Radiocarbon age anomalies in land snail shells from Texas: Ontogenetic, individual, and geographic patterns of variation

Accelerator mass spectrometric (AMS) radiocarbon analyses of live-collected , prebomb samples of shell carbonates of the land snails Rabdotus dealbatus and R. alternatus from Texas were carried out to quantify the characterist ic age anomalies of land snails from limestone areas. Age anomalies are sim ilar for the two species; they average +700 yr and vary by +/-180 yr (1 sig ma) among samples. Serial analysis of I shell reveals a significant ontogen etic trend in C-14 age anomalies, with older apparent ages (up to 1200 yr) in the apical part of the shell and younger and uniform ages in the last wh orl. No trend in age anomalies was found across a broad range of rainfall c onditions (from 300 to 1000 mm mean annual rainfall).