THE "SPECIES PROBLEM" IN PALEOBIOLOGY--IT'S MUCH MORE COMPLICATED FOR US

Although paleobiologists are aware of controversies in neobiology over species delimitation and "ultimate concepts", we have seldom contributed anything substantial to these debates. Most of us assume our morphospecies are "real" reproductively isolated species; we work on our favorite groups of organisms the way we want to, developing pragmatic methods of species recognition as we go along. And in the new efforts of analytic paleobiologists, there is little concern about species delineation and concepts--the emphasis is to get on with the modeling. The species problem is more complicated for us for several reasons: (1) we have conflated alpha taxonomy, competing methods of delineation, and role of species in evolution; (2) are just beginning to consider that speciation processes are complex, the geographic contexts varied, and that speciation products can be strikingly different; and (3) we have given little attention to the nasty problem of equivalence of fossil and modern species taxa (e.g., could the slight morphologic variations in an Ordovician brachiopod morphospecies indicate separate species-lineages?). As the discussion warms up, we need to be aware of some encouraging developments. Neobiologists are talking about a "unified species concept"--essentially a modernized version of Simpson's evolutionary species concept--viewing species as fundamentally lineages consisting of metapopulations extended in time. The various criteria (isolation, recognition, cohesion, morphology, ecology, diagnosable characters, monophyly, gene trees) used by advocates of the competing operational concepts are now seen as secondary properties of species (some have them, some don't) that can be used in practical combinations to delimit species taxa of all kinds. And some ambitious moves in paleobiology actually have helped to clarify the nature of species. Many fossil species display stability over millions of years, with most phenotypic evolution occurring during cladogenesis, validating the unified concept. Finally, ideas about turnover pulses, sloshing buckets, and coordinated evolution point up previously unappreciated connections between environmental forcing, history of large ecologic systems, and formation, status and persistence of species-lineages.