Karyotypes of side-necked turtles (Testudines: Pleurodira)

Karyotypes are presented for 13 of the 14 genera of side-necked turtles (suborder Pleurodira, families Pelomedusidae and Chelidae). Pelomedusids have low diploid numbers and few microchromosomes (2n = 26–36); the five largest chromosomes are homologous in the three genera. Chelids have high diploid numbers and many microchromosomes (2n = 50–64) and are similar in this respect to cryptodires (2n = 50–66). The pelomedusid karyotype is regarded as derived, probably from an ancestral condition like that seen in chelids. Gross karyotypic differences are slight or nil within genera and among closely related pleurodiran genera. Triploidy probably occurs in Platemys platycephala (family Chelidae) which has 96 chromosomes. No sex chromosome heteromorphism was observed.