Fig. 1

Bored clast preserved as an external mould in chert, BMNH PEI 5339, from the Upper Cretaceous of Morocco. a Broken interior view of clast showing heterogeneous nature of chert, external mould of lost internal substrate (wood? limestone?), sheet-like fracture filled with chert (near centre), and chert-filled borings. b Enlargement of borings showing the contrast in size and number of specimens of the two morphologies, as well as a boring which has been partially truncated by weathering (far right). c Linear array of four clavate borings, Gastrochaenolites clavatus (Leymerie), flanked by numerous small, simple borings, Oichnus isp. cf. O. simplex Bromley. Note also the roughness of the clast surface. d Clavate borings bearing small, simple borings. Specimen uncoated. Scale bars represent 50 mm (a, b) or 10 mm (c, d)