tail drag. The trackways occur in the deposits of a seasonally active dryland river channel. Sedimentological context suggests, for the first time, that early amniotes existed in water-stressed environments, where the cleidoic egg would have presumably conferred reproductive advantage.