Phylogeny of Early Vertebrate Skeletal Induction and Ossification Patterns

Abstract

The past 40 years has witnessed the demise of paleontology as a panacea with the ability to vindicate great phylogenetic theories. Today the role of fossils has been quite sharply defined (e.g., Hennig, 1965; Schaeffer et al., 1972; Nelson, 1978; Gaffney, 1979; Cracraft, 1979; Patterson, 1981a,b). The fossil record nevertheless provides useful data by refuting putative synapomorphies and by revealing nonhomology among living taxa, by suggesting sequential acquisitions of characters, and by providing supplemental biogeographic data (Patterson, 1981a). In these regards, fossils perform like newly discovered Recent taxa, but the paleontological data are potentially more dynamic in adding the element of geological time (hence giving minimum dates for taxic divergence and for biogeographic and other evolutionary events). Furthermore, the chances of discovering phylogenetically intermediate taxa (whether they are called “sister groups,” “ancestors,” “stem taxa,” “missing links,” or whatever) are inherently greater in fossil biotas than in Recent ones (vide the taxic paucity of “living fossils,” such as monotremes, coelacanths, cladistians [polypterids], agnathans, etc., versus the relative abundance of primitive Mesozoic mammals, fossil sarcopterygians, “palaeoniscoids,” and Paleozoic agnathans).