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.

Figure 1

Location of the studied area and the distribution of Dimetropus tracks in the Boskovice Basin. Horizons: He Helmhacker, Z Zbýšov, Ří Říčany, Ch Chudčice, Zb Zbraslavec, ZS Zboněk-Svitávka, Lu Lubě, Ko Kochov, Mí Míchov, Ba Bačov, Su Sudice. Modified after. The geological map and lithostratigraphy follow^,,. Chronostratigraphy follows and Jirásek (pers. comm.).

Figure 2

The manus-pes couple of MZM Ge 29610 (convex hyporelief) (A), image‐based modeling (B), and the outline drawing (C). Scale bar 2 cm.

Figure 3

The pes imprint of MZM Ge 29610 with highlighted soft tissue impressions (A), including digital (B), plantar (C), and transverse (D) creases. Scale bars: (A) 2 cm, (B–D) 1 cm.

Figure 4

The manus-pes couple and two isolated incomplete tracks of MZM Ge 33072 (convex hyporelief) (A), image‐based modeling (B), and the outline drawing (C). Scale bar 4 cm.

Figure 5

Three isolated tracks of MZM Ge 33073 (convex hyporelief) (A), image‐based modeling (B), and the outline drawing (C). Scale bar 4 cm.

Figure 6

The track of MZM Ge 33071 convex hyporelief (A), image‐based modeling (B), and the outline drawing (C). Scale bar 2 cm.

Figure 7

The slab showing (A) many incomplete step cycles of MZM Ge 33074 (concave epirelief); (B,C) Dimetropus isp. tracks (convex hyporelief); (D) indeterminate track resembling Ichniotherium (concave epirelief); and (E) image‐based modeling and (F) outline drawing of the whole slab. Scale bars: (A,E,F) 20 cm, (B–D) 2 cm.

Figure 8

Stratigraphic distribution of medium-to-large-sized early-diverging synapsid species from Europe (green) and North America (black) in the uppermost Pennsylvanian/lower Permian. The time span of the Boskovice Basin is highlighted by orange stripe. The stratigraphic ranges of particular taxa and locality ages are based on Refs.^,,,–,,.