Marine subsidization of dinosaurian ecosystems

Marine subsidization (MS) of terrestrial ecosystems, in the form of marine-derived organic matter, energy, and nutrients, is a well-known phenomenon on modern coastlines. However, MS is rarely mentioned or considered in studies of Cretaceous terrestrial coastal ecosystems. Many studies of Cretaceous coastal ecosystems have noted `anomalous' carbon isotope (δ 13 C) values much higher than anticipated from comparisons of the bioapatite of dinosaurs and other vertebrates and their presumed dietary δ 13 C value. Since macroalgae and marine plants use a modified C 3 photosynthetic pathway resulting in a relatively increased δ 13 C value, bioapatite of MS consumers will be more enriched in 13 C relative to C 3 consumers. We used stable carbon isotope analysis of tooth enamel to determine if Cretaceous coastal organisms utilize marine resources by comparing coastal to upland ecosystems. These ecosystems include a variety of vertebrate taxa such as fish, neosuchians (e.g., crocodilians), and dinosaurs. The ecosystem deposits are the following: the Dunvegan Formation of British Columbia and Alberta, Canada; the Wayan Formation and Draney Limestone of Idaho, USA; the Antlers Formation of Oklahoma and Texas, USA; the Woodbine Formation/Group and Lewisville Formation of Texas, USA; and the Mussentuchit Member of the Cedar Mountain Formation, Utah, USA. The δ 13 C values of coastal assemblages are compared to assemblages of the Cloverly Formation of Wyoming and Montana, USA, an inland intercontinental deposit where MS was expected to be minimal based on known stratigraphic interpretations. We find evidence of MS of coastal ecosystems with relatively high δ 13 C value of coastal vertebrate enamel (up to >5.5‰ above expected δ 13 C enamel values) but not in upland environments. This has implications for back-calculations of dietary plant δ 13 C value from dinosaur herbivore enamel as previous estimates did not include marine-derived carbon sources in calculations. Therefore, future estimations of Cretaceous vertebrate isotopic offsets must consider the influx of 13 C-enriched, marine-derived organic matter and hence, MS of deep-time terrestrial ecosystems. The effects of MS within Cretaceous ecosystems must also be acknowledged as potential major ecosystem and trophic drivers.