Fossil Shell Identification for Dummies

Symmetry of brachiopods compared to pelycepods (clams)

Somewhere in some introductory journalism class, wannabe "communications" students are apparently taught that, if you know nothing about a topic, you can CYA by throwing all manner of disconnected factoids on the page and walking away. That probably isn't really the case – we certainly hope educators are less laissez faire about the topic – but based on some of the output of people who've taken that career path, it sure looks like some of them got that advice! Today's DotD nominee falls squarely in that category: she's eHowian Karen S. Garvin, whose "How to Identify Shell Fossils"¹ at Sciencing.com tripped a staffer's bullcrap detector.

It's undeniable that the topic is quite broad, especially if you define "shell" as the remnants of any of several phyla of invertebrates. Most people will zero in on the Mollusca, though, the phylum that includes clams, cephalopods, and gastropods (among others); in particular the clams. Garvin tried to get to that, but was immediately sidetracked... badly:

"The first step in identifying shell fossils is to make sure the item you are examining is a true fossil, not a modern shell. Shell fossils are formed when an animal dies and sinks to the bottom of a lake or ocean. If the animal becomes covered with dirt and is not eaten, it will be protected from erosion and other environmental hazards. As sediment accumulates, the weight compacts the underlying area. In a process called lithification, the pressure from this weight turns the dirt into sedimentary rock, and the hard parts of the animal are mineralized."

Ummm... Karen, the hard parts are already mineralized: they're calcite! Garvin's problem here is that she just burned through more than 40% of her post (98 of 231 words) and still hasn't said jack about identification! She's left to throw random factoids at the page and assume (correctly) that her content editor is as clueless as she. That's why her readers must assimilate such rubbish as

• "Fossil shells may be circular, egg-shaped, cup-shaped, tubular or spiral..."
• "Spiral shells are often snail fossils or ammonites..."
• "Some brachiopod shells are biconvex, which means both sides of the shell curve outward..."
• "Some hinges are flat; others are pointed..."
• "Patterns on the shell are called decoration, and they can be useful in identifying species..."

Karen then completes her dumbassery by suggesting that her readers "identify shell fossils with the aid of a fossil field guide"! And that's before her "warning" that "Dendrites are crystal formations that resemble fossils but are not fossils." Sheesh...

Our geologist reached back in time to introductory paleontology class and told us that most people asking this question want to know the difference between a pelecypod (aka "clam") and a brachiopod. The answer is simple: if the top and bottom shells are different but each one has left-right symmetry, it's a brachiopod. If the top and bottom shells are identical but a shell is not left-right symmetrical, it's a pelecypod. But, then, she's not our Dumbass of the Day: Karen S. Garvin is...

¹ The post has been rewritten by the Leaf Group "cleanup crew." We'll get to that later, but the original can still be accessed using the Wayback machine at archive.org. Its URL was   ehow.com/how_6101980_identify-shell-fossils.html

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