Hoploscaphites Scaphite & Spenodiscus Ammonite Association

Description: During the Upper Cretaceous, a huge shallow inland sea stretched from what currently is the Gulf of Mexico northward and through Canada. Ammonites including members of Ammonita Superfamily Scaphitaceae (the scaphites) were ubuiquitous. The Fox Hills Formation, which spans from Alberta down into Colorado, was formed when the Western Interior Seaway retreated in the late Cretacous. It contains a diverse biota, including Tyrannosauroid dinosaurs like T-Rex and marine mosasaurs. The formation is also well known for several species of scaphites having their exterior shells preserved as mother of pearl, an opal-like and iridescent mineral sometimes called ammolite; the color you see often changes as the angle of viewing or of light source changes, because of multiple reflections within layers of the material. Fox Hill scaphites and ammonites typically exhibit red and/or green hues, and browns, a mixture of red and green. Others are whitish, a nearly uniform mixture of the color spectrum.

The primary diagnostic feature of scaphites is somewhat J-shaped, bauplan, one that is less tightly coiled than most ammonites. They are grouped among the heteromorph ammonites comprising suborder Ancyloceratina, because of these irregularly-coiled shells. The scaphites of Fox Hills Formation are normally found in concretions, like fossils of Mazon Creek, some very large, that weather out from stream beds and hillsides. And like Mazon Creek, exquisite preservation is often found. Some of the different scaphite species exhibit shell ornamentation, including tubercles, sutures, keels, and ribs.

This is a scaphite and ammonite association rarely found at the Fox Hills Formation. The larger is Hoploscaphites cheyennensis scaphite retains most of its shell. The Spenodiscus lenticularis is stunning, in places showing the intricate suture pattern the genus is noted for. Also, depending on angle of view, the Spenodiscus exhibits a rainbow of colors, including a bluish-lavender I've seldom seen - the many pictures are a futile attempt to capture those colors. Also note a third small ammonoid half embedded and perpendicular to the matrix.