Morphometric Analysis of the Early Cambrian mollusc Mackinnonia and the Incipient Species Concept
(English)In: Palaeontology, ISSN 0031-0239, E-ISSN 1475-4983Article in journal (Other academic) Submitted
Phylogenetic relationships within the helcionelloids have been difficult to establish. One of the reasons for this is that qualitative approaches to investigating morphological variation in this group have struggled to identify clear patterns. An alternative method of identifying these patterns is to study these organisms quantitatively. Here we exemplify this approach by employing morphometric methods to investigate patterns of subtle morphological variation in two species of Mackinnonia Runnegar in Bengtson et al. Specifically, we conduct a combination of elliptical Fourier and multivariate analyses to study intra- and interspecific variation in protoconch form and variation in ontogenetic trajectory of two species of Mackinnonia. The material we use consists of two assemblages of Mackinnonia rostrata (Zhou & Xiao), from the Shackleton Limestone of Antarctica and Ajax Limestone of Australia, and an assemblage of Mackinnonia taconica (Landing & Bartowski) from the Bastion Formation of Greenland. Results of our study show significant (p=<0.0001) differences in protoconch shape between all three groups. Ontogenetic sequences of outline curves truncated at successive rugae significantly (p=<0.05) discriminate between M. rostrata and M. taconica. We discuss the uncovered significant intraspecific morphological variation of disparate assemblages of M. rostrata despite shared qualitative features and develop a conceptual framework for understanding such patterns of variation. We define the incipient species concept using Mackinnonia as an empirical example.
IdentifiersURN: urn:nbn:se:uu:diva-319485OAI: oai:DiVA.org:uu-319485DiVA: diva2:1087694