Quantifying the morphological evolution of the Nautiloidea through the Phanerozoic

This study analyzes the dynamics of the morphological evolution of the Nautiloidea from their origination in the Late Cambrian to the Recent. Previously undocumented patterns emerge, in particular a drastic shift of the variety of nautiloid morphologies in the Early Carboniferous.; First, an extensive character list that is applicable to all aspects of nautiloid morphology, internal and external, was developed. The resulting 50 characters were used to quantify the shell features of 583 nautiloid genera that span the temporal/stratigraphic range of the group. A Principal Coordinates Analysis was performed on the matrix of character states to generate a morphological space that illustrates the morphological dissimilarity between the nautiloid genera.; The nautiloid morphospace was partitioned into a stage-level time-series spanning approximately 500 Myr, from the Late Cambrian to the Recent. Many patterns emerge, particularly, an initial Cambrian-Ordovician radiation, subsequent extinctions and recoveries, and a major Early Carboniferous radiation.; A new metric is introduced that provides a more accurate view of the permutations in morphospace occupation over time, particularly concerning the actual range of realized morphologies. The new metric is based on a computational geometric method that describes a shape within the morphospace that contains all the genera mapped therein. The new method was able to quantify not only the shift in morphologies in the Early Carboniferous but also the bifurcation of occupied morphospace later in that period, which was not elucidated two established methods.; Finally, the morphological evolution of the nine nautiloid orders throughout their respective stratigraphic ranges was studied. The primary goals of this analysis were to understand the morphological history of each order in the context of nautiloid evolution on the whole and how the individual orders affect the filling of nautiloid morphospace over time. All nautiloid orders, except for the nautilids, were faithful to the varieties of morphologies shown within the first few stages of their originations, and thus fall into the latter category. Only the nautilids made a drastic change in their array of utilized morphologies, and as such they are the sole order involved in expanding the range in the Early Carboniferous.