Bajocian Paragarantiana. A case of proterogenesis and neoteny

What is it about?

Representatives of the Submediterranean-NW European genera Paragarantiana and Metagarantiana inhabited the central part of the Anglo-Paris Basin (in the sector of the present day area of Maizet-Bretteville-Sully), at least with six miodemic species showing intraspecific dimorphism. The Late Bajocian species of Metagarantiana and Paragarantiana herein identified in the western Neotethys, as members of the Mediterranean-Caucasian Subrealm, formed separate gradational series of morphological change or peramorphoclines, undergoing greater ontogenic variation and development by hypermorphosis and acceleration respectively, during the Subgaranti-Bomfordi subzonal interval of the Garantiana and Parkinsoni zones. In contrast, rapid proterogenesis undergoing smaller ontogenic variation originated and diversified some garantianin lineages, giving paedomorphic members of neotenic type, such as Paragarantiana sullyensis sp. nov.

Featured Image

Why is it important?

Such phyletic relations identified among latest Bajocian ammonites of the Paris Basin are crucial to the zonal chronocorrelation among bioprovinces of the Mediterranean-Caucasian Subrealm.