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Asphinctites tenuiplicatus [M] and Polysphinctites secundus [m] from the Asphinctites tenuiplicatus Zone (Early Bathonian), are usually considered as a sexual dimorphic pair, although authors describe them as separate species. We used statistical methods to test the sexual dimorphic correspondence between those morphospecies, based on a rather large sample of well-preserved macro- and microconchs derived from a single horizon of calcareous concretions in the Polish Jura. Our results indicate that both dimorphs or sexes have identical ontogeny up to a critical diameter, from which they diverge towards the characteristic morphology and sculpture of each dimorph. Thus, both dimorphs are described as a single species: Polysphinctites tenuiplicatus [M and m]. After review of the several nominal species usually assigned to the genera Asphinctites and Polysphinctites throughout their stratigraphic and biogeographic range in the Early Bathonian of the Tethys, it is concluded that they actually correspond to only two species of a single lineage. The corresponding name for the lineage should be Polysphinctites (= Asphinctites as a junior synonym).

The external area-to-volume ratio of the ammonite shell has been held to be related to morphology but never evaluated quantitatively. A dimensionless ratio, the Vogel number, was computed for large samples of Devonian to Cretaceous ammonites with a new method based on the ADA-model. The estimated ratios range from 2.4 to 3.4. The highest values are exhibited by uncoiled serpenticone ammonites, lowering in the sequence serpenticone-oxycone-spherocone. It is shown that the area-to-volume relationships are controlled by the involution (degree of overlapping) and the relative width of whorl section. The typical evolutionary trends serpenticone–spherocone and/or serpenticone–oxycone, broadly documented through the history of the Ammonoidea, could have been driven, at least in part, by the lowering of the area-to-volume ratio.

Seven previous proposals of aptychus (sensu stricto) function are reviewed: lower mandible, protection of gonads of females, protective operculum, ballasting, flushing benthic prey, filtering microfauna and pump for jet propulsion. An eighth is introduced: aptychi functioned to actively stabilize the rocking produced by the pulsating jet during forward foraging and backward swimming. Experiments with in-air models suggest that planispiral ammonites could lower their aperture by the forward shift of a mobile cephalic complex. In the experiments, the ventral part of the peristome is lowered from the lateral resting (neutral) position by the added “ballast” of a relatively thin Laevaptychus to an angle

The new genus Cieneguiticeras , assigned to the family Oppeliidae, is described on the basis of Andean lower-middle Tithonian ammonites from Arroyo Cieneguita, west-central part of the Neuquen-Mendoza Basin, Argentina. The macroconchs are closely homoeomorphic with Neochetoceras Spath and the microconchs have a ‘glochiceratid’-type morphology. The stratigraphic range of Cieneguiticeras nov. gen. includes the lower and middle Tithonian by means of a succession of two or three species which are interpreted as members of a phyletic lineage. Ammonites from the Tithonian of Cuba, Mexico and France are more or less confidently included in this new genus.

New findings of the Early Tithonian genus Virgatosimoceras SPATH (Simoceratidae) from Hungary confirm the existence of a new chronospecies (Virgatosimoceras dunaii n. sp.) which fills the gap between V. albertinum and V. rothpletzi. The successive chronospecies demonstrate a well defined lineage through the Early Tithonian Darwini, Semiforme and Fallauxi zones, opening the possibility of enhancement of the time-correlation of the Submediterranean Province with adjacent regions. All figured records of Virgatosimoceras are revised. Micro- and macroconchs are tentatively distinguished for the first time. The similarities between Virgatosimoceras and some homoeomorphic perisphinctids are discussed. Based on the known records, is concluded that the genus was restricted to the western Tethys.

Ammonites are of outstanding importance in dating events of the Mesozoic and in the study of mechanisms, modes and timing of evolutionary processes. These applications rely on a detailed understanding of their morphology and the modes of variation. It has been known for a long time that their shape is composed of a number of highly correlated features. A new model, called the ADA-model, is introduced for the study of shell morphology (size and shape). The new model is based on classic dimensions which are stable parameters throughout ontogeny, giving very close agreement between predictions and actual observations. It was applied in the exploration of the morphospace occupied by the planispirally coiled and the regularly uncoiled Mesozoic Ammonoidea, based on two new reduced morphospaces introduced for the analysis. Results obtained expose close relationships between size and shape, and general patterns in the ammonite shell morphology and morphogenesis. (i) The relative apertural height of the whorl sect...

A significant assemblage of Oxfordian perisphinctids was collected at Chacay Melehue, Neuquen, Argentina. It is composed of well preserved specimens belonging to the family Perisphinctidae:Perisphinctes aff.promiscuus Bukowski (Perisphinctinae),Tenuisphinctes herreroduclouxi (Leanza) (Perisphinctinae), andSubvinalesphinctes pseudokranaus n. sp. andS. prophetae (Gygi & Hillebrandt) (Vinalesphinctinae). The family Ataxioceratidae is represented byLithacosphinctes aff. janus (Choffat) (Ataxioceratinae). The subfamily VinalesphinctinaeMelendez & Myczynski, 1987 is discussed and organized into three genera:Subvinalesphinctes Wierzbowski,Vinalesphinctes Spath andCubasphinctes Judoley & Furrazola, which seems to cover the whole of the subfamily, ranging, at least, from the lowerplicatilis to the lowerbifurcatus zones, Middle Oxfordian in Cuba, part of Mexico, Chile and Argentina. The root of the subfamily is most likelyS. pseudokranaus n. sp. The paleobiogeographic affinites are mainly Tethyan, and Tethyan-Caribbean during the Middle Oxfordian.

The lectotype ofPerisphinctes internispinosus Krantz, 1926, type species ofWindhauseniceras Leanza, 1945, from the upper Middle Tithonian of Cerro Lotena (Neuquen-Mendoza Basin, Argentina) is designated. The type series, housed in the Palaontologisches Institut der Universitat Bonn, was originally illustrated by hand-drawings of two of the eleven specimens. The lectotype is illustrated by a photograph for the first time. The specimen is probably a large microconch; the most likely corresponding macroconch appears to beH. aff.steinmanni (Steuer, 1897) from Cerro Lotena.Windhauseniceras internispinosum is the index and guide species of theInternispinosum Biozone, upper Middle Tithonian, most probablyPonti Zone in age. The occurrence in Arroyo del Yeso (Mendoza) below a succession ofMicracanthoceras species includingM. mirum (Leanza, 1945) which is very close toM. microcanthum, strongly supports this correlation. The species occurs throughout the Neuquen-Mendoza Basin and probably also in the Tarapaca Basin, Northern Chile.