Circular 173—Statistical method for analysis of planispiral coiling in shelled invertebrates

By A. L. Gutjahr and S. C. Hook, 1981, 14 pp., 8 tables, 6 figs.

Discusses a statistical method for evaluating and comparing planispiral growth among invertebrates. This method is predicted on simple logarithmic growth patterns and employs simple and multiple linear regression combined with analysis of variance and covariance techniques. This method is first discussed in general terms and then is used to study planispiral growth in two Ordovician nautiloid genera, Plectolites Flower and Litoceras Hyatt. The analysis of coiling in these two genera indicates that the coiling angle of the shell alone is a sufficient criterion by which to distinguish one from the other. Preliminary results indicate that this method can also be applied to fusulinids and ammonoids and, presumably, to other planispirally coiled invertebrates.

Planispiral coiling among shelled invertebrate species is a rather widespread phenomenon; it occurs in such diverse taxonomic groups as the Foraminifera, Brachiopoda, Gastropoda, and Cephalopoda. Although shell coiling developed independently in these distinct lineages and differences in coiling form and functional significance are readily noted, most types of planispiral coiling have enough geometric characteristics in common to make rigorous comparisons both between and within groups possible.

In this paper the authors present a general statistical model for comparing and studying growth patterns in planispirally coiled invertebrate species. The authors then use this general model to study and evaluate growth patterns in several specimens belonging to two genera of fossil nautiloids. The statistical methods are predicated on simple logarithmic growth of the shells.