A highly diverse Pennsylvanian tetrapod ichnoassemblage from the Semily Formation (Krkonoše Piedmont Basin, Czechia)

Semily formation with focus on the Ploužnice Horizon

The Semily Fm. represents a ∼500 m thick sequence of predominantly reddish conglomerates, sandstones, siltstones and claystones (Pešek et al., 2001; Opluštil et al., 2016b). In its typical development, the formation is divided into three parts—lower, middle and upper (Fig. 2; cf. Pešek et al., 2001), each with distinct lithofacies development. The lower part of the formation is dominated by coarse clastic deposits that are particularly concentrated along the northern, tectonically-driven basin margin. These are represented by up to ca. 120 m thick (cf. Pešek et al., 2001) often poorly-sorted coarse-grained conglomerates or even breccias containing mostly phyllite and quartz clasts from the nearby Krkonoše–Jizera Crystalline Complex (Fig. 1B). In the south, the basal part of the Semily Fm. is formed by conglomerates up to ∼40 m thick (cf. Pešek et al., 2001) with good sorting and clast rounding and coarse-grained sandstones.

The middle part of the formation is dominated by fine-grained deposits and is ∼130 m thick in the south and ∼100 m thick in the north. In the south, the middle part of the formation contains a succession formed by varicoloured siltstones, claystones with subordinate limestones, and contains distinctive lenses of cherts, interpreted as lacustrine deposits grouped into the Ploužnice Horizon. This unit is formed by two lacustrine intervals (lower and upper Ploužnice Horizons), each ∼10–60 m thick, separated by alluvial deposits—brownish-reddish interval of predominantly mudstones and fine-grained sandstones, ∼10–30 m thick (Pešek et al., 2001). The lacustrine deposits are also represented by the Štepanice–Čikvásky Horizon, a presumed continuation of the Ploužnice Horizon to the northern part of the Central sub-basin (Fig. 1C). Both units are traditionally termed as ‘horizons’, although their greater thickness and varied lithology contradict the concept of ‘stratigraphic horizon’ as a thin marker of distinctive lithology (cf. Courel et al., 2008), and should be defined as a member of the Semily Fm.

The Ploužnice Horizon reportedly contains numerous flora remains of lycopsids, Equisetids (Calamites, Sphenophylls), Ferns (Marattiales, Zygopteridales, Filicales), Pteridosperms (Medullosales, Lyginopteridales, Callistophytales, Peltaspermales) and Gymnosperms (Cordaitopsids, Coniferopsids) as well as a rich fauna of bivalves, ostracodes, conchostracans, blattoid insect, arachnids, elasmobranchs, actinopterygians, and tetrapod footprints (Fig. 2; Fritsch, 1901; Frič, 1912a; Frič, 1912b; Kamarád, 1951; Kamarád, 1959; Rieger, 1958; Rieger, 1968; Pešek et al., 2001; Zajíc, 2007; Štamberg, 2001; Štamberg & Lapacík, 2018; Štamberg, 2023; Štamberg, 2024; Štamberg & Zajíc, 2008; Mencl et al., 2013; Opluštil et al., 2016a; Opluštil et al., 2016b; Opluštil, Šimůnek & Mencl, 2022; Schneider et al., 2020).

The Late Pennsylvanian fossil fauna of the KPB has been known since the beginning of the 20th century based on the discoveries in the railway cut between Ploužnice and Kyje (Figs. 3A, 3C) and the Krsmol locality (Fritsch, 1901; Frič, 1912a; Frič, 1912b) representing the localities of the Ploužnice Horizon (Stephanian C). Above the Ploužnice Horizon, alluvial-lacustrine deposits of the upper part of the Semily Fm. pass into the Vrchlabí Fm. whose basal part of is lithologically similar but devoid of cherts and features monotonous colours (brownish/reddish and/or greyish). This interval contains the Carboniferous-Permian boundary (Opluštil et al., 2013; Opluštil, Šimůnek & Mencl, 2022). Based on the litho- and biostratigraphic correlation of the Ploužnice Horizon with the Klobuky Horizon (Líně Fm.) in central Bohemia, dated at 298.97 ± 0.09 Ma (Opluštil et al., 2016a), and unpublished dating of the base of the Vrchlabí Fm. at 298.72 Ma (cf. Nádaskay et al., 2024), the uppermost part of the Semily Fm. is likely early Permian in age.

Kyje–Ploužnice railway cut (Ploužnice Horizon)

Palaeontological material has been documented from this section of the Kyje–Ploužnice railway cut since the early 20th century (Frič, 1912a; Frič, 1912b), making it one of the historically significant fossil sites in the region. The railway cut created several outcrops in the Ploužnice Horizon between Kyje and Ploužnice railway stops (Fig. 3A) and was already described in detail by Frič (1912a: figs. 12, 13; 1912b: figs. 12, 13) and Purkyně (1929; Fig. 3C). The series of railway cuts was studied sedimentologically by Blecha et al. (1997). Among the several exposures described by these authors, this paper focuses on the section closest to the Kyje railway stop, where the Ploužnice Horizon is well exposed on both sides of the railway (Fig. 4A). The Kyje section (Fig. 5A) displays two fining-upward cycles. The lower cycle is formed by mudstones at the base, overlain by fine-grained sandstones with ripple cross-bedding (Fig. 4B) or low-angle cross-bedding, often with sharp bases and sometimes with conspicuous channelization (Fig. 4B). The alternation of mudstones and sandstones is topped by a silty-sandy limestone, which is overlain by a pedogenic horizon (Fig. 4B) characterised by distinct vertic slickensides and abundant carbonate nodules. The lower cycle (Fig. 5) is predominantly brown- or red-brown coloured. The middle cycle (Fig. 5) starts at the base with very fine to fine-grained sandstones, often silty or argillaceous, with mud drapes or even thin interbeds of mudstones (Fig. 4C). Mud drapes are occasionally associated with rain rills and rain-drop impressions (Fig. 4D), sometimes with wrinkle structures (Fig. 4E) possibly left by microbial mats and with invertebrate burrows (Fig. 4F). Mudcracks (Fig. 4G) are present both in red- and violet/grey-coloured deposits.

These sandstones pass upward into ∼7–8 m thick sequence of predominantly violet and grey mudstones with cm to first dm thick interbeds of greyish sandstones (Fig. 4A). The upper part of this sequence is apparently finer, mudstone-dominated, and contains nodular interbeds of reddish cherts and ∼1 cm thick volcaniclastic layers. The top of the section, inclined towards the Kyje railway stop, is represented by alternation of violet to brownish mudstones and brownish sandstones. These deposits represent a lower part of an upper, incompletely exposed cycle.

Concerning fossil finds, the flora is represented by lycopsids (Asolanus camptotaenia, Halonia (Ulodendron), Stigmaria ficoides, Lepidostrobus variablis, Lepidophyllum sp.), equisetales (Sphenophyllum oblongifolium, Asterophyllites equisetiformis, Annularia spinulosa, Calamites gigas, C. cruciatus, C. undulates, C. suckowii, C. cistii, Calamostachys tuberculata etc.), ferns (Cyathocarpus arboreus, Pecopteris arborescens, Scolecopteris cyathea, Acitheca polymorpha etc.), pteridosperms (Odontopteris subcrenulata, O. schlotheimii, Callipteridium pteridium, Ca. costei, Neuropteris zeilleri, N. cordata , Neurodontopteris auriculata etc.) and gymnosperms (Culmitzschia cf. speciosa, Walchia piniformis, Ernestiodendron filiciforme, Cordaites borassifolius) (Purkyně, 1929; Němejs, 1932; Štamberg & Lapacík, 2018; Šimůnek, Lapacík & Mencl, 2022; Opluštil, Šimůnek & Mencl, 2022). Fossil fauna comes from thin layer (∼0.5 m) of dark red claystone originally called “bonebeds” by Frič (1912a) and Frič (1912b) and from the lower part of varicoloured tuffitic claystones (Štamberg, 2023). Fossils are represented by wings of the blattoid insect Spiloblattina lawrenceana, Sysciophlebia rubida, Neorthroblattina cf. multineuria and Anthracoblattina sp., scales of elasmobranchs Xenacanthidae and Sphenacanthus sp., scales and fin spines of Acanthodes sp., scales and bones of actinopterygians Elonichthys sp., Sphaerolepis kounoviensis, Spinarichthys disperses, Progyrolepis speciosus and Zaborichthys fragmentalis and bones of branchiosaurid (Frič, 1912a; Frič, 1912b; Schneider, 1983; Zajíc, 2007; Štamberg & Lapacík, 2018; Štamberg, 2023). As mentioned above, Frič (1912a) and Frič (1912b) described a tetrapod ichnotaxon Saurichnites calcaratus=Dromopus lacertoides (Geinitz, 1861) in a “dark” shale (the layer corresponds to a red mudstone containing ichnofossils of Dromopus; e.g., MZM Ge34179) in an outcrop near the railway milestone marking the distance 60.5 km. Later Haubold & Katzung (1975) expanded the list of ichnotaxa from the Kyje–Ploužnice railway cut with Anthichnium salamandroides=Batrachichnis salamandroides (Geinitz, 1861), Amphisauropus latus=Amphisauropus kablikae (Geinitz & Deichmüller, 1882), Dromopus lacertoides and Ichniotherium cottae, which are revised in this study and described and depicted for the first time.

Krsmol—locality “Hluboká rokle” (Ploužnice Horizon)

The locality Krsmol is well known from the beginning of the palaeontological research in the KPB (Fritsch, 1901; Frič, 1912a; Frič, 1912b). The outcrop is located in the upper part of a deep erosional gorge. Its current condition is described in detail by Štamberg (2024). From the base of profile, he described 30 cm thick chert, five cm thick massive red sandstone, well bedded 10 cm thick grey siltstone, with fauna on the base and 100 cm thick purplish siltstone with fauna. According to Štamberg (2024), these layers are comparable to the “bonebed” at the Kyje–Ploužnice railway cut. Flora is represented by lycopsids (Sigillaria brardi, Lepidodendron sp. etc.), equisetales Calamites gigas and pteridosperms Odontopteris schlotheimii, Neurodontopteris auriculata and Callipteridium pteridium (Purkyně, 1929; Němejs, 1932; Opluštil, Zajíc & Svoboda, 2022). The fauna is represented by bivalves Carbonicola bohemica, arachnids Anthracolysa sp., wings of blattoid insect Sysciophlebia rubida, fin spines, scales, teeth, and fin spin of elasmobranchs Turnovichthys magnus, Lissodus sp., Orthacanthus sp. and Bohemiacanthus sp., scales of acanthodians and scales and teeth of the actinopterygians Elonichthys sp. and Sphaerolepis kounoviensis (Fritsch, 1901; Frič, 1912a; Frič, 1912b; Štamberg, 2001; Štamberg, 2024; Zajíc, 2007).

Štikov—roadcut

This locality featured a temporary outcrop (e.g., Fig. 4H) created during the construction of a new road bypassing the town of Nová Paka (Fig. 3B), which was exposed during the years 2023–2024. The approximately 700 m long outcrop exposes a NE dipping sequence (Fig. 3D) of conglomerates and sandstones alternating with siltstones (ca. 5 m thick; Fig. 4I) that forms the lower part of the Semily Fm., i.e., beneath the Ploužnice Horizon (Fig. 5B). This sequence is underlain by whitish arkoses (Fig. 4H) and contains grey mudstones with thin interbeds of violet-grey sandstones, which belong to the Syřenov Fm. (Fig. 5B). Upsection, the conglomerates of the basal part of the Semily Fm., typically clast-supported, poorly-sorted with pebbles of quartz and micaschists (Fig. 4J) pass into alternating sandstones and siltstones (∼5 m thick), and the exposed part of the sequence ends with red mudstones. In the upward direction, a colour of the sediments changes from grey-violet to red. The fossil tracks of Ichniotherium come from the sequence of conglomerates alternating with ∼30 cm thick siltstones interbeds containing Dromopus isp. (MZM Ge34182), cf. Batrachichnus (MZM Ge34182) and cf. Ichniotherium (MZM Ge34183) footprints (M Stárková, pers. comm., 2023). This sequence is overlain by predominantly red mudstones.

Systematic palaeoichnology

Referred material. CGS JZ626—convex hyporelief; CGS JZ632—concave epirelief. The specimens are convex hyporelief and concave epirelief of the same original sample.

Description:

The manus imprints are pentadactyl and plantigrade whereas the pes imprints are incomplete semidigitigrade to digitigrade. The manus imprints are about 9 mm long and about 11.5 mm wide (Table S1). The palm impressions show a rectangular shape. The length of the manual digit impressions gradually increases from I to IV. Digit V is shorter than digit II. The imprints of manual digits II–III are distally bent inward. Manual digits I have the typical basal pad. The digits show round terminations. The manus imprint is turned inward compared to the pes imprint. The trackway shows an alternating arrangement of successive manus and pes imprints. There is no overprinting within the manus-pes couple.

Remarks:

The specimens described above show the main diagnostic features of Amphisauropus kablikae, including pentadactyl wide manus imprint with relatively thick digits with rounded terminations, the longest manual digit IV is similar in size as digit III, relatively short manual digit V imprints, rectangular palm impressions, and a strongly inwards oriented manus imprint in relation to the pes imprint (e.g., Voigt, 2005; Voigt et al., 2012; Marchetti et al., 2015a).

Amphisauropus tracks have been known from the Pennsylvanian to the Cisuralian (early Permian), while the vast majority of specimens have been discovered in the Cisuralian of Europe (e.g., Fritsch, 1901; Pabst, 1905; Haubold, 1971; Haubold, 1996; Voigt, 2005; Voigt, 2015; Gand & Durand, 2006; Avanzini et al., 2008; Voigt et al., 2012; Marchetti, Avanzini & Conti, 2013; Marchetti et al., 2015a; Marchetti et al., 2015b; Marchetti, Mujal & Bernardi, 2016; Marchetti, Voigt & Santi, 2018; Mujal et al., 2016; Santi et al., 2020; Calábková, Březina & Madzia, 2022), North America (Haubold et al., 1995; Lucas, Lerner & Haubold, 2001; Lucas, Spielmann & Lerner, 2009; Van Allen, Calder & Hunt, 2005; Voigt & Lucas, 2015a; Voigt & Lucas, 2015b; Voigt & Lucas, 2016; Voigt & Lucas, 2017; Marchetti et al., 2019; Marchetti et al., 2020a), and North Africa (Voigt et al., 2011a). The Amphisauropus tracks from the Ploužnice Horizon represent indisputable evidence of the occurrence of this ichnotaxon in the Gzhelian. The older occurrence of Amphisauropus was designated by Lucas & Stimson (2025) and Marchetti et al. (2021), which comes from the Keota Sandstone Member of Middle Pennsylvanian in Oklahoma.

Referred material. CGS XA738—convex hyporelief, trackway consists of four manus-pes couples; MZM Ge31124—convex hyporelief, isolated three tracks.

Description:

The manus imprints are tetradactyl and plantigrade, and the pes imprints are pentadactyl and plantigrade to digitigrade. The footprints are up to ∼27 mm long. The manus imprints are about 1/5 smaller than the pes imprints. The manus imprints are slightly wider than long, whereas the pes imprints are almost as long as wide (Table S1). The manual digits imprints are relatively short with rounded terminations. The length of the manual digits increases from I to III, and digit IV is about as long as the digits I or II. The length of the pedal digits increases from I to IV, and V is shorter than III. The manual digit I often has a distinctly impressed basal pad. The palm and sole impressions are most often wider than long. The manus imprints are slightly turned inward, whereas the pes imprints are oriented parallel to the midline or slightly rotated outward from the midline. The trackway shows an alternating arrangement of successive manus and pes imprints. Overprinting does not occur.

Remarks:

The small-sized tetradactyl manus imprints with short, thick digits ending in rounded terminations, and pentadactyl pes imprints are clearly assignable to the ichnospecies Batrachichnus salamandroides.

The Batrachichnus has been reliably documented from the Mississippian to the Middle Triassic of Europe (Makowsky & Rzehak, 1884; Fritsch, 1901; Pabst, 1908a; Pabst, 1908b; Haubold, 1970; Haubold, 1971; Haubold & Katzung, 1975; Gand, 1987; Voigt, 2005; Mujal et al., 2016; Marchetti, Avanzini & Conti, 2013; Marchetti et al., 2015b; Marchetti et al., 2020a; Marchetti et al., 2020b; Marchetti et al., 2022) North America (Lucas et al., 2011; Stimson, Lucas & Melanson, 2012; Voigt & Lucas, 2015a; Voigt & Lucas, 2015b; Voigt & Lucas, 2017; Klein & Lucas, 2021; Allen et al., 2022), South America (Melchor & Swithin Sarjeant, 2004), and Africa (Voigt et al., 2011a; Voigt et al., 2011b; Cisneros et al., 2020; Zouicha et al., in press).

Referred material. NPM P3573—convex hyporelief, manus-pes couple; CGS XA741—convex hyporelief, manus-pes couple

Description:

The manus imprints are tetradactyl and plantigrade, whereas the pes imprints are pentadactyl and plantigrade to semiplantigrade. The footprints are up to ∼30 mm in length. The manus imprints are about 1/3 wider than they are long, whereas the pes imprints are almost as long as wide. The manus imprint of the specimen NPM P3573 is roughly about half the size of the pes imprint (Table S1). The manus imprints are inwardly rotated compared with the pes imprint. The sole and palm impressions are rectangular in shape. Manual digit imprints are relatively short and thick. The manual and pedal digits show rounded terminations. The length of the manual digit imprints is similar and slightly increases from I to III, whereas digit IV is about as long as digit II. In the specimen NPM P3573, digit IV is separated from digits I–III and rotated outwards. The length of the pedal digits increases from I to IV, and V is shorter than III. The pedal digit impressions are in close vicinity to the manus imprint. The trackway shows an alternating arrangement of successive manus and pes imprints. The manus imprints show the most deeply impressed medial area within the tracks. Specimen ČGS XA741 (Figs. 8C–8D) shows distinct pads of digit I.

Remarks:

The specimens NPM P3573 and CGS XA741 have manus imprints noticeably wider than the total length of the footprint. The length of manual digits IV is as long as digit II in contrast with a very similar ichnotaxon Batrachichnus, which commonly has manus imprints as long as wide or slightly wider than they are long, and the manual digit IV is often shorter than digit II (Voigt, 2005). In addition, Batrachichnus pes imprints typically reach up to 20 mm in length. However, the distinct differences of digit proportions are not always clearly present. For this reason, some authors presented the Batrachichnus-Limnopus plexus (see Voigt et al., 2011a; Voigt et al., 2011b).

The specimen CGS XA741 (Figs. 8C–8D) was labelled as Amphisauropus latus = A. kablikae with the initial of H. Haubold, and this determination was used in the study by Haubold & Katzung (1975). We argue that the distinct pad impression of digit I was apparently mistaken for the digit I impression itself. The manual digits V of the Amphisauropus tracks are only slightly longer than the digits I (see Voigt, 2005; Voigt, 2015; Calábková, Březina & Madzia, 2022), which is inconsistent with the specimen CGS XA741. These facts most likely explain why the Amphisauropus tracks from the Ploužnice Horizon have never been described in subsequent studies. The morphology of the CGS XA741 is closely similar to that of Limnopus from the study of Voigt (2005).

Limnopus is well known from the Pennsylvanian to the Cisuralian of Europe (Tucker & Smith, 2004; Voigt, 2005; Voigt, 2015; Marchetti, Avanzini & Conti, 2013; Marchetti et al., 2015a; Marchetti et al., 2015b; Marchetti et al., 2020a; Niedźwiedzki, 2015; Meade, Jones & Butler, 2016; Mujal et al., 2016), Greenland (Milàn et al., 2016), North America (Martino, 1991; Van Allen, Calder & Hunt, 2005; Lucas & Dalman, 2013; Voigt & Haubold, 2015; Voigt & Lucas, 2015a), and North Africa (Voigt et al., 2011a; Lagnaoui et al., 2018).

Referred material. MZM Ge34174—convex hyporelief, incomplete manus-pes couple.

Description

The large tetradactyl plantigrade manus imprint is ∼72 mm long. The manus and palm imprints are about 1/3 wider than they are long (Table S1). The digits are straight, thick, and short with rounded terminations. The digit IV impression is turned outward. The manual digits show almost the same length but increase slightly from I to III, while digit IV is almost the same length as digit II. The pes imprint is not completely preserved. The pedal digit imprints are thick, and relatively long with rounded terminations.

Remarks

The large tetradactyl manus imprints characterized by short, thick digits with rounded distal terminations, and rectangular palm impression correspond well to the large Limnopus tracks (Lucas & Dalman, 2013; Meade, Jones & Butler, 2016; Milàn et al., 2016; fig. 11). Regarding the incomplete pes impression, we assign the specimen MZM Ge34174 to Limnopus isp.

Referred material. MZM Ge34184—convex hyporelief, manus-pes couple with two isolated tracks; CGS XA737—convex hyporelief, manus-pes couple; CGS XA739—hyporelief, isolated pes imprint; NPM P103—concave epirelief, isolated pes imprint; NPM P307—concave epirelief, isolated pes imprint.

Description

The manus and pes imprints are plantigrade and pentadactyl. The footprints are up to ∼135 mm long. The pes imprints are about 1/3 larger than the manus imprints. The pes imprints are slightly longer than wide or as wide as long, whereas the manus imprints are as wide as long, or wider than they are long (Table S1). The palm and sole impressions are deeply impressed with subcircular to elliptical shapes. The pedal digit imprints are rather straight and the manual digits II–IV are slightly bent inward. The digit terminations are distally extended and rounded, and they represent one of the most deeply impressed parts of the tracks. In the manus and pes imprints, the lengths of the digits increase from I to IV. The manual digits V are slightly shorter than the digits II or are of the same length. The pedal digits V reach approximately half the length of digit IV. The trackway shows an alternating arrangement of successive manus and pes imprints. No overprinting occurs within the manus-pes couple. The Ichniotherium track of NPM P307 (Figs. 9G–9H) is accompanied by Dimetropus manus-pes couple (Fig. 9I; see below for description) and small Batrachichnus tracks with tetradactyl manus impressions.

Remarks

The specimen MZM Ge34184, NPM P103, NPM P307, CGS XA737 and CGS XA 739 all show diagnostic features of Ichniotherium cottae, such as the relatively short pedal digit V with pV/pIV ratio < 0.60 (average value), deeply impressed elliptical to circular palm and sole, and deeply impressed distal parts of the digits (Voigt, Berman & Henrici, 2007). MZM Ge34184 (Figs. 9A–9B) shows a doubled sole impression, which was described in sole impressions of early Permian I. cottae from the Tambach Fm., Thuringian Forest, (see e.g.,Voigt, Berman & Henrici, 2007, fig. 3) as well as in palm impression of I. cottae from the Boskovice Basin, Czechia, in lowermost Permian deposits (Calábková et al., 2023a, fig. 2). I. cottae differs from I. sphaerodactylum in having a significantly shorter pedal digit V, in contrast to the longer digit V in Ichniotherium sphaerodactylum, which can reach about 80% of the length of pedal digit IV (see e.g., Voigt, Berman & Henrici, 2007; Calábková et al., 2023a; Calábková, Ekrt & Voigt, 2023b). The CGS XA737 specimen (Figs. 9E–9F) preserves impressions of flexion creases on the digits, which are often present on Ichniotherium cottae tracks (e.g., Voigt, 2005; Marchetti, Voigt & Santi, 2018; Calábková et al., 2023a).

The first occurrence of I. cottae comes from the Alveley locality, Birmingham, UK (Moscovian–Kasimovian) (Haubold & Sarjeant, 1973; Buchwitz & Voigt, 2018). Another Pennsylvanian occurrences come from the Gzhelian of Saar-Nahe Basin in Germany (Voigt, Berman & Henrici, 2007) and Ohio, USA (Baird, 1952). However, most of the I. cottae come from the Cisuralian of Europe (von Hochstetter, 1868; Frič, 1887; Fritsch, 1901; Haubold & Sarjeant, 1973; Haubold & Katzung, 1975; Voigt & Haubold, 2000; Voigt & Haubold, 2015; Voigt, 2005; Voigt & Ganzelewski, 2010; Voigt et al., 2012; Voigt et al., 2024; Mujal & Marchetti, 2020; Calábková et al., 2023a), USA (Voigt, Small & Sanders, 2005; Voigt & Lucas, 2015a; Voigt & Lucas, 2017), and North Africa (Lagnaoui et al., 2018).

Material. NPM P307—concave epirelief, manus-pes couple.

Description

The pes imprint is plantigrade, about 1/3 longer than it is wide, proximo-distally elongated, and ∼95 mm long (Table S1). The manus is imprinted only on its lateral part. The manus imprint seems distinctly smaller than the pes imprint. The manual and pedal digit impressions are relatively short, straight with a sharp clawed termination. The pedal digit impressions show a continuous increase in the length from I to IV, whereas the impressions of digits IV–V are not clearly identified. The impression of pedal digit I is orientated inwards. The manus-pes distance is relatively high.

Remarks

The elongated proximal part of the footprints, and relatively short and sharp terminated digit impressions are typical features for the ichnotaxon Dimetropus leisnerianus (Voigt, 2005). However, given the poorly preserved tracks and incompletely impressed manus, we assigned the track to Dimetropus isp., which shows great similarities with Dimetropus specimens from Morocco (Voigt et al., 2011b, fig. 5; Lagnaoui et al., 2014, fig. 5; Lagnaoui et al., 2018, fig. 6–7) and France (Gand, 1987, fig. 58A, planche 6B).

Dimetropus is known from the Pennsylvanian and the Cisuralian of Europe (Haubold, 1971; Gand & Haubold, 1984; Gand, 1987; Voigt, 2005; Niedźwiedzki & Bojanowski, 2012; Voigt & Ganzelewski, 2010; Voigt et al., 2012; Voigt & Lucas, 2015a; Voigt & Lucas, 2015b; Marchetti, 2016; Meade, Jones & Butler, 2016; Mujal et al., 2016; Matamales-Andreu et al., 2021; Matamales-Andreu et al., 2022; Calábková et al., 2023c; Marchetti et al., 2025), North America (Tilton, 1931; Haubold et al., 1995; Van Allen, Calder & Hunt, 2005; Sacchi et al., 2014; Voigt & Lucas, 2015a; Voigt & Lucas, 2015b; Lucas et al., 2016; Marchetti et al., 2020a), and North Africa (Voigt et al., 2011a; Voigt et al., 2011b; Lagnaoui et al., 2018). Except for the most common Dimetropus leisnerianus, the ichnospecies Dimetropus osageorum has been described from the Kungurian (lower Permian) of Oklahoma, USA (Sacchi et al., 2014), which differs from D. leisnerianus in that it shows a high degree of heteropody, short, subcircular manus imprints separated into two portions, short digit impressions which are subequal in length, and the pes imprint with a subelliptical to subcircular pad impression in the proximal central part of the sole. The morphological features of D. osageorum do not correspond to those of the specimen NPM P307.

Referred material. NM M4949a—concave epirelief, manus-pes couple and three isolated tracks; CGS XA735—convex hyporelief, three manus-pes couples and two isolated tracks; CGS XA742—convex hyporelief, isolated two tracks; CGS XA743—convex hyporelief, three manus-pes couples; CGS XA744—convex hyporelief, at least 8 tracks; NPM P104—convex hyporelief, manus-pes couple; NPM P3608—convex hyporelief, pes imprint; MZM Ge34176—convex hyporelief, manus-pes couples and two isolated tracks; MZM Ge34177—convex hyporelief and concave epirelief, at least 15 tracks; MZM Ge34178—convex hyporelief and concave epirelief, manus-pes couple; MZM Ge34179—concave epirelief, isolated track; MZM Ge34180—convex hyporelief and concave epirelief, manus-pes couple; MZM Ge 34181—convex hyporelief, manus-pes couple.

Description

The pentadactyl plantigrade to digitigrade manus and pes imprints of similar size and shape. The pes footprints are up to ∼70 mm long. The manus imprints are about 1/5 shorter than the pes imprints. The manus and pes imprints are longer than they are wide (Table S1). The manus imprints often show a slightly inward orientation to the midline, whereas the pes imprints show a parallel or slightly outward rotation to the midline. The impressions of the digits are long and slender with tapered terminations. Palm and sole impressions are short and often not impressed. The length of the digits increases from I to IV, and the digit V is about as long as digits II or III. Overprinting of the manus imprints by the pes imprints is common. The specimen NM M4949a (Figs. 10A–10B) shows also a several circular structures with a diameter between 3–5 cm.

Remarks

The manus and pes imprints, which are similar in shape and size, with long and slender digit imprints, correspond well to the ichnospecies Dromopus lacertoides (Voigt, 2005). The CGS XA742 footprints are among the largest Dromopus lacertoides which have been described to date. The Dromopus tracks are known from Late Pennsylvanian to late Permian deposits of Europe (Makowsky & Rzehak, 1884; Fritsch, 1901; Pabst, 1908a; Pabst, 1908b; Gand, 1987; Voigt, 2005; Voigt et al., 2012; Gand & Durand, 2006; Avanzini, Bernardi & Nicosia, 2011; Marchetti, Avanzini & Conti, 2013; Marchetti et al., 2015a; Marchetti et al., 2015b; Voigt & Haubold, 2015; Mujal et al., 2016), North America (Van Allen, Calder & Hunt, 2005; Lucas et al., 2011; Voigt & Lucas, 2015a; Voigt & Lucas, 2015b; Voigt & Lucas, 2017; Marchetti et al., 2020a), and North Africa (Voigt et al., 2011a; Voigt et al., 2011b). The circular structure on NM M4949a (Figs. 10A–10B) likely formed as a result of gas escaping from the sediment after it was compressed by passing tetrapods.

Spatiotemporal significance of vertebrate ichnoassemblage

Tetrapod ichnofauna typically occurs earlier and has a wider palaeogeographic occurrence than the body fossils of their presumed trackmakers (e.g., Niedźwiedzki et al., 2010; Long et al., 2025; Romilio et al., 2025). Therefore, the ichnological record plays a crucial role for tracing the spatiotemporal distribution of specific tetrapod groups, especially where the body fossils of terrestrial fauna are absent (Fig. 2). The tetrapod ichnoassemblage from the Semily Fm. revealed early occurrences of Amphisauropus tracks (ČGS JZ626, 632; Fig. 6) from the Ploužnice Horizon, which represents both the second oldest occurrence of this ichnotaxon worldwide, and the only thoroughly described Amphisauropus specimen from the Late Pennsylvanian. Although Amphisauropus was mentioned by Haubold & Katzung (1975) as originating from the Ploužnice Horizon (material stored at the Czech Geological Survey), this specimen was neither described nor figured in their study and most probably corresponds to the Limnopus track (CGS XA741) in our present study. The trackmakers of Amphisauropus are considered to be members of the Seymouriamorpha (Fichter, 1979; Marchetti, Mujal & Bernardi, 2016; Mujal & Marchetti, 2020), a group known primarily from lower Permian deposits in North America, Europe, and Asia (Amalitzky, 1921; White, 1939; Tchudinov & Vjuschokov, 1956; Tatarinov, 1968; Ivakhnenko, 1981; Berman, Reisz & Eberth, 1987; Berman & Martens, 1993; Klembara, 1995; Klembara, 2005; Klembara, 2009a; Klembara, 2009b; Sullivan & Reisz, 1999; Klembara & Batík, 2000; Bulanov, 2003; Klembara et al., 2020; Calábková, Březina & Madzia, 2022). The genus Discosauriscus is generally the most abundant representative of seymouriamorphs due to the hundreds to thousands of their larval stages discovered in the Letovice Fm. (Asselian) of the Boskovice Basin (location in Fig. 1A), Czechia. Discosauriscus larvae have also been found in the Prosečné Fm. (Asselian) of the KPB (Klembara et al., 2020). One of the oldest known seymouriamorphs is the discosauriscid Utegenia shpinari, which comes from the Kugaly Fm. in Kazakhstan (Kuznetsov & Ivakhnenko, 1981). This formation has been suggested to be either Pennsylvanian or Cisuralian in age (Kuznetsov & Ivakhnenko, 1981). Other early finds belong to Discosauriscus cf. pulcherrimus from the upper part of the Ilmenau Fm., which contains the Carboniferous–Permian boundary (Lützner et al., 2021; Klembara et al., 2023). Therefore, the identification of Amphisauropus tracks in the Late Pennsylvanian deposits of the KPB carries significant implications for understanding the spatiotemporal distribution of Seymouriamorpha. While skeletal remains of this group are predominantly known from the lower Permian strata across North America, Europe, and around the Urals (Amalitzky, 1921; White, 1939; Tchudinov & Vjuschokov, 1956; Tatarinov, 1968; Ivakhnenko, 1981; Berman, Reisz & Eberth, 1987; Berman & Martens, 1993; Klembara, 1995; Klembara, 2005; Klembara, 2009a; Klembara, 2009b; Sullivan & Reisz, 1999; Klembara & Batík, 2000; Bulanov, 2003; Klembara et al., 2020; Calábková, Březina & Madzia, 2022), our ichnofossil record, together with the Amphisauropus from the Middle Pennsylvanian of the USA (Lucas & Stimson, 2025; Marchetti et al., 2021), fundamentally support their earlier presence in the Pennsylvanian.

Ichniotherium cottae (MZM Ge34184; Figs. 9A–9B) from the Štikov, which falls into the lower part of the Semily Fm. (Stephanian C; Fig. 2) represents a rare occurrence of this ichnospecies from the European part of Pangaea in the Pennsylvanian. The morphology of I. cottae tracks and trackways closely corresponds to the structure of the autopodia and body posture of representatives of Diadectomorpha (see Voigt, Berman & Henrici, 2007; Buchwitz & Voigt, 2018). Although Ichniotherium is widespread in Permian deposits of the KPB (Frič, 1887; Frič, 1912a; Frič, 1912b) as well as in the nearby Intra-Sudetic Basin (Voigt et al., 2012; Voigt et al., 2024) and the Boskovice Basin (Calábková et al., 2023a; Fig. 1A), these tracks still represent the only evidence for the presence of diadectomorphs in the Pennsylvanian of Czechia. As diadectomorphs belong to one of the oldest lineages of herbivorous tetrapods, having evolved the ability to consume and process plant matter with a high fibre content (e.g., Beerbower, Olson & Hotton, 1992; Hotton, Olson & Beerbower, 1997; Sues, 2000), their occurrence in a lake ecosystem extremely rich in flora (Fig. 2) is expected.

The studied Limnopus (Fig. 8) specimen represents the first record of this ichnotaxon from the territory of Czechia and thus expands our understanding of the distribution of large Pennsylvanian temnospondyls in the basins of the Central European Variscan Belt. While Limnopus trackmakers are generally accepted as medium to large-sized temnospondyls, particularly members of the Eryopidae clade (Baird, 1965; Gand, 1987; Haubold, 2000; Voigt, 2005), skeletal fossil records of such large temnospondyls in the KPB are rare and restricted only to younger Asselian strata (Fig. 2). These include eryopid and archegosaurid temnospondyls from the Vrchlabí Fm. (Steen, 1938; Milner, 1981; Štamberg & Zajíc, 2008) and an unspecified eryopid from the Prosečné Fm. (Štamberg, 2014).

Likewise, smaller Batrachichnus tracks (Fig. 7) indicate the presence of small-sized temnospondyls (Haubold, 1996; Voigt, 2005; Stimson, Lucas & Melanson, 2012) or even lepospondyls (Stimson, Lucas & Melanson, 2012; Allen et al., 2022). To date, no body fossils of lepospondyls have been discovered in the KPB, whereas Frič (1912a) and Frič (1912b) provided limited skeletal evidence of temnospondyls in his description of scarce remains of unspecified branchiosaurids from the Kyje–Ploužnice railway cut.

Dimetropus tracks are typically attributed to various non-therapsid synapsid groups, such as mostly carnivorous sphenacodontians and ophiacodotids, or herbivorous edaphosaurids, and caseasaurs (Tilton, 1931; Romer & Price, 1940; Haubold, 1971; Haubold, 2000; Fichter, 1979; Voigt, 2005; Niedźwiedzki & Bojanowski, 2012; Voigt & Ganzelewski, 2010; Sacchi et al., 2014; Romano, Citton & Nicosia, 2016). Skeletal evidence for early-diverging synapsids in Czechia is extremely rare and includes only Macromerion schwarzenbergii, discovered by Fritsch (1875) in the Pennsylvanian deposits of the Kounov locality (Gzhelian, Stephanian B) within the Slaný Fm., Kladno–Rakovník Basin (Fig. 1A). This locality also yielded an isolated dorsal vertebra of edaphosaurid Bohemiclavulus mirabilis (Fritsch, 1895). Additionally, an element of the dorsal spine of the edaphosaurid Ramodendron obvispinosum was discovered in the Gzhelian strata (Stephanian C) of the nearby Boskovice Basin (Švestka, 1944). Studied ichnofossils of Dimetropus (Fig. 9I) demonstrate the earlier presence of synapsids in the Pennsylvanian of the KPB.

Dromopus is undoubtedly the most abundant vertebrate ichnofossil in the Gzhelian deposits of the KBP. These tracks are referred to bolosaurid parareptile, aeroscelid diapsid or non-varanodontine varanopid trackmakers (e.g., Haubold, 1971; Haubold, 2000; Voigt, 2005; Marchetti et al., 2021). Notably, no skeletal remains of provable early sauropsids or varanopids have been reported directly from KPB (Fig. 2). Only the unrevised material of potential sauropsids, tentatively assigned to “?Macromerion”, was figured by Fritsch (1885) from the Kounov locality (Gzhelian, Stephanian B) in the Kladno–Rakovník Basin. Additionally, the unrevised Sphenosaurus sternbergii, figured by Fritsch (1885), comes from an unknown locality in Bohemia, which Štamberg & Zajíc (2008) described as an “unknown Lower Permian locality (the red sandstone probably comes from the Krkonoše Piedmont Basin or from the Intra-Sudetic Basin)”. The extremely rich discoveries of Dromopus footprints from the KPB (Fig. 10) contribute significantly to our understanding of the initial diversification of amniotes, especially in areas where the fossil record of bodies is very limited.

Outside of the KPB, the only other Carboniferous tetrapod traces documented in Czechia come from the Radnice Member (Westphalian C, Pennsylvanian) of the Pilsen Basin, including Gracilichnium (?) chlupaci and Lunichnium gracile, interpreted as temnospondyl swimming, walking, and resting traces (Turek, 1989) and tetrapod footprints not described in more detail (Opluštil, Zajíc & Svoboda, 2022) from the Žacléř Formation (upper part of the Lampertice Member, Westphalian A, Pennsylvanian). Taken together, the tetrapod ichnoassemblage of the KPB is exceptionally crucial for understanding the diversity and evolution of terrestrial tetrapods in this intra-Variscan part of equatorial Pangea.

Palaeoecological implications

The Štikov roadcut section is interpreted as deposits of a river mouth, possibly a braided delta, where individual gravel- or sand-filled distributary channels incised into violet-grey mudstones—i.e., lacustrine nearshore deposits. The lacustrine deposits are considered here to result from the expansion of the Ploužnice Lake during a more humid period in the latest Pennsylvanian (Fig. 11)—a trend recorded by the contemporary Líně Fm. in central and western Bohemia (Nádaskay et al., 2025). The colour changes into red in upsection, which indicates lake-shore retreat and formation of a nearshore mudflat, accessible to the diadectomorphs, as well as eventually sauropsid and temnospondyl trackmakers.

The Kyje section (part of Kyje–Ploužnice railway cut) can be interpreted in terms of cyclic alternation of fluvial–alluvial and lacustrine environment of the so-called Ploužnice Lake (Fig. 11). The lowest of three identified cycles (cf. Blecha et al., 1997), with predominant reddish-brownish sediments, represents a vertical transition from lacustrine nearshore with intense clastic supply, probably close to a river mouth (Fig. 11) as evidenced by numerous sandstone bodies interpreted as mouth bars or alluvial bars, and one possibly incised alluvial or delta-plain channel. These are overlain by deposits of lacustrine coastal mudflat topped by a pedogenic horizon (Fig. 4B) that could be interpreted as a vertic calcisol. This indicates emergence of the lake coast for a longer period under a predominantly dry climate with seasonal precipitation (Fig. 11; cf. Mack & James, 1994). The overlying cycle is interpreted as a transition from the nearshore to the more distal portion of the lake. The tetrapod footprints were found in fine-grained sandstones in the lowermost part of this cycle, and were accompanied by mud drapes (sometimes with wrinkled surface possibly left by microbial mats), mudcracks, occasional rain-drop impressions, and invertebrate burrows (Figs. 5, 11). These features point to a sandy lake nearshore that repeatedly emerged for relatively short periods of time (cf. Melchor & Swithin Sarjeant, 2004; Minter et al., 2007; Mujal et al., 2016), inferred from the absence of significant rooting or pedogenic features. Similar environments can be interpreted from the topmost part of the Kyje section above the more distal lacustrine deposits. The footprints were left by early sauropsids, non-therapsid synapsids, diadectomorphs, seymouriamorphs, and temnospondyls, which roamed these areas during periods of low water level (no more than a few cm).

Concentric structures (Figs. 10A–10B) associated with Dromopus tracks, some of which overlie the tracks, are the most likely eroded subaerial parts of sand volcanoes that formed after the footprints. Formation of sand volcanoes is most commonly driven by dewatering related to earthquakes (e.g., Montenat et al., 2007; Van Loon & Maulik, 2011), and it is possible that in this case they were generated by liquefaction of unconsolidated sand underlying the surface on which the trackmaker roamed. Build-up of pressure within the sandbed that preceded the “explosion” of a sand volcano (Owen, 1996) could have been ensured by a sealing mud layer covering the sandbed. Although sand volcanoes are among the frequently occurring structures of inorganic origin at vertebrate footprint sites (e.g., Thulborn, 1990), their direct relationship to footprints—i.e., their formation due to the loading of a sandbed by a passing trackmaker, has not been widely discussed. In contrast, other soft-sediment deformation structures have been interpreted as being produced by trackmakers (e.g., Plint et al., 2025). The formation of sand volcanoes has also been attributed to the accumulation of gases from microbial mats (e.g., Smith, Marsicano & Wilson, 2009; Taj, Aref & Schreiber, 2014), which were likely present at the margins of the Ploužnice Lake, as indicated by wrinkle structures on mud drapes.

By comparison, fossil-rich “bonebeds” are found within decidedly distal deposits of an open lake, since they contain bone fragments of predominantly aquatic (nektonic) vertebrates such as sharks, fishes and acantodes (Fig. 2). Sparse body fossils found in grey or violet–grey mudstones also provide evidence for a relatively open-lake environment, probably shallow and well-oxygenated (Blecha et al., 1997).

The sedimentary record of both studied localities allows for the interpretation of the lacustrine environment (Ploužnice Lake) that occupies the central part of the basin, fed by fluvial systems entering the basin from the south, forming fan deltas (Štikov section) or more widely distributed fluvial deltas on a flatter basin margin (Kyje section). We assume that the evolution of the Ploužnice Lake (Fig. 11) was strongly influenced by relatively short-term (100–400 Kyr) climate fluctuations reflected by the decrease and increase in precipitation, as suggested by the evolution of a coeval depositional system of the Líně Fm. (with Klobuky Lake) in central Bohemia (Nádaskay et al., 2025).

The abundance of footprints in the Semily Fm. suggests that the lake ecosystem was a sought-after habitat for terrestrial and semi-terrestrial tetrapods, whether as a source of water, food, or a place for reproduction. The occurrence of Limnopus tracks, most probably left by large temnospondyls, corresponds well with the abundant fish fossils (Fig. 2), as representatives of eryopids and stereospondylomorphs were mostly piscivorous (Boy, 2003; Schoch, 2021). The diverse plant assemblage (Fig. 2) provided a rich food source for all herbivores such as diadectomorphs, indicated by Ichniotherium tracks. It remains unclear whether the Dimetropus tracks were left by herbivorous or carnivorous synapsids. In any case, the studied Pennsylvanian ecosystem of the KPB provided sufficient prey for apex predators of the Late Carboniferous such as synapsids. Finally, the abundance of fossil insects (Fig. 2) demonstrates good food availability for early sauropsids, as well as for many varanopids, which are represented by their relatively rich Dromopus track record.

The most complete data on fossil biota are provided by the lacustrine fossiliferous horizons within the KPB, where conditions for fossil preservation were most favourable. The Pennsylvanian taxonomic diversity likely persisted across the Carboniferous-Permian boundary, as the taxonomic richness of the fossil assemblages in the Semily Fm. appears comparable to that of the Vrchlabí Fm. (Fig. 2). During the early Permian, after deposition of the Rudník Horizon (Vrchlabí Fm., lowermost Asselian), a slight decline in the taxonomic richness of the fossil record is observable within the following Kalná Horizon (Prosečné Fm., Asselian). However, the question remains whether this apparent decline reflects a real reduction in palaeodiversity or is the result of taphonomic bias. Only a comprehensive analysis of the fossil record from Permian formations in the KPB can provide adequate data.