The Albian vegetation of central Alberta as a food source for the nodosaurid Borealopelta markmitchelli

Abstract

During the Cretaceous, large herbivorous dinosaurs (megaherbivores) acted as keystone species—just as large mammals do today (e.g., elephants)—yet despite their significance in Cretaceous ecosystems, what plant taxa these dinosaurs ate is unclear. The Albian armoured dinosaur Borealopelta markmitchelli (Ornithischia; Nodosauridae) was discovered in northern Alberta, Canada and has well-preserved stomach contents dominated by fern leaf tissues, with low amounts of gymnosperm material, implying selective feeding. The lower Albian Gates Formation (Grande Cache Member) macroflora of central Alberta is contemporaneous and spatially proximal with B. markmitchelli and therefore provides information on local vegetation available to this nodosaurid and other megaherbivores in this area. In this study we provide census-sampled abundance data for the Gates Formation macroflora. These data also provide the means to further investigate the feeding ecology of Borealopelta by summarizing the vegetation and local food options available. Census collections at five sites within the Grande Cache Member exposed in the Grande Cache Coal Mine reveal that the local vegetation there was dominated by conifers (44–70%) across all sites. Athrotaxites, Elatides, and Pityocladus were the most common conifers. Other gymnosperms present were ginkgophytes (e.g., Ginkgoites; 11%) and Taeniopteris (9%). Caytoniales (Sagenopteris) were found at one study site but uncommon (2%). Ferns (e.g., Cladophlebis, Coniopteris, Gleichenites) accounted for 14% of the total site counts while cycadophytes (Bennettitales; 4%) and Equisetites (1%) were less common. When comparing the Gates Formation macroflora to the stomach contents of Borealopelta, these data suggest that B. markmitchelli was selectively feeding on ferns, or in a recently disturbed fern-dense area within the local landscape.