Auguritidae and Pinacitidae showing the peculiar umbilical lid. A-D, Celaeceras mirandum, PIN No. 1869/4, lower Emsian, North Urals, Russia. The specimen and its mould from both sides (B, D) and in apertural view (C). Note the mould of a whorl fragment of Erbenoceras or a closely related early ammonoid taxon on the top left in A, documenting the rapid evolution from loosely to tightly coiled ammonoids, which resulted in the co-occurrence of both morphological extremes. E, Kimoceras lentiforme associated with a fragment of a loosely coiled anetoceratid, PIMUZ 28869, lower Emsian of Shirdak Stow, Zeravshan, Uzbekistan. F-I, Weyeroceras angustum, PIMUZ 28449, lower Emsian, Bou Tchrafine, Tafilalt, Morocco. F, left side; note the broad yellowish umbilical lid. G, apertural view; note the slender oxyconic shell morphology and the relatively complicated suture line. H, right side; note the subventral position of the siphuncle. I, septal perforation (refigured from ). J, Exopinacites singularis, internal mould, PIMUZ 28866, middle Eifelian, El Kahla, Tafilalt, Morocco; note the relatively complicated ventral part of the suture line.
Monnet et al. BMC Evolutionary Biology 2011 11:115 doi:10.1186/1471-2148-11-115