J. Hohenegger, DETERMINATION OF UPPER TRIASSIC AND LOWER JURASSIC ICHTHYOLARIAS USING MORPHOGENETIC PROGRAMS, Micropaleontology, 39(3), 1993, pp. 233-262
Species of the genus Ichthyolaria from the Upper Triassic and Lower Ju
rassic are investigated and described. First the morphology of each ch
amber, rib and the keel surrounding the test are transferred to geomet
rical functions reducing complete test morphology to a small set of pa
rameters. Then dependencies of each parameter on growth are modelled b
y geometrical functions representing the morphogenetic programs. Param
eters of these growth independent functions are used as characters in
classification analyses based on clustering and ordination methods. Gr
oups demonstrating homogeneity in characters can now be interpreted as
biological species using the criterion of cohesion in morphogenetic p
rograms. Classification of Ichthyolarias results in 10 species, where
one of lowermost Jurassic age (Ichthyolaria gigantea) and two of Trias
sic age (I. serotriadica, I. parvolimbata) are new. Evolutionary tende
ncies and phylogenetic relationships are proven using multivariate dis
criminant analyses.