Specimens to Macroevolution to Specimens Again: Deciphering Macroevolutionary Trends

Specimens are the fundamental unit of paleontology, and our knowledge of the evolutionary history of a group is as much or more a function of the specimens available and the history of study of that material than models, techniques, or numerical analysis of these data. At any juncture, we can assemble what we know, but this primarily points to what we don't know. A compilation identifies the gaps in knowledge and where this knowledge is muddled. Thus, a compilation establishes a research agenda of critical intervals or boundaries (temporal, facies, or geographic) where new data must be found and where existing data needs to be revised (phylogenetic, temporal, or geographic). In both instances, specimens are the essential key to improved compilations. Specimens may also provide new data that previous workers could never imagine.

The study of crinoids is a prime example. The macroevolutionary transition from the early to the middle Crinoid Evolutionary Fauna (through the Ordovician-Silurian boundary) has been plagued by very few data, whereas the understanding of the middle Mississippian transition from the middle to the late Crinoid Evolutionary Fauna has been obscured because of too much data, much of which was muddled by obsolete taxonomy. New data from the Ordovician-Silurian boundary interval have demonstrated that non-random error existed in previous compilations. With well-defined generic concepts, the evolutionary dynamics of the middle Mississippian macroevolutionary transition can be addressed. Preliminary results indicate this transition was not synchronous globally, clade success was differential both temporally and biogeographically, and evolutionary history of individual clades are understood within the larger macroevolutionary transition.