Abstract

The process of time-averaging can have deleterious effects on the recognition of morphological variability in the fossil record. To explore this issue, a geometric morphometric study was conducted on a life and death assemblage of the terebratulide brachiopod Terebratalia transversa. The results from several geometric morphometric techniques (including Procrustes analysis and thin-plate spline) confirm a high degree of morphological variability with little change in mean shape between the living and sub-fossil assemblages. Additionally, there is no evidence of distinct morphogroups in either assemblage, as postulated for the species in previous studies. These trends persist at all depths and size classes. The similar range of morphological variability at each site suggests a common causal factor such as a similar array of microenvironments available at all depths. One implication of this consistency in morphological variability between the living and sub-fossil assemblages is that the variability of a fossil assemblage of this species could be used to estimate single-generation variability during the time-averaged interval. Furthermore, the potential for recognizing the full range of shape variability in the sub-fossil record of a highly variable species is encouraging for the pursuit of species recognition in the fossil record. Very good fidelity of the sub-fossil assemblage with respect to morphological variability is documented here for the first time in brachiopods, and agrees well with the findings of similar studies of other taxa.

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