EXTRAORDINARY TRACE FOSSILS FROM THE UPPER DEVONIAN (FAMENNIAN) CATSKILL FORMATION, NORTH-CENTRAL PENNSYLVANIA: IMPLICATIONS FOR INTERPRETING EVOLUTION, PALEOENVIRONMENT, PALEOHYDROLOGY, AND PALEOCLIMATE

Research in the Upper Devonian Catskill Formation (Fm) has uncovered extraordinary trace fossils in continental deposits. New occurrences of (1) deep cylindrical, vertical burrows (Camborygma), (2) diagonal burrows elliptical in cross-section, and (3) large-diameter subhorizontal burrows (Reniformichnus) likely represent the burrowing activity of freshwater decapod crustaceans, scorpions, and amphibians, respectively, based on their architectural and surficial burrow (SM) morphologies. They bear resemblance to burrows of their extant relatives and likely occupied similar habitats.

Burrows occur at Burlington, Dry Run, Ralston, and Roaring Branch in red mudrocks interpreted as paleosols. These traces, with the exception of the vertebrate burrows, were previously found as isolated examples. Burrows attributed to freshwater decapod crustaceans are 1–2+ m deep and mostly vertical. The SM contains scrape marks, scratch marks, knobby hummocky features, and mud-linings; these features are similar to modern crayfish burrows. At Ralston, up to 90 individual burrows, many of which overprint one another, occur in a <10-m-wide outcrop face. Burrows interpreted as scorpions are subhorizontal, at ~15º angle from the paleosurface, elliptical in cross-section, and become horizontal near the terminus. The SM contains abundant short, chevron-shaped marks and body impressions; the combination of these features is similar to simple modern scorpion burrows. Two burrows, both partially preserved, are attributed to amphibians. One burrow is subhorizontal, subcircular in cross-section, and at least 80 cm long and 40 cm in diameter, with large longitudinal scratch marks subparallel to the burrow walls. The other is ~40 cm in diameter and its burrow walls contain crosscutting scratch marks, each ~1 cm wide and 10–15 cm long.

These discoveries shed new light on the Late Devonian ichnodiversity, paleoenvironments, paleohydrology, and paleoclimate. Decapod burrows were constructed in pedogenically modified floodplain deposits to the depth of the water table, likely reflecting seasonality in rainfall. Scorpion burrows were constructed in the vadose zone, whereas amphibian burrows occurred in settings when the water table was near to the surface. Burrows offered protection during the dry season and from predators.