Complex sentence: Many other groups reached New Caledonia after it separated from Australia, which took place as part of a widespread movement of Indo-Malesian elements that expanded into Australasia during the early and middle Tertiary.
Split into simpler sentences: Many other groups have reached New Caledonia after it separated from Australia. This took place as part of a widespread movement of Indo-Malesian elements that expanded into Australasia during the early and middle Tertiary.