The stable isotope compositions of biologically precipitated apatite in bone, teeth, and scales are widely used to obtain information on the diet, behavior, and physiology of extinct organisms and to reconstruct past climate. Here we report the application of a new type of geochemical measurement to bioapatite, a "clumpedisotope" paleothermometer, based on the thermodynamically driven preference for 13 C and 18 O to bond with each other within carbonate ions in the bioapatite crystal lattice. This effect is dependent on temperature but, unlike conventional stable isotope paleothermometers, is independent from the isotopic composition of water from which the mineral formed. We show that the abundance of 13 C-18 O bonds in the carbonate component of tooth bioapatite from modern specimens decreases with increasing body temperature of the animal, following a relationship between isotope "clumping" and temperature that is statistically indistinguishable from inorganic calcite. This result is in agreement with a theoretical model of isotopic ordering in carbonate ion groups in apatite and calcite. This thermometer constrains body temperatures of bioapatite-producing organisms with an accuracy of 1-2°C. Analyses of fossilized tooth enamel of both Pleistocene and Miocene age yielded temperatures within error of those derived from similar modern taxa. Clumped-isotope analysis of bioapatite represents a new approach in the study of the thermophysiology of extinct species, allowing the first direct measurement of their body temperatures. It will also open new avenues in the study of paleoclimate, as the measurement of clumped isotopes in phosphorites and fossils has the potential to reconstruct environmental temperatures.apatite | isotope | paleoclimate | thermophysiology | paleothermometry T he mechanisms by which animals regulate their body temperatures are among the most fundamental aspects of their biology. The acquisition of endothermy, the ability to maintain high and stable body temperatures through internal heat production, is a major physiological change that occurred at an unknown stage during the evolutionary transition to mammals and birds from their ancestors among the nonmammalian therapsids and nonavian dinosaurs, respectively (1). Approaches to understanding the physiology of extinct animals and the evolution of endothermy have largely focused on biophysical modeling, anatomical observations, growth rate analysis from bone histology, and behavioral studies such as estimating predator/prey ratios (1-7). The validity of each of these approaches is uncertain (for contrasting viewpoints on approaches to dinosaur thermoregulation see refs. 4 and 5).Modern endothermic mammals and ectotherms, such as alligators and crocodiles, generally have significant differences in average body temperatures. With rare exceptions, mammals have high and stable body temperatures around 36-38°C regardless of their environment, whereas the body temperatures of ectotherms are generally lower on average and often fluctuate depending o...

The 18 m.y. history of the subfamily Equinae (exclusive of Archaeohippus and “Parahippus”) in North America consisted of a 3-m.y. radiation phase, a 9-m.y. steady-state diversity phase, and a 6-m.y. reduction phase. During the steady-state phase, species richness varied between 14 and 20, with two maxima at about 13.5 and 6.5 Ma. Species richness of the tribes Hipparionini and Equini was about equal through the middle Miocene, but hipparionines consistently had more species in the late Miocene and early Pliocene. Overall mean species duration was 3.2 m.y. (n = 50), or an average extinction rate of 0.31 m.y.-1 During the radiation phase, speciation rates were very high (0.5 to 1.4 m.y.-1), while extinction rates were low (<0.10 m.y.-1). Speciation and extinction rates both averaged about 0.15 m.y.-1 during the steady-state phase, with extinction rates having more variation. Extinction rates increased fourfold during the reduction phase, while speciation rates declined slightly. Late Hemphillian extinctions affected both tribes severely, not just the three-toed hipparionines, and were correlated with global climatic change.

A shallow-marine fossil biota was recovered from the Blue Bluff unit (formerly part of the McBean Formation) in the Upper Coastal Plain of eastern Georgia. Biochronologically significant mollusks (e.g., Turritella nasuta, Cubitostrea sellaeformis, Pteropsella lapidosa) and calcareous nannoplankton (e.g., Chiasmolithus solitus, Reticulofenestra umbilica, Cribocentrum reticulatum) indicate a latest Lutetian-earliest Bartonian age, or about 40 to 41 Ma. Georgiacetus vogtlensis new genus and species is described from a well-preserved, partial skeleton. Georgiacetus is the oldest known whale with a true pterygoid sinus fossa in its basicranium and a pelvis that did not articulate directly with the sacral vertebrae, two features whose acquisitions were important steps toward adaptation to a fully marine existence. The posterior four cheek teeth of G. vogtlensis form a series of carnassial-like shearing blades. These teeth also bear small, blunt accessory cusps, which are regarded as being homologous with the larger, sharper accessory cusps of basilosaurid cheek teeth.

The giant fl ightless terror bird Titanis walleri is known from Florida and Texas during the late Neogene. The age of T. walleri 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 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 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 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 from Texas were compared to two groups (early Pliocene versus latest Pleisto cene) of fossil mammals from the same locality. The REE patterns of T. walleri from Florida are indistinguishable from those of the co-occurring late Pliocene mammals. Likewise, the REE pattern of T. walleri from Texas is indistinguishable from those of the co-occurring early Pliocene mammals. Given these REE constraints, the revised age of T. walleri is early Pliocene in Texas (ca. 5 Ma) and late Pliocene (ca. 2.2-1.8 Ma) in Florida. As such, T. walleri 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 in North America.