Fish trails from the Lower Old Red Sandstone of Tredomen Quarry, Powys, southeast Wales

Abstract

Alluvial deposits of the St Maughans Formation (Lower Old Red Sandstone, Early Devonian) of Tredomen Quarry, near Brecon, southeast Wales, have yielded the oldest known trails of swimming fish as well as body fossils of heterostracans and osteostracans, their inferred producers. Undichna unisulca comprises a single sinusoidal wave (of varying amplitude and wavelength) and is attributed to the caudal lobe or fin of a swimming heterostracan or osteostracan. Variation in the dimensions of U. unisulca trails, together with functional analysis of their inferred producers, suggests different fish sizes and swimming speeds. Undichna cf. simplicitas shows a more complex arrangement of intertwined waves and is interpreted as being produced by a combination of the caudal fin, anal spine and paired pelvic spines of an acanthodian. A new ichnotaxon, Undichna trisulcata isp. nov., consists of three isolated furrows arranged in parallel with associated pectoral fin imprints, and is interpreted as either the trail left by a 'cruising' cephalaspid, intermittently pushing off the substrate with its pectoral fins, or a trail made by a cephalaspid landing on the substrate. The presence of Undichna within these relatively proximal fluvial sediments (displaying no evidence of marine influence) is indicative of an in situ vertebrate freshwater community. Taphonomic constraints on Undichna preservation, in combination with sedimentological analysis, suggest weak bottom currents and/or rapid burial, post-trail formation. Arthropod trackways (Diplichnites gouldi Types A and B, Protichnites isp., and Palmichnium pottsae), a bilobed trail (cf. Cruziana), worm burrows (cf. Cochlichnus) and large meniscate backfilled burrows (Beaconites barretti) contribute invertebrate components to this ichnofauna. The association of Diplichnites trackways on the same surfaces as Undichna supports a semi-aquatic habit of their inferred myriapod producers.

First record of Lower Triassic Undichna spp. fish swimming traces from Emei, Sichuan Province, China

“…Their hypichnial ridges were narrower and lacked the shallow central furrow (refer to text and Figure 4c [16,18]). The wavelength and amplitude of the traces we found were more constant and had more regular symmetry than those specimens described by Gibert et al [16], Morrissey et al [18] and Soler-GijÓn et al [17]. However, the former were smaller in dimension and shorter in length than the latter.…”

“…However, the former were smaller in dimension and shorter in length than the latter. The ratio amplitude/wavelength（A/）was approximately twice that compared to the specimens described by Gibert et al [16] and Morrissey et al [18].…”

Eurypterid trackways from Early Devonian tidal facies of Alken an der Mosel (Rheinisches Schiefergebirge, Germany)

“…Track series in Palmichnium may either diverge or converge in the direction of travel, sometimes even in trackways made by the same animal (Hanken and Størmer 1975). In Palmichnium pottsae, the track series generally converge in the direction of travel (Braddy and Anderson 1996;Morrissey et al 2004), as inferred here. Sediment mounds can result from the backward stroke of an appendage on the sediment ('push-back pile'), but they may also be formed by the recovery stroke of an appendage in a deeper undertrack level ('drag pile') (Goldring and Seilacher 1971;Seilacher 2007).…”

“…The genus Adelophthalmus shows a great diversity in Permocarboniferous deposits and is interpreted to be the producer of Palmichnium pottsae from the Late Carboniferous of Wales (Braddy and Anderson 1996) and the Early Permian of New Mexico/ USA (Minter and Braddy 2009). The Early Devonian examples from Wales, being somewhat smaller, were likely produced by the closely related hughmilleriids (Morrissey et al 2004). However, it is unlikely that Adelophthalmus produced the largest Alken trackways.…”

“…Based on a large degree of morphological similarity, we thus prefer to assign the Alken trackways to P. pottsae despite the lack of a medial impression in previously described examples of this ichnospecies (cf. Braddy and Anderson 1996;Morrissey et al 2004;Minter and Braddy 2009), which we consider as a minor preservational variation.…”