What, if anything, is a "Tyrannosaurus rex"?
Paleontologists distinguish between fossils preserving the remains of organisms (body fossils) and fossils preserving evidence of an organism’s activities (trace fossils). As with extant organisms, the naming of body fossil species is guided by principles consistent with a descriptive theory of names. By contrast, the naming of trace fossil species is explicitly guided by the causal theory of naming. Consequently, paleontologists conventionally maintain a strict distinction between body fossil and trace fossil nomenclatures.
I argue that metaphysical and semantical considerations undermine conventional justification for distinct nomenclatures. Body fossils are materially and causally more similar to traces than they are to living organisms. The names of body fossil species and trace fossil species play the same role in paleontological theories. If convention is maintained, then theorists must admit that a nomenclature including both extant and fossil species is metaphysically heterogeneous. If convention is revised or rejected, then theorists must admit that fossil nomenclature has no single consistent foundation in semantic theory. Paleontologists are therefore left with a choice between one kind of theoretical discordance or another.