A tale of two quarries; biologic and taphonomic signatures in the oxygen isotope composition of tooth enamel phosphate from modern and Miocene equids

• Published in: Palaios 1996-08, Vol.11 (4), p.397-408
• Main Authors: Bryant, J. Daniel, Froelich, Philip N, Showers, William J, Genna, Bernard J
• Format: Article
• Language: English
• Subjects: Barstovian; Burge Member; Burge Quarry; Cenozoic; Cheek; chemical composition; Cherry County Nebraska; Chordata; diagenesis; enamel; Equidae; Equus; Equus burchelli; Equus caballus; Eutheria; Foals; Fossils; growth; Hemingfordian; Hippomorpha; Holocene; Horses; interpretation; isotope ratios; isotopes; Jaw; juvenile taxa; living taxa; lower Miocene; Mammalia; mass balance; Merychippus primus; mineralization; Miocene; modern analogs; Nebraska; Neogene; O-18/O-16; Oxygen; Oxygen isotopes; paleoclimatology; Paleontology; pattern recognition; Perissodactyla; Phosphates; Pliocene; Pseudhipparion retrusum; Quaternary; reconstruction; seasonal variations; Sheep Creek Formation; Sioux County Nebraska; Skeletal Records of Ecologic Change; stable isotopes; statistical analysis; taphonomy; Teeth; Tertiary; Tetrapoda; Theria; Thomson Quarry; Tooth enamel; United States; Valentine Formation; Vertebrata; vertebrate
• ISSN: 0883-1351; 1938-5323
• DOI: 10.2307/3515249

The oxygen isotope composition of tooth enamel phosphate (δP) from cheek teeth in jaws of modern equids is compared with that of fossil equids from Thomson and Burge quarries (Miocene, Nebraska) to determine if paleobiologic and taphonomic signatures are preserved in the δP of fossil teeth. Three distinct patterns of δP variation are found in modern and fossil jaws. Each pattern can be related to the season of birth. An oxygen isotope mass balance model that incorporates seasonality and nursing of foals during tooth enamel mineralization is used to interpret the δP pattern along the toothrow. The range of δP for the same tooth position among "Merychippus" primus jaws from Thomson Quarry is relatively small (2.2 per mil), and the cheek tooth δP pattern is similar among individual jaws. This is comparable to a modern living population and consistent with a taphonomic interpretation of catastrophic accumulation for the Thomson "M." primus population. The range of δP for the same tooth position among Pseudhipparion retrusum jaws from Burge Quarry is larger (4 per mil), and the cheek tooth δP patterns are not similar among individual jaws. This is consistent with an attritional accumulation over a long period of time. Such wide ranges in δP limit application to continental paleoclimate reconstruction because of the low signal to noise ratio.