Amber from a Tyrannosaurus rex bonebed (Saskatchewan, Canada) with implications for paleoenvironment and paleoecology

Abstract

The Frenchman Formation (Maastrichtian) exposed within Chambery Coulee in southwestern Saskatchewan, Canada, has yielded exceptional vertebrate fauna specimens, including one of the largest known Tyrannosaurus rex individuals. The site has excellent preservation of a rich and diverse paleobotanical assemblage containing amber, which is analyzed in detail and compared to other sources of paleoecological data herein. Fourier-Transform Infrared (FTIR) spectroscopy of the fossil resin suggests a botanical source among the Cupressaceae (cypress trees). The ecological requirements of the crocodilians imply a mean annual temperature of 16 °C, which is slightly higher than previous estimates based on paleobotanical analyses. Stable isotope analyses of amber in the deposit provided insight into the environment and the ecological conditions at the time of resin secretion. The δD values showed a marine enrichment that suggests proximity to oceanic waters, and by extension, strong influence of the Western Interior Seaway in the region during the latest Cretaceous. The carbon isotope composition might also indicate that a potential ecological stress affected the trees such as a drought. These results highlight the interest of including amber in bonebed studies: even in the absence of identifiable inclusions, valuable paleoenvironmental, paleoecological, and even paleogeographic clues can be derived from chemical analyses of fossil resins.