Defining the morphological quality of fossil footprints. Problems and principles of preservation in tetrapod ichnology with examples from the Palaeozoic to the present

LORENZO MARCHETTI; MATTEO BELVEDERE; SEBASTIAN VOIGT; HENDRIK KLEIN; DIEGO CASTANERA; IGNACIO DÍAZ-MARTÍNEZ; DANIEL MARTY; LIDA XING; SILVERIO FEOLA; MELCHOR, RICARDO N.; JAMES O. FARLOW

EARTH-SCIENCE REVIEWS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2019

0012-8252

The morphology of fossil footprints is the basis of vertebrate footprint ichnology. However, the processes actingduring and after trace fossil registration which are responsible for the final morphology have never been preciselydefined, resulting in a dearth of nomenclature. Therefore, we discuss the concepts of ichnotaphonomy, ichnostratinomy, taphonomy, biostratinomy, registration and diagenesis and describe the processes acting on footprintmorphology. In order to evaluate the morphological quality of tetrapod footprints, we introduce the concept ofmorphological preservation, which is related to the morphological quality of footprints (M-preservation, acronymMP), and distinguish it from physical preservation (P-preservation, acronym PP), which characterizes whether ornot a track is eliminated by taphonomic and diagenetic processes. M-preservation includes all the morphologicalfeatures produced during and after track registration prior to its study, and may be divided into substages (ichnostratinomic, registrational, taphonomic, stratinomic, diagenetic). Moreover, we propose an updated numericalpreservation scale for M-preservation. It ranges from 0.0 (worst preservation) to 3.0 (best preservation); intermediate values may be used and specific features may be indicated by letters. In vertebrate footprint ichnotaxonomy, we regard the anatomy-consistent morphology and to a lesser extent the trackway pattern as the only acceptable ichnotaxobases. Only footprints showing a good morphological preservation (grade 2.0?3.0) are usefulin ichnotaxonomy, whereas ichnotaxa based on poor morphological preservation (grade 0.0?1.5) are consideredichnotaphotaxa (nomina dubia) characterized by extramorphologies. We applied the preservation scale on examples from the Palaeozoic to the present time, including three ichnotaphotaxa and 18 anatomy-consistent ichnotaxa/morphotypes attributed to several vertebrate footprint producers. Results indicate the utility, feasibility andsuitability of this method for the entire vertebrate footprint record in any lithofacies, strongly recommending itsuse in future ichnotaxonomic studies