The paper Early adaptation to eolian sand dunes by basal amniotes is documented in two Pennsylvanian Grand Canyon trackways [1]: > The narrow width of both tra

The paper Early adaptation to eolian sand dunes by basal amniotes is documented in two Pennsylvanian Grand Canyon trackways [1]: > The narrow width of both trackways indicates that both trackmakers had relatively small femoral abduction angles and correspondingly relatively erect postures. They represent the earliest known occurrence of dunefield-dwelling amniotes―either basal reptiles or basal synapsids... This geological formation was from the Moscovian age (315.2 to 307 Ma) or the Kasimovian age (307 to 303.7 Ma) in the Pennsylvanian period. [1] https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0237636 https://journals.plos.org/plosone/article?id=10.1371/journal...