11.1 Wednesday, Jan. 4 Alligator growth plate thickness as indicator of longitudinal growth rate and circulatory pattern OWERKOWICZ, T; YANG, J*; BLANK, JM; EME, J; HICKS, JW; California State Uni, San Bernardino; California State Uni, San Bernardino; California Polytechnic State Uni, San Luis Obispo; Uni North Texas; Uni California, Irvine email@example.com
Avian and non-avian dinosaurs possess long bone growth plates with a convoluted chondro-osseous border. This similarity has been used to argue that the avian-style developmental pattern evolved before the origin of birds. In order to test whether such growth plate microstructure is indeed a synapomorphy of dinosaurs, and whether growth plate thickness can be used as an indicator of skeletal growth rate, we studied the microstructure of the femoral growth plates of juvenile female alligators raised for two years under laboratory conditions. Some of the animals (n=24) had undergone surgery to ablate their left aorta and alter their circulatory pattern from in-parallel to in-series, whereas others (n=36) were sham operated. All animals received injections of fluorochrome dyes (calcein and alizarin), to determine their mineral apposition rates. We quantified the height of the calcified cartilage columns (CCC) of the growth plate, and longitudinal growth rate (LGR) of the femur. We found CCC height correlates with LGR, and is significantly augmented (+35%) in alligators with in-series circulation compared to similarly-sized sham controls with in-parallel circulation. We suggest the highly interdigitated chondro-osseous junction is an ancestral character of archosaurs and its presence in fossils of non-avian dinosaurs does not imply an avian-style physiology. We propose thicker growth plates appeared concurrently with the origin of in-series circulation, and may thus have set the stage for later acquisition of fast growth and endothermic metabolism of birds. Funded by NSF IOB 00445680 to JWH.