Surface Patterns on Selected Mississippian Conodonts

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Four distinct surface patterns occur among Mississippian and some other Late Paleozoic conodonts; smooth surfaces, raised reticulate networks, parallel columns, and lamellar scarps. The bar surfaces of bar forms and platform surfaces of specimens of Gnathodus and Pseudopolygnathus appear smooth at magnifications of as much as 1300X. In contrast, specimens of other platform genera, such as Polygnathus, Siphonodella, and Palmatolepis, bear raised reticulate network on the oral surface. Reticulation appears to be an organic property of the conodont rather than an artifact of preservation, and closely resembles patterns resulting from ameloblastic secretion of mammalian dental enamel. Denticle sides are characterized by a pattern resembling the surface of irregularly bundled fibers. Similar patterns have been observed on fish teeth, but not on scolecodonts. The aboral surface possesses an attachment scar composed of concentrically arranged scarps and slopes. Each scarp is the edge of an individual conodont lamella and appears to be the point of juncture between the lamellae of the basal material and those of the conodont. The distinction between conodont lamellae and those of the basal material appears to be one of composition, crystal size, and durability within an otherwise continuous mass. This observation fails to support Gross9 (1960) concept of a cycle of secretion of conodont lamellae, their partial resorption, and the subsequent independent secretion of basal-material lamellae.