Photograph by Mark A. Wilson of an encrusting graptolite Thallograptus sphaericola on a fossil cystoid Echinosphaerites aurantium, Middle Ordovician, northeastern Estonia.
Photograph by Mark A. Wilson of Xenocrinus baeri (Meek, 1872), an Upper Ordovician crinoid calyx from the Bull Fork Formation, Caesar Creek, Ohio, collected by Bianca Hand.