Trypanites borings in the Oil Shale brachiopods
Abundant Trypanites borings, were found in brachiopods Clitambonites, Estlandia, Nicolella, in Ordovician (Caradoc) oil shale in North Estonia. About 43% of the 21 brachiopod genera have been bored. The Trypanites are host specific, and the rate of bored valves varies from 6.5% in Bekkerina to 51 % in Estlandia. Three types of Trypanites boring activity could be recognised within the oil shale brachiopod fauna: 1, brachiopods with abundant multiple borings in live and dead hosts; 2, brachiopods with seldom almost always single borings in dead hosts; 3, brachiopods left untouched by boring organisms (large thin-shelled strophomenids, Sowerbyella, Porambonites).
The boring organisms were host-selective, and the rate of borings differs more than seven times between the most bored (Estlandia) and less bored (Bekkerina and Septomena) brachiopod taxa. They preferred hosts with the thick lamellose shells, such as the clitambonitids, especially C. schmidti. The boring organisms were size-selective, and they preferred large adult specimens of the same host taxon. The majority (about 90%) of borings were made in living hosts and are orientated perpendicular to the commissure of brachiopod. The dead shells were seldom bored.
Oriented Trypanites borings in dorsal valve of Clitambonites schmidti