Mark Wilson July 28th, 2013
This weathered beauty is a stem fragment of the articulate crinoid Apiocrinites negevensis from the Matmor Formation (Middle Jurassic, Callovian) of the Negev, southern Israel. The regular divisions you see making up the stem are the columnals, which look a bit like a stack of poker chips. You can even make out the crenulations on the articulating faces of the columnals, seen as tiny zig-zags. What is unusual about this stem, of course, are the large swellings with multiple holes. These appear to be something like the galls you sometimes see in plant stems formed when a parasite is surrounded by living plant tissue.
Senior Independent Studies student Lizzie Reinthal (’14) is working on these odd structures (we have dozens of examples) as part of her investigation of the taphonomy of A. negevensis in the Matmor Formation. We know that the swellings were made by the interaction of some sort of organism with the living crinoid, but we don’t yet know the timing or mechanism. It could be that the holes were drilled first into the stem and the crinoid grew the extra skeletal tissue to essentially push them away, or the swellings could have been the equivalent of galls and some sort of enclosed animal bored its way out of the structure. (And an extra point to those of you who spotted the barnacle boring! Note that it has no swelling around it and thus was likely drilled after the death of the crinoid.)
These infected crinoid stems were first described from the Matmor by Feldman and Brett (1998). They suggested they were from parasitic myzostome worms, which are usually found on crinoid arms and have a long fossil record (see Meyer and Ausich, 1983, and Hess, 2010). They could also be from some sort of embedded organism like that represented by Phosphannulus on Paleozoic crinoid stems (Welch, 1976).
Lizzie will be pursuing the mystery by careful sectioning some of these swellings and seeing if she can relate the crinoid skeletal growth patterns to either a borer or an embedded parasite. Unfortunately that means we must destroy some specimens to better understand the phenomenon, a classic dilemma paleontologists sometimes face.
Feldman, H.R. and Brett, C.E. 1998. Epi- and endobiontic organisms on Late Jurassic crinoid columns from the Negev Desert, Israel: Implications for co-evolution. Lethaia 31: 57–71.
Hess, H. 2010. Myzostome deformation on arms of the Early Jurassic crinoid Balanocrinus gracilis (Charlesworth). Journal of Paleontology 84: 1031-1034.
Meyer, D.L. and Ausich, W.I. 1983. Biotic interactions among recent and fossil crinoids, p. 377–427. In: Tevesz, M.J.S. and McCall, P.L., eds., Biotic interactions in recent and fossil benthic communities. Plenum Press, New York.
Welch, J.R. 1976. Phosphannulus on Paleozoic crinoid stems. Journal of Paleontology 50: 218-225.