Precision and resolution in mammalian chronostratigraphy: principles, practices, examples

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Abstract
This paper addresses the principles and practices applicable to developing highly resolved correlations in mammalian chronostratigraphy. A FAD (first appearance datum) is only as sound as the precision and accuracy of the LSDs (lowest stratigraphic datums) of which it is composed. Precision in boundary definition stems from improved analytical procedures in morphological as well as radioisotopic analysis, magnetostratigraphic correlations, and consideration of the completeness of stratigraphic sections. The so-called Hipparion Datum is examined as an example of these topics. More correctly known as the Hippotherium Datum, this event apparently took place at about 10.8 Ma and is resolvable within an interval of about 0.5 my. Discussion of evolutionary rates ends with a proposal for developing a catalog of such rates in geologically young situations in which the ± factors of the radioisotopic ages are less than the intervals being discriminated. These examples then may be compared with those developed in geologically older contexts, and tested for the duration of intervals in which species originate.