Promopalaeaster Mutant Starfish
A nice 6-armed fossil starfish specimen was found
recently in the Upper Ordovician of southwestern Ohio, USA. The specimen
is moderately large, aboral side up, and sitting on a hard, bioturbated
wackestone. The surface on which the starfish sits was likely a
firmground on the original ocean floor. Daniel Blake, a fossil starfish
researcher at University of Illinois at Urbana-Champaign, has tentatively
identified the specimen as a hexaradial variant of Promopalaeaster sp.
Because features of the oral side are hidden from examination, a more precise
determination is difficult at present.
Locality:
loose talus along cut wall of Caesar Creek Lake’s emergency spillway,
northeastern side of Clarksville Road, northeastern Warren County, southwestern
Ohio, USA.
Stratigraphy: float piece, likely derived from the top meter of the Liberty
Formation or possibly from the lower 1-2 meters of the Whitewater
Formation (a known fossil starfish horizon occurs 0.8 meters below the Liberty-Whitewater
contact at this locality), Richmondian Stage, upper Cincinnatian Series, upper
Upper Ordovician.
Promopalaeaster hexaradial variant (field of view 14.1 cm across)
from the Richmond Group (upper Upper Ordovician) at Caesar Creek Lake’s
emergency spillway, southwestern Ohio, USA.
Orientation: madreporite on lower side of central disc.
Promopalaeaster hexaradial variant (4.4 cm across) - central disc of
6-armed fossil starfish from the Richmond Group (upper Upper Ordovician) at
Caesar Creek Lake’s emergency spillway, southwestern Ohio, USA.
Orientation: madreporite on lower side of central disc.
Promopalaeaster hexaradial variant (1.45 cm across) - madreporite (=
radiating structure at left-center) of fossil starfish from the Richmond Group
(upper Upper Ordovician) at Caesar Creek Lake’s emergency spillway,
southwestern Ohio, USA.
Promopalaeaster hexaradial variant (2.45 cm across) - distal arm of
6-armed fossil starfish from the Richmond Group (upper Upper Ordovician) at
Caesar Creek Lake’s emergency spillway, southwestern Ohio, USA.
This is the same arm that extends to 3 o’clock in the
top photo above.
Promopalaeaster hexaradial variant (2.55 cm across) - distal arm of
6-armed fossil starfish from the Richmond Group (upper Upper Ordovician) at
Caesar Creek Lake’s emergency spillway, southwestern Ohio, USA.
This is the same arm that extends to 1 o’clock in the
top photo above.
Promopalaeaster hexaradial variant (2.7 cm across) - middle third of
arm of 6-armed fossil starfish from the Richmond Group (upper Upper Ordovician)
at Caesar Creek Lake’s emergency spillway, southwestern Ohio, USA.
This is the same arm that extends to 11-12 o’clock in
the top photo above.
Collected & donated by Richard Hand. This specimen is now on public display at
Orton Geology Museum (School of Earth Sciences, Ohio State University,
Columbus, Ohio, USA).