A quantitative description of the Wurmiella P1 element's basal platform in lateral profile, using the standardized cubic spline approach outlined in this paper, is useful for understanding the nature and levels of variation both within and among species of Wurmiella. Examination of the homogeneity of individual stratigraphic samples resulted in the detection of three distinct morphotypes within the SP-VII section, two assignable to the described species W. wurmi and W. tuma, and another belonging to an as yet undescribed species, W. n. sp. The standardized spline also leads to qualitative descriptions of the morphological differences among the taxa. W. wurmi differs from W. tuma primarily in the shape of the basal cavity in lateral view; the cavity is represented by a noticeably "pinched" region of the profile in W. tuma, while in W. wurmi it marks a change in the curvature of the profile between anterior and posterior regions. The new species is distinctly different, with a significant overall crownward arching of the entire element.

The use of a geometric morphometric approach to description of the profile, including the calculation of Bookstein-type shape coordinates, allows a clean separation of geometric shape and scale. Rescaling according to baseline length removes scale information from the configuration of landmarks for each specimen thus placing all specimens on a fixed scale for the purposes of shape comparison. Scale information is recorded separately as the centroid size (Bookstein 1991) of the standardized but unscaled spline coordinates. Information regarding size may nevertheless be present in scaled geometric analyses because of the allometric covariation of shape coordinates and centroid size. Allometric information was recovered in this study by examining the covariation of shape and centroid size, and reconstructing (via regression) "average" splines at three points in the size range for any single stratigraphic sample of an individual species. The points used were the minimum and maximum sizes, as well as mean size. Comparison of the resulting splines lead to a set of very interpretable graphics of shape change, during development, of any of the species at a particular stratigraphic level.

Using this analysis, one developmental feature common to both W. wurmi and W. tuma becomes obvious immediately; increasing size is associated with an increase in the degree of crownward arching of the element (Figure 7). The lack of detectable allometry in the single sample in which W. n. sp. is dominant (8) prohibits a similar comparison, but it is interesting to note that qualitative extrapolation of the growth trend of W. wurmi leads to both an increase in the degree of arching, as well as a shallowing of the basal cavity, a condition seen in all specimens of W. n. sp. We cannot yet determine the roles that these developmental characters may have played in the evolution of the Wurmiella clade, because we do not currently have a phylogenetic hypothesis of sister-species relationships for the genus. Nevertheless, this is the type of morphological information, which is required for the addition of hypotheses of evolutionary process to hypotheses of phylogenetic pattern.

The distribution of W. wurmi samples throughout the section allows an examination of the pattern(s) of microevolution exhibited by the species. The description of this mode uses a random walk as a null model of evolutionary change (Bookstein 1988; Roopnarine 2001). Of the three most significant factors of the SVD analysis, two conformed to the expectation of stasis (SVD I and SVD III), and one exhibited an interval of significant directional change (SVD II). SVD I, a description of the overall crownward arch of the element, varied very little, undergoing no net change through the section. This type of pattern conforms to constrained stasis (Roopnarine 2001), where the degree of variation is less than what would be expected of an unbiased random walk. Such patterns suggest the action of one or more mechanisms that limit variation, such as stabilizing selection or functional constraints (Roopnarine 2001). SVD III, the relative position of the basal cavity, varied broadly and randomly in the lower part of the section, but then also seems to follow a constrained pattern. SVD II, on the other hand, a description of the crownward concavity of the profile posterior to the basal cavity, underwent a period of directional change from samples 9D-10Li. The trend is a subtle, but significant decrease in concavity. Examination of the allometric curves (Figure 7) shows that the trend is rooted in the changing development of the profile, where the posterior section of the profile fails to increase in concavity with increasing size as one moves up the SP VII section. This is a significant conclusion since it links within-sample changes in allometry/development to a longer term microevolutionary trend.

The long geological history, generally high abundance, and morphological richness of conodonts and their fossil record combine to make them ideal subjects for long-term microevolutionary studies. In this study we have been able to use a single element of the Wurmiella apparatus, preserved in a single stratigraphic section, to discriminate three species, describe ontogenetic changes in individual samples of each species, describe patterns of character evolution in one of the species (W. wurmi), and link long-term directional evolution in one of those characters to evolution at the ontogenetic level. The obvious extensions of the present study include 1) broader geographic sampling in order to understand spatial variation of the patterns observed, 2) longer stratigraphic sampling to capture temporal variation throughout the entire geological span of the species, including times of cladogenesis, and 3) a phylogenetic framework of sister-group relationships in which to test hypotheses of the relationship between the microevolutionary observations and a macroevolutionary pattern. These are the basic steps toward understanding some of the questions raised by macroevolutionary theory, namely the role of microevolutionary processes in macroevolutionary patterns, the pattern of microevolution during the non-cladogenetic span of a species, and the distribution of microevolutionary rates during the geological span of a species.

The combination of a good fossil record, careful stratigraphic sampling and analysis, and appropriate methods for quantitative morphological and stratophenetic data analysis, will allow paleobiologists to address evolutionary questions with growing confidence. As paleontology continues to move increasingly from descriptive to analytical phases, the understanding of the quantitative nature of the discipline's unique data will become increasingly fundamental (Roopnarine 2002).