Abstrakt
Order Dictyoptera (so-called "roachoids") is an ancient insect group whose Paleozoic representatives had long ovipositors and assumably laid single eggs. A gradual shortening of the ovipositor is observed throughout the evolution of this group.
In the Cretaceous, groups with both external and concealed ovipositors co-existed. The internalization of the ovipositor is related to the ability to form ootheca, a structure that encompasses the hardened case and the eggs.
It is produced by the collateral glands of female cockroaches. It evolved to protect embryos from drying, predation, and infections.
Here, I report oothecae attached to the body of cockroaches preserved in Cenomanian Myanmar amber and describe possible modes of oviposition of extinct cockroaches. The ancestral mode of ootheca oviposition, known from the superfamilies Corydioidea and Blattoidea, is to drop the ootheca just after it is formed.
Towards an investment in parental care, the ootheca is held to increase the time with maternal protection and is dropped later on, as observed in the superfamily Blaberoidea. Finally, some representatives in the same superfamily retract the ootheca into a vestibulum formed by sternite 7, where it is completely protected from external factors.
The most derived mode, known as true viviparity, is present in the small subfamily Diplopterinae and is thought to have originated during the Cenozoic, characterized by the mother giving birth to live young. The oldest definitive oothecae are recorded from Early Cretaceous localities of Yixian (China) and Crato (Brazil), as well as mid/Late Cretaceous Myanmar amber.