STASIS IN TERATORNS FROM THE LA BREA TAR PITS DURING THE LAST GLACIAL-INTERGLACIAL CYCLE

Conventional evolutionary biology suggests that birds evolve rapidly in response to climate change, as exemplified by the Galapagos finches. However, previous studies of birds from the Rancho La Brea tar pits showed no significant size or shape changes over the last glacial-interglacial cycle, despite significant climate changes during the last 35,000 years. We studied the largest birds at Rancho La Brea, Teratornis merriami, to determine if they showed size or shape changes in response to the climate. Even though teratorns seem to exhibit a weak Bergmann’s rule effect, with larger body sizes in colder climates, the Rancho La Brea teratorns showed complete stasis over this interval, with almost no statistically significant changes in size or robustness even during the peak glacial interval at 18,000-20,000 years ago, when the climate at Rancho La Brea was dominated by coniferous forests and snowy winters. These results are consistent with earlier studies on all the other large birds at Rancho La Brea. This result also suggests that the Galapagos finch model of rapid change in response to climate may not be appropriate for all birds.