(urth) megatherians = vanished gods?

[Andrew Mason]

Some people do find it controversial whether the name 'megatherians'
refers to the monsters (Erebus, Abaia and co.), but that's by the by.

As James says, there is definitely a connection between the Mother on
Blue and Scylla on Urth - I think they are said to be sisters. There
are indications, notably the bean story, that the monsters on Urth
came from space; this may mean either that they came from Blue, or
that they came to both Urth and Blue from a third planet.