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Evolutionary and taphonomic implications of a new species of Amphoracrinus from the early Viséan of Kentucky

Published online by Cambridge University Press:  02 July 2021

William I. Ausich
Affiliation:
Department of Geological Sciences, 155 South Oval Mall, The Ohio State University, Columbus, Ohio 43210, USA
Steven C. Koenig
Affiliation:
Department of Cardiovascular and Thoracic Surgery, University of Louisville, Louisville, Kentucky 40202, USA Department of Bioengineering, University of Louisville, Louisville, Kentucky 40292, USA
Alan Goldstein
Affiliation:
Falls of the Ohio State Park, 201 W. Riverside Drive, Clarksville, Indiana 47129-3148, USA
Gretel Monreal
Affiliation:
Department of Cardiovascular and Thoracic Surgery, University of Louisville, Louisville, Kentucky 40202, USA

Abstract

The youngest species of Amphoracrinus, A. tenax new species, is described from the Muldraugh Member of the Borden Formation (early Viséan) of north-central Kentucky. With this new occurrence, both the oldest and youngest named species of Amphoracrinus are from North America. Numerous Tournaisian and Viséan crinoid faunas are documented in the United States, but only four are known to contain Amphoracrinus. Morphological analysis indicates that A. tenax is more closely aligned with species from China than with species from Western Europe or other species from North America, where Amphoracrinus was most diverse and abundant, which has implications for understanding paleogeographic dispersal. The holotype of A. tenax was partially disarticulated on the seafloor before burial, and final burial occurred early during disarticulation. The relative state of disarticulation from pinnules to columnals suggests that plates bound only with ligaments disarticulated as a function of surface area of ligaments binding an articulation.

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Type
Articles
Copyright
Copyright © The Author(s), 2021. Published by Cambridge University Press on behalf of The Paleontological Society
Figure 0

Table 1.Species of Amphoracrinus listed by country occurrence with appropriate international ages as well as regional stages.

Figure 1

Table 2.Chronostratigraphy of the Mississippian. Correlation of International series, European and North American regional stages, and time bins of Ausich and Kammer (2006) and Kammer and Ausich (2007).

Figure 2

Figure 1.Amphoracrinus tenax n. sp. holotype from the Muldraugh Member (early Viséan) of the Borden Formation, north-central Kentucky. Posterior side of entire specimen. USNM PAL 771320, holotype.

Figure 3

Figure 2.Road cut in Hardin County, north-central Kentucky, where A. tenax n. sp. was collected from the Muldraugh Member of the Borden Formation. Lithostratigraphy noted on right; arrow indicates its location on the bench.

Figure 4

Figure 3.Results from morphological analyses of Amphoracrinus. (1) Dendrogram from cluster analysis of morphological characters of Amphoracrinus species. (2) A 50% majority-rule tree of nine species of Amphoracrinus with three outgroup taxa. Values at nodes indicate the percentage of most parsimonious trees that recovered that relationship (data in Supplemental Tables 1, 2, 3).

Figure 5

Figure 4.Holotype of A. tenax n. sp. USNM PAL 771320. (1, 2) Well-articulated posterior side of the crown; (3) proximal portion of column, compare with Figure 1; (4) portion of middle column, compare with Figure 1; (5) poorly articulated anterior side of crown. (2–5) Coated with ammonium chloride.