LUNGFISH BURROWS AND EARLIEST RECORD OF ESTIVATION BY VERTEBRATES, UPPER DEVONIAN CATSKILL FORMATION, PENNSYLVANIA, USA

We compared large-diameter, vertical, non-branching burrows (LDB) of the Upper Devonian (Frasnian–Famennian) Catskill Formation (CF) in north-central Pennsylvania with morphologically similar burrows in order to interpret the tracemaker, behavior they represent, and their ichnotaxonomy. LDB are common throughout pedogenically modified CF deposits and rarely occur in bedding plane concentrations >5 per m². LDB have an elliptical cross section and range in maximum diameter from 15.0–142.6 mm and minimum diameter from 13.8–121.6 mm. The maximum/minimum diameter ratio ranges from 1.026 to 1.537. Burrows are up to 400 mm long. LDB surficial morphologies are characterized by transverse striae, produced during burrow construction. A detailed comparison of the architectural and surficial morphologies of LDB with fossil and modern lungfish estivation burrows indicates that they represent lungfish estivation—a state of torpor during seasonal drought to avoid desiccation. LDB are morphologically distinct from decapod burrows and amphibian estivation burrows, which are morphologically similar. The morphological uniqueness of CF LDB merits their placement in a new ichnotaxon. Lungfish skull roof material and tooth plates also occur in several different localities of the CF, however this material is fragmental. CF LDB represent the earliest evidence of estivation by vertebrates, previously thought to be Carboniferous based on burrows from the Michigan basin, interpreted to be lungfish burrows. Estivation is significant as it allows an organism to live in areas that would otherwise be inhospitable. Lungfish used estivation in the Late Devonian to cope with the seasonal variability in water levels in rivers and floodplain ponds.