Paedomorphosis in the Turonian (Late Cretaceous) collignoniceratine ammonite lineage from the north Pacific region

Ontogenetic development and variation of shell ornament of the four Turonian collignoniceratine ammonites, Collignoniceras woollgari (Mantell 1822), Subprionocyclus neptuni (Geinitz 1850), S. normalis (Anderson 1958) and S. minimus (Hayasaka & Fukada 1951) have been compared on the basis of large population samples from Hokkaido (Japan), California and the US Western Interior Province. Our study revealed that the ornament types observed in the early-middle stage of C. woollgari occur in the middle-late stage of the three other species, and that those in the early-middle stage of S. neptuni appear in the middle-late stage of S. normalis and S. minimus. These species are generally regarded as closely related phylogenetically, because they share several common morphological features such as the presence of double ventrolateral tubercles and a serrated keel. If a postulated phylogeny starting from C. woollgari to S. normalis and S. minimus via S. neptuni is accepted, the mode of morphological evolution in the lineages can be explained by paedomorphosis. Available palaeobiogeographical data suggest that this paedomorphic evolution occurred independently on the northwestern and northeastern sides of the northern Pacific, where the C. woollgari – S. neptuni – S. minimus, and C. woollgari – S. neptuni – S. normalis sublineages evolved.     

西藏北部色哇-安多地区侏罗纪菊石类与缺氧黑色页岩相

西藏北部色哇和安多地区32°-33°N,88°-91°E范围内的菊石化石证明了东特提斯北缘侏罗纪土阿辛期(Toarcian)和阿林期(Aalenian)地层的存在。文内描述11种,大多数属种都在国内首次报道,包括相当于土阿辛期末期的aalensis菊石带和阿林期中期的murchisonae菊石带的种,它们分别隶属于2亚目、3超科、5科、9属,其中以Hildocerataceae超科的类型占主体。藏北菊石动物群和西特提斯地中海区同期菊石动物群具有更加密切的亲缘关系。土阿辛阶的种有Dumortieriasp.,Dactyliocerascf.directum(Buckman),Hildocerassp.,Clevicerascf.elegans(Sowerby),Clevicerassp.,PolyplectusdiscoidesZieten,Phymatocerascf.binodata(Buckman),Pleydelliacf.aalensis(Zieten)。阿林阶的种有Phyllocerassp.,Planammatocerascf.lepsiusi(Gemmellaro),Erycitessp.。菊石和沉积岩资料表明,在早土阿辛末期和晚土阿辛末期至早阿林期是藏北地区缺氧黑色页岩沉积时期;菊石动物群的扩散和黑色页岩相的发生是全球高海平面的地区性响应。     

LATE EARLY SINEMURIAN (EARLY JURASSIC) AMMONITES FROM THE TASEKO LAKES MAP AREA, BRITISH COLUMBIA

Abstract:  Abundant and well-preserved Early Jurassic ammonite assemblages occur in the Taseko Lakes map area on the Cadwallader Terrane in the southern Coast Mountains of British Columbia. The ammonite assemblage described herein includes nine genera and 14 species, most of them already known from classical localities of northern and southern Europe. The presence in particular of Caenisites brooki (Sowerby) and C. turneri (Sowerby) permits high-resolution correlation with the Turneri Zone of the north-west European Sinemurian zonation. The specimens were collected at four localities but most come from an olistolith where the ammonite assemblage is dominated by Coroniceras ( Paracoroniceras ) mutabile Macchioni, Smith and Tipper, associated with Lytotropites fucinii (Bonarelli) and Hypasteroceras montii (De Stefani). The latter two species, whose exact age is here established for the first time, have a Mediterranean distribution.     

Heteromorph ammonites from the Tata Limestone Formation (Aptian–Lower Albian), Hungary

An important new ammonite fauna was collected by Fülöp in 1953 and 1960 from basal lenses between a Tithonian hardground and the overlying Tata Limestone Formation containing many heteromorph ammonites. This assemblage of ammonites has been determined as being of Early Albian ( tardefurcata Zone) age. Among the heteromorphs are species of Tonohamites and Ptychoceras , which are familiar components of Late Aptian or Early Albian ammonite faunas. The genera Ephamulina , Hamites and Protanisoceras are also recorded, the earliest species of which had previously come from sediments of late Early Albian ( mammillatum Zone) age. While Hamites and Protanisoceras are common in Europe, Ephamulina had previously only been known from Madagascar. The discovery of Ephamulina , Hamites and Protanisoceras supports the view that these phylogenetically significant ammonites had radiated close to the Aptian/Albian boundary. Four new species of Hamites ( H. czaszari , H. fazekasensis , H. fueloepi and H. kalvariensis ) and one new species of Tonohamites ( T. boldii ) are described.     

Further fossil cephalopods from Jamaica

Fossil cephalopods are rare in the Antillean region. A deformed conch of a kossmaticeratid ammonite,Pseudokossmaticerasl sp., from the Maastrichtian of the Blue Mountain Inlier is the first ammonite from southeastern Jamaica. This tentative systematic assignment is in agreement with the age otherwise assigned to these rocks.Cimomia sp. cf.C. vaughani (Gardner) is a hercoglossid nautiloid from the Lower-Middle Eocene Chapelton Formation of western central Jamaica. This is only the fourth nautiloid from this unit; all previous records were ofHercoglossa sp. The specimen is unusual amongst Antillean fossil cephalopods in including the sponge boringEntobia isp., probably indicating a period of post-mortem residence on the sea floor.      

Allocrioceras from the Cenomanian (mid-Cretaceous) of the Lebanon and its bearing on the palaeobiological interpretation of heteromorphic ammonites

Specimens of the mid-Cretaceous heteromorphic ammonite Allocrioceras cf. annulatum (Shumard, 1860) from the Upper Cenomanian lithographic limestones of the Lebanon provide an in situ record of aptychi and interpreted remnants of internal soft tissue and stomach content. Based on this exceptionally well-preserved material, Allocrioceras is interpreted as a pelagic, aperture-upwards drifter that probably fed on comatulid crinoids.     

Recent advances in heteromorph ammonoid palaeobiology

Heteromorphs are ammonoids forming a conch with detached whorls (open coiling) or non-planispiral coiling. Such aberrant forms appeared convergently four times within this extinct group of cephalopods. Since Wiedmann's seminal paper in this journal, the palaeobiology of heteromorphs has advanced substantially. Combining direct evidence from their fossil record, indirect insights from phylogenetic bracketing, and physical as well as virtual models, we reach an improved understanding of heteromorph ammonoid palaeobiology. Their anatomy, buoyancy, locomotion, predators, diet, palaeoecology, and extinction are discussed. Based on phylogenetic bracketing with nautiloids and coleoids, heteromorphs like other ammonoids had 10 arms, a well-developed brain, lens eyes, a buccal mass with a radula and a smaller upper as well as a larger lower jaw, and ammonia in their soft tissue. Heteromorphs likely lacked arm suckers, hooks, tentacles, a hood, and an ink sac. All Cretaceous heteromorphs share an aptychus-type lower jaw with a lamellar calcitic covering. Differences in radular tooth morphology and size in heteromorphs suggest a microphagous diet. Stomach contents of heteromorphs comprise planktic crustaceans, gastropods, and crinoids, suggesting a zooplanktic diet. Forms with a U-shaped body chamber (ancylocone) are regarded as suspension feeders, whereas orthoconic forms additionally might have consumed benthic prey. Heteromorphs could achieve near-neutral buoyancy regardless of conch shape or ontogeny. Orthoconic heteromorphs likely had a vertical orientation, whereas ancylocone heteromorphs had a near-horizontal aperture pointing upwards. Heteromorphs with a U-shaped body chamber are more stable hydrodynamically than modern Nautilus and were unable substantially to modify their orientation by active locomotion, i.e. they had no or limited access to benthic prey at adulthood. Pathologies reported for heteromorphs were likely inflicted by crustaceans, fish, marine reptiles, and other cephalopods. Pathologies on Ptychoceras corroborates an external shell and rejects the endocochleate hypothesis. Devonian, Triassic, and Jurassic heteromorphs had a preference for deep-subtidal to offshore facies but are rare in shallow-subtidal, slope, and bathyal facies. Early Cretaceous heteromorphs preferred deep-subtidal to bathyal facies. Late Cretaceous heteromorphs are common in shallow-subtidal to offshore facies. Oxygen isotope data suggest rapid growth and a demersal habitat for adult Discoscaphites and Baculites. A benthic embryonic stage, planktic hatchlings, and a habitat change after one whorl is proposed for Hoploscaphites. Carbon isotope data indicate that some Baculites lived throughout their lives at cold seeps. Adaptation to a planktic life habit potentially drove selection towards smaller hatchlings, implying high fecundity and an ecological role of the hatchlings as micro- and mesoplankton. The Chicxulub impact at the Cretaceous/Paleogene (K/Pg) boundary 66 million years ago is the likely trigger for the extinction of ammonoids. Ammonoids likely persisted after this event for 40–500 thousand years and are exclusively represented by heteromorphs. The ammonoid extinction is linked to their small hatchling sizes, planktotrophic diets, and higher metabolic rates than in nautilids, which survived the K/Pg mass extinction event.     

Les faunes de Cardioceratinae (Ammonoidea) du Callovien terminal et de l'Oxfordien inférieur et moyen (Jurassique) de la Suisse septentrionale: Stratigraphie,paléoécologie,taxonomie préliminaire

The first photographs of Cardioceratinae out of exactly defined horizons from the Latest Callovian to the Middle Oxfordian of northern Switzerland are given in this article. Most specimens were either collected in large-scale excavations, or from measured sections. The Cardioceratinae from the Cordatum Subzone are important because they are very numerous, and because particularly well-preserved specimens are abundant. Cardioceratinae of this subzone are uncommon elsewhere in Europe. All representatives of the subfamily from the Cordatum Subzone, macro- as well as microconchs, are grouped into the single genus Cardioceras. An abrupt morphological change has been recognized between the Cardioceratinae of the Densiplicatum Zone and those of the Transversarium Zone.Most of the figured specimens have been found in an incomplete sequence of thin or even condensed horizons. These beds are the distal, starved basin facies of a thick, argillaceous, shoaling-up succession in northwestern Switzerland. Sedimentologic and taphonomic methods have been used in order to work out the time sequence of sediments and ammonite faunas in condensed beds, and to arrive at a correct zonation. These methods as well as observations on the distribution of chamosite and glauconite, and the ammonite assemblages, in two coeval horizons lead us to the conclusion that the Cardioceratinae of the Cordatum Subzone in northern Switzerland lived preferentially in water less than about 100 m deep.