A Geographical Information System (GIS) study of Triassic vertebrate biochronology.

Rayfield, E. J. and Barrett, P. J. and McDonnell, R. A. and Willis, K. J. (2005) A Geographical Information System (GIS) study of Triassic vertebrate biochronology. Geological Magazine, 142. pp. 327-354. DOI 10.1017/S001675680500083X

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Abstract

Geographical Information Systems (GIS) have been applied extensively to analyse spatial data relating to varied environmental issues, but have not so far been used to address biostratigraphical or macroevolutionary questions over extended spatial and temporal scales.Here,we use GIS techniques to test the stability, validity and utility of proposed Middle and Late Triassic ‘Land Vertebrate Faunachrons’ (LVFs), a global biostratigraphical framework based upon terrestrial/freshwater tetrapod occurrences. A database of tetrapod and megafloral localities was constructed for North America and Western Europe that also incorporated information on relevant palaeoenvironmental variables. This databasewas subjected to various spatial analysis techniques. Our GIS analysis found support at a global level for Eocyclotosaurus as an Anisian index taxon and probably Aetosaurus as a Norian indicator. Other tetrapod taxa are useful biostratigraphical/biochronological markers on a regional basis, such as Longosuchus and Doswellia for LateCarnian time. Other potential index fossils are hampered, however, by taxonomic instability (Mastodonsaurus, Metoposaurus, Typothorax, Paleorhinus, Pseudopalatus, Redondasaurus, Redondasuchus) and/or are not clearly restricted in temporal distribution (Paleorhinus, Angistorhinus, Stagonolepis, Metoposaurus and Rutiodon). This leads to instability in LVF diagnosis. We found only in the western Northern Hemisphere is there some evidence for an Anisian–Ladinian biochronological unit amalgamating the Perovkan and Berdyankian LVFs, and a possible late Carnian unit integrating the Otischalkian and Adamanian. Megaplants are generally not useful for biostratigraphical correlation in the Middle and Upper Triassic of the study area, but there is some evidence for a Carnian-age floral assemblage that corresponds to the combined Otischalkian and Adamanian LVFs. Environmental biases do not appear to strongly affect the spatial distribution of either the tetrapods or megaplants that have been proposed as index taxa in biostratigraphical schemes, though several examples of apparent environmental bias were detected by the analysis. Consequently,we argue that further revision and refinement ofMiddle and Late Triassic LVFs is needed before they can be used to support global or multi-regional biostratigraphical correlations. Caution should therefore be exercised when using the current scheme as a platform for macroevolutionary or palaeoecological hypotheses. Finally, this study demonstrates the potential of GIS as a powerful tool for tackling palaeontological questions over extended timescales.

Item Type:	Article
Uncontrolled Keywords:	2005 AREP 2005 P IA49
Subjects:	04 - Palaeobiology
Divisions:	04 - Palaeobiology
Journal or Publication Title:	Geological Magazine
Volume:	142
Page Range:	pp. 327-354
Identification Number:	10.1017/S001675680500083X
Depositing User:	Sarah Humbert
Date Deposited:	20 Aug 2010 10:08
Last Modified:	23 Jul 2013 09:59
URI:	http://eprints.esc.cam.ac.uk/id/eprint/1792

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