Paradoxichnium, Muller, 1959

Marchetti, Lorenzo, Belvedere, Matteo & Mietto, Paolo, 2017, Lopingian tetrapod footprints from the Venetian Prealps, Italy: New discoveries in a largely incomplete panorama, Acta Palaeontologica Polonica 62 (4), pp. 801-817 : 808-809

Paradoxichnium isp.

Fig. 6 .

Material.—MCV 8, possible right pes-manus couple; MCV 9, left manus; MCV 10, right manus; MCV 11/05, right manus; all tracks are preserved in convex hyporelief; Ulbe ( Italy), Lopingian.

Description.—Pentadactyl manus, longer than wide and long about 70 mm, with thick and almost parallel digits increasing in length from I to IV. The digit V is relatively short, the bases of digits I and V are proximally positioned, both digits are shorter and thinner than digits II–IV. The digits II–IV terminate in large triangular claws, claws of digits I and V are smaller and acuminate. The palm is wider than long, and relatively short. The manual functionality is on digits II–IV, the palm and digits I and V can be absent. Pedal tracks larger with longer digits, lateral to the manus and usually not impressed.

Remarks.— The very characteristic morphology of the manual tracks allow a confident determination of these footprints as Paradoxichnium Müller, 1959 , specifically the well-impressed and grouped digits II–IV terminating in large triangular claws and the smaller and proximally-positioned lateral digits (MCV 9, 10; Figs. 5 , 6 ). Some specimens preserve only the digits II–IV of the manus, appearing as tridactyl impressions (MCV 8, 11, 11/05). This is clearly a taphonomic effect due to the higher functionality of digits II–IV. The rarity of pedal tracks is probably a taphonomic effect, the reason can be observed in the trackway holotype (pedal impressions are less-deeply impressed and more incomplete than manual impressions, FG 20/1; Fig. 6 ). The footprints classified as? Paradoxichnium radeinensis Ceoloni, Conti, Mariotti, and Nicosia, 1988 from the same formation do not show the main features of the ichnogenus, thus they have to be assigned to a different ichnotaxon. Paradoxichnium is tentatively attributed to protorosaurid archosauromorphs, mainly because of their eureptilian affinity, the functional prevalence of digits II–IV and the trackway pattern that implies a low coupling value ( Voigt 2012).

Figures

Fig. 6. Putative protorosaurid archosauromorph trace Paradoxichnium isp. A, B. Paradoxichnium isp. from Ulbe (Italy), Lopingian. A. MCV 10, right complete manus, note the proximally-positioned digits I and V and the triangular claw impressions. B. MCV 9, complete left manus impression. Note the proximally-positioned digits I and V, the parallel digits II–IV and the triangular claw impressions. C. Paradoxichnium problematicum Müller, 1959, holotype FG 20/1 from Culmitzch (Thuringia, Germany), Lopingian; right (C1) and left (C2) pes-manus couples; note the manual morphology similar to MCV 9. Convex hyporelief, spacing 0.5 mm. Photo (A1, B1), interpretive drawing (A2, B2), false-color depth map (A3, B3), contour lines (A4, B4). Scale bars 10 mm.

Fig. 5. Pareiasaurian parareptile trace Pachypes isp. (MCV 3) from Ulbe (Italy), Lopingian. Left manual imprint showing digits I–IV, convex hyporelief. Photo (A), interpretive drawing (B), false-color depth map (C), contour lines (D). Scale bar 10 mm.