| Summary: | Proceedings of the 8th International Meeting of the Society of Avian Paleontology and Evolution Although the importance of assessing ontogenetic age or developmental stage of fossil materials is widely recognized, information on avian postnatal skeletal ontogeny, which forms a basis for ageing criteria for bird fossils, is seriously lacking. One potentially useful ontogenetic ageing method in avian paleontology is textural ageing, in which surface textures of long bones are examined to assess developmental stage. To date, ontogenetic change of surface textures in long bones has been intensively described in only one species, the Canada Goose (Branta canadensis). In this study, through original preparation and examination of an ontogenetic series of specimens, which consists of 13 chicks (including one fledgling), two juveniles (birds under one-yearold) and two adults, postnatal ontogenetic changes of macroscopic morphology and surface texture of six major long bones (humerus, ulna, carpometacarpus, femur, tibiotarsus and tarsometatarsus) of the Gray Heron (Ardea cinerea, Ardeidae) are described and illustrated. Most long bones continue to grow in length until reaching their adult size range around the time of fledging. Epiphyses are generally not ossified before fledging; in both ends of femur and proximal end of tibiotarsus, distinct ossification centers can be observed. Generally, long bones of chicks are characterized by rough surface textures, including striated structures near epiphyses and fibrous/ porous surface with frequent penetrating pits in the midshaft. Long bones of juveniles are characterized by faint grooves and/or dimples, but rough striated structure may remain in the proximal regions of tibiotarsus and tarsometatarsus. In adults smooth surface pattern dominates. Inter-elemental variation in surface texture in one species is likely to represent taxon-specific patterns of relative timings of maturity among long bones, which would be related to various aspects of skeletal ontogeny in birds. At this time, textural ageing on birds with interrupted growth might be somewhat problematic because of a lack of sufficient data.
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