Christian Pander, a German biologist, made pioneering studies in the 1850s of microscopic fossils which he considered to be a kind of fish teeth which he called conodonts.

Not until the 1930s did anyone in the palaeontological world bother much with conodonts, but from then onwards new techniques, such as acid dissolution of limestones, became commonplace in the search for useful microfossils within economically important strata. Residues from work on Palaeozoic and early Mesozoic limestones frequently included conodonts among other microfossils. Being made of calcium phosphate mineral, conodonts could survive gentle acid solution of the rock material. The problem with their identity arose because mostly they are found isolated from one another and without any other preserved clues as to the shape or size of the animal to which they belong.

Because conodonts are so abundant in some deposits and evolved relatively quickly, they became very useful indicators of stratigraphic age for marine strata of late Cambrian to end Triassic age. Consequently, a great deal of effort was put into identifying their innumerable taxa and trying to classify them. But the nomenclature was originally based on the identification of individual conodont 'elements', as they are called. Their general tooth-like form varies from single simple cones, through serrated bars, to flatter platform-shaped elements. So there was a proliferation of names without a sense of which elements belonged together, as happened with the different parts of fossil plants.

Ever since 1S79, occasional clusters of particular conodont elements have been found together on shale surfaces. We now know, in retrospect, that those clusters found in the late nineteenth century, by the English palaeontologist G. J. Hinde, were actually assembled by animals that had eaten conodont animals and that the conodont elements had passed through the gut of the predator quite unharmed. Not until 1934 were natural conodont assemblages first found in the rock record and then it was not until the late 1950s that the penny dropped and it was realised that these were true natural assemblages and gave important clues about how conodonts were arranged in the parent animal.

Different elements occurred in overlapping and elongate pairs, with the points of the teeth facing one another to form a kind of narrow basket with the most sharply pointed cones at one end and the platform elements at the other. But there was still a great deal of disagreement among experts as to what the apparatus represented, how it worked and where it was placed in the original animal. By the late 1950s and 1960s conodont experts were recognising that different element types form recurring associations, thus reinforcing the idea of natural assemblages, which was then incorporated into the taxonomy.

Realising the importance of what they had found, Briggs and Clarkson called in British conodont expert Richard Aldridge. Meanwhile, a student of Clarkson's, Neil Clark, who had just finished his final exams and was awaiting his results, asked Clarkson where he might usefully go fossil hunting. Clarkson jokingly suggested that he could always go and find some conodont animals among the fossil shrimps on the Granton foreshore. Much to Clarkson's surprise, his protégé returned with several specimens.

Close examination revealed that Clydagnathus winds or ensis^ as it was called, had at one end a cluster of conodont elements arranged as a bilaterally symmetrical apparatus. At last, a conodont animal had been found. Between 21 and 55 mm long, it looked as if fossilisation processes had preserved traces of a notochord running the length of its narrow body, with serially arranged, V-shaped muscle blocks on either side, paired eye capsules and a tail fin with numerous small finrays. With the discovery of this remarkable find, palaeontologists had to seriously consider the possibility that conodonts were chordates and what that status implied for the early phylogeny of the vertebrates.

Million Years Ago -,o

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