Complex sentence: The first dipterocarp pollen has been found from the upper Oligocene of Myanmar, at that time part of the Indian plate, and increases slowly in diversity and abundance across the region into the mid-Miocene.
Split into simpler sentences: The first dipterocarp pollen has been found in Myanmar (which at that time was part of the Indian plate) and it dates from the upper Oligocene. The sample appears to slowly increase in terms of diversity and abundance across the region into the mid-Miocene.