I’m going to crowd source this one,
but I think I covered all the bases here. In this subset of the large reptile tree (LRT, 1165 taxa) I’ve divided placental mammals born helpless (blue) from mammals born able to walk, swim and see (pink). I’ll need your help if there are any exceptions, like pangolins, that I missed one way or the other. Fossils are colorized based on phylogenetic bracketing.
Marine taxa need to be ready to go from the first minute.
Apparently so do the large plant-eaters ( including ant and copepod eaters), beginning with long-legged former tree shrew, Onychodectes.
Dens and nests
are associated with basal mammals, like us. Not so much with the derived herbivores (and anteaters) of the plains and forests. All of them get milk from their mothers before they start to dine on meat, plants, ants and copepods. Some of them have to keep up with here. Some of them have to keep up with her underwater.
there also seems to be a behavioral node at Maelestes in which succeeding taxa are all leaving the trees for good. Of course, that also happens exceptionally with the various mole and aquatic clades in more basal mammals.