Article contents
Conodonts from the Middle Devonian Plum Brook Shale of north-central Ohio
Published online by Cambridge University Press: 14 July 2015
Abstract
The Plum Brook Shale of north-central Ohio lies disconformably between the Eifelian (lower Middle Devonian) Delaware Limestone and the middle Givetian (upper Middle Devonian) Prout Dolomite. Its diverse conodont fauna indicates that it represents a transgression into the area in earliest Givetian time accompanied by the products of a notable adaptive radiation within two lineages of Icriodus. One of these (I. expansus Group) includes I. expansus, I. arkonensis and I. brevis, and complete intergradation of forms suggests that the group at this level involves conspecific ecotypes. A more extensive radiation involved descendants of I. regularicrescens (I. regularicrescens Group), including three new species, I. eriensis, I. janeae and I. ohioensis. Other representatives of this lineage occur here as well as in strata of comparable age in the type region of the Givet Limestone as described by Bultynck (1987). A third lineage is represented by I. excavatus in both areas, but evidence of radiation within this branch is limited to the Givet Limestone. Remarkable diversity also occurs among forms considered herein to involve Polygnathus pseudofoliatus and its descendants. The existence of intermediate forms and shared characteristics between and among the various species, including some that first appeared well before the end of the Eifelian, implies that they may be conspecific ecotypic variants at this level. New morphotypes within this group are treated informally. The greatest overall diversity occurs just above the basal Plum Brook, in strata interpreted to reflect inner-sublittoral conditions. The entire Plum Brook belongs to the upper ensensis Zone. A considerable part of the type Givetian placed in the Lower varcus Subzone by Bultynck (1987) lies below the lowest occurrence of its index species (P. timorensis); it contains some of the species found in the Plum Brook, and much of this section may also belong to the ensensis Zone.
- Type
- Research Article
- Information
- Copyright
- Copyright © The Paleontological Society
References
- 15
- Cited by