The LDG is old at least in the oceans
Based on the data we just saw, it looks like the tropics have been a diversity hotspot for millions of years. Most of the graphs we saw showed a peak at low latitudes.
But did you notice anything unusual about the sorts of species we were looking at? Brachiopods, ammonites, foraminiferans, and bivalves are all shelly ocean-dwellers. What about the mammals, insects, birds, and all the other animals plants that live on land? Where have they been living for the hundreds of millions of years they've been around?
We don't yet have enough fossils of land-dwellers to be very confident about where they all lived in the past but we have so many fossils of shelly ocean dwellers, like clams, that we can be pretty sure that they've been packing into the tropics for millions of years. But why? What's so great about the tropics?
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Photo of outcrop with fossil shells by Susan Kidwell, University of Chicago
Understanding Evolution © 2015 by The University of California Museum of Paleontology, Berkeley, and the Regents of the University of California