Development of yolk sac and chorioallantoic membranes in the Lord Howe Island skink, Oligosoma lichenigerum

A unique developmental pathway for the yolk sac and chorioallantoic membrane in the oviparous Lord Howe Island skink, Oligosoma lichenigerum, was identified. Unlike viviparous squamates, where the yolk cleft forms a placenta, this species' yolk cleft transforms into a tube-like structure filled with cells, leading to distinct extraembryonic membrane topology. Early development mirrors viviparous species, but the bilaminar omphalopleure persists over the abembryonic yolk surface before being displaced by allantoic mesoderm. The resulting chorioallantoic membrane shares structural similarities but differs in its developmental origin. This study used light microscopy on a developmental series to elucidate these differences, providing insights into the evolutionary adaptations of squamate reproduction.

Stewart, J. R., Russell, K. J., & Thompson, M. B. (2012). Development of yolk sac and chorioallantoic membranes in the Lord Howe Island skink, Oligosoma lichenigerum. Journal of Morphology, 273(10), 1163–1184. Portico. https://doi.org/10.1002/jmor.20052