TRACE-ELEMENT MAPPING OF CONODONTS – IMPLICATIONS FOR HISTOLOGY AND FUNCTION

Microprobe and laser-ablation ICP-MS analyses of suites of early to middle Paleozoic coniform, ramiform, and pectiniform conodont elements were used to construct detailed trace-element maps and transects that permit the complex biogeochemical differentiation of single conodonts to be documented. Such important trace elements as F, Na, Sr, and Ba were measured, together with transition and REE elements. The trace-element maps and transects define clearly concentrations within and variations between individual growth lamella of the basal plate and crown and through zones of white matter, resulting in a distinct ‘tree-ring' pattern of elemental zoning. We suggest that some of the chemical abundances and elemental ratios recorded in the conodonts are primary and were preserved during diagenesis. The variation in element abundances may accurately reflect changing biochemical accumulation and enrichment rates through the life of the animal.

One result of the mapping is that the lamella-scale variations in Sr content, which characterize highly crystalline hyaline apatite in the crown, pass unchanged through white matter. This supports previous studies suggesting that white matter is a secondary hard tissue formed from hyaline apatite, preserving in part the original, primary biochemistry of the crown. Another result is that the maps clearly delineate wear/growth and resorption/regeneration surfaces, further supporting our hypothesis that some trace-element zones are a primary, and not diagenetic, record of biochemical uptake by the conodont. We speculate that the chemical zoning and concentrations preserved within the conodonts may (a) reflect episodic sequestering of potentially biotoxic elements present in the surrounding environment; (b) be related functionally to the strength or stability of the teeth; or (c) in the case of biolimiting elements, represent accumulation sites or chemical ‘banks' that could be selectively accessed later by resorption, releasing the elements for use by the conodont animal. It is hoped that additional trace-element mapping of conodonts will provide not only more detailed data on coeval ocean chemistry, but also new insights into the paleobiology of this complex and enigmatic group of organisms.