Morphodynamic Perspectives on Convergence between the Feet and Limbs of Sauropods and Humans: Two Cases of Hypermorphosis

Abstract

Only two vertebrate groups, humans and sauropod dinosaurs, have a well-developed entaxonic foot (with the big toe, or digit I, the largest), and both have vertical limbs. Thus, convergence applies not only to the feet but also to the limbs. When viewed in relation to their closest relatives among the hominoids and saurischian dinosaurs, and in the context of known developmental growth patterns in higher vertebrates, both humans and sauropod dinosaurs appear to be excellent examples of peramorphosis (specifically hypermorphosis). Thus, it is essential to understand morphodynamics as a field that is inseparable from the study of heterochrony.

The morphodynamic developmental perspective, while recognized as important in genetics and embryology, has for many generations been overlooked in studies of feet, footprints and limbs (i.e., the marco-morphology of organs). Investigating these dynamics reveals striking recursive (or fractal) patterns of anterior-posterior and proximal distal development, which in turn demonstrate that vertebrate growth proceeds in an organized or “formal” manner. Thus, convergence is not merely, or only, a by-product of functional adaptation to the external environment but also a manifestation of the complex but intelligible internal organization of dynamic organic systems.

Keywords:

• Hominid feet
• footprints
• sauropod dinosaurs
• heterochrony
• morphodynamics

ACKNOWLEDGEMENTS

Thanks to Ken McNamara, Western Australia Museum; Mark Riegner, Prescott College Arizona; Wolfgang Schad, Witten Herdecke University (Germany); and Jim Farlow, Indiana University for reading earlier versions of this manuscript and offering many useful and challenging suggestions. We also thank Matt Bonnan for providing useful information on sauropod phalangeal formulae, and Jeff Meldrum, Idaho State University, for his permission to use the diagram reproduced as Fig. 13. Spencer Lucas, New Mexico Museum of Nature and Science, and Craig Holdrege, Nature Institute, Ghent New York, reviewed the submitted manuscripts and offered helpful and thought-provoking suggestions