Extremes of Pit Infestation and Growth Deformity in a Crinoid Column,Permian of Timor

Crinoids are diverse and well-known from the Permian of Timor, but the literature has failed to document the numerous specimens of crinoid pluricolumnals from the fauna, many showing unusual morphology or yielding palaeoecological information. A curious and instructive specimen demonstrates the relationship between a living Permian crinoid and coeval invasive, pit-forming, invertebrates in detail. The pit-former is not preserved; most likely it was unmineralized or, if mineralized, then the shell simply dropped out. The infesting organism made pits assigned to the ichnospecies Oichnus paraboloides Bromley. The pit-former was unusually site selective. Either (1) one spatfall attached to just one side of the elevated (either up-current or down-current) or recumbent column and each individual centered their pits on the sutures between adjacent columnals; or (2) a single individual migrated along the column. The living crinoid showed an extreme reaction to this infestation. Excess stereom growth on the side of the pits transformed what was a circular column by addition of a thick, triangular ridge on the pitted side.