Revised age of the late Neogene terror bird (Titanis) in North America during the Great American Interchange

The giant flightless terror bird Titanis walleri</em> is known from Florida and Texas during the late Neogene. The age of T. walleri</em> is problematic because this taxon co-occurs with temporally mixed (i.e., time-averaged) faunas at two key sites. Thus, prior to this study, T. walleri</em> from the Santa Fe River, Florida (type locality), was either as old as late Pliocene (ca. 2.2 Ma) or as young as latest Pleistocene (ca. 15 ka). Likewise, T. walleri</em> from the Nueces River, Texas, was either early Pliocene (ca. 5 Ma) or latest Pleistocene (ca. 15 ka). In order to better resolve this age range, the rare earth element (REE) patterns of T. walleri</em> from the Santa Fe River, Florida, were compared to two biochronologically distinctive groups (late Pliocene versus late Pleistocene) of fossil mammals from the same locality. Similarly, the REE patterns of T. walleri</em> from Texas were compared to two groups (early Pliocene versus latest Pleistocene) of fossil mammals from the same locality. The REE patterns of T. walleri</em> from Florida are indistinguishable from those of the co-occurring late Pliocene mammals. Likewise, the REE pattern of T. walleri</em> from Texas is indistinguishable from those of the co-occurring early Pliocene mammals. Given these REE constraints, the revised age of T. walleri</em> is early Pliocene in Texas (ca. 5 Ma) and late Pliocene (ca. 2.2 1.8 Ma) in Florida. As such, T. walleri</em> is interpreted as an early immigrant during the Great American Interchange prior to the formation of the Isthmian land bridge. No evidence currently exists for Pleistocene T. walleri</em> in North America.