Nine proposals of aptychus ( sensu stricto ) function have been published (in historical order): operculum, micromorphic males, lower mandible, protection of gonades, ballast for lowering of aperture, flushing of benthic prey, filtering microfauna, pump for jet propulsion, and active stabilizer against rocking produced by the pulsating jet during forward foraging and backward swimming. Some ammonites bear thick, laevaptychus- and lamellaptychus-type aptychi (aspidoceratids and haploceratoids) that may have improved lowering of the aperture as part of a mobile cephalic complex, enabling many of these functions. Aptychi were multifunctional, most commonly combining feeding (jaw, flushing, filtering) with protection (operculum), and/or with propulsion (ballast, pump, diving and stabilizing plane). Multifunctionality would have been a strong constraint in ontogeny and evolution as shown by the limited diversity of aptychi with respect to the wide variety of shell morphologies known in the Mesozoic Ammonitina. Calcification of aptychi in the Jurassic Ammonitina is known from the Early Toarcian Hildoceras which is also the first ammonite with males bearing well-formed lateral peristomatic projections or lappets. Calcification allowed aptychi to be involved in functions, which would have improved, in different degrees and combinations, feeding, propulsion and protection. It is herein suggested that multifunctional calcareous aptychi allowed the gradual development of a wide variety of new life-styles. These new life-styles would have led to the origin and early evolution of haploceratids and stephanoceratids producing the wide diversification of the Ammonitina observed from the Early Aalenian.

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 < 25 degrees from horizontal with adequate stability to withstand the counter-force produced by the jet of the recurved hyponome. However, of the shell forms tested, only brevidomes with thick aptychi, e.g., the Upper Jurassic Aspidoceratidae with Laevaptychus and average whorl expansion rates, were stable enough to swim forward by jet propulsion at about Nautilus speed (similar to 25 cm/s). We propose that aptychus function most commonly combined feeding (jaw, flushing, filtering) with protection (operculum), and, more rarely, with locomotion (ballast, pump, diving and stabilizing plane). Aptychi may thus have been multi-functional. (C) 2014 Elsevier Masson SAS. All rights reserved.

Well preserved Podagrosiceras spp. have been found in the Puchenquia malarguensis assemblage at the quasi-type locality in Neuquen, establishing their age as latest Aalenian to earliest Bajocian (Concava-Discites Zones). P. athleticum Maubeuge et Lambert, type species, is a microconch with lateral lappets; the septal suture is as in Hammatoceratinae. P. sp. nov. is described from the same assemblage. Podagrosiceratidae Maubeuge et Lambert, 1955, without status because of missing diagnosis or description, are intermediate between Hammatoceratinae and Erycitinae. They may require validatian at the subfamily level if diversity can be demonstrated.

The co-occurrence of ammonites with palynomorphs in the Athol Formation of the Tusk-1 and Tusk-2 wells drilled in the offshore Carnarvon Basin, Western Australia confirms the Early Bajocian (Middle Jurassic) age of the Dissiliodinium caddaense dinoflagellate cyst Oppel Zone. The macrofaunas refine this Early Bajocian age to the early Laeviuscula Chronozone. A belemnite from the Tusk-1 well has a strontium isotope (87Sr/86Sr) ratio consistent with the biostratigraphical age. All the identifiable ammonites belong to Pseudotoites robiginosus (Crick). Pseudotoites is prominent in the Early Bajocian of the Indo-Pacific Realm, being known mainly from onshore Western Australia and the Southern Andes, together with rare occurrences in Irian Jaya (west New Guinea); somewhat surprisingly, it is also rarely present in southern Alaska. The palynofloras studied from the Tusk-1 and Tusk-2 wells contain abundant specimens of the marine dinoflagellate cyst Dissiliodinium caddaense, and are assigned to the Dissiliodinium caddaense Oppel Zone. The Athol Formation is a correlative of the Newmarracarra Limestone of the onshore Perth Basin, Western Australia; the distribution of both these units indicates a marine transgression onto the Australian block during the Early Bajocian.

The present paper is a report of work completed by the group ‘Friends of Paleobiogeography’ on the principles of palaeobiogeographic classification and nomenclature of palaeobiogeographic units (biochoremas). These principles are intended to complement those of neobiogeography and are aimed at enhancing palaeobiogeography in general by a simplified and standardised terminology.

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Finite-element analysis of circular septum models indicates that (1) anticlastic fluting weakened the last septa of the same radius of curvature by a factor of about 2.5 relative to the tensile stresses in a sphere of nacre, (2) septa with ammonitic sutures were stronger than those with goniatitic sutures of the same thickness, and (3) septa with more “complex” ammonitic sutures were stronger at the edge between lobes and saddles than “simple” ones. These results contradict recent claims that ammonoid septa became weaker as sutural complexity increased from goniatitic through ammonitic, so that the most complex sutures were limited to the shallowest habitats. The smaller marginal flutes of complex septa were relatively strong, allowing them to be thinner than the central septum and still act as elastic wall supports. Many Mesozoic ammonoids with highly sinuous sutures occurred in deep epeiric and open-ocean habitats, whereas it is those with secondarily reduced, ceratitic sutures that were typically associated with restricted shallow basins.

We present evidence defending the hypothesis that specimens of the ammonite Placenticeras from the Upper Cretaceous Bearpaw Formation of southern Alberta were preyed upon by mosasaurs. Perforations linked to diagenetic modification of limpet home scars are anomalous features that are rare in comparison to true tooth marks.Point loading of the ammonite phragmocone wall by mosasaur teeth produced distinct perforations without the development of long, angular fractures. This was due to low pressure and rate of loading permitted by the unusually loose articulation of the lower jaw of mosasaurs, combined with the nearly uniform internal support of the shell wall by complexly fluted septa and their sutures, In contrast, the body-chamber, which lacked septal support (except at its posterior end), tended to shatter. Remnants of the body-chamber preserve distinctive notches that resemble tooth marks and sometimes show evidence of healing. Thorough reassessment of the perforations and associated features indicates that the large majority of perforations in shells of Placenticeras, at least those from southern Alberta, are best explained by predatory activities of mosasaurs.The currently popular hypothesis that all perforations preserved in shells of Cretaceous ammonites were produced by sediment loading and collapse of limpet home scars fails to explain many diagnostic features of the perforations. These include the shape, siting and arrangements of perforations as well as the equal puncturing of all size classes of alleged limpet home scars. The limper hypothesis also fails to consider structural differences between shells of ammonoids and Nautilus and erroneously assumes point loading by sediment compaction. Furthermore, the extreme rarity of limpets that had the potential of excavating home scars in Placenticeras from the Upper Cretaceous Bearpaw Formation of Alberta. Canada, cannot be attributed to preservational bias and is at odds with the large number of perforated specimens known from this formation. The mosasaur-bite hypothesis, on the other hand, accommodates all of these features. (C) 2001 Elsevier Science B.V. All rights reserved.

Paleobiogeographic terminology has increased dramatically in recent decades, but the absence of ‘rules’ or even a guide has resulted in confusion and misunderstanding. The Friends of Paleobiogeography are attempting to solve problems related to classification, definition and nomenclature of the biogeographic units (biochores), in conjunction with neobiogeographers. Historic and current developments are discussed. Biochores are highly dynamic units that not only expand and shrink in range, but also change in rank (tier) through time. They should be based on as many higher taxa as possible representing the biota, but from a single major biome, e.g. pelagic versus benthic; different biomes may need distinct sets of biochores. The following tentative ‘rules’ are proposed for a prospective guide for the distinction, ranking and naming of biochores, with emphasis on stability. (1) Definition: a biochore is defined by the overall endemism of its biota (not particular taxa) within a geographic envelope around a core area, whereas biochore boundaries are defined by the temporary range limits of their constituent endemic taxa. (2) Ranks (tiers): the biochores ranks are, with ‘bold’ for obligatory use and an additional tentative rank for exceptional conditions in brackets: [Superrealm], Realm, Subrealm, Province, Subprovince; ‘region’ is for informal use. Ranks scale with the degree of endemism as well as duration and biota distribution (range). (3) A typical region or chorotype and a typical stage (age) or chronotype are designated for each biochore. (4) Nomenclature: biochore names are geographic and related terms, not taxa-based. Nomenclatural priority begins with Uhlig [Mitt. Geol. Ges. Wien 4 (3) (1911) 229–448]. ‘Rules of Homology’ and ‘Synonymy’ apply in guide form only, e.g. long-term disuse of name or poor definition of biota invalidates synonym or homonym even if senior.

Consensus among the Friends of Paleobiogeography produced tentative guidelines to the classification and nomenclature of marine biogeographic units, i.e. biochores. Based on these loose ‘rules’, the present paper is a critical review of all published Mesozoic marine Realms, Subrealms, and ?Superrealms (formerly called ‘climatic belts’).Biochores are defined by the overall endemism within geographic and time envelopes that include choro- and chrono-types, without consideration of facies or climate. The hierarchy of ranks or tiers is: ?Superrealm, Realm, Subrealm, Province, Subprovince (only ranks in italics are obligatory); ‘region’ is informal. These ranks scale with endemism, geographic range, and persistence in time. Biochores are named geographically, following nomenclatural guidelines (not strict rules) of synonymy and homonymy, with priority beginning with Uhlig's paper of 1911. Uhlig's two ‘climatic belts’ are tentatively accepted as optional, top-ranking ‘Superrealms’ for times of exceptional global endemism; available names for them are ‘Euroboreal’ (or ‘Panboreal’, new) and ‘Tethys–Panthalassa’. The validity of the 29 existing names for realm-group biochores (Realms, Subrealms and Superrealms) in the marine Mesozoic is discussed; 19 names are rejected for a variety of reasons, including synonymy, homonymy and usefulness. The most important realm-group biochores are: Arctic and Boreal–Atlantic in the Boreal/?Euroboreal Realm or ?Superrealm; and Tethyan, Mediterran–Caucasian, Indo-Pacific (Jurassic–Early Cretaceous) and Austral (Middle–Late Cretaceous) in the ?Tethys–Panthalassa ?Superrealm.

Evidence for the Lower Bathonian Substage in most of the Pacific area has been lacking or controversial because index ammonoids of the Tethyan Subrealm in southern Europe and North Africa were unknown. During the Bathonian, the East Pacific margin belonged to either the Boreal Realm or the East‐Pacific Subrealm of the Tethyan Realm, each with faunas distinctly different from the Eurafrican Tethyan faunas that form the basis for the chronostratigraphical standard. The first representatives of Morphoceras from South America, M. gulisanoi sp. nov., here described from a single locality in southern Mendoza Province, clearly document the Lower Bathonian Substage, probably the Zigzag Zone. Associated ammonoids are the perisphinctoidean Procerites cf. schloenbachi de Grossouvre and the oppeliid Oxycerites (O.) cf. aspidoides (Oppel), also typical Tethyan elements but less useful for dating.

The reconstructed Carboniferous bactritoid Eoparabactrites, a possible belemnite ancestor, only became neutrally buoyant when two-thirds of the length of the phragmocone was flooded, which permitted it to live horizontally. But in the large, reconstructed belemnite Cylindroteuthis the advantageous horizontal poise, which is evident from its facies distribution, was presumably maintained more directly by the shifting of the centre of gravity ventral to the centre of buoyancy. We propose different structural and behavioral adaptations to this effect, e. g. ventral thickening of dense tissue, angling-up of phragmocone, ventral flattening of rostrum, minor ventral deposits and septal thickening in early chambers, and hanging-down of arms during rest periods.

A single, conical specimen from the Upper Bathonian of Chacay Melehue, west-central Argentina, displays the characteristic features of ammonoid lower jaws, inner pit and lateral platforms, as well as the beak of the upper jaw. There are no direct taxonomic clues but its large size, circular outline, and associated cephalopod fauna indicate: that it belonged to Lytoceratinae, possibly Lytoceras.

The new genus Sulaites comprises the mainly Late Oxfordian species group of "Perisphinctes" sularus and moluccanus, Boehm spp., originally described from the Sula Islands of eastern Indonesia, and the Late Oxfordian-?Early Kimmeridgian species group of "Pseudoparaboliceras aramaraii" Gerth, originally described from Irian Jaya. The designated type-species of Sulaites is Perisphinctes sularus Boehm 1907. All syntypes of P. sularus and moluccanus have been destroyed. Because no microconchs resembling Boehm's illustrated specimens are available from Sula, a complete microconch from Papua New Guinea is designated as the neotype. "P." moluccanus is included in the type-species. Both Gerth's (1965) genus-group name Pseudoparaboliceras and species epithet aramaraii have no designated types and are therefore nomina nuda. The substitute name proposed is Sulaites gerthi n. sp. Sulaites is known from Papua New Guinea, and probably New Zealand and Nepal.

Multidisciplinary research on the habitats and life-habits of ammonoids of the Upper Cretaceous Bearpaw Formation is based on hydrostatics and hydrodynamic aspects of shell shapes, occurrence in lithofacies, evidence of predation, and stable-isotopic data. The large and well-streamlined, oxyconic Placenticeras, with large chitinous anaptychus, had the weakest shells known, and suffered mosasaur tooth perforations at minimal ambient pressure. Anomalously light δ18O signatures preserved in their aragonitic shells suggest that they grew in brachyhaline water. Juveniles and some adults of orthoconic Baculites had a vertical life orientation and primarily resided in the lower to middle levels of the water column, flourishing during oxygenation events. Some adults, however, may have changed to a mainly horizontal swimming habit in mid-water. Attitudinal change is indicated by relative shortening of the body-chamber during late ontogeny. Neutral buoyancy at maturity could have been achieved only with a partially liquid-filled phragmocone, implying the exceptional use of cameral liquid as an apical counterweight. Juvenile scaphitids were planktic or sluggishly nektic, as implied by sphaeroconic and discoconic immature whorls, respectively. The adults had different habits, as indicated by their strongly modified body-chambers, which gave high stability suited to vertical swimming. Adult Hoploscaphites and most Jeletzkytes, with open-hooked (scaphitoconic) body-chambers, were demersal and lived close to the sea floor during oxygenation events, whereas adult Rhaeboceras, with an elliptical, contracted body-chamber (elliptosphaerocone), lived in mid-water.

Pre- and post-19th century hypotheses relating hydrostatic pressure to the mechanical function of sutural complexity are compared. The old ideas gave rise to the 19th century ‘Buckland hypothesis’, which is in turn largely synonymous with the ‘Westermann model’. Buckland (1836) postulated that fluted septa buttressed the weak flanks of the phragmocone wall. Two new parameters are introduced to define the covariation between the strength of cylindrical segments of the wall flank bounded by the distance between adjacent lobe and saddle-flutes in transverse sections. The product of the index of wall strength (IWS) and this inverse support angle (ISA) predicts the buckling pressure in a cylinder of infinite length, and it implies that coiled nautiloids were more likely to be imploded via their whorl flanks than the apparently weaker oxyconic ammonoids. The widely used index of sutural complexity (ISC) measures the marginal corrugation which obscures this trend and acts as an elastic bed for both strong and weak walls. However, the ISC is more proportional to habitat depth than the buckling pressure when all other factors are constant. The central thickness of each fluted septum was increased in direct proportion to the distance spanned by the septum and the hydrostatic pressure on it in the ‘last septum’ position. The marginal thickness was maintained at a more constant value, which permitted the suture to increasingly act like a spring or shock absorber, as the wall thickness was enlarged during ontogeny. Both the ratios, between the central and marginal thicknesses and the closely related ISC, therefore, increased with shell diameter and habitat depth.

New Zealand's highly endemic fauna with scarce ammonites had resulted in regional stages (also series but no standard zones) based on bivalves, belemnites and brachiopods. A number of cosmopolitan, Tethyan or Andean ammonite taxa have recently been identified (*) that improve correlations of the regional Middle and Upper Jurassic stages with the standard stages. Temaikan: base defined by first Belemnopsis mackayi/deborahae; U. T. with Chondroceras*, Stephanoceras*, Teloceras*, Toxamblyites*, Sphaeroceratinae 2 n. gen.* (L. Baj.); Lilloettia-Xenocephalites (U. Bath.) U. Toarcian - U. Bathonian. Heterian: base defined by also first Retroceramus ''galoi'' = ?patagonicus/stehni; Eurycephalitinae indet. [cf. Araucanites, Iniskinites; = ''Epimayaites'', ''Epicephalites''] (Call.); ''Perisphinctes'' [n. gen.*] gr. sularus-moluccanus, ''Pseudoparaboliceras''* [nom. nud., = ''Idoceras''. ?''Kossmatia'' part.] (U. Oxf. - L. Kimm.) = M/U. Callovian L. Kimmeridgian. Ohauan: base defined by first Retroceramus haasti; also ?Ataxioceratidae, ?Torquatisphinctes/[= ''Aulacosphinctoides'' part.], Kossmatia, ca. U. Kimmeridgian, PUAROAN: base defined by first Hibolites arkelli grantmackiei; also Uhligites, ?Kossmatia, ?Aulacosphinctoides = ca. L./basal Tithonian.

Most New Zealand Ammonitina are extremely rare, but the number of known genera has almost doubled by recent field work and taxonomic revision. The biogeography based on Mid-Jurassic Ammonitina genera and species indicates that (Early) Bajocian faunas were principally endemic with Tethyan and cosmopolitan accessories. In contrast, Bathonian-Callovian faunas were Andean with cosmopolitan accessories. During much of the Mesozoic Era, New Zealand was in a southern high-latitude position, possibly in the vicinity of the South Pole. I propose that the change in biogeographic affinity was caused by a shift in the direction of the unstable south-polar current system, perceivably due to rifting. New Zealand faunas were influenced at first by the Paleo-East Australia Current arriving from the southwest Pacific, which during the Late Bajocian - Early Bathonian was replaced by the Arctic Peninsula Current that brought southeast Pacific water masses. Significantly, this change in ''anti-boreal'' biogeographic affinitty and implied south-polar ocean current system was roughly coincident with an aprupt increase in ammonite provincialism in other parts of the globe, i.e. the differentiation of the East-Pacific Subreal (Tethyan Realm) and the Boreal Realm.