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After more than 130 years of the debate, definitive evidence has finally been discovered that allows the conodonts to be assigned to the vertebrates. The conodonts are a group of marine organisms that flourished for about 300 million years, ranging from Late Cambrian to Late Triassic. They are represented in the fossil record by tooth-like microfossils (conodont elements) usually from 0.2 to 2 mm in dimension, rarely as long as 14 mm. These elements are composed of calcium phosphate (carbonate fluorapatite) and are readily extracted from the host rock. They receive considerable attention in the paleontological literature (some 280 publications in 1991) because of their importance as biostratigraphic indicators in the correlation of sedimentary sequences. Conodont elements can reveal the thermal history of sedimentary basins, because they undergo a proportional color change on heating due to their content of organic matter. In addition they retain a trace element and isotopic ratio signature that reflects the chemistry of the oceans in which they lived. Although conodont elements were first reported in 1856, the rest of the organism was completely unknown until specimens preserving traces of the soft tissues were described from the Lower Carboniferous of the Edinburgh district, Scotland, in 1983 (1). This discovery cast some light on the enigma of conodont affinities (they had previously been assigned to a range of invertebrate and vertebrate groups, and even plants) but a number of crucial questions remained unresolved.
The Scottish specimens which preserve the soft tissue morphology of conodonts revealed that the animal was elongate, laterally compressed, and somewhat eel-like (1, 2). These examples, at least, represent a swimming carnivore. The elements form a bilaterally symmetrical feeding apparatus in the head, flanked by a pair of dark lozenge-shaped lobes that may represent the eyes. The trunk is divided into...