That this is near universal behaviour for both, and when there is at least some evidence for this in dinosaurs, does imply that it was an ancestral trait for the collective group and thus most dinosaurs likely gave some care to their offspring pre- and post-hatching.
If so, the find is a prime example of a species co-opting an ancestral trait.
This is generally thought to involve genetically "reactivating" the ancestral trait (e.g., see Marshall et al. 1994).
The large number and wide distribution of genera with ERs add support to the hypothesis that the presence of ERs is an ancestral trait for aerial Loranthaceae.
The case of whale limb buds can now be added to other well-known cases, such as our pharyngeal gill arches, where the traces of ancestral trait loss remain in the embryos of modern organisms.
If a related lineage has retained the ancestral trait, the two lineages will share a similar feature, not because of inheritance from a common ancestor but because of an evolutionary reversal in one lineage.
They deduced that it's a 150-million-year-old ancestral trait shared by most members of the group and exapted twice by river-bound species that need to flee frequent floods.
The tuatara has gastralia, rib-like bones also called gastric or abdominal ribs, the presumed ancestral trait of diapsids.
Therefore the mouse lemurs, such as the gray mouse lemur, were thought to have shared this plesiomorphic (ancestral) trait with the ancestral lemurs.
Also more aligned with dwarf lemurs, the first two upper molars (M1 2) have a more anterior hypocone that sits opposite the metacone, compared to the mouse lemurs' more posterior hypocone, which is presumably a symplesiomorphic (ancestral) trait.
This led to the alternative suggestion that pro-sociality is an ancestral trait among primates [8].
