PALEOECOSYSTEM OF THE EARLY CRETACEOUS LANZHOU-MINHE BASIN, NW CHINA REVEALED FROM TOOTH ISOTOPIC COMPOSITION OF LANZHOUSAURUS MAGNIDENS

Stable isotopic analyses of tooth enamel phosphate and carbonate were collected from a maxillary and dentary tooth of the advanced iguanodontid Lanzhousaurus magnidens from the early Cretaceous Hekou Group, NW China. A long isotopic record representing over a year is available for these teeth, as Lanzhousaurus teeth are the largest herbivorous dinosaur teeth ever discovered (~10cm). O isotopic composition was collected to determine the isotopic composition of drinking water and seasonality of the early Cretaceous Lanzhou-Minhe basin of Northwest China. Tooth carbonate C and O isotopic composition was used to determine Lanzhousaurus diet and therefore dominant plant type. Isotopic composition of tooth phosphate (δ¹⁸O_p) ranged from +18.72 to +22.64‰ V-SMOW and averaged +20.30‰ for the dentary and +16.79‰ to +23.37‰ and averaged +21.62‰ for the maxilla. Seasonal variability was observed and typically ranged 1 to 2‰, but was as much as ~4‰. A long term increasing trend in isotopic composition was also observed. Isotopic composition of tooth enamel carbonate oxygen (δ¹⁸O_co3) currently analyzed on the dentary ranged between +26.01 and +22.59 ‰ V-SMOW. Carbon isotopic composition ranged from -5.39 to -6.57‰ V-PDB. δ¹⁸O_p and δ¹⁸O_CO3 of individual samples are linearly correlated (r² = 0.72) suggesting little diagenetic alteration of enamel carbonate. Based on physiological equations and testing a range of relative humidities from 50 to 70%, isotopic composition of drinking water ranged between an average δ¹⁸O value of -9.2‰ for 50% relative humidity to -5.2‰ for 70% relative humidity. Estimated plant diet δ¹³C values suggest a dry C₃ dominated ecosystem and ranged between -24.57‰ and -23.39‰ and averaged -24.00‰. These values will be compared to additional water isotope proxies (turtle δ¹⁸O_p) as well as bulk and picked organic C from the surrounding sediment. These values will help determine if Lanzhousaurus was consuming meteoric water or high elevation water derived from the nearby mountains, revealing a clearer picture of the terrestrial ecosystem of the early Cretaceous Lanzhou-Minhe Basin.