THE PHANEROZOIC RECORD OF VERTEBRATE TRACE FOSSILS AND THE TAXOPHILE EFFECT

The principal categories of vertebrate trace fossils are tracks, coprolites, regurgitalites, consumulites, dentalites (bite marks), nests, burrows and gastroliths. Most have their earliest occurrences in the Devonian. The exceptions are coprolites, which have an earliest record in the Late Ordovician, and nests, which are not recorded before the Late Triassic. The fossil record of vertebrate traces fossils defines distinct acme zones.

The Mississippian-Pennsylvanian has increased numbers of trace fossils (notably tracks, coprolites, dentalites and burrows). The early Permian is an acme for both tracks and coprolites. The Late Triassic yields abundant tracks and coprolites, and tracks are also common in the Early Jurassic. The Late Jurassic/Cretaceous represents the time with the apparent greatest diversity of vertebrate traces (tracks, coprolites, consumulites, dentalites, nests and gastroliths). The Quaternary also represents a time of ichnological abundance (tracks, coprolites, regurgitalites, dentalites, nests and burrows).

In the early-mid Paleozoic, there were generally high sea levels, low tetrapod diversity, wet greenhouse climates and thus relatively few vertebrate traces. The late Paleozoic and Quaternary acmes for trace fossils were during times of generally low sea level and seasonal climates. The Jurassic-Cretaceous acme does not fit, and we believe that large body size (increased recognition) and a disproportionate amount of study of the dinosaur fossil record biases the trace fossil record. The latter we attribute to the Taxophile Effect – a bias introduced by a disproportionate volume of research on a popular taxonomic group Thus, many dinosaur dentalites warrant individual papers, whereas most Tertiary dentalite records are merely noted within the text of taxonomic descriptions.

Other factors that influence the pattern of the fossil record of vertebrate traces fossils include: (1) taxonomy – regurgitalites, gastroliths and burrows are notably restricted to a small number of taxonomic groups, which control the stratigraphic range of these traces; (2) functional morphology - e.g., the more efficient dental occlusion of mammals resulted in increased dentalites as this Class diversified; and (3) ethology – burrows, nests and regurgitalites reflect specific behaviors.