The St. Mary River Formation is a geologic formation of Late Cretaceous (71.9-67 Ma) age of the Western Canada Sedimentary Basin in southwestern Alberta and northwesternmost Montana. It was first described from outcrops along the St. Mary River by George Mercer Dawson in 1883, and it takes its name from the river.
Fossils from the formation include remains of dinosaurs,Weishampel, David B; et al. (2004). "Dinosaur distribution (Late Cretaceous, North America)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press, pp. 574-588. . as well as bivalve shells, plant fossils, and trace fossils.
Lithology The St. Mary River Formation is generally considered to consist of two units. The lower of the formation was deposited in brackish water environments, and is characterized by fine-grained sandstones, grey shales, coquinoid beds, carbonaceous mudstones and coal beds. The remainder of the formation was deposited in freshwater fluvial and floodplain environments and is characterized by interbedded sandstone and siltstone, with minor occurrences of carbonaceous shale and coal.
Thickness and distribution The St. Mary River Formation is part of an eastward-thinning wedge of sediments derived from the erosion of the mountains to the west. It is about thick in the exposures along the Crowsnest and Castle Rivers, and about thick along the Oldman River.
Relationship to other units The St. Mary River Formation conformably overlies the Blood Reserve Sandstone, or the Bearpaw Formation where the Blood Reserve Sandstone is absent, and it is conformably overlain by the Willow Creek Formation. It extends from Glacier County, Montana to as far north as the Little Bow River in Alberta, where it grades into and intertongues with the contemporaneous strata of the Horseshoe Canyon Formation.
Fossil content Flora Eighteen species of plant leaves were described from the St. Mary River Formation in 1949.Bell, W.A. 1949. Uppermost Cretaceous and Paleocene floras of western Canada. Geological Survey of Canada, Bulletin 13, 231 p. More recent work downstream from the St. Mary Reservoir increased the total to at least 32 species. The assemblage includes remains of ferns, Ginkgo, conifers, a Trapa-like plant,Stockey, R.A. and Rothwell, G.W. (1997). The aquatic angiosperm Trapago angulata from the Upper Cretaceous (Maastrictian) St. Mary River Formation of southern Alberta. International Journal of Plant Sciences 158(1): 83-94, and at least six types of large monocot leaves in addition to a sabaloid palm.Riley, M.G. and Stockey, R.A.(2004). Cardstonia tolmanii gen. et sp. nov (Limnocharitaceae) from the Upper Cretaceous of Alberta, Canada. International Journal of Plant Sciences 165(5): 897-916.
Plants Genus Species Presence Material Notes Images CardstoniaC. tolmanii Near Cardston, Alberta. Belongs in Limnocharitaceae. HydropterisH. pinnata"Riverbank exposure on the north side of the St. Mary River approx. 50 m below the spillway of the St. Mary Reservoir, east of Cardston, Alberta."Large segments of intact plants.A hydropteridale fern.TolmaniaT. aquaticaNear Cardston, Alberta."Sixteen compression/ impression specimens".A floating aquatic angiosperm.TrapagoT. angulataSouthern Alberta."Nearly 500 specimens of various isolated and attached organs".ZlatkoviaZ. crenulataNear Cardston, Alberta."Sixty-seven coalified compression specimens of leaves, one attached to a stem".An amphibious eudicot.
Molluscs Beds of Ostrea and Corbicula shells are common in the basal, brackish water portion of the formation. The overlying freshwater beds include shells of freshwater and terrestrial molluscs. Shells of unionid freshwater mussels are common in the fluvial sandstones.
Mammals The mammals of the St. Mary River Formation were described by Sloan and Russell in 1974.Sloan, R.E. and Russell, L.S. 1974. Mammals of the St. Mary River Formation (Cretaceous) of southwestern Alberta. Life Sciences Contributions, Royal Ontario Museum, Number 95.
Mammals Genus Species Presence Material Notes ImagesCimolodonC. nitidusLocality 11, 15 miles north of Lundbreck, Alberta.NMC 17667, a right M2.A cimolodontid.CimolomysC. gracilisScabby Butte, Alberta."NMC 17662, 17663, 17664, 3 tooth fragments from at least 2 individuals."A cimolomyid.Didelphodon?D.? sp.Scabby Butte, Alberta."ROM 7848, the badly worn trigonid of a right molar."Eodelphis?E.? sp.Scabby Butte, Alberta."ROM 7849, a worn, broken right molar".LeptalestesL. toevsiMontana.A pediomyid.MeniscoessusM. conquistaScabby Butte, Alberta."3 teeth from at least 2 individuals (ROM 7846, 7847, 7850)".A cimolomyid.MesodmaM. cf. thompsoniScabby Butte, Alberta.NMC 17665.Miacidae?Genus and species undetermined. Scabby Butte, Alberta."NMC 9821, trigonid of a left lower molar".Assignment to Miacidae is tentative until the complete tooth is known.NidimysN. occultusMontana.A ptilodontoid. ParacimexomysP. propriscus Montana. A multituberculate.PediomysP. cf. cookiScabby Butte, Alberta.NMC 21307, buccal portion of right upper molar.P. cf. krejciiScabby Butte, Alberta.NMC 9820, right M1.PtilodontoideaGenus and species indet.Montana.MOR 2535.A ptilodontoid comparable in size to the smallest Mesodma species.TurgidodonT. russelliMontana.An alphadontid. Dinosaurs
Dinosaur tracks The St. Mary River Formation has produced relatively few dinosaur fossils from its outcrops in southwestern Alberta.Ryan, M. J., and Russell, A. P., 2001. Dinosaurs of Alberta (exclusive of Aves): In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, Introduction, page 281. However, footprints and trackways have been found along the St. Mary and Oldman Rivers. More than 100 track-bearing stratigraphic units were documented in one section thick, which is one of the highest densities of track-bearing layers reported from any succession. One footprint from the formation includes the first record of skin impressions from the bottom of a hadrosaur foot.
Ornithischians Ornithischians Genus Species Location Stratigraphic position Material Notes ImagesAnchiceratopsA. ornatusListed as "? A. ornatus" in "1.4 Alberta, Canada; 13. St. Mary River Formation," in Weishampel, et al. (2004). Pages 577-578. Alberta"1.4 Alberta, Canada; 13. St. Mary River Formation," in Weishampel, et al. (2004). Pages 577-578.Remains later found to be referrable to Anchiceratops, but it's not known what species.EdmontoniaListed as "Edmontonia cf. longiceps" in "1.4 Alberta, Canada; 13. St. Mary River Formation," in Weishampel, et al. (2004). Pages 577-578.E. longiceps AlbertaMontanoceratops"3.11 Montana, United States; 11. St. Mary River Formation," in Weishampel, et al. (2004). Pages 583-584.M. cerorhynchus MontanaPachyrhinosaurusP. canadensis Alberta RegaliceratopsBrown, Caleb M.; Henderson, Donald M. (June 4, 2015). "A new horned dinosaur reveals convergent evolution in cranial ornamentation in ceratopsidae". Current Biology (online). doi:10.1016/j.cub.2015.04.041.R. peterhewsi Alberta
Theropods Theropods Genus Species Location Stratigraphic position Material Notes ImagesAlbertosaurus AlbertaSaurornitholestesListed as "cf. Saurornitholestes sp." in "1.4 Alberta, Canada; 13. St. Mary River Formation," in Weishampel, et al. (2004). Pages 577-578.cf. Saurornitholestes sp. AlbertaTroodonListed as "? Troodon sp." in "1.4 Alberta, Canada; 13. St. Mary River Formation," in Weishampel, et al. (2004). Pages 577-578.Troodon sp." Alberta
See also List of dinosaur-bearing rock formations
References