Let’s identify the trackmaker of those Early Permian ‘Dimetropus’ tracks from the Czech Republic

Calábková et al 2023 described
“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… assignable to the ichnotaxon Dimetropus.”

See figure 1.

Calábková et al 2023 concluded
“It is impossible to assign the studied tracks beyond early-diverging, or ‘pelycosaur-grade’, Synapsida at present.”

No pelycosaur manus and pes graphics were presented and compared to the tracks by the authors, so let’s apply them here (Fig 1).

Figure 1. Dimetropus tracks described by Calábková et al 2023 and identified as the ichnotaxon, Dimetropus, here matched to the Early Permian synapsids Ophiacodon, Aerosaurus and Varanops. PILs applied here.

Calábková et al report,
“From a general perspective, early-diverging, or ‘pelycosaur-grade’, synapsids are extremely rare in the Permo-Carboniferous basins of the Czech Republic, and all originate from Pennsylvanian (upper Carboniferous) coal seams.”

“Among these, the ophiacodontid Archaeothyris sp. from the Moscovian (Westphalian D) of Nýřany (Pilsen Basin, Kladno Formation), the stratigraphically oldest European sphenacodontid Macromerion schwarzenbergi and the historically oldest European edaphosaurid Bohemiclavulus mirabilis both from the Gzhelian (Stephanian B) of Kounov (Kladno-Rakovník Basin, Slaný Formation), and the largest known edaphosaurid, referred to as ‘Ramodendron obvispinosum’, from the Gzhelian (Stephanian C) of Oslavany (Boskovice Basin, Rosice-Oslavany Formation), likely represent the most significant specimens. In this contribution we provide the full description of the synapsid tracks and trackways, illustrate the material using three-dimensional modeling, and assess it especially with respect to the taxonomic affinities of their trackmakers.”

The manus and pes were not preserved in the above named taxa.

“The Dimetropus leisnerianus footprints are most commonly considered to belong to sphenacodontids, orearly-diverging sphenacodontians in general, which is associated especially with their typically elongated ulnare,a character that is reflected by proximodistally elongated palm impressions of D. leisnerianus. In ophiacodontids, caseids, varanopids, and edaphosaurids, the ulnare is typically relatively shorter.”

“Ophiacodontids are extremely rare in Europe.”

Basal synapsid fossils are extremely rare all over the planet.

Application of manus and pes graphics to the ichnites
(Fig 1) were instructive enough to score the pes in phylogenetic analysis in the large reptile tree (LRT, 2206 taxa). Parallel interphalangeal lines (PILs, Peters 2000, Peters 2011) were applied.

Tested against Lepidosauromorphs
the footprint nests with just two taxa. Eocaptorhinus had very short metacarpals, not longer than the phalanges, so they don’t match the tracks under study (Fig 1). Sphenodon appears too late and has a gracile pes.

Tested against Archosauromorphs
the footprint nests in an unresolved array of nine taxa. Among those of the proper age, Gephyrostegus had digits that were too short medially and too long laterally. The rest were basal synapsids. The digit length and width disparity were likewise too great in Varanodon. Only digits 3 and 4 were too long in Varanops and Aerosaurus.

Figure 2. Ophiacodon. PILs added here.

The best match, so far,
(Fig 1) is with Ophiacodon, (Figs 2, 3) supplemented with two slightly longer metatarsals, 1 and 2. Ophiacodon was not selected by the LRT because metatarsals one, two and three align. By contrast, in the track under study (Fig 1), metatarsals 2 and 3 appear to align with pedal 1.1.

Colleagues, use Photoshop
to apply fossil graphics to ichnites. Use PILs to understand and mark wherever phalanges flex in sets or do not.

Figure 3. Varanosaurus, Ophiacodon, Cutleria, Biarmosuchus and Nikkasaurus.

The present hypothesis of trackmaker identity
awaits confirmation, refutation or modification.

References
Calábková G et al (3 co-authors) 2023. Synapsid tracks with skin impressions illuminate the terrestrial tetrapod diversity in the earliest Permian of equatorial Pangea. Nature scientific reports. (2023) 13:1130.
Peters D 2000. Description and interpretation of interphalangeal iines in tetrapods
Ichnos, 7:11-41.
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605