Evolutionary Stasis In Golden Eagles Over the Last Glacial-Interglacial Cycle (35,000 years ago to present)

Pleistocene fossils from Rancho La Brea represent 26,000 years of morphology and lived during a period of dramatic climate change. According to classic evolutionary theory, the effects of this instability should be seen as morphological changes in the most commonly preserved bird, the golden eagle, Aquila chrysaetos, over the last 35,000 years. Five variables each were measured on over 600 well-preserved tarsometatarsi from the Page Museum at Rancho La Brea, and the same measurements were taken from a sample of 63 extant golden eagle bones. Change in size over time is shown through bivariate comparisons of the tarsometatarsi in the Pleistocene-aged and extant golden eagles. Interestingly, the data shows no significant change in size between 35,000 to 9,000 years b.p. or over the entire 35,000 years. Data analysis suggests that Aquila chrysaetos experienced evolutionary stasis even during the irregular climatic changes of the most recent glacial-interglacial cycle. This is consistent with other studies that show stasis in Rancho La Brean condors and turkeys, and in most of the large mammals.