WASHINGTON COPROLITES AGAIN (AND AGAIN)

The study of coprolites (fossil feces) has come into and gone out of fashion, but has endured since the Reverend Buckland first applied the name in 1829. Recent decades have seen increased (if not widespread) interest as paleontologists recognize that documented coprolites can provide a more nuanced interpretation of fossil faunas and floras. Coprolites range from pellets produced by invertebrates (in part the pelloids of carbonate classifications) to feces of large and small vertebrates. In the case of vertebrates, documentation involves recognition of signs of fecal origin: indigestible fur, feathers, bone fragments and teeth. Generally, there is little in their external morphology to signal an obvious fecal origin. The Miocene-Pliocene “coprolites” of southwestern Washington State have a long history of study; interpretations of origin range widely and include organic and inorganic genesis. A landmark paper in 1958 concluded that they are coprolites based on several diagnostic criteria, all of which described some aspect of external form. Beginning in 1993 a series of studies reinterpreted them as inorganic; work was stimulated in part by the conspicuous absence of any diagnostic internal features. In 2001, a study concluded that Washington specimens were “cololites” (fossilized intestinal casts). The attribution was based primarily on external form. Recent study of a collection of over 400 examples from Washington shows that specimens fall into several distinct shape categories, within which they vary primarily (and widely) in size. Few of them show morphologies typical of supposed cololites. They are variously curvilinear and complexly contorted, little resembling the digestive tract of any known animal, vertebrate or otherwise. One category shows surface features that bear strong resemblance to the impressions of wood grain. No specimen from the Washington locality has shown any internal indigestible residue. The Washington specimens are pseudo-coprolites of inorganic origin.