several haramiyidans, "maiopatagium", "xianshou", "vilevolodon" and "arboroharamiya", took it one step further and developed the ability to glide, having extensive membranes similar to those of modern colugos. in many of these taxa, the coracoid bones (absent in modern therians but present in many other mammal groups, albeit highly reduced) are remarkably large and similar to those of birds and pterosaurs, presumably due to impact stresses at landing.