Barskov I.S. 2017. Conch ornamentation in nonammonoid cephalopods: form and function // Invertebrate Zoology. Vol.14. No.1: 2–7 [in English].
A.A. Borissiak Paleontological Institute Russian Academy of Sciences, Profsoiuznaya Str. 123, Moscow, 117321 Russia. E-mail: email@example.com
ABSTRACT. The initial appearance and the functional significance of external conch ornamentation in main orders nonammonoid cephalopods (Plectronocerida, Ellesmerocerida, Orthocerida, Pseudorthocerida, Actinocerida, Endocerida, Oncocerida, Discosorida, Tarphycerida, Barrandeocerida) is discussed. The origin and primary functions of conch ornamentation is considered. The first type of ornamentation to appear was the annulated shell of some Early Ordovician Plectronocerida and Ellesmerocerida, and its function was increase in buoyancy of the phragmocone. Annulated conchs only appeared from the Middle Ordovician in Orthocerida, Pseudorthocerida, Actinocerida, Endocerida. The functional significance of longitudinal ornamentation in cyrtoceraconic and orthoceraconic and spiral ornamentation in coiled conch not apparent. The lateral apertural flanges (lappets), present in some Devonian and late Paleozoic Nautilida probably served as directing planes/wings, which allowed the animal to maintain an oriented position while moving rapidly using its hyponome.
KEY WORDS. Nonammonoid cephalopods, conch ornamentation, comparative morphological analysis, Paleozoic.