Let’s Get Rheal

Among the terrific birds WC was privileged to see on a recent to trip to Brazil was the Western Hemisphere’s biggest bird, the Greater Rhea. WC has written about the Greater Rhea before, but a bird this extraordinary deserves additional attention.

Greater Rhea, Pantanal, Brazil

The Greater Rhea isn’t a Big Bird; it’s a huge bird. They weight 45-60 pounds, and stand just a little less than four to five feet tall. They are very fast runners, and can reach speeds of 40 miles per hour.

Hot enough even the Rheas were uncomfortable

The Rhea is flightless, of course, but for a ratite they have fairly large wings. They extend the wings when running for balance and, as shown here, to cool off a bit when the temperatures are high.

Oddly enough, Rheas are biological proof of plate tectonics. Gondwana, the hypothetical single large continent, broke apart in stages. Africa split off first, and then Australia. That matches the speciation of Ostriches in Africa, Emus in Australia, extinct Moas in New Zealand and Rheas in South America fairly well, based on both the bids’ DNA and mitochondrial DNA (mDNA). Ornitholigists speculate that after the Dinosaur Killer meteor collision, it took about 10 million years before mammals evolved large predators, giving the birds time enough to evolve to larger sizes.

The dispersal and time of dispersal of Ratites – the large family of mostly flightless birds that includes Ostriches, Emus and Rheas, among other birds – matches the geology of the southern hemisphere against the biology of the birds. All of which makes the ancestral ratite really, really old, possible 80 million years old. If that’s true, the Greater Rhea is the closest thing to a living dinosaur.

Paleobiologists can work themselves into a froth over the details of all this. But the fundamental facts are reasonably clear: the Greater Rhea, whose evolution began on long-vanished Gondwana, is a relic dinosaur. Pretty cool.