and that these plants and animals, both in the Old and New Worlds, began slowly to migrate southwards as the climate became less warm, long before the commencement of the Glacial period.
(the Old and New Worlds; began slowly; to migrate southwards as the climate became less warm) (these plants and animals, both in; to migrate; southwards; T:as the climate became less warm) (the climate; became; less warm)
the Old and New Worlds these plants and animals, both in the climate
began slowly to migrate became
to migrate southwards as the climate became less warm
southwards T:as the climate became less warm
less warm