The standard deviation of suture complexity or, reflects the interspecies variation of the trait (fig 7) and also increased up to the Jurassic. Figure 8 presents the relationship between the mean and the standard deviation of the distributions; the linear correlation coefficient r = +0.98 is highly significant (P < 0.005).
Sharp changes in total 7 usually correspond to the periods of radical renovation of Ammonoidea fauna. Taking into account the allometric relationship between the suture length and body size (Newell, 1949), we also studied the dynamics of shell-size distribution. Figure 6 shows a clear trend towards a decrease in the mean shell size V from the late Devonian to the late Carbonian; later, in the early Permian, the trend reversed and the parallelism in the growth of p and 7 became explicit.
Nauka, Moscow Newell ND (1949) Phyletic size increase - an important trend illustrated by fossil invertebrates.