This is a follow-up post to our entry on Christmas Day two weeks ago. Above is a trepostome bryozoan (the long porous piece) with specimens of the atrypid brachiopod Zygospira modesta clustered around it. They are positioned with their ventral valves outward because in life they were attached to this bryozoan with tiny fleshy stalks called pedicles. They were buried quickly enough that this spatial relationship was preserved. Cool. This assemblage was found in the Liberty Formation (Upper Ordovician) exposed in a roadcut in southern Indiana.
This is a view of the dorsal side of Zygospira modesta showing the pedicle opening in the ventral valve at the apex of the shell.
References:
Copper, P. 1977. Zygospira and some related Ordovician and Silurian atrypoid brachiopods. Palaeontology 20: 295-335.
Sandy, M.R. 1996. Oldest record of peduncular attachment of brachiopods to crinoid stems, Upper Ordovician, Ohio, USA (Brachiopoda; Atrypida: Echinodermata; Crinoidea). Journal of Paleontology 70: 532-534.
Interesting to speculate whether the pedicles of the brachiopods were divided at their ends into threads that could anchor within the zooidal apertures of the bryozoan. Also whether the bryozoan was alive, dead or moribund in the region of attachment.
Some clever SEM work could be fun with these situations, Paul!