Footprints of the earliest reptiles: Notalacerta missouriensis – Ichnotaxonomy, potential trackmakers, biostratigraphy, palaeobiogeography and palaeoecology

Abstract

The origin of reptiles in the tetrapod footprint record has always been a debated topic, despite the great potential of fossiliferous ichnosites to shed much light on reptile origins when compared to the much less extensive skeletal record. This is in part due to an unclear ichnotaxonomy of the earliest tracks attributed to reptiles that has resulted in unreliable trackmaker attributions. We comprehensively revise the earliest supposed reptile ichnotaxon, Notalacerta missouriensis, based on a neotype and a selection of well-preserved material from the type locality and other sites. A synapomorphy-based track-trackmaker attribution suggests eureptiles and, more specifically, ́protorothyridids ́ such as Paleothyris as the most probable trackmakers. A revision of the entire PennsylvanianCisuralian record of this ichnotaxon unveils an unexpected abundance and a wide palaeogeographical distribution. The earliest unequivocal occurrence of Notalacerta is in the middle Bashkirian (early Langsettian) at the UNESCO World Heritage Site, Joggins Fossil Cliffs (Joggins, Nova Scotia, Canada). This occurrence also coincides with the earliest occurrence of reptile body fossils (Hylonomus lyelli), which are found at the same site. Notalacerta is abundant and widely distributed during the Bashkirian, mostly in sediments deposited in tidal palaeoenvironments, and less common in the Moscovian and Kasimovian. During the Gzhelian and Asselian, Notalacerta occurrences are unknown, but it occurs again during the Sakmarian and is widespread but not abundant during the Artinskian, mostly in fully continental palaeoenvironments.