Figure 4
Dorsal view of the skulls of Ornithorhynchus anatinus and Eretmorhipis carrolldongi. (a) E. carrolldongi. (b) O. anatinus, based on a published figure. Colors: black, cranial fenestrations; brown, prenasal groove; light blue, prenasal and labial cartilages; light yellow, bone; pink, groove for labial cartilage. Symbols: exn23, external naris; fn, fenestra naria, located below exn; lc, labial cartilage; lg, labial groove for labial cartilage; nc, nasal capsule; op, os paradoxum; orb, orbit; pf, pineal foramen; pg, prenasal groove; pnc, prenasal cartilage of unknown homology; utf, upper temporal fenestra; *unnamed foramen for passage of a branch of the ethmoidal nerve; **foramen analogous to *. Brown dotted lines mark the anterior extent of the external naris, and therefore of the nasal capsule and associated structures, illuminating that the intercrural space of Eretmorhipis is in front of the nasal capsule, unlike in Ornithorhynchus. Scale bars are 1 cm long.
