Archive for August 25th, 2013

Wooster’s Fossil of the Week: A crab’s meal from the Pliocene of Cyprus

August 25th, 2013

Astraea rugosa side view_585This week’s fossil was collected on a Keck Geology Consortium expedition to Cyprus in the summer of 1996. My Independent Study student on that adventure was Steve Dornbos (’97), now a professor at the University of Wisconsin, Milwaukee (and a new father!). The other students on our paleontological project were Ellen Avery and Lorraine Givens. One day Steve and I stumbled across a beautifully-exposed coral reef weathering out of the silty Nicosia Formation (Pliocene) on the hot and dry Mesaoria Plain in the center of the island near the village of Meniko (N 35° 5.767′, E 33° 8.925′). The significance of this reef was that it represents the early recovery of marine faunas following the Messinian Salinity Crisis and the subsequent refilling of the basin (the dramatic Zanclean Flood). Steve and I published our observations and analyses of this reef community in 1999.

Our featured fossil is the herbivorous turbinid gastropod Astraea rugosa (Linnaeus, 1767). That beautiful generic name means “star-maiden” in Greek and was originally used by Linnaeus in homage to the mythological Astraea, daughter of Zeus (maybe) and a “celestial virgin”. The species name rugosa means “rough” or “wrinkled”, in reference to the many ridges on the shell. The common name for this species, which is still alive today (as you can see in this video) is “rough star”.

What was most interesting to Steve and me was how this shell is broken. Most of the shell appears to have been peeled away, leaving the central axis and top in excellent shape. This is characteristic of crab predation. The crab, usually using one enlarged claw, peels the shell open by breaking it at the aperture and moving up the spiral. Eventually it hits the terrified snail pulled up as far as it could go in its twisty spiral of doom.
Astraea_Screen Shot 2013-08-22 at 8.37.54 PM copyThe image above, from this Spanish webpage, shows one of the further defenses Astraea rugosa had against crab predation: a thick calcareous operculum blocking the aperture like a heavy door. In some places these opercula are commonly preserved, but we found only a few and could not associate them with any particular species.
Astraea rugosa apical_585Finally, here is the top view of Astraea rugosa from the Pliocene of Cyprus. There is wonderful detail still preserved in the apical region of the shell, including characteristic star-like projecting spines.

We’ll see more fossils from the Pliocene of Cyprus in this space!

References:

Cowper Reed, F.R. 1935. Notes on the Neogene faunas of Cyprus, III: the Pliocene faunas. Annual Magazine of Natural History 10 (95): 489-524.

Cowper Reed, F.R. 1940. Some additional Pliocene fossils from Cyprus. Annual Magazine of Natural History 11 (6): 293-297.

Dornbos, S.Q. and Wilson, M.A. 1999. Paleoecology of a Pliocene coral reef in Cyprus: Recovery of a marine community from the Messinian Salinity Crisis. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 213: 103-118.