A word which once applied to some tiny enigmatic (but very important) fossils now applies to the (sort of) vertebrate animal now known to have produced them. It appears that our distant ancestors developed teeth (or more accurately, combine harvesters) before they developed bones.

In the mid 19th Century, Russian zoologist Christian Heinrich Pander (not the German footballer), not content with being one of the founders of embryology, turned his attention to paleontology. When he turned his microscope to rocks around St. Petersburg, he found thousands of minute bony structures. There were at least a dozen different forms, but the most common were thin, elongate structures, lined with serrations capped with enamel.

As a century passed after Pander's first monograph on the subject in 1856, conodonts (the fossils) were found to be ubiquitous in Paleozoic strata. The evolution of their forms was also ideal for stratigraphers to use as indices to date Paleozoic rocks. Due to their importance in stratigraphy, an entire lexicon developed to describe the different types of elements.

But no-one had any idea of what type of organism, if any, conodonts (fossils) might belong to, and how they might function. A paleontologist's "in" joke involved vertebrate researchers claiming that conodonts belonged to invertebrates, and invertebrate researchers insisting the fossils belonged to some vertebrate animal.



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In the 1930s and 1940s, conodont fossils were found in "assemblages" in which the various types lined up to form some sort of "apparatus", giving paleontologists the first clear evidence that they were dealing with an animal.

In 1982, Euan N. K. Clarkson was rummaging around in the basement of the museum at the University of Edinburgh when he came across a slab of Carboniferous shale preserving the imprint of a lamprey-like creature. In the head region was an unmistakable assemblage of conodont elements! It was now possible to speak of a conodont animal with a complicated chewing "apparatus" made up of several types of "elements". In most rocks, only the bony elements survived.

Conodonts were eel-like creatures that ranged from 4mm to 20mm in length. At the head end, there were two bulges above the mouth (which, of course, led to the chewing apparatus). Most paleontologists believe the bulges to be eyes, but at least one believes them to be supports for the chewing muscles. Conodonts appear to have slid along the bottom, scooping even smaller planktonic animals into their mouths, and grinding them up with their chewing apparati.

In 1995, a fossil conodont impression was found in South Africa showing a clear groove for a notochord and it became clear that the animals were jawless chordates, similar to lampreys and hagfishes. However, their place on the cladistic tree is still too uncertain to classify them as "fish" -- for the time being, they represent a distinct subgroup of Craniata with a lineage independent of other craniates (i.e. fish plus tetrapods). To me1, conodont "S" elements bear a striking resemblance to the gill arches of fishes, and perhaps it was the outer pair of "M" elements which evolved into jaws.

Ranging from the Cambrian period to the early Jurassic Period, condononts were the most successful vertebrate animals of all geologic history -- it is estimated that 2/3 of all vertebrate species were conodonts. Although they were nearly wiped out by the end-Permian exctinction event, they were one of the few types of marine organisms to survive.

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1Neither a professional paleontologist nor an anatomist, mind you.

Co"no*dont (?), n. [Gr. cone + , , tooth.] Zool.

A peculiar toothlike fossil of many forms, found especially in carboniferous rocks. Such fossils are supposed by some to be the teeth of marsipobranch fishes, but they are probably the jaws of annelids.

 

© Webster 1913.

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