Morphological characters that are restricted to a few growth-independent characters (such as the embryonic apparatus of nummulitids) or measurements at arbitrarily chosen growth stages (such as the second whorl in planispiral tests) do not adequately explain the phylogenetic relationships of fossil forms. Molecular-genetic investigations enlighten phylogenetic relations, but have two main disadvantages. First, they are restricted to living forms, and second, these relations are based on an extremely small part of the DNA and never on developmental and structural genes that regulate morphology. Morphometric methods based on growth-invariant characters allow modelling the test shape for each growth stage and thus point to the underlying complex of regulatory and structural genes responsible for shape and size. They can therefore be used in fossil forms. Growth-independent and growth-invariant parameters were developed to model planispirally enrolled tests using living nummulitids from the West Pacific, where the molecular genetic relations are known. Discriminant analyses based on growth-invariant parameters demonstrate a perfect correlation with biological species. The taxonomic distances (Mahalanobis Distance) indicate phylogenetic relationships and agree well with molecular-genetic relations. The exception is the strong misclassification of the only living representative (Palaeonummulites) of the important fossil Nummulites-group by molecular genetic methods: that approach places this species with the morphologically completely distinct Planostegina-group. The close morphological relation between O. dicoidalis and O. ammonoides and between O. elegans and O. complanata, both supported by molecular genetic investigation, is an argument for being ecophenotypes of the two biological species O. ammonoides and O. complanata. The use of growth-invariant variables and characters can thus be today's strongest tool to shed light on phylogenetic relationships in fossil forms.
"Growth-invariant Meristic Characters Tools to Reveal Phylogenetic Relationships in Nummulitidae (Foraminifera),"
Turkish Journal of Earth Sciences: Vol. 20:
6, Article 1.
Available at: https://journals.tubitak.gov.tr/earth/vol20/iss6/1