Friday, July 27, 2012

Edriocrinus from the Licking Creek formation of Virginia

This past April I took a trip through Virginia and West Virginia exploring some sites that were listed in the book "Fossil Collecting in the Mid-Atlantic States" by Jasper Burns. One of the more productive sites was in the Licking Creek formation, which is lower Devonian in age (Lockhovian to Pragian stage), where all the fossils were replaced by quartz and could be found eroded loose out of the rock.

One of the most common fossils I found at the site was a small, hollow, jelly bean shaped thing. Further reading of the entry in the book revealed that these are likely the base of the calyx for an Edriocrinus.

Specimen #1

Specimen #2

Note the curved or scalloped edges along the top of the hollow. Also many specimens have vertical striations on the interior hollow area.

Specimen #3, This specimen is missing the rounded bottom part and instead has exposed what could be some internal anatomy or just selective replacement by the quartz that makes up the fossil.

Check out this link which has an image from an old text which shows a reconstruction of Edriocrinus (first image, second fossil from the left in the first row numbered 1).  Some of the curved shapes I see on the specimens I found seem to match what is shown in the picture.

This Flickr page for the WV Geological & Economic Survey Museum has a picture of a similar fossil.

Here is a description of Edriocrinus pocilliformis from the book "Lower Devonian: Text, Volume 5, Part 1" by the Maryland Geological Survey, 1913:

Plate XL, Figs. 13-15
Edriocrinus pocilliformis Hall, 1859, Pal. N. Y., vol. iii, p. 121, pi. v, figs. 8-12, 1861.
Edriocrinus pocilliformis Meek and Worthen, 1868, Geol. Survey 111., vol. iii, p. 370, pLvii, figs. 5a, b.
Edriocrinus pocilliformis Keyes, 1894, Missouri Geol. Survey, vol. iv, pt. i, p. 221, pi. xxx, fig. 7.
Edriocrinus pocilliformis Talbot, 1905, Amer. Jour. Sci., 4th ser., vol. xx, p. 23, pi. iv, figs. 1-6.

Description.—" Base hemispheric or subturbinate, often less than a hemisphere, externally smooth or finely granulate: upper margin scolloped with five large and one smaller depression for the insertion of the radial and anal plates. Interior more or less deeply concave, with depressions corresponding to those on the edge of the cup; the concavity not parallel to the exterior convexity. Radial plates and arms unknown." Hall, 1859. " Infrabasals present but so fused that their number is uncertain. Height from one-half to two-thirds that of the cup as ordinarily found. Basals five, completely fused with each other and with the infrabasals or distinguished from the latter as a narrow protruding band. Suture lines sometimes apparent on the interior. Upper margin scolloped for the attachment of the radials and the anal plates. Height about half that of the infrabasals. Radials five, often as high as the infrabasals and basals combined, and like them, fused to form a part of the cup. In most instances, however, the suture lines between the radials are plainly discernible. As a rule, the union between the radials and basals is not so strong as that of basals with infrabasals; and the cup is generally broken off at the top of the basals. Since in no specimens are brachials preserved, the union of  brachials with radials must have been still weaker. Anal plates as high as the radials, but only half as wide. Radials and anal gently convex, sloping in all directions from the center of the plate. Arms and ventral disc unknown. The attachment scar is visible on a number of specimens, and in some is a short distance up on the side of the cup, rather than on the bottom." Talbot, 1905.

All of the above specimens came from a roadcut along US route 220 in Highland county, Virginia. The cut is listed as site #16 in the book "Fossil Collecting in the Mid-Atlantic States" by Jasper Burns. The Licking Creek formation is equivalent to the Shriver Chert member of the Old Port formation in Pennsylvania and the Birdsong formation in Tennessee which means that the fossils are part of the Helderbergian fauna.

No comments:

Post a Comment