THE BEARPAW FORMATION
The uppermost Formation in the Manyberries area is the marine Bearpaw Formation. This was deposited at the bottom of the inland sea after the coastal plain was flooded and the shoreline moved west to the area now occupied by the front ranges of the Rocky Mountains. A diverse assemblage of marine invertebrates is present in these beds, some of the most notable of which are the ammonites Placenticeras, Baculites, and Hoploscaphites, the remains of crayfish and a diverse array of clams. Many of these are preserved in nodules and can be exquisitely well preserved when the nodules are undamaged by weathering.
Vertebrates, although rare, are present as well. A number of mosasaur skeletons have been collected, but only the isolated remains of the long-necked plesiosaurs have been found so far. Marine turtles are one of the recent additions to the reptile assemblage. A complete skull has been found in equivalent beds near Lethbridge, and a partial braincase was found in the Manyberries area last summer. These specimens mark the northern-most occurrence of marine turtles in the western interior seaway. This probably closely reflects their original distribution, since they decrease in abundance going from a more southerly localities, such as Alabama, to the far northerly locality of Anderson River on the Arctic coast.
Marine fish have been found, mostly as partial specimens in nodules. The front half of a skeleton preserved in a nodule was found in the Bearpaw Formation south of Lethbridge to the west. One of the more unusual occurrences is a partial fish found in the living chamber of an ammonite.
We have not yet found bird or pterosaur remains in the Bearpaw formation of Alberta, although they were likely present since they are typical members of marine vertebrate assemblages in other locations in the interior seaway, and are typically more abundant in the more northerly localities.
Surprisingly, dinosaur remains are found in the Bearpaw formation. These are most reasonably interpreted as animals that were washed out into the ocean during a flood, either as a living animal overcome by the current or as a boated carcass. Such specimens can be quite well preserved. A skeleton of a hadrosaur was found in the Bearpaw formation in the Manyberries area in 1983, and a second one was found in the Lethbridge area in 19(?). Interestingly, both specimens are of Prosaurolophus, one of the relatively rare hadrosaurs, and both specimens are of juveniles. This probably reflects something about the biology of Prosaurolophus. Perhaps it was one of the hadrosaurs that are most common in the more coastal areas. Perhaps juveniles were more vulnerable to floods, and thus were more likely to be swept out into the ocean.
© 2007 The Southern Alberta Dinosaur Research Group.