page_title: Bearpaw Formation
section_title: Fauna
hierarchical_section_title: Bearpaw Formation / Fauna
caption_attribution_description: Ammolite (5.5 cm across at its widest) - diagenetically altered, iridescent Placenticeras ammonite shell material (nacreous aragonite, CaCO3) from the Upper Cretaceous Bearpaw Formation of the St. Mary River Valley, Alberta, Canada. Ammolite is biogenic gem material from Alberta, Canada. It has stunningly intense, iridescent rainbow colors. Ammolite is fossil shell material from Placenticeras ammonites. Ammonites are an extinct group of swimming squid-like organisms with planispirally coiled shells (the chambered nautilus in modern oceans is a distant relative of ammonites, but has a similar body plan). Ammonite shells were originally nacreous aragonite (“mother of pearl”) (CaCO3). Geologic studies have shown that ammolite gem material formed from slight diagenetic alteration of the original ammonite nacreous aragonite shell. Diagenesis has significantly intensified and brightened the play of colors. Ammolite is mined, polished, and treated by resin- or epoxy-impregnation to stabilize it. Very rarely, complete specimens of Placenticeras ammonite shells preserved in ammolite are recovered - such specimens are exceedingly valuable (for example, see figure 2 of Mychaluk et al., 2001). Name &amp; classification: Placenticeras meeki or Placenticeras intercalare (Animalia, Mollusca, Cephalopoda, Ammonoidea, Ammonitina) Stratigraphy &amp; age: Bearpaw Formation, Campanian Stage, upper Upper Cretaceous, ~70-75 Ma. Locality: mine in the St. Mary River Valley west or northwest of Welling and south-southwest of Lethbridge, southern Alberta, southwestern Canada. Reference cited: Mychaluk, K.A., A.A. Levinson &amp; R.L. Hall. 2001. Ammolite: iridescent fossilized ammonite from southern Alberta, Canada. Gems &amp; Gemology 37(1): 4-25.
context_page_description: The Bearpaw Formation, also called the Bearpaw Shale, is a geologic formation of Late Cretaceous age. It outcrops in the U.S. state of Montana, as well as the Canadian provinces of Alberta and Saskatchewan, and was named for the Bear Paw Mountains in Montana. It includes a wide range of marine fossils, as well as the remains of a few dinosaurs. It is known for its fossil ammonites, some of which are mined in Alberta to produce the organic gemstone ammolite.
context_section_description: The Bearpaw Formation is famous for its well-preserved ammonite fossils. These include Placenticeras meeki and Placenticeras intercalare, and the baculite Baculites compressus, some of which are mined south-central Alberta to produce the organic gemstone ammolite.
  Other fossils found in this formation include many types of shellfish, bony fish, sharks, rays, birds, and marine reptiles like mosasaurs such as Prognathodon overtoni and Plioplatecarpus peckensis, plesiosaurs such as Dolichorhynchops herschelensis, Albertonectes and Nakonanectes, and sea turtles. Dinosaur remains have occasionally been discovered, presumably from carcasses that washed out to sea.
caption: A specimen of Placenticeras ammolite  from the Bearpaw Formation.
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