Records of turtle remains from Pleistocene deposits in western North America are scarce, suggesting that turtles were uncommon in western landscapes throughout the Pleistocene. However, low numbers of fossils do not necessarily correlate with rarity in the past because taphonomic bias can have a marked impact on shaping what is preserved in the fossil record. We compiled minimum species richness data for 8 geographic regions by depositional setting (caves and open-air sites) and used a 2-factor analysis of variance to examine the effects of geographic region and depositional setting on turtle species richness. We did not find a statistically significant effect of depositional setting on turtle richness, suggesting that the paucity of turtles in the Pleistocene of western North America does not result from that particular form of taphonomic bias. Also, we found a strong regional variation in turtle richness that was dependent on time interval, suggesting a potential shift in regional patterns of richness since the Pleistocene.

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