No implantation in an extra-uterine pregnancy of a placentotrophic reptile

Placentation is a common feature of live-bearing reptiles and mammals. Placentae are variable between species and can be classified by the extent that embryonic tissue breaches (invades) the uterus. Non-invasive placentation in eutherians is maternally imposed as extra-uterine embryos of species with epitheliochorial placentation will readily invade non-uterine tissues. This study documents the first observation of an extra-uterine pregnancy in a reptile; Pseudemoia entrecasteauxii, which in-utero exhibits non-invasive epitheliochorial placentation. The extra-uterine embryo did not invade maternal tissue suggesting fundamental differences between the nature and evolution of placentation in P. entrecasteauxii and eutherian mammals.