FOSSIL SPECIES: PLAY THE HAND YOU'VE BEEN DEALT

If anything is clear from the extensive debates about the nature of biological species it is that a one-species-concept-fits-all solution will never be found. Given that the most salient feature of the living world is its variability (in all systems, at all levels), we should not be surprised if sequoias, shorebirds, sand dollars, and Streptococcus differ in the ways they organize themselves.

Coyne and Orr (2004, p. 26) argue that when choosing a species concept, “one should first identify the nature of one’s species ‘problem’, and then choose the concept best at solving that problem.” For a paleontologist interested in species formation, this means: 1) accepting that morphospecies are an imperfect but generally good guide to something like the Biological Species Concept, which itself works reasonably well for sexually-reproducing animals, 2) appreciating that a paleontologist has a variety of tools at his/her disposal to augment morphological information (e.g. geographic and stratigraphic ranges, paleoecology), and 3) appreciating that detailed, long-term patterns of morphologic stability and change are as essential to understanding the nature of species as are genetic or ecological data.

Data suitable for illuminating long-term patterns of evolution within a fossil species are unavailable in a great many cases, but well-chosen species-level taxa are arguably less problematic than fossil taxa of higher rank. The reproductive compatibility of living species confers on them a reality that other groups lack. Observing how this dynamic plays out over space and long intervals of time, through the proxy of paleomorphospecies, is necessary for a fully realized understanding of these most compelling evolutionary units.