Tetrapod footprints - their use in biostratigraphy and biochronology of the Triassic

Abstract

Triassic tetrapod footprints have a Pangaea-wide distribution; they are known from North America, South America, Europe, North Africa, China, Australia, Antarctica and South Africa. They often occur in sequences that lack well-preserved body fossils. Therefore, the question arises, how well can tetrapod footprints be used in age determination and correlation of stratigraphic units?The single largest problem with Triassic footprint biostratigraphy and biochronology is the non-uniform ichnotaxonomy and evaluation of footprints that show extreme variation in shape due to extramorphological (substrate-related) phenomena. Here, we exclude most of the countless ichnospecies of Triassic footprints, and instead we consider ichnogenera and form groups that show distinctive, anatomically-controlled features.Several characteristic footprint assemblages and ichnotaxa have a restricted stratigraphic range and obviously occur in distinct time intervals. This can be repeatedly observed in the global record. Some reflect distinct stages in the evolutionary development of the locomotor apparatus as indicated by their digit proportions and the trackway patterns. Essential elements are archosaur tracks with Rotodactylus, the chirotherian ichnotaxa Protochirotherium, Synaptichnium, Isochirotherium, Chirotherium and Brachychirotherium, and grallatorids that can be partly linked in a functional-evolutionary sequence. Non-archosaur footprints are common, especially the ichnotaxa Rhynchosauroides, Procolophonichnium, Capitosauroides and several dicynodont-related or mammal-like forms. They are dominant in some footprint assemblages.From the temporal distribution pattern we recognize five distinct tetrapod-footprint-based biochrons likened to the known land-vertebrate faunachrons (LVFs) of the tetrapod body fossil record: 1. Dicynodont tracks (Lootsbergian=Induan age); 2. Protochirotherium (Synaptichnium), Rhynchosauroides, Procolophonichnium (Nonesian=Induan–Olenekian age); 3. Chirotherium barthii, C. sickleri, Isochirotherium, Synaptichnium (‘Brachychirotherium’), Rotodactylus, Rhynchosauroides, Procolophonichnium, dicynodont tracks, Capitosauroides (Nonesian–Perovkan=Olenekian–early Anisian); 4. Atreipus–Grallator (‘Coelurosaurichnus’), Synaptichnium (‘Brachychirotherium’), Isochirotherium, Sphingopus, Parachirotherium, Rhynchosauroides, Procolophonichnium (Perovkan–Berdyankian=Late Anisian–Ladinian); 5. Brachychirotherium, Atreipus–Grallator, Grallator, Eubrontes, Apatopus, Rhynchosauroides, dicynodont tracks (Otischalkian–Apachean=Carnian–Rhaetian).Tetrapod footprints are useful for biostratigraphy and biochronology of the Triassic. However, compared to the tetrapod body fossil record with eight biochrons, the five footprint-based biochrons show less resolution of faunal turnover as ichnogenera and ichnospecies at best reflect biological families or higher biotaxonomic units. Nevertheless, in sequences where body fossils are rare, footprints can coarsely indicate their stratigraphic age.

The Permo-Triassic Tetrapod Faunal Diversity in the Italian Southern Alps

“…1). For example the ichnogenus Procolophonichnium has been attributed to different biological groups such as procolophonids (Anapsida), therapsids (Synapsida) and basal amniotes (see Klein & Lucas, 2010;Klein et al, in press). The least inclusive group that bounds these taxa is the Amniota and Procolophonichnium is here conservatively considered as produced by an indeterminate stem group amniote (i.e., basal amniote).…”

The Triassic timescale: an introduction

“…In this volume, Klein & Lucas (2010) review the use of tetrapod footprints in Triassic biostratigraphy. They argue that several characteristic Triassic footprint assemblages and ichnotaxa have restricted stratigraphic ranges and thus represent distinct time intervals.…”

Early Triassic Archosaur-Dominated Footprint Assemblage from the Argana Basin (Western High Atlas, Morocco)

“…However, it was linked to the (Triassic) Timezgadiouine Formation (Hofmann et al, 2000;Tourani et al, 2000;see above). The disvovery of a Protochirotherium-Synaptichnium footprint assemblage in T3 is of biostratigraphic importance (see Klein and Haubold, 2007;Klein and Lucas, 2010 Triassic Detfurth and Wióry formations of Germany and Poland (see above). Beyond lithostratigraphic linkages, the Early Triassic age of the latter units is based on biostratigraphic data from conchostracans and palynomorphs (Bachmann and Kozur, 2004;Kozur and Bachmann, 2005;Niedzwiedzki and Ptaszynski, 2007).…”

“…This implies that certain ichnogenera and ichno-assemblages are restricted by their stratigraphic range and accordingly are useful for biostratigraphy and biochronology (Lucas, 2003(Lucas, , 2007. Protochirotherium-Synaptichnium are widespread and characteristic of the Early Triassic (Klein and Haubold, 2007;Klein and Lucas, 2010). Derived from the European record, these taxa precede typical Middle Triassic associations with Chirotherium barthii that first appear near the OlenekianAnisian boundary (Peabody, 1948;Haubold, 1967Haubold, , 1969Haubold, , 1971aHaubold, , b, 1984Haubold, , 2006Avanzini et al, 2001;Avanzini and Mietto, 2008;Demathieu 1970;Demathieu and Haubold, 1972;Demathieu and Oosterink, 1983;Demathieu and Demathieu, 2004;Gand, 1979;Gand and Demathieu, 2005;Klein,2000, 2002;King et al, 2005;Haubold, 2004, 2007;Klein and Lucas, 2010).…”