Fish trails from the Upper Carboniferous of south-west England

The ichnogenus Undichna Andersen, 1976, consisting of wavy horizontal grooves representing the drag marks of fish fins, is reported from the lacustrine Bude Formation. Two of the three species erected by Anderson are present. Two additional types of trail share strong similarities with Anderson's established species, but exhibit new features which warrant the erection of two new species, namely U. britannica and U. consulca. The new features necessitate modification of the original generic diagnosis. U. consulca includes a broad, shallow furrow, suggesting that the fish swam with its belly brushing the sediment. This behaviour would have been impossible unless the pectoral fins were mounted abnormally high, to avoid fouling the sediment. Of four species of fossil fish previously known from the Bude Formation, one (Cornuboniscus budensis White, 1939) is remarkable for its high pectoral fins. It is suggested that the high fins were an evolutionary adaptation which enabled the fish to hug the bottom in search of food. This food may have included xiphosurid crabs, whose trackways (Kouphichnium) are intimately associated with the fish trails. Of the four species of fossil fish found in the Bude Formation, two cannot be correlated with any of the trails; this suggests that the two species in question were mid- to surface-water feeders. None of the four known Bude fish species is morphologically suitable to have produced U. britannica, suggesting that a fifth species awaits discovery.