In this paper, I investigate the variety and richness of the taxonomical practices between the end of the nineteenth and the early twentieth centuries. During these decades, zoologists and paleontologists came up with different quantitative practices in order to classify their data in line with the new biological principles introduced by Charles Darwin. Specifically, I will investigate Florentino Ameghino’s mathematization of mammalian dentition and the quantitative practices and visualizations of several German-speaking paleontologists at the beginning of the twentieth century. In (...) so doing, this paper will call attention to the visual and quantitative language of early twentieth-century systematics. My analysis will therefore contribute to a prehistory of the statistical frame of mind in biology, a study which has yet to be written in full. Second, my work highlights the productive intertwinement between biological practices and philosophical frameworks at the turn of the nineteenth century. Deeply rooted in Kantian bio-philosophy, several biologists sought to find rules in order to apply ordering principles to chaotic taxonomic information. This implies the necessity to investigate the neglected role of Kantian and Romantic bio-philosophy in the unfolding of twentieth-century biology. (shrink)