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Nomenclatural review of Polyptychoceras and 18 related taxa (Ammonoidea: Diplomoceratidae)
Abstract
The nomenclature of Polyptychoceras, a Late Cretaceous heteromorph ammonite genus, and 18 related taxa is examined with a view to clarifying their nomenclatural availability, authors, dates of publication, and name-bearing types, on the basis of the International Code of Zoological Nomenclature (Fourth Edition). It is concluded that one family-group name, four genus-group names, and 12 species-group names are currently available. In contrast, the names Po. subundatum and Po. jimboi are unavailable. We also showed that Po. yubarense had been established by Shimizu (J Shanghai Sci Inst, Sect II, 1(11):159–226, 1935a).
Three heteromorph ammonite families are represented within upper Campanian (Upper Cretaceous) strata of the Northumberland Formation exposed on Hornby Island, British Columbia: Baculitidae, Diplomoceratidae and Nostoceratidae. A variety of species are distinguished within these families, of which only three taxa – Baculites occidentalis Meek, 1862, Diplomoceras (Diplomoceras) cylindraceum (Defrance, 1816) and Nostoceras (Nostoceras) hornbyense (Whiteaves, 1895) – have been reported previously. Over the last decade, large new collections and the further preparation of existing collections has provided new taxonomic and morphometric data for the Hornby Island ammonite fauna, from which new descriptions of heteromorph taxa are formulated. Eleven taxa are recognized, including the new species Exiteloceras (Exiteloceras) densicostatum sp. nov., Nostoceras (Didymoceras?) adrotans sp. nov. and Solenoceras exornatus sp. nov. Morphometric analyses of over 700 specimens demonstrate the considerable phenotypic plasticity of these ammonites, which exhibit a broad spectrum of variability in their ornamentation and shell dimensions. A large population sample of Nostoceras (Nostoceras) hornbyense provides an excellent case study of a member of the Nostoceratidae; the recovery of nearly complete, well-preserved specimens enables the re-evaluation of diagnostic traits within the genus Nostoceras. The north-east Pacific Nostoceras (Nostoceras) hornbyense Zone and the global Nostoceras (Nostoceras) hyatti Assemblage Zone are here regarded as correlative, reinforcing a late Campanian age for the Northumberland Formation.
http://zoobank.org/urn:lsid:zoobank.org:pub:EEF7416A-3AC7-47CC-8667-806F6A7FE567
A new Cretaceous heteromorph ammonoid, Phylloptychoceras horitai sp. nov., is described from the lowest Maastrichtian of Hokkaido, Japan. Its shell is ornamented with very weak, broadly rounded ribs and its suture line is characterized by a deeply incised, trifid dorsal lobe and three bifid lateral saddles with minor indentations. This occurrence suggests that Phylloptychoceras evolved in the North Pacific during late Campanian or early Maastrichtian time and then achieved worldwide distribution during late Maastrichtian time.
The cephalopods from Union y Progreso represent the first fossil assemblage described from the Parras Shale in Coahuila, Mexico. Pseudoschloenbachia (Pseudoschloenbachia) aff. P. (P.) mexicana (Renz, 1936), P. (P.) mexicana (Renz, 1936), Baculites haresi Reeside, 1927, and Menabites (Delawarella) vanuxemi (Morton, 1830) have a geographically restricted occurrence. Didymoceras juv. sp., Menuites juv. sp., Polyptychoceras juv. sp., Pseudoxybeloceras (Parasolenoceras) juv. sp., and Scaphites sp. ex gr. S. hippocrepis (DeKay, 1828) are represented by juveniles and could not be determined to species level. Desmophyllites diphylloides (Forbes, 1846) is the only long-ranging, cosmopolitan species described from this assemblage. Three new species are described: Eutrephoceras irritilasi n. sp., Hypophylloceras (Neophylloceras) arturoi n. sp., and Tetragonites silencioensis n. sp. The morphotype Baculites n. sp. is also inferred to be distinct. The faunal composition of this assemblage indicates a late early Campanian age. This assemblage shows a high degree of endemism. The causes for this endemism are currently unknown and difficult to assess. Nevertheless, the generic composition of the Union y Progreso ammonite assemblage suggests a short-term early Campanian endemic event. INTRODUCTION
The International Commission on Zoological Nomenclature has voted in favour of a revised version of the amendment to the International Code of Zoological Nomenclature that was proposed in 2008. The purpose of the amendment is to expand and refine the methods of publication allowed by the Code, particularly in relation to electronic publication. The amendment establishes an Official Register of Zoological Nomenclature (with ZooBank as its online version), allows electronic publication after 2011 under certain conditions, and disallows publication on optical discs after 2012. The requirements for electronic publications are that the work be registered in ZooBank before it is published, that the work itself state the date of publication and contain evidence that registration has occurred, and that the ZooBank registration state both the name of an electronic archive intended to preserve the work and the ISSN or ISBN associated with the work. Registration of new scientific names and nomenclatural acts is not required. The Commission has confirmed that ZooBank is ready to handle the requirements of the amendment.
To date, the two highest units (Nekum and Meerssen members) of the Maastricht Formation in the Maastrichtian type area (southeast Netherlands, northeast Belgium) have yielded some twenty ammonite species, the majority of which are heteromorph. Baculitids and scaphitids predominate, while diplomoceratines and nostoceratids are extremely rare and do not appear to range higher than the basal portion (subunit IVf-1) of the Meerssen Member. From subunits IVf-5 and IVf-6 of that unit as exposed at the quarries of ENCI-Heidelberg Cement Group (Maastricht) and Ankerpoort-Curfs (Geulhem), two specimens of the polyptychoceratine Phylloptychoceras cf. sipho have recently been collected, from an interval a few metres below the Cretaceous/Paleogene (K/Pg) boundary. Elsewhere in Europe, Ph. sipho has previously been recorded from the uppermost Maastrichtian of Denmark and the lower upper Maastrichtian of the Bay of Biscay sections (France, Spain).
The International Commission on Zoological Nomenclature has voted in favour of a revised version of the amendment to the International Code of Zoological Nomenclature that was proposed in 2008. The purpose of the amendment is to expand and refine the methods of publication allowed by the Code, particularly in relation to electronic publication. The amendment establishes an Official Register of Zoological Nomenclature (with ZooBank as its online version), allows electronic publication after 2011 under certain conditions, and disallows publication on optical discs after 2012. The requirements for electronic publications are that the work be registered in ZooBank before it is published, that the work itself state the date of publication and contain evidence that registration has occurred, and that the ZooBank registration state both the name of an electronic archive intended to preserve the work and the ISSN or ISBN associated with the work. Registration of new scientific names and nomenclatural acts is not required. The Commission has confirmed that ZooBank is ready to handle the requirements of the amendment.
To understand the inter- and intraspecies variation and ontogenetic change in shell ornamentation of Polyptychoceras (Cretaceous diplomoceratid), reproduction of shell morphologies was carried out based on the creeping soft-part model and the lazy messenger effect. As a result, we found several constructional rules on this ammonite as follows. (1) The shell surface of Polyptychoceras consists of "striation-" and "smooth-parts", and the former was much more slowly formed than the latter. (2) The changes in shell ornamentation during growth of Polyptychoceras (Polyptychoceras) haradanum were probably caused by change in shell prolongation rate, and were successfully restored if the striation- and smooth-parts were assumed to be formed through gradual expansion and intermittent forward movement of the soft-part, respectively. (3) The formation of the multiple ribs observed in Polyptychoceras (Subptychoceras) yubarense can be attributed to a refractory period for propagation of the morphogenetic signals just after the formation of the continuous smooth-part including ribs. Our conclusion is that the great variability of shell ornamentation developed in Polyptychoceras is the result of compound effect of two factors, i.e. the rate of shell prolongation and the duration of the refractory period for ribbing.
Polyptychoceras, a Cretaceous heteromorph ammonite genus, is characterized by a trombone like shell called a "hamitoid" shell. In order to clarify the shell forming mechanism, a large sample, which consists of more than 320 specimens of P. pseudogaultinum (Yokoyama) obtained from the Upper Santonian of Hokkaido, was biometrically analyzed. Besides the shell coiling, cyclic changes of growth pattern are recognized by the analyses of the shell ornamentation, the relative growth rate of shell height, and the distance between septa. Intermittent shell growth, which was also deduced from the ontogenetic stage distribution in the population samples, is probably the cause of such peculiar shell coiling. Also, we carried out some computer simulations to reconstruct hydrostatically the ontogenetic change of the living attitude of P. pseudogaultinum. It is suggested that the rate of absolute shell growth possibly depends on the living attitude of this ammonite in the water column; the shell grows slowly when the shell aperture faces upward, and grows rapidly when the aperture faces in other directions. It is likely that every individual of this ammonite spent most of its life time with an upward facing aperture.
Polyptychoceras, an Upper Cretaceous diplomoceratid heteromorph ammonite, commonly preserved in the calcareous nodules with a oblique posture against the bedding plane. In order to interpret this peculiar mode of occurence, detailed observation of fossiliferous nodules, hydrostatic calculations, and sedimentational experiments were carried out. As a conclusion, a presumable taphonomic history of Polyptychoceras spp. is reconstructed as follows: 1) Soon after the death of organism, shells of Polyptychoceras spp. were waterlogged and were laid down on the sea floor just like many shells of other ammonites, 2) when the floor is covered with fine and new sediment, which probably forms a softground and behaves as a viscous fluid, some shells having a highly polarized density like a peculiar growth stage of Polyptychoceras spp. had rotated in the sediments, because the bouyancy acting on a distant point from the center of gravity had considerably increased in such condition, 3) for a while, turning-part of phragmocone in some shells had possibly been jutting out from the sediments, and the part had eroded or sometimes lost away, 4) sooner or later, the shells had entirely buried by the succeeding sediments, and a calcareous nodule had been formed before the sediments around the shells were highly compressed throughout the diagenetic process. The post-burial movement of some ammonite shell, above mentioned, is named as "Zombie model", and this mechanism is possibly applicable to several other heteromorphic ammonite shells buried in the muddy sediments.
All actual data about ammonite faunas from the Upper Cretaceous of southern Sakhalin and northwestern Kamchatka (North-East Russia) are revised and summarized. 21 poorly known and 3 new species (Scaphites talovkensis, Polyptychoceras sakhalinum and Pachydiscus denseplicatus) are described. 24 other species are illustrated and mentioned in the discussion. The definition of the stage bases is discussed and nine new ammonite zones are recommended for the NW-Pacific Upper Cretaceous.
The microstructure of aptychi (bivalved calcareous coverings on lower jaws) of three genera of Late Cretaceous Ancyloceratina, Baculites, Polyptychoceras and Jeletzkytes is described for the first time on the basis of well-preserved and in situ material from the Western Interior of the USA and Hokkaido, Japan. Optical and scanning electron microscope observations of aptychi on polished median and cross-sections reveal some variation in their relative size, shape and microstructure among the three genera. The aptychus of Baculites is composed of two calcitic layers: one with tilted lamellae and the other one with horizontal lamellae, whereas those of Polyptychoceras and Jeletzkytes consist of a thin layer with horizontal lamellae. Comparison with aptychi (e.g. Laevaptychus) of Jurassic Ammonitina shows that the aptychi of Ancyloceratina differ from those of Jurassic Ammonitina in the smaller number of layers and the absence of a sponge-like structure. We propose for the first time growth models for a sponge-like aptychus of Jurassic Ammonitina and the lamellar aptychus of Cretaceous Ancyloceratina. The remarkable microstructural variation of aptychi observed in Mesozoic Ammonoidea is probably related to the diversity of their modes of feeding and the secondary function of the lower jaws as opercula.
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- International Commission on Zoological Nomenclature