Orientation and Anatomical Notation in Conodonts

Abstract

All aspects of conodont paleontology rely on the identification and description of homologous anatomical units or elements. But the current schemes of anatomical notation and terms for orientation were formulated at a time when little was known of conodont anatomy or skeletal architecture, resulting in some confusion and difficulties in their application. With improving knowledge of cono-donts, these problems are becoming increasingly acute. In an attempt to address current problems, we introduce new terms for orientation in conodonts and their elements, and a modified scheme of anatomical notation. The principal axes of the conodont body are identified as rostrocaudal, dorsoventral, and mediolateral, with opposite lateral sides designated dextral and sinistral. Anatomical notation is defined according to topological relationships between elements with reference to the principal axes of the body and takes the form of letters with numeric subscripts (e.g., P 1 , P 2 , S 0-S 4). The ozarkodinid apparatus serves as a standard, but the P n-S n scheme can be applied rigorously to all taxa that are known from natural assemblages or where an hypothesis of topological homology can be inferred from secondary morphological criteria.

Darriwilian species ofHistiodella(Conodonta) in the Argentine Precordillera

“…In the descriptions, we have used the conventional orientational terms-anterior, posterior and lateralnoting that these do not relate to the anatomical orientation of elements (see Purnell et al 2000).…”

Lower Silurian conodonts from the Shine Jinst region, southwestern Mongolia

“…Apparatus notation is based on that of Purnell et al (2000), although terms to describe orientation (e.g., anterior, posterior, inner, outer, upper, and lower) are used conventionally (Sweet, 1981(Sweet, , 1988 and do not refer to true biological orientation. Descriptions are based on both Yamaan Us specimens and works cited herein.…”

Frasnian reef evolution and palaeogeography, SE Lennard Shelf, Canning Basin, Australia

“…5; hereafter 'conodont zone' is shortened to 'Zone'). Yields are composed mostly of P 1 elements (notation of Purnell et al 2000) of Polygnathus (c. 60%) and Ancyrodella (c. 20%). The remaining 20% are P 1 elements of Palmatolepis species (typically broken or juvenile specimens) and indeterminate P 2 and other ramiform elements.…”