Synapsid tracks with skin impressions illuminate the terrestrial tetrapod diversity in the earliest Permian of equatorial Pangea

Abstract

Lower Permian deposits of the Boskovice Basin in the Czech Republic have long been renowned for extraordinarily abundant specimens of discosauriscid seymouriamorphs, some of which showing exceptional preservation, including widespread soft tissues. The only other tetrapods from the strata are represented by rare temnospondyls. However, recent fieldwork in the Asselian (lowermost Permian) of the Boskovice Basin has yielded a diverse assemblage of tetrapod tracks, illuminating a hidden terrestrial tetrapod diversity. Here, we describe well-preserved isolated tracks, manus-pes couples, and a slab with trackways composed of approximately 20 tracks in at least four different directions belonging to early-diverging, or ‘pelycosaur-grade’, synapsids. The material originates from three localities situated within the Letovice and Padochov formations and is assignable to the ichnotaxon Dimetropus. The best-preserved specimen further shows rare skin impressions, which have not been observed from the hands or feet of early-diverging mammal-line amniotes before. The new material adds to the scarce record of synapsids from the Carboniferous/Permian transitional interval of equatorial Pangea. At the same time, it highlights the significance of the ichnological record of the Boskovice Basin which has long been neglected despite offering evidence for the presence of diverse faunal components that have not been reported from these basinal deposits before.

A diadectid skin impression and its implications for the evolutionary origin of epidermal scales

“…Skin impressions associated with Palaeozoic tetrapod footprints have long been known [37,38], although reports of relevant finds significantly increased in number rather recently [21,[39][40][41][42][43][44][45][46][47]. Almost all finds of Palaeozoic skin impressions refer to amniotes.…”

Tracking ‘transitional’ diadectomorphs in the earliest Permian of equatorial Pangea

“…From the viewpoint of tetrapod fossil record, the lowermost Permian strata of the Boskovice Basin have long been renowned for materials of taxa inhabiting aquatic environment, including extraordinarily abundant specimens of discosauriscid seymouriamorphs ( e.g ., Špinar, 1952 ; Klembara, 1995 , 2005 , 2016 ) and rare temnospondyls ( Augusta, 1947 ; Milner, Klembara & Dostál, 2007 ; Klembara & Steyer, 2012 ; Werneburg et al, 2023 ). However, recent fieldwork conducted in the basinal strata at several localities provided diverse assemblages of tetrapod footprints which fundamentally enriches our knowledge of the tetrapod biodiversity in the Permian terrestrial settings in this area, revealing the presence of large-bodied seymouriamorphs ( Calábková, Březina & Madzia, 2022 ), early-diverging synapsids ( Calábková et al, 2023 ), and now two distinct diadectomorphs.…”

“…Chronostratigraphy follows Štamberg (2014) and J. Jirásek, 2021, personal communication. Figure is modified from Calábková et al (2023) .…”

“…The faunal components of the Padochov Formation consist of bivalves, clam shrimps (‘conchostracans’), insects, acanthodians, xenacanthids, branchiosaurids, indeterminate, very rare finds of discosauriscids, and tetrapod fossil tracks ( e.g ., Kukalová, 1959 , 1965 ; Schneider, 1984 ; Ivanov, 2003 ; Milner, Klembara & Dostál, 2007 ; Štamberg & Zajíc, 2008 ; Schneider & Werneburg, 2012 ; Štamberg, 2014 ; Calábková, Březina & Madzia, 2022 ; Calábková et al, 2023 ). No fossil fauna has been recorded from the Veverská Bítýška Formation.…”

“…The diadectomorph footprints from Čebín, therefore, provide the first evidence of the presence of faunal components in this formation. The fauna of the Letovice Formation contains bivalves, clam shrimps (‘conchostracans’), insects, acanthodians, actinopterygians, temnospondyls, discosauriscids and tetrapod fossil tracks ( e.g ., Kukalová, 1963 , 1964 ; Schneider, 1980 , 1984 ; Klembara, 1997 , 2005 , 2009 ; Schneider & Werneburg, 2006 , 2012 ; Štamberg, 2007 , 2014 ; Klembara & Steyer, 2012 ; Klembara & Mikudíková, 2018 ; Werneburg et al, 2023 ; Calábková, Březina & Madzia, 2022 ; Calábková et al, 2023 ).…”