Ecological structure and stage of ecogenesis of Paleozoic ammonoids in the Uralian paleobasin

The ecological structure of Paleozoic ammonoid assemblages of the Uralian paleobasin is discussed. Life forms (nektobenthic, planktonic, and benthopelagic) are used as ecological units. Four stages in evolution of the communities, with distinct structure and evolutionary pathways, are recognized.     

Ammonoid evolution in marine ecosystems prior to the Permian-Triassic crisis

Evolutionary trends in ammonoid communities in the Middle and Late Permian are analyzed in connection with the changes in their taxonomic, morphological, geographical, and ecological structure. It is shown that the processes that led to the almost complete disappearance of the subclass began long before the global Permian-Triassic crisis.     

Evolution of the early Permian family Paragastrioceratidae (Ammonoidea) in the Urals

This paper discusses the evolution of the Early Permian ammonoid family Paragastrioceratidae in the Urals, with an emphasis on the terminal Artinskian-Kungurian stage of evolution in this group. New data on the Kungurian members of the family are discussed. Patterns of morphological and ecological changes of the Uralian paragastrioceratids are analyzed.     

Ammonoid recovery from the Late Permian mass extinction event

Previous research indicated that ammonoid taxonomic diversity exploded after the Late Permian mass extinction, regaining pre-extinction levels by the Late Induan (Dienerian substage). From taxonomic analyses it had been inferred that ammonoids recovered rapidly, relative to other marine invertebrate groups. Complementing taxonomic metrics with morphologic and spatial data revealed more complex recovery dynamics. Morphological analysis indicated that ammonoids did not fully recover until the Spathian or Anisian. Taxonomic diversity is a poor predictor of disparity during the recovery. Spatial partitioning of taxonomic and morphological diversity revealed spatially homogeneous recovery patterns. Combining taxonomic, morphological, and spatial data refined interpretations of Triassic ammonoid recovery patterns and indicated that ecological, not intrinsic, factors were the probable control on ammonoid recovery rates. To cite this article: A.J. McGowan, C. R. Palevol 4 (2005).     

泰国早二叠世与Perrinites菊石动物群共生的verbeekinacean(筳)类

泰国中南部Saraburi地区Saraburi群的灰岩中,Kungurian期的verbeekinacean类与Perrinites菊石群在该地区的碎屑灰岩中共生。两种生态完全不同的生物群的共同存在,对只含单一类型化石的地层之间的区域地层对比有"搭桥"性的意义。     

Mechanische Simulation und funktionelle Evolution des Ammoniten-Septums

Simulation of nautiloid and ammonoid septa and suture lines illustrates the fabricational constraints and possibilities that controlled their evolution towards the paradigm of a pressure resistant structure.     

Ammonoid palaeobiology

This, the second in the series of virtual issues of Palaeontology, charts the development of concepts in ammonoid palaeobiology, with reference to nine selected papers published in this journal from 1965 onwards. These cover a broad range of topics: goniatite bed palaeoecology, systematics and evolution in Scaphites, flow dynamics of cephalopod shells, shell growth and differential geometry, septal function, ammonoid assemblage analysis, evolutionary trends, stratocladistics, and soft part preservation. Despite the growth and success of palaeobiological interpretations of ammonoid evolution, life, morphology and environments over the last 50 years, ammonoid research retains a great potential for the future.     

Phylogenetic relationships of Early Triassic ammonoids (new data on the inner shell structure of some Olenekian ammonoids of Southern Primorye)

The inner shell structure for several ammonoid taxa (Inyoceras singularis, Anasibirites simanenkoi, A. nevolini, Yvesgalleticeras proximus, and Koninckitoides popovi) from the Olenekian of Southern Primorye is studied. The family-group level taxonomy of ammonoids is discussed.     

A new ammonoid fauna from the Carnian (Upper Triassic) Kasimlar Formation of the Taurus Mountains (Anatolia,Turkey)

We describe a new ammonoid fauna from the Taurus Mountains of southern Turkey. The Carnian ammonoid fauna from A?a?iyaylabel is presented for the first time. Ammonoids were obtained from limestone to marl beds of an approximately 35‐m‐thick section, which presents the rare opportunity to investigate ammonoid faunas across the Lower–Upper Carnian boundary. Intense sampling near the village of A?a?iyaylabel led to the recognition of a new Lower Carnian (Julian 2) to Upper Carnian (Tuvalian 1) ammonoid fauna from the Kasimlar Formation. The genus Kasimlarceltites gen. nov. is reported for the first time from the Taurus Mountains, which represents the main faunal element and occurs as huge mass occurrence (n ? 1 million). Kasimlarceltites krystyni gen. et sp. nov., Klipsteinia disciformis sp. nov. and Anasirenites crassicrenulatus sp. nov. occur within the Lower Carnian Carbonate member (Units A–B) of the Kasimlar Formation from the Taurus Platform Units. Ammonoids described from the marls of the Tuvalian Marlstone member were deposited during a major, Tethyan‐wide climate crisis – the so‐called Carnian crisis – characterized by a demise of carbonate platforms. Based on the biostratigraphic relevance of certain ammonoid taxa described herein, the age of the analysed parts of the Kasimlar Formation is Julian 2 to Tuvalian 1. The discovery of the new ammonoid assemblages from A?a?iyaylabel substantiates the significance of Upper Triassic faunas within the Taurus Mountains and facilitates the correlation with faunal assemblages from other regions in the Tethyan Realm. The ammonoid fauna and facies indicate a general deepening from open‐platform margins, over deeper shelf settings down to an open marine‐influenced basinal environment. The tentative habitat for Kasimlarceltites gen. nov. is a shallow platform environment to upper mid‐ramp.     

The connecting rings of Nautilus and Mesozoic ammonoids: implications for ammonoid bathymetry

The fresh conchiolinous ('horny') connecting rings of Nautilus pompilius decrease ontogcnctically in the strength index (100 times; wall thicknessh/inner radius r), i.e. from ≥ 16 to – 12. A similar decrease of 100 h/ r is the rule in Ammonitina. This may reflect depth migration but, more likely and in analogy with Nautilus, is compensated for by increased conchiolin strength. The mature ammonoid siphunclc, therefore, provides the more reliable indicator for depth limits. No marked shrinkage of connecting rings is evident in fossil nautiloids, but Mesozoic nautilid connecting rings are rarely preserved. Post-mortem alteration of the abundantly preserved ammonoid connecting rings entails mechanical distortion and fragmentation by differential filling of the siphunclc and camerac with sediment, and probable microbial decomposition, proceeding from the body chamber and resulting in pitting and perforation; shrinkage occurred rarely. This is probably related to the high phosphate content as here documented for Haplo-phylloceras. If the phosphate prevalent in ammonoid connecting rings is a primary constituent, rather than of early diagenetic origin, calibration of the ammonoid strength index on the non-phosphatic Nautilus connecting rings may not be justified. The strength indices of ammonoid connecting rings would thus provide only a relative scale of depth limits. Another example of a phylloccratid, Ptychophylloceras, has been found with a connecting ring extending well into the body chamber. D Connecting rings, ammonoids. Nautilus, bathymetry.     

Zur paläobathymetrischen zuverlässigkeit von ammonoideen-faunen-spektren

The Jurassic ammonoid faunal spectrum of the Mediterranean faunal provinces always exhibits a large quota of Phylloceratina and Lytoceratina. As a rule, these ammonites are supposed to be index fossils of deeper-water deposits. An example from Spain suggests that this is not always the case. Nevertheless general zoogeographical aspects of ammonoid distribution, irrespective of the depth of water, still merit our attention.     

Animal behavior frozen in time: gregarious behavior of Early Jurassic lobsters within an ammonoid body chamber

Direct animal behavior can be inferred from the fossil record only in exceptional circumstances. The exceptional mode of preservation of ammonoid shells in the Posidonia Shale (Lower Jurassic, lower Toarcian) of Dotternhausen in southern Germany, with only the organic periostracum preserved, provides an excellent opportunity to observe the contents of the ammonoid body chamber because this periostracum is translucent. Here, we report upon three delicate lobsters preserved within a compressed ammonoid specimen of Harpoceras falciferum. We attempt to explain this gregarious behavior. The three lobsters were studied using standard microscopy under low angle light. The lobsters belong to the extinct family of the Eryonidae; further identification was not possible. The organic material of the three small lobsters is preserved more than halfway into the ammonoid body chamber. The lobsters are closely spaced and are positioned with their tails oriented toward each other. The specimens are interpreted to represent corpses rather than molts. The lobsters probably sought shelter in preparation for molting or against predators such as fish that were present in Dotternhausen. Alternatively, the soft tissue of the ammonoid may have been a source of food that attracted the lobsters, or it may have served as a long-term residency for the lobsters (inquilinism). The lobsters represent the oldest known example of gregariousness amongst lobsters and decapods in the fossil record. Gregarious behavior in lobsters, also known for extant lobsters, thus developed earlier in earth's history than previously known. Moreover, this is one of the oldest known examples of decapod crustaceans preserved within cephalopod shells.     

Tithonian ammonoid biostratigraphy in eastern Himalayan Tibet

The Tithonian and Lower Berriasian sediments in the eastern Himalayas of Tibet contain an extensive sequence of ammonoid fauna. New collections in situ through the Lanongla, Pure, Gucuo and Jiapeila sections have facilitated a major revision of the ammonoid assemblages. Probably due to depositional facies segregation, the Belemnopsis galoi-bearing beds can be regarded as the oldest Tithonian sediments in which the basal Tithonian ammonoid Kossmatia is not present. The Lower Tithonian includes the Virgatosphinctes-Aulacosphinctoides and Uhligites-Aulacosphinctes assemblages; the Upper Tithonian includes the Haplophylloceras pingue, Blanfordiceras wallichi and Haplophylloceras strigile-Corongoceras-Himalayites assemblages. The Spiticeras assemblage is suggested to be from the Lowermost Berriasian. The new ammonoid assemblages at well-defined levels in Himalayan Tibet provide some crucial links for correlation with other regions of the SW Pacific domain where these ammonoid genera have been widely distributed.     

Rhythms of ammonoid shell secretion

From measurements of the thickness of successive growth rings shell growth curves were constructed for seven ammonoid genera of different taxonomic position and geological age. All the curves have 'sinusoidal' aspect due to the alternation of maximum and minimum growth increments of the shell tunc. Growth curves made for two ammonoid shells belonging to the genera Proloxyclymenia (D₃fm) and Euphylloceras (K₁a) show regularly recurring minima and maxima at intervals of 14–16 growth rings. The fact that the minima and maxima of the growth curves recur exactly at intervals of 14–16 growth rings seems to reflect the relationship between the shell tube secretion and the formation of septa. This fact also seems to support the views about fortnightly or 28-day cycles in the construction of ammonoid hydrostatic chambers. By counting the total number of septa in the phragmocones, the duration of phragmocone secretion for 23 shells was estimated. Preliminary inferences on the presence in ammonoid shells of daily, bidaily and weekly growth rings are made. □ Ammonoidea, growth rhythms.     

Buckman's Paradox: variability and constraints on ammonoid ornament and shell shape

Buckman's Law of Covariation states that ammonoid shell shape and ornamentation are typically correlated, such that compressed, involute forms have light ornament while more inflated, evolute forms have heavier ornament. Such covariation has been observed in many ammonoid groups, and implies a link between the morphogenesis of shell shape and ornamentation. However, other evidence suggests that while ornament growth is controlled by the genetic‐developmental program of the ammonoid, shell shape is strongly influenced by environmental factors. These differing viewpoints lead to Buckman's Paradox – are ornamentation and shell shape tightly linked, as implied by Buckman's covariation, or is the morphogenesis of ornament controlled genetically, while shell shape is controlled environmentally? To address this issue, the variability of shell shape and rib morphology has been compared for a group of endemic acanthoceratid ammonites from the Cretaceous Western Interior Seaway of North America. If Buckman's Law holds due to a morphogenetic connection between shell shape and ornamentation, we would expect taxa with more variable shell shapes to also show more variable rib features and growth. Morphometric analysis of seven shell shape and two rib characters for the Western Interior acanthoceratids finds no such correlation, suggesting that shell shape and rib growth are controlled by different processes. Indeed, rib growth appears to be more constrained than shell shape, consistent with the view that ornamentation is more tightly controlled by the developmental‐genetic growth program of the ammonoid. These results emphasize the complexity of ammonoid morphogenesis and highlight our limited understanding of the causes underlying Buckman's Law.     

Irregular calcareous sheets preserved in a conch of the Cretaceous ammonoid Hypophylloceras from Hokkaido,Japan

The mantle tissue is essential for understanding the diverse ecology and shell morphology of ammonoid cephalopods. Here, we report on irregular calcareous sheets in a well-preserved shell of a Late Cretaceous phylloceratid ammonoid Hypophylloceras subramosum from Hokkaido, Japan, and their significance for repairing the conch through the mantle inside the body chamber. The sheets are composed of nacreous layers arranged parallel to the irregularly distorted outer whorl surface. The nacreous sheets formed earlier are unevenly distributed and attached to the outer shell wall locally, whereas the last formed sheet covers a wide area of the outer shell wall. The absence of any interruption of ribbing around the irregular area suggests that these sheets were secreted inside the body chamber from the inner mantle. Gross morphological and X-ray computed tomography observations revealed that the spacing of septal formation was not affected by this event. The complex structure of the irregular sheets suggests a highly flexible mantle inside the body chamber.     

The Carboniferous carbonates of the Dombar Hills (western Kazakhstan) and the problem of the Viséan–Serpukhovian boundary

The Upper Viséan–Serpukhovian ammonoid-rich carbonates in the Dombar Hills (Aktobe Region, western Kazakhstan) provide an excellent opportunity to calibrate the ammonoid and conodont zonations around the base of the Serpukhovian Stage, and are important for interregional correlation. A section in the Dombar Hills spanning the Viséan–Serpukhovian boundary is measured and its fossil content is analyzed. Two ammonoid genozones (Hypergoniatites-Ferganoceras and Uralopronorites-Cravenoceras) and two conodont zones (Lochriea nodosa and Lochriea ziegleri) are recognized. The section displays a contact between the Hypergoniatites-Ferganoceras and Uralopronorites-Cravenoceras ammonoid genozones in a continuous succession and an evolutionarily early appearance of the genus Cravenoceras. The base of the Serpukhovian Stage is drawn at the level of the first appearance datum (FAD) of the conodont Lochriea ziegleri, which, as in the Verkhnyaya Kardailovka section (potential GSSP candidate, South Urals, Russia) enters within the Hypergoniatites-Ferganoceras ammonoid Genozone.     

The development of ammonoid septa: An epithelial invagination process controlled by morphogens?

Suture lines are important in ammonoid taxonomy. Their complex morphologies, caused by iterated invaginations of the posterior body wall, can be explained using a mechano‐chemical model inspired by modem developmental models for epithelial folding in kidneys, lungs, teeth, mammary glands and other organs. A morphogen, organized to form a regular spacing pattern by reaction‐diffusion dynamics or similar processes, induces changes in cell shape and/or rate of proliferation, causing invagination and the formation of lobes. Interactions between mechanical and chemical effects, combined with expanding size due to overall growth, produce a “fractal”; pattern of smaller (secondary) invaginations superimposed on larger (primary) ones. The pattern of increasing sutural complexity that is observed in ammonoid evolution may be a simple heterochronic effect, that allowed iterated invagination to be extended to higher and higher levels of folding. In contrast with some earlier theories, the present model is based on the view that the development of ammonoid septa must have been under relatively strict genetic control.     

New Early Carboniferous and Bashkirian Ammonoids from the eastern slope of the South Urals

In the Early Carboniferous-Bashkirian the most diverse ammonoid assemblages were associated with deep-water settings of the outer shelf and the carbonate platform slope. At the end of the Early Bashkirian, ammonoid assemblages of basins of the eastern slope of the South Urals were associated with shallow-water settings and bioherm buildups, which probably contributed to their endemism. New species of the genera Neogoniatites, Schartymites, and Stenoglaphyrites are described from localities of the eastern slope of the South Urals.     

Biodiversity and biogeography of middle–late liassic ammonoids: implications for the early Toarcian mass extinction

In Western Tethyan areas, the Toarcian stage begins with two important evolutionary events in ammonite faunas: (1) the disruption of Tethyan–Boreal provinciality; (2) a biological crisis linked with the oceanic anoxic event OAE. The analysis of these events has been addressed by constructing curves of ammonoid diversity (species richness, origination and extinction rates) in the Late Pliensbachian (= Domerian)–Early Toarcian interval in selected localities. Two diversity drops are recognized. The first one is recorded at the end of the Dactylioceras mirabile subzone and reflects the disruption of Tethyan–Boreal provinciality, through the progressive extinction of the Boreal endemic family Amaltheidae that occupied the north-western European seas during the whole Pliensbachian on the one hand, and the extinction of Late Domerian Ammonitina endemic to the Mediterranean areas on the other hand. The Early Toarcian homogeneization of Mediterranean and north-western European ammonoid faunas was reached via elimination of both Boreal and Mediterranean endemics with differential rates of extinction in the two palaeogeographic domains and the subsequent geographical expansion of Tethyan-derived ammonoids. The second, dramatic drop in ammonite diversity in the upper part of the Dactylioceras semicelatum subzone coincided with the onset of OAE. It also affected epioceanic ammonoid clades like Phyllocerataceae and Lytocerataceae. These two drops are interpreted as two distinct extinctions and not as episodes of a single, stepwise event. Complex relations between ammonoid diversity and sea-level changes are suggested by trends in endemism, which may be reversed during either a single transgression or a single regression.