“Stick ‘n’ peel”: Explaining unusual patterns of disarticulation and loss of completeness in fossil vertebrates

Abstract

Few fossil vertebrate skeletons are complete and fully articulated. Various taphonomic processes reduce the skeletal fidelity of decaying carcasses, the effects of most of which are reasonably well understood. Some fossil vertebrates, however, exhibit patterns of disarticulation and loss of completeness that are difficult to explain. Such skeletons are one of two variants. They are incomplete, often markedly so, but the preserved parts are highly articulated. Alternatively, they are complete, or nearly so, but articulation varies markedly between parts of the body. A characteristic feature is the absence of skeletal elements that, on the basis of their larger size and/or greater density, would be predicted to be present. Here we erect a model, termed “stick ‘n’ peel”, that explains how these distinctive patterns originate. The model emphasizes the role of decay products, especially fluids released from the carcass while resting on the sediment surface. These fluids permeate the sediment below and around the carcass. As a result, skeletal elements on the downward facing side of the carcass become adhered to the sediment surface, and are less likely to be remobilized as a result of current activity than others. The pattern of articulation and, especially, completeness is thus not what would be predicted on the basis of the size, shape and density of the skeletal elements. The effects of stick ‘n’ peel are difficult to predict a priori. Stick ‘n’ peel has been identified in vertebrate fossils in lacustrine and marine settings and is likely to be a common feature of the taphonomic history of many vertebrate assemblages. Specimens becoming adhered to the substrate may also explain the preservation in situ of the multi-element skeletons of invertebrates such as echinoderms, and integumentary structures such as hair and feathers in exceptionally preserved fossils.