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The North American Land Mammal Ages, defined in 1941 by the Wood Committee, provide good examples of the use of strict nominal stratotypes in fixing the names and establishing the minimum durations of provincial biochronologic units. The lithostratigraphic "type sections" of each Age served a name-bearing and exemplary function, not a boundary-defining function. Despite some inconsistencies in their work, the common charge that the Wood Committee defined many of their Ages as lithochrons is a myth. Nevertheless, the potential or actual temporal overlap of some of the original nominal stratotypes of the Ages is a significant problem, and their redefinition is permissible in order to preserve the original intentions of the Wood Committee.

The Berkeley school of North American mammalian stratigraphic paleontology has been the most influential force in theoretical discussions in this field since the 1960s. D.E. Savage retained most of the Oppelian views of R.M. Kleinpell, while M.O. Woodburne and D.R. Prothero departed from that tradition and adopted some of the views of H.D. Hedberg and W.A. Berggren, thus emphasizing single-taxon definitions, "datum-planes," and boundary stratotype definitions for "stages." However, recommendations by members of the Berkeley school that we turn our land mammal ages into "formal stages" are ironic because their own writings show they still hold the anti-Hedbergian view that "stages" are flexible biostratigraphic/ biochronostratigraphic entities. Nevertheless, in partial agreement with at least some members of the Berkeley school, the transformation of our provincial biochronologic units into golden spike-defined Ages/Stages would defeat their purpose, which is to summarize our evolving knowledge of the true sequence of important paleobiological events in each major fossil group that occurred in a given province.

In principle and in practice, Hedberg’s attempt to restrict the terms Age/Stage to golden spike-defined entities has failed. However, Hedbergians and traditional stratigraphic paleontologists can find common ground if they will admit that aurichronologic and biochronologic units are both legitimate subcategories of geochronologic units. If so, Hedberg’s major program would be vindicated in that golden spikes would still be used to define the Phanerozoic Standard Global Geochronologic Units, while traditional stratigraphic paleontologists would retain the ability to modify the boundaries of their provincial Ages/ Stages as they saw fit, provided that such modifications did not violate the strict nominal stratotypes of those Ages/Stages. (c) 2004 Elsevier B.V All rights reserved.