The earliest reptile body impressions with scaly skin

Epidermal scales are a widespread and fundamental skin structure for present-day reptiles.¹ They differ from bony dermal scales, which occur in Paleozoic fishes and early tetrapods.² However, little is known regarding the origin and early evolution of this type of soft tissue.³ Stem reptiles first appeared in the late Carboniferous⁴ and increased in abundance during the early Permian. Their skeletal remains do not normally preserve soft parts, and, when they do, the record is often poorly preserved or of uncertain taxonomic affiliation.⁵ Complementary data regarding the early evolution of integumentary structures can be derived from trace fossils, which preserve multiple scaly skin and body impressions, sometimes with exceptional quality.⁶ Here, we present the earliest definite fossil occurrence of epidermal scales in stem reptiles, from the early Asselian Goldlauter Formation of Germany.^7,8 These scales are preserved on a newly described resting trace Cabarzichnus pulchrus n. igen. n. isp., representing the oldest and most complete body-impression occurrence of a Paleozoic stem reptile. The unequivocal association with Varanopus microdactylus footprints indicates a bolosaurian trackmaker.⁴ Furthermore, some anterior tail scale impressions have a unique morphology around a sub-horizontal vent-like impression, similar to modern squamates.⁹ The early record of dermal and epidermal scales^2,10,11 provides evidence for the co-existence of epidermal and dermal scales in late Carboniferous stem amniotes and for epidermal scale differentiation in Asselian stem reptiles. Therefore, this adaptation precedes the main phases of the early Permian global warming and aridification¹² and probably enabled the diversification of stem reptiles.¹³ VIDEO ABSTRACT.