| Abstract: |  and  ratios of vertebrate tooth enamel are related to those of ingested water and food, respectively. Because apatite in tooth enamel is resistant to diagenetic alteration, and of fossil tooth enamel can be used to investigate terrestrial environments of the past.
In this study, tooth enamel from theropod dinosaurs was analyzed from four North American localities in order to reconstruct patterns in of precipitation during the Cretaceous. These sites include Big Bend, Texas (~30N), Alberta and Montana (~45-48N), and Alaska (~75N), and are all late Campanian/early Maastrictian in age. In addition, oxygen isotope data from scales of co-existing fish can be used in combination with the theropod data to estimate mean annual temperature (MAT) at each locality during the Cretaceous. In general, absolute values were higher, and this implies that the atmosphere was able to hold more water vapor at that time. A smaller range in values implies that less moisture was lost from air masses as they underwent latitudinal transport relative to the present. MATs were also higher at all localities, especially in polar regions. Both inferences are consistent with warmer global temperatures and shallower latitudinal temperature gradients inferred from marine isotope records and from fossil leaf assemblages.
In addition to theropod dinosaurs, tooth enamel was also sampled from herbivorous dinosaurs in order to estimate of plants over North America. Sampled localites include Baja, Mexico, Big Bend, Texas, Montana, North Dakota, and Alaska. In four cases it was possible to collect samples from two coexisting herbivorous dinosaurs, and significant differences in average were common between them. Such differences provide the first geochemical evidence for ecological niche partitioning between herbivorous dinosaurs.
Average for a single type of dinosaur (hadrosaurs) also varied extensively between localities and indicates that varying environmental conditions and/or differences in local plant communities can strongly influence of organic matter. This observation indicates that caution is needed when using of organic matter as a chemostratigraphic marker in terrestrial settings, as variations in may be due to local rather than global factors. |