Article: Paedomorphosis in Scottish olenellid trilobites (early Cambrian)

Olenellus (Olenettoides) armatus Peach, 1894 has been restudied and interpreted as having evolved by paedomorphosis. By comparison with olenellid ontogenies, O. (Olenellus) hamoculus, O. (Olenellus) intermedius, and O. (Olenellus) reticulatus, also from the 'Fucoid' Beds, are likewise considered to have evolved by paedomorphosis from O. (Olenellus) lapworthi. Paedomorphosis may have occurred in response to adaptation to zones of higher oxygen content, in shallower water. The paedomorphic mechanism was progenesis which may have been triggered off by the higher temperatures of the shallower water environment which the olenellid larvae occupied.