Fish and tetrapod trace fossils from the Upper Carboniferous of Puertollano, Spain

Well-preserved fish and tetrapod trace fossils occur in Carboniferous (Stephanian C) beds at Puertollano. They represent the first evidence of vertebrate ichnites in the Carboniferous of Spain. The fish swimming traces are assigned to Undichna britannica and Undichna unisulca. The dimensions and morphological features of the traces indicate that Orthacanthus (Xenacanthidae: Elasmobranchii), a shark very common in the basin, might have been the trace-producer. A morpho-functional analysis of the traces suggests an axial undulatory (=anguilliform) mode of locomotion of xenacanth sharks. This conclusion is consistent with the eel-like body found in all known xenacanthids. Tetrapod trackways, referred to Puertollanopus microdactylus ichnogen. et ichnosp. nov., and resting traces are described. Both walking and resting tracks are assigned to a small terrestrial tetrapod. Dimensions and proportions of the tracks, and size and morphology of the impressions of manus and pes suggest a microsaur amphibian or a small reptile as the track-maker. This represents the first evidence of these vertebrates in the basin. The superposition of fish trails and tetrapod trackways strongly suggests tidal processes in a marginal-marine depositional setting. This interpretation agrees with recent sedimentological, geochemical and palynological data from the Puertollano basin.