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.
Tag Archives: fossil
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.
Teredo-bored Petrified Wood
Teredo borings with woodgrain
Teredo-bored petrified wood is North Dakota’s state fossil. It is found in 60 million year old Paleocene deposits, found in the southwestern area of the state. These are areas that were covered by the Cannonball Sea, now exposed at the surface. Before fossilizing, it was drift wood (ginkgo, bald cypress, metasequoia, etc.) that had been drilled (bored) into by small worm-like clams (Teredo), creating a Swiss-cheese effect.
Modern day example
Part of the fossilization included filling the borings with sediment or crystals, often seen as a different color or texture. If slabbed, the tiny clams can even be seen in cross section as little white crescents. The clams, also called shipworms, still pose a problem for wooden boats or docks today.
Borings with Teredo cross-sections
Teredo-bored petrified wood was adopted in 1967, and added to the Smithsonian Institution’s mineral collection. The selection was brought to the legislature by R. W. Carlson of Bismarck, former present of the Central Dakota Gem and Mineral Society, and H. A. Brady of Mandan. State Represenative W. G. Sanstead of Minot proposed the state fossil selection in House Bill 933.
Magnification of Teredo
https://www.dmr.nd.gov/ndgs/outofprint/NewsLetters/1993Spring.pdf (publication page 4 & 5)
http://ndstudies.gov/state_fossil
https://www.dmr.nd.gov/ndfossil/kids/FIND%20ISSUE%2011%20small.pdf
Ammolite
Ammonite – click for larger image
Ammolite is both fossil and gemstone. It comes from the aragonite mother-of-pearl surrounding ammonites – jokingly called “grandmother-pearl”. Many ammonites still exhibit an iridescent sheen to them, however the ones from mines in southern Alberta exhibit a rainbow spectrum of gem-quality colors. Aragonite in life is an unstable organic crystal form of carbonate, and generally when a shell fossilizes, as it’s already a mineral, simply reverts to a more stable form of calcite. With Ammolite, the aragonite layers haven’t reverted – and the more layers there are, the more colors are refracted.
Ammolite grades
It was given gem status in 1981 by the World Jewelry Confederation. It is one of three organic gemstones – the other two being amber and pearls. If used in jewelry, because of the soft nature of the stone (only a 3.5-4 on the Mohs scale), it should only be set in earrings or pendants – not rings.
http://www.canadafossils.com/canadianammonites.php
Central Dakota Gem & Mineral Society 