Patterns of Variation in the Cranial Osteology of Three Species of Endemic Australian Lizards (Ctenophorus: Squamata: Agamidae): Implications for the Fossil Record and Morphological Analyses made with Limited Sample Sizes

摘要

Australian Agamidae often are recovered from Australian Cenozoic fossil deposits but remain largely unidentified and unpublished. Accurate fossil identification could expand our understanding of the origin, distribution, evolution, and extinction of Australian agamid species over geologic time. We began to address this issue by critically examining skeletal morphologic features that were previously proposed for Australian Agamidae. We compared 60 morphological features (44 from the literature and 16 new features) for three taxa of the most speciose of the Australian agamid genera, Ctenophorus caudicinctus (n = 18), Ctenophorus isolepis (n = 20), and Ctenophorus reticulatus (n = 20). Of the 180 morphological features (60 per species) that were expected to be invariant for all specimens within a species, only 39 did not vary. All taxa have at least one unique feature that did not vary with ontogeny (i.e., apomorphy). Invariant features also are shared between two species or all three. Seventeen morphological features were invariant for all three taxa. In addition to invariant features, one to three morphological features varied within each species with either ontogeny or sex. We also found that few morphological features could be identified from disarticulated material. Given that the current museum collections are wholly inadequate for addressing these issues, larger collections of extant agamid skeletal material are needed to understand skeletal morphological variation. A fossil record of Australian Agamidae already exists; we just need to develop the tools to interpret it accurately.