Fossil Record 21(1): 171-182, doi: 10.5194/fr-21-171-2018
Rostrum size differences between Toarcian belemnite battlefields
expand article infoPatrícia Rita, Kenneth De Baets, Martina Schlott
‡ Geozentrum Nordbayern, Friedrich-Alexander Universität Erlangen-Nürnberg, 91054 Erlangen, Germany
Open Access
Body size changes have been reported across crisis intervals. Belemnites –now considered extinct stem-decabrachians – have rarely been investigatedfor this purpose, and the few studies have resulted in ambiguous outcomes.Here we investigate two Toarcian belemnite accumulations in southern Germanyfrom a morphometric point of view with the support of computed tomographydata. The aim of this study is to test whether a difference in size can beobserved between the rostra of the two studied samples, from individuallineage to community, and which proxy is more reliable. A significantdecrease in median size from the Early Toarcian (Dactyliocerastenuicostatum Zone) to the Middle Toarcian (Haugia variabilis Zone)is recognized. This is observed at the community level of organization,considering the whole assemblage, but also withinPassaloteuthis–Acrocoelites lineage, at the genus level. It is alsodemonstrated that diameter-based measurements or maximum preserved length arenot reliable proxies for size, and therefore apical length orthree-dimensional approximations, such as the geometric mean or thepost-phragmocone volume, are more advisable. This is especially importantwhen comparing specimens with markedly different rostrum shapes. Furtherstudies are, however, still necessary to disentangle the mechanisms behindthe reduction in rostrum size within the Toarcian and their putativeenvironmental causes.