Why Were Female Giant Moa's So Much Bigger Than Males?

Male and female birds often show differences in body size, with males typically being larger. Some birds, like many ratites – large, flightless species such as emus and cassowaries – are the opposite, with the females towering over the males.  But some extinct ratites, among the largest female birds in the world, were almost twice as big as their male mates. A new paper says that the size difference in giant moa was not due to any specific environmental factors but instead evolved as a result of scaling-up of smaller differences in male and female body size shown by their smaller-bodied ancestors. read more

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