STASIS IN THE EXTINCT LA BREA FRAGILE EAGLE (BUTEOGALLUS FRAGILIS) IN RESPONSE TO CLIMATE CHANGE

The evolution of the Galápagos finches is one of the most famous examples of how the environment drives the evolution of traits in birds. Other examples of modern birds also suggest that birds evolve rapidly in response to climate change. However, of all the birds studied so far from the Pleistocene asphalt deposits of Rancho La Brea, none of them show change in the size or proportions due to climate changes of the last glacial maximum and the subsequent Holocene warming, from about 37 ka to 9 ka, when the chaparral typical of today was replaced by the snowy coniferous forests during the peak of the glacial maximum, about 18-20 ka. To test this further, we measured the tarsometatarsus (TMT) of Buteogallus fragilis, the extinct La Brea Fragile Eagle. We found complete stasis in both the size and proportion of the leg bones from 37,000 years ago until the end the Pleistocene. Like other La Brea birds, Buteogallus fragilis shows no response to the climate changes of the late Pleistocene.