Modelling the morphology and evolution of the linea sinuosa (crown–root junction) in arvicolid rodents; a test with Pliocene Ogmodontomys from Kansas, USA

Abstract

The linea sinuosa of 39 specimens of Pliocene Ogmodontomys sawrockensis and Ogmodontomys poaphagus from the Meade Basin of southwestern Kansas, USA, was deconstructed into eight enamel segments, representing the major peaks and troughs that characterized Ogmodontomys. Coordinates for the positions of the major peaks and troughs were determined from standard Cartesian coordinate drawings, and then scaled for uniformity. Descriptive statistics for the amplitude (vertical) and drift (lateral) variation were calculated for each coordinate. A modified cubic spline analysis showed that accurate representations of the linea sinuosa, both of individuals and species, could be generated given these coordinate data. Comparisons of individual coordinates by analyses of variance distinguished O. sawrockensis from O. poaphagus, and the same coordinates were statistically distinguishable when the samples of O. sawrockensis were combined and tested against the combined samples of O. poaphagus by Student's t-tests. A mosaic of evolutionary trends, predominantly in peak morphology, was documented for Ogmodontomys from early through middle Pliocene time. Principal components analysis of coordinate data distinguished the linea sinuosa pattern of Ogmodontomys from a small sample of Pliomys lenki. This combined statistical approach offers a new and relatively simple quantitative method to model the form and evolution of the arvicolid linea sinuosa, thereby leading to more accurate phylogenetic and biostratigraphic reconstructions.