DEVELOPMENT OF A CONODONT ELEMENT MORPHOSPACE AND A METRIC THAT CAN BE USED TO ANALYZE PATTERNS IN THE EVOLUTION OF CONODONT COMPLEXITY AT TWO LEVELS OF ORGANIZATION

Approaches to the characterization of complexity of organic form have been limited by the fact that quantitative analyses are generally undertaken at a single, common level of structural organization. Here, an empirical morphospace is developed that makes it possible to characterize the forms of individual conodont elements as well as the complexity of the entire apparatus, for taxa in which this can be reconstructed with confidence. Analysis of data derived from the conodont morphospace by means of a Brillouin expression facilitates quantitative comparison of complexity among elements and from one apparatus to another. As more data accumulate, this will make it possible to map changes in complexity at both levels of organization, over time.

Variables on which the conodont morphospace is based include curvature of the element, the numbers of denticles, processes and platforms, the form of the basal structure and the presence of nodes, "spurs and grooves", striations, a reticulate pattern, and the structure of the blade, if present. The complexity of any single element can be defined by the presence, absence or states of these variables. These observations can be expressed numerically in terms of a Brillouin function. Likewise, the complexity of an articulated or reconstructed apparatus can be measured by another, different Brillouin expression. At this higher level of organization, complexity is a function of the number of discrete types of elements present in the apparatus, and not the character states represented in the forms of individual elements.

The data compiled so far shows that both Early Cambrian paraconodonts and the earliest euconodonts of the Late Cambrian were extremely simple in form at both levels of organization. However, most potential forms of individual conodonts seem to have been fully exploited by the end of Ordovician time. The subsequent pattern of evolution of complexity at the level of the apparatus as a whole remains to be determined.