Megaconchs is a paleobiological term introduced by A.N. Ivanov. Megaconchs are very large macroconchs. Ivanov suggested that megaconchs were a specific type of ammonite, whose growth never stopped. However, he gave many examples of signs of growth resulting in megaconchs. In many Boreal ammonites, the signs of the ending of growth (terminal apertures) are not clearly visible and it could be assumed that their development never stopped. However, a detailed study shows that megaconchs, as well as macroconhs, have terminal apertures. Therefore, they are not a separate type of ammonite, but are large macroconchs. Since fast-growing modern cephalopods reach maturity at different sizes, depending on the ambient temperature, we can assume that ammonoids shared the same type of development. In such case megaconchs are shells of ammonite females (macroconchs) which could have lived in relatively cold conditions. The macroconchs of large species (such as Dorsoplanites, Titanites) are also often called megaconchs.

The text was added and/or edited by: Alex