Birding by Foot: A Critical Look at the Synapomorphy- and Phenetic-Based Approaches to Trackmaker Identification of Enigmatic Tridactyl Mesozoic Traces

Abstract

One of the goals of vertebrate ichnology is to use trace fossils as an additional source of data to determine the palaeoecological makeup of vertebrate paleoecosystems. The features in both the synapomorphy-based and phenetic-based methods of attributing a trace to an osteologic trackmaker are those that are affected by preservational conditions, convergent due to size and/or habitat of the trackmaker, and are morphologically variable within taxa. Despite the drawbacks, the phenetic-based, or “gestalt” method, is still the most comprehensive, if not always synapomorphy-supported, means of using the largest amount of data (morphologic and behavioral) preserved for identifying tracks as avian. To date there are too few synapomorphies that are both pedes specific and are consistently preserved in footprints to be a practical method for attributing tracks to an avian trackmaker. There is still much more comparative ichnological and statistical work to be done to discern novel traits that can be used to delineate between the traces of large avian and small nonavian Mesozoic theropods.