Taphonomy of an Eocene micromammal assemblage in a lake-margin depositional setting elucidates an ancient food web

Abstract

The taphonomy of the micromammalian assemblage from an unusually widespread lake-margin depositional context in the early Priabonian How Ledge Limestone, Totland Bay Member, Headon Hill Formation, Isle of Wight, UK, was studied in order to understand its method of accumulation, the trophic interrelationships between species and families, and their spatial relationships in the palaeoenvironment. The fossil remains studied consist of mainly dissociated bones and teeth, belonging to 28 species, which show selective anatomical representation and characteristic types of damage (fragmentation, etching, puncture marks), which are documented quantitatively. Predation and scavenging were important factors in the accumulation of the assemblage, with little subaerial weathering. The main predators are identified as the mammals Paramiacis sp. and Amphiperatherium species B, both present as fossils and themselves also predated, plus two possible owls not represented in the fauna. Scavenging is attributed to the predators, plus glirids, possibly nyctitheres and insects. The accumulation of remains in the lake environment is interpreted to result from seasonal retreat and advance of the lake margin, with minimal hydraulic transport. Comparison is made with a previous study of a similar micromammalian assemblage in the younger Priabonian Osborne Member, whose depositional environment is a floodplain pond. The similarities and differences are assessed in the context of a similar assemblage, although with a different dominant mammalian predator. Low post-mortem transport in each case is shown to have resulted in the preservation of an assemblage, which closely reflects the original community with some of its key trophic interactions.