Invertebrate vs. vertebrate Ichnology.or One Ichnology?

RICARDO NESTOR MELCHOR; FERNANDO GENISE, JORGE

Trelew

Congreso; Ichnia 2004, First International Congress on Ichnology; 2004

Museo Paleontológico Egidio Feruglio

The ichnotaxonomical approach to the study of tetrapod tracks, mostly reflecting the influence of vertebrate paleontology, is different from that of invertebrate trace fossils. The taxonomy of tetrapod tracks has been largely based on anatomical features of the supposed producers, whereas other features (called “extramorphologic”) have been commonly ignored. In contrast, a consensus exist that the main parameters used for classification of invertebrate trace fossils are morphologic features that reflect behavior. The main goal of vertebrate ichnotaxonomy is the identification of the producer, which is not considered in invertebrate ichnotaxonomy. Similar tetrapod traces of different age or geographic provenance are commonly recognized under different ichnotaxa. This bone-based reasoning relies on the fact that the vertebrate faunas have changed through geologic time, then the track producers should be different, and the track types are thus distinguished under different, sometimes provincial, ichnotaxa. For instance, vertebrate ichnofacies are commonly restricted to a definite time interval (e.g. Late Permian Chelichnus ichnofacies). In contrast, the age or geographic location is not regarded as of taxonomic value for invertebrate trace fossils. The circular reasoning of using age as a valid ichnotaxobase undermines most ichnostratigraphic and ichnofacies approaches. Tetrapod track ichnotaxonomy based on morphologic characters that reflect behavior (including “extramorphologic” features) will result in the synonymy of morphological identical ichnogenera (e.g. Chelichnus, Laoporus and Brasilichnium). In turn, it will facilitate the comparison of similar ichnofaunas of different age that occur in the same sedimentary facies (e.g. eolian ichnofaunas). This is an essential step for the unification of the continental ichnofacies models by consideration of both invertebrate and vertebrate trace fossils.