Morphodynamic Perspectives on Convergence between theFeet and Limbs of Sauropods and Humans: Two Cases ofHypermorphosis

摘要

Only two vertebrate groups, humans and sauropod dinosaurs,have a well-developed entaxonic foot (with the big toe, or digitI, the largest), and both have vertical limbs. Thus, convergenceapplies not only to the feet but also to the limbs. When viewedin relation to their closest relatives among the hominoids andsaurischian dinosaurs, and in the context of known developmentalgrowth patterns in higher vertebrates, both humans and sauropoddinosaurs appear to be excellent examples of peramorphosis(specifically hypermorphosis). Thus, it is essential to understandmorphodynamics as a field that is inseparable from the study ofheterochrony. The morphodynamic developmental perspective, while recog-nized as important in genetics and embryology, has for many gener-ations been overlooked in studies of feet, footprints and limbs (i.e.,the marco-morphology of organs). Investigating these dynamicsreveals striking recursive (or fractal) patterns of anterior-posteriorand proximal distal development, which in turn demonstrate thatvertebrate growth proceeds in an organized or "formal" manner.Thus, convergence is not merely, or only, a by-product of functionaladaptation to the external environment but also a manifestationof the complex but intelligible internal organization of dynamicorganic systems.