Abstract
Neontological studies of reptilian growth are important as they provide a proxy allowing investigation of the life history of extinct relatives. As such, finding modern correlates for bone growth and histological types that can then be used in a skeletochronological capacity are important for unraveling prehistoric mysteries that involve the growth of the extinct relatives of modern taxa. Most skeletochronology studies have focused on the lines of arrested growth, or LAGs, generated in the femur, as femoral size is large enough to study in even small reptiles and round in cross-sectional shape such that growth occurs evenly in all directions in the transverse plane of reference. No single study has yet to section every bone type in the body of an animal. This would allow for exploration of the extent to which other elements preserve the growth record and provide alternative elements to study growth, which may prove useful when the femur is not available. Modern archosaurs such as crocodilians, and in particular the American alligator (Alligator mississippiensis), not only allow for not only an interesting modern system but also provide a proxy for the past given their close evolutionary ties to fossil archosaurs such as dinosaurs. With the goal of generating a histological map of elements useful for aging in archosaurs, I conducted a histological analysis of an alligator previously in the care of the Florida Fish and Wildlife Commission was conducted. A representative of every type of bone was sectioned at multiple points and chemical label counts and tissue type characterizations were made. Aside from major long bone elements commonly used in histological studies, other skeletal structures such as ribs and phalanges exhibit areas of excellent LAG deposition that make them potentially useful in skeletochronologic analysis. From this data a “map” of the alligator skeleton was constructed regarding where along skeletal elements researchers are likely to find unobstructed deposition of LAGs. The results of this study elucidate which bones are best suited for analysis, as well as where along those bones information is preserved. Because histological analysis is a destructive technique, this information will allow researchers to make more informed decisions with regards to which skeletal elements to sample, thus reducing the potential for damaging more elements than is necessary. This will also open the possibility to age partial skeletons in which the femur is missing or unavailable for sampling.
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