March 3. Conodonts

For decades, no one knew what conodonts were. They are little fossils, at most 3 millimeters long, typically with little projections like teeth on them. They first appear in the very late Cambrian or earlier, but they survived the end-Cambrian extinction to really proliferate in the Ordovician. And they lasted 200 million years, but perished in the mass extinction at the end of the Triassic Period.

They’ve been known since at least 1856 when a Russian scientist, C.H. Pander, named them for the conical tooth-like projections they have. He thought they were fish teeth. But it was more than 120 years before we learned for sure what they are.

Even without knowing what they were, they were useful little critters. The tiny bits are made of calcium phosphate, the mineral apatite, like human bones and teeth and kidney stones, and when they are heated up in nature, they change color in predictable ways. This change has been used in petroleum exploration for years to estimate temperatures in the subsurface, which in turn is valuable in figuring out things about generation of oil and natural gas. And because there are clearly defined species of conodonts, they also serve as biomarkers in studies aimed at determining the details of stratigraphy.

It was presumed that the small phosphatic fossils were parts of some larger animal, and the search for the “conodont animal” continued for decades. One good candidate, a large fossil associated with many of the small tooth-like elements, was ultimately shown to be a critter that ate the conodont animals – whatever it was.

Reconstructed animal (right) and teeth (left).
The animal is a couple centimeters long.

Eventually, in the early 1980s, good fossils of soft-bodied eel-like animals were discovered with the tooth-like pieces clearly displayed in their mouth area. The first confirmed discovery was in a museum, in old specimens from Carboniferous rocks of Scotland, and they’ve also been found in Ordovician rocks of South Africa. And there’s another locality in Iowa with excellently preserved conodont animals. The whole critter was only one or two centimeters long, and there are only a handful of good examples of the entire animal. 

Conodonts are thought to be chordates, the same group that includes vertebrates, but that’s not absolutely certain, and many scientists classify them in their own phylum. If they are chordates, then their calcium phosphate “teeth” may be the first hard parts created by chordates, rather than a backbone, as suggested by Neil Shubin in his excellent book, Your Inner Fish, which I recommend if you are interested in the evolution of the human skeleton.

—Richard I. Gibson

Reconstructed conodont image by Philippe Janvier under CC-A 3.0

Further reading:
http://en.wikipedia.org/wiki/Conodont
What are conodonts? 
Derek Brooks paper on the conodont animal
good pictures

Iowa locality
Excellent overview and photos