Utility and validity of Middle and Late Triassic ‘land vertebrate faunachrons’

ABSTRACT

A tetrapod-based biochronologic framework for the terrestrial Triassic, which subdivides the Triassic into eight ‘Land Vertebrate Faunachrons’ (LVFs), has been proposed and developed by Lucas and coworkers. In a recent article, these authors reiterated their support for this scheme and used this opportunity to respond to criticisms dealing with the validity and utility of Triassic LVFs. This article is a reply to Lucas and colleagues and demonstrates that many aspects of this Triassic biochronology are dependent on: (1) subjective opinions regarding the taxonomic assignments of key specimens; and (2) unjustified extrapolation of correlations on the basis of geographically restricted endemics. Furthermore, it is suggested that the methodological basis for recognizing the onset of a particular LVF, the identification of the ‘first appearance datum’ for those taxa deemed to be biochronologically significant, leads to imprecision in correlation and potential ambiguity in dating. Finally, it is argued that geographic information systems are ideal tools for testing biostratigraphic hypotheses.