February 26, 2000 - Mississippian Fossils, Franklin Co, AL

Fig. 1 - examples of blastoids over a range of sizes.

Fossils were found in two "modes":
loose specimens lying in the
sand, or encased specimens lying in strong limestone matrix. I show
pictures of specimens in both modes here. The first picture shows a
variety of blastoids from the sand, up to a penny in size. These were
quite common and everyone there found at least a few if they got down
on their knees and looked closely at the sand. Much larger blastoids
have been found at this site. I recall two years ago how Ken Hoyle
picked up a giant blastoid 1-2 inches in length. This kind of blastoid
is much rarer than the pieces in the
photograph.

According to the Fossil Handbook by Rich et al. (1996),
blastoids
represent stemmed echinoderms whose top sections resemble petrified
"nuts". The pieces in the picture represent the calyx of the original
animal. Fine details are usually seen in the calyx, such as ridges, a
five-fold symmetry, and small holes around the apex representing mouth
and possibly anus.

The second photograph shows a
variety of crinoid columns (or stems),
some with unusual side holes that I think represent nodes where
possibly small branches emerged.

Typically these pieces are less than an inch in length, and
some
have interesting five-petaled flower or star designs on stem plates
(columnals) themselves. Even single stem plates could be found in the
sand.
The third photograph shows loose "Archimedes" spirals or corkscrews.
These represent a type of animal known as a bryozoan, or moss animal.
Archimedes spirals are members of a group of bryozoa known as
Cryptostomata, that includes the lacey grid-like fossils seen on other
larger rocks from the same site. The two features were part of the same
animal according to the Fossil Handbook. The authors of the Fossil
Handbook state that the combination of a lacey support and a central
column in the form of a wide-flanged corkscrew was an efficient feeding
arrangement.