An enhanced developmental staging table for the painted turtle, Chrysemys picta (Testudines: Emydidae)

Normal developmental staging tables often undergo expansion and enhancement in response to advancing research paradigms and technologies. The Painted Turtle, Chrysemys picta, has long been a preferred reference taxon for comparative embryology and recently became the first turtle species to feature a sequenced genome. However, modern descriptive studies on embryogenesis are lacking and an earlier developmental staging table has been ignored. To address these problems, we re-evaluated descriptions of developmental stages by studying embryos under standardized laboratory conditions. We created an enhanced normal developmental staging table that clarifies and validates previous descriptions of developmental processes in this species. Moreover, we emphasized description of turtle-specific developmental characters such as the carapacial ridge. We demonstrated that embryo growth rate, length of incubation period, and timing to developmental stages are predictable under controlled environmental conditions. The appearance of characters associated with eye, limb, and shell anatomy was congruent with observations made in other turtle species. To reduce experimental bias, we recommend the use of our enhanced staging table when describing embryogenesis in the Painted Turtle.