The origin of Lower Devonian spore-rich coprolites

Kate Habgood
    Dept. Earth Sciences, Cardiff University, P.O. Box 914, CF10 4YE (Correspondance Address: Praxis Critical Systems, 21 Manvers St., Bath, BA1 1PX)

Small (less than 5mm long), spore-rich coprolites are common in certain Upper Silurian and Lower Devonian horizons within the lower Old Red Sandstone group. Two L. Devonian assemblages of terrestrial fossils, one preserved in fluvial sedimentary rocks in the welsh borderland and the other in the siliceous Rhynie Chert from Aberdeenshire, include unusually abundant and diverse coprolites.

The two assemblages, although similar in age and both preserved amongst plant fossils and organic debris, differ significantly in preservation and taphonomy. Coprolites from the Welsh Borderland are coalified and relatively compressed, and preserved in transported sediments. Conversely fossils silicified within the Rhynie Chert were preserved more rapidly and much closer to their source if not in situ. Coprolites from both sites are diverse in morphology and content, and comparison of the two assemblages reveals interesting differences, but in each case spore-rich coprolites comprise a significant proportion of the total faecal assemblage, and spores contained within the coprolites are apparently well-preserved and relatively rarely damaged.

Spore populations present within faeces from these assemblages provide clues to the nature of the coprolite-producing fauna and their diet. This and further evidence, ranging from the nature of the primary productivity available to Lower Devonian terrestrial fauna, to the results of experimentation using modern analogues, suggest that spores may not have provided a good source of nutrient for early terrestrial animals, and point to other origins for these spore-rich coprolites.