Tag Archives: fossil
Campeloma
Campeloma are common freshwater snails, with an ancestry dating back to the Cretaceous of North Dakota. These gastropods (“stomach foot”) can be found at times with other snail genus, mainly Viviparus or Lioplacodes. Campeloma shells tend to be bulbous, with highly convex body whorls – the spirals that make up the shell, and about an inch long. Viviparus are about the same size as Campeloma, but the whorls are nearly flat on the outside, giving the shell a smooth cone appearance. Lioplacodes has bulbous whorls like Campeloma, but the overall cone-shape of the shell is much more pointy (like a stubby unicorn horn). Like their modern counterparts, these snails most likely lived between 3-11 years. They had a varied diet, including carrion and vegetation.
Orthoceras
External shell
Orthoceras (meaning “straight horn”) is an extinct animal related to squid and octopus. Unlike tasty calamari, their shells (being in the phylum mollusca) are on the outside of their bodies, instead of the pen-bone or gladius seen today. They are often mistaken for another straight-shelled cephalopod, Baculites, however lived much earlier during the Ordovician through Triassic (488-190 mya), rather than the Cretaceous (145-65 mya). Limestone deposits containing mass die-offs of Orthoceras are common in Morocco. The ones from this location tend to be white in color, with a black background – often used in decorative carvings, bowls, and even countertops.
Their straight shells are divided horizontally by “septa”, which separate living chambers of the
animal. When it grew too large for one chamber, it would add on another. A tube running through the length of the shell, called a “siphuncle”, helped regulate water and air in the shell, allowing for both movement and buoyancy. They vary in size, from tiny centimeter long shells, to more than 6 feet long (more, if you add the tentacles!).
Polished Orthoceras, showing siphuncle and septae.
Central Dakota Gem & Mineral Society 