i know that stuff happens but anyway… all this by random mutations ?
In Poeciliopsis fish, eggs are retained within the follicle after fertilization and throughout embryonic development (Wourms and Lombardi 1992). Most species are lecithotrophic, relying on yolk, but in others, a highly folded, follicular epithelium forms a “follicular placenta” with the embryonic pericardial sac. This epithelial layer is lined with microvilli, while the surrounding tissue is highly vascularized, presumably to facilitate maternal-fetal exchange (Kwan, et al. 2015).https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5033709/
This type of placental structure has arisen several times during Poeciliopsis evolution (Kwan, et al. 2015) and has been subsequently lost and regained many times, making it a model for the evolution of placentation (Pollux, et al. 2014).
and similar stuff happened here:
Have Wings Come, Gone and Come Again?https://www.sciencedirect.com/science/article/pii/S0960982203003646
Can complex traits be re-evolved by lineages that have lost them? Phylogenetic study now suggests that wings may indeed have reappeared several times within the ancestrally wingless stick insects.