“ossils of Devonian ammonoids are abundant and well-preserved in the Anti-Atlas of Morocco; as such they provide
an invaluable record of regional morphological disparity changes (diversity of shapes) that characterise the first steps of
ammonoid evolution. However, they were rarely analysed quantitatively with respect to their morphological spectrum.
Here, we investigated the morphological disparity of the Early–Middle Devonian ammonoids of the Moroccan Anti-
Atlas by analysing the shape of their whorl profile. A geometric morphometric approach based on the acquisition of
outline semilandmark coordinates was used to analyse the whorl profiles. For comparison, morphometric ratios based on
classical conch measurements were also analysed to investigate the overall conch geometry. Several standard disparity
estimators were computed to measure different aspects of morphological disparity fluctuations through time. It appears
that a major increase in disparity occurred throughout the Early Devonian, followed by fluctuating disparity during
the Middle Devonian constituting a general decreasing trend. Only the end-Eifelian Kačák Event shows a significant
decrease in disparity. Thus, the ammonoids explored the range of possible shapes fairly quickly during their initial radi-
ation; however, we found no evidence for an early burst of shape diversity (i.e., the rise does not exceed the expectations
given diversity). Nevertheless, correlation tests between diversity and disparity time series support that they are partially
decoupled. The highly resolved biozone record highlights that the increase in disparity began earlier than the increase in
diversity that characterises the late Emsian.” Free to read in APP