this region. Vertebrates present in the Horseshoe Canyon Formation at the time of Pachyrhinosaurus included reptiles, and amphibians. Sharks, rays, sturgeons, bowfins, gars and the gar-like Belonostomus made up the fish fauna. Reptiles such as turtles and crocodilians are rare in the Horseshoe Canyon Formation, and this was thought to reflect the relatively cool climate which prevailed at the time. A study by Quinney et al. (2013) however, showed that the decline in turtle diversity, which was previously attributed to climate, coincided instead with changes in soil drainage conditions, and was limited by aridity, landscape instability, and migratory barriers. The saltwater plesiosaur Leurospondylus was present and freshwater environments were populated by turtles, Champsosaurus, and crocodilians like Leidyosuchus and Stangerochampsa. Evidence has shown that multituberculates and the early marsupial Didelphodon coyi were present. Vertebrate trace fossils from this region included the tracks of theropods, ceratopsians and ornithopods, which provide evidence that these animals were also present. Non-vertebrates in this ecosystem included both marine and terrestrial invertebrates. See also Timeline of ceratopsian research References Centrosaurines Late Cretaceous dinosaurs of North America Maastrichtian life Taxa named by Charles Mortram Sternberg Fossil taxa described in 1950 Horseshoe Canyon fauna Paleontology in Alberta Paleontology in Alaska Campanian genus first appearances Maastrichtian genus extinctions Ornithischian genera