New bryozoans from the Devonian-Carboniferous boundary beds of Transcaucasia

New species of Transcaucasian bryozoans are described: Primorela remota and Pseudoascopora subtilis (order Rhabdomesida) from the Upper Famennian and Anisotrypa hamata (order Trepostomida), Paranicklesopora stupenda, Euthyrhombopora barbara, Primorella testata, Ipmorella clara (order Rhabdomesida), and Taeniodictya vermiculata (order Cryptostomida) from the Tournaisian.     

Morphospace occupation in thalattosuchian crocodylomorphs: skull shape variation, species delineation and temporal patterns

Abstract: Skull shape variation in thalattosuchians is examined using geometric morphometric techniques in order to delineate species, especially with respect to the classification of Callovian species, and to explore patterns of disparity during their evolutionary history. The pattern of morphological diversity in thalattosuchian skulls was found to be very similar to modern crocodilians: the main sources of variation are the length and the width of the snout, but these broad changes are correlated with size of supratemporal fenestra and frontal bone, length of the nasal bone, size of the orbit and premaxilla and position of the narial opening. Patterns of shape variation, in combination with discrete‐state morphology and stratigraphic and geographic range data were used to distinguish nine species of teleosaurid and 14 species of metriorhynchid, with the four currently recognized Callovian species being split into eight. Metriorhynchids were found to be more disparate from the average shape of morphospace than teleosaurids. However, short‐snouted metriorhynchids and long‐snouted teleosaurids showed the greatest amount of disparity with respect to snout morphotypes, indicating that each group tended to explore opposite areas of morphospace. Phylogeny was found to have a moderate influence on the pattern of morphospace occupation in metriorhynchids, but little effect in teleosaurids suggesting that other factors or constraints control the pattern of skull shape variation in thalattosuchians. A comparison of thalattosuchians with dyrosaur/pholidosaurids shows that thalattosuchians have a unique skull morphology, implying that there are multiple ways to construct a ‘long snout’. Moreover, the skull geometry of the problematic species Pelagosaurus typus was found to converge on the teleosaurid area of morphospace. Finally, the temporal distribution of thalattosuchian species and morphotypes demonstrate a clear and highly correlated relationship with sea level curves and mass extinction events through the Jurassic and the Early Cretaceous.     

Exploring the Morphospace of Communication Efficiency in Complex Networks

Graph theoretical analysis has played a key role in characterizing global features of the topology of complex networks, describing diverse systems such as protein interactions, food webs, social relations and brain connectivity. How system elements communicate with each other depends not only on the structure of the network, but also on the nature of the system''s dynamics which are constrained by the amount of knowledge and resources available for communication processes. Complementing widely used measures that capture efficiency under the assumption that communication preferentially follows shortest paths across the network (“routing”), we define analytic measures directed at characterizing network communication when signals flow in a random walk process (“diffusion”). The two dimensions of routing and diffusion efficiency define a morphospace for complex networks, with different network topologies characterized by different combinations of efficiency measures and thus occupying different regions of this space. We explore the relation of network topologies and efficiency measures by examining canonical network models, by evolving networks using a multi-objective optimization strategy, and by investigating real-world network data sets. Within the efficiency morphospace, specific aspects of network topology that differentially favor efficient communication for routing and diffusion processes are identified. Charting regions of the morphospace that are occupied by canonical, evolved or real networks allows inferences about the limits of communication efficiency imposed by connectivity and dynamics, as well as the underlying selection pressures that have shaped network topology.     

Sedimentary and biofacies records in calciturbidites at the Devonian-Carboniferous boundary in Moravia (Moravian-Silesian Zone, Middle Europe)

Summary At the Devonian/Carboniferous boundary, major climatic and oceanographic changes influenced sedimentation on carbonate platforms and in peri-platfrom asreas. Three deep-water carbonate successions in Moravia, which were selected to represent different paleotectonic settings, have been studied with the aim of testing the influence of eustatic, climatic and tectonic controls on sedimentation and conodont paleoecology and taphonomy. On the slopes of the wide carbonate platforms of the Moravian Karst Development (Lesní lom and Grygov sections), an exemplary highstand shedding systems developed in the upper Famennian (expansa Zone), marked by a pronounced thickness of their respective calciturbidite successions and an abundance of shallow-water skeletal grains.Palamatolepis— andBispathodus-dominated conodont assemblages contain an admixture ofPolygnathus representing a transported, near-shore component. The eustatic sea-level fall in the praesulcata Zone and the lowstand conditions at the D/C boundary resulted in a decline of carbonate platform production and condensed deposition or nondeposition. In the Lesní lom section, a condensed sequence of turrbiditic calcarenites and shales (Middle praesulcata—lowermost sulcata Zone) was followed by lime mud calciturbidites (sulcata and duplicata Zones). In the conodont assemblages, the first event in the Lower praesulcata Zone was associated with the reduction of ‘mesopelagic’Palmatopic and a bloom of epipelagicPolygnathus communis. The second event in the Middle praesulcata Zone corresponds to the onset of polygnathidprotogranthodid biofacies, indicating a carbonate slope environment. In the Grygov section, a pronounced thickening and upward-coarsening succession of tubiditic calcilutites through calcarenites and intraclast breccias, with poor palmatolepid-bispathodid connodont assemblages (expansa Zone), indicates a progradation of the calciturbidite system associated with sea-level highstand. After a break in sedimentation, covering the interval from the Lower praseulcata to the base of Lower crenulata Zone, thick-bedded, fine-grained calciturbidites were deposited in the Lower crenulata Zone, and are associated with poor, mixed assemblages where siphonodellids and polygnathids predominate. At the isosticha-Upper crenulata/Lower typicus boundary, coasre grained, turbiditic calcarenites and breccias rich in clastic quartz grains and mixed conodont assemblages with reworked Frasnian and Famennian conodonts indicate a deep erosion of the source area, presumably due totectonic uplift (relative lowstand). In the Jesenec section, on the flanks of the volcanic seamount (the Drahany Development), a deep-water Upper Famennian condensed succession of calciturbidites and presumably winnowed pelagic limestones is marked by conodont assemblages of palmatolepid-bispathodid biofacies. More proximal calciturbidites with mixed deep-water and shallowwater conodonts prograde at the top of the Upper Famennian succession (Middle to Upper expansa Zone). A striking hiatus, covering the interval from the Early preaesulcata to the base of Lower crenulata Zone, resulted from extreme condensation and submarine bottom current erosion due to sea-level lowstand in the late Famennian and early Tournaisian. The renewed middle Tournaisian calciturbidite sedimentation with strong evidence of erosion at the source area indicates global eustatic rise and tectonic uplift of the Drahany Development seamounts (relative lowstand). The earlier occurrence of the uplift in the Jesenec area, relative to the Grygov section, shows the advance of tectonic processes over time in the Moravian-Silesian basin (orogenic polarity) as a consequence of Variscan orogenic movements.     

Ecological structure of Paleozoic ammonoids

Ecological specialization of Paleozoic ammonoid orders is discussed along with changes in the ecological structure of the ammonoid assemblages in the Early Devonian-Late Permian. Two large cycles of change in the ecological structure, Devonian and Carboniferous-Permian are recognized.     

Life-cycles of some Devonian ammonoids

Whorl expansion rates of six representative ammonoid genera from late Emsian and Eifelian strata of Morocco were calculated for each whorl. The corresponding body chamber lengths and the orientations of the apertures were computed based on these values. The resulting body chamber length and orientation of the aperture graphs were compared with other conch features, ecology of Recent cephalopods, and sedimentological data of the host rocks in the Tafilalt (eastern Anti-Atlas, Morocco). A subdivision of the ontogeny of these ammonoids was achieved comprising the early and late embryonic periods, the juvenile period, the preadult, and the adult growth period. All growth periods are defined by specific changes in growth, conch morphology, and mode of life. According to this reconstruction, hatchlings were probably already capable of active movements. Differentiation in two main modes of life of the examined taxa occurred in the late juvenile or early preadult period. As preadult animals, most of the Mimagoniatitoidea and Agoniatitoidea became active swimmers (Nektonic), whereas the representatives of the Anarcestoidea were capable of slow movements only (Planktonic). As adults, most representatives of the three superfamilies had an approximately horizontally oriented aperture, allowing active swimming and possibly active choice of spawning sites. Additionally, the new ammonoid taxon Rherisites tuba gen. nov., sp. nov. from the late Emsian is introduced.     

The Cranial Morphospace of Extant Marsupials

Journal of Mammalian Evolution - Marsupials represent a major mammalian diversification today restricted geographically to the Americas (but chiefly to the Neotropical Region) and Australasia. The...     

Quantification of ontogenetic allometry in ammonoids

Ammonoids are well‐known objects used for studies on ontogeny and phylogeny, but a quantification of ontogenetic change has not yet been carried out. Their planispirally coiled conchs allow for a study of “longitudinal” ontogenetic data, that is data of ontogenetic trajectories that can be obtained from a single specimen. Therefore, they provide a good model for ontogenetic studies of geometry in other shelled organisms. Using modifications of three cardinal conch dimensions, computer simulations can model artificial conchs. The trajectories of ontogenetic allometry of these simulations can be analyzed in great detail in a theoretical morphospace. A method for the classification of conch ontogeny and quantification of the degree of allometry is proposed. Using high‐precision cross‐sections, the allometric conch growth of real ammonoids can be documented and compared. The members of the Ammonoidea show a wide variety of allometric growth, ranging from near isometry to monophasic, biphasic, or polyphasic allometry. Selected examples of Palaeozoic and Mesozoic ammonoids are shown with respect to their degree of change during ontogeny of the conch.     

On Frasnian ammonoids of the New Siberian Islands

Ammonoids from the basal beds of the Nerpalakh Formation (Lower Frasnian) of Belkovsky Island (New Siberian Archipelago) are systematically studied. Taxonomically, the assemblage studied (Manticoceras insulare sp. nov., Tornoceras typum (Sandberger, 1851), and T. contractum Glenister, 1958) is similar to the Early Frasnian ammonoid assemblage of South Timan, from which its is distinguished by the absence of the genera Timanites and Komioceras. The same beds contain conodonts of the Palmatolepis transitans Zone (= MN 4 Zone of the Montagne Noire standard succession), which allow the correlation of the beds studied with the Timanites keyserlingi and Komioceras stuckenbergi ammonoid zones of South Timan. The Early Frasnian ammonoids could supposedly have entered the region of the New Siberian Archipelago from the southwest at the time of a major transgression, which facilitated the distribution of the genera Manticoceras and Tornoceras. A new species of the genus Manticoceras is described.     

Biogeographic evolution of Permian ammonoids

The distribution of Permian ammonoids within the five major biogeographic provinces (Arctic, Uralian, American, Tethyan, and Australian) is discussed. Changes in the taxonomic and biogeographic structure of assemblages according to stages in the evolution of Permian ammonoids are considered for each region. It is shown that the geographical distributions and taxonomic diversity of ammonoids changed continuously throughout the Late Permian.     

The mode of life in ammonoids

The following structural features clearly indicate that ammonoid shells were adapted to withstand considerably higher hydrostatic pressures thanNautilus shells: (1) the corrugated and marginally fluted septa gave the shell wall efficient support against implosion; (2) the secondary connecting rings could grow a great deal in thickness; and (3) the last formed chambers remained full of liquid which supported the last septum. On the basis of the following characters it is concluded that ammonoids were incapable of swimming efficiently by jet-propulsion: (1) the retractor muscles were weakly developed; (2) the life position was unstable and highly variable; and (3) in animals with a ventral apertural rostrum the hyponome was probably absent. Ammonoids are considered here as having been pelagic cephalopods which lived in the upper 1000 m of the oceans, and which probably undertook considerable diurnal vertical migrations, similar to those inSpirula. Only some groups may have adopted a life in shallow epicontinental seas. In the late Mesozoic, ammonoids have been replaced by modern oceanic squids which are extremely numerous in the corresponding pelagic environment.     

Permian ammonoids of the Kolyma-Omolon Region: Ogonerian association

The Ogonerian association of Early Permian ammonoids from the Upper part of the Munugudzhakian Formation (upper part of the Ogonerian Horizon) contains Uraloceras omolonense Bogoslovskaya et Boiko, U. kolymense Bogoslovskaya et Boiko, Neoshumardites munugudzhensis sp. nov., N.? nassichuki sp. nov., and Bulunites gracilis sp. nov. These taxa suggest the Sakmarian-Artinskian boundary beds examined are geochronologically older than the level with Neoshumardites triceps Ruzhencev in the South Ural Mountains.     

Soft-part anatomy of the siphuncle in Permian prolecanitid ammonoids

Exceptionally well-preserved remains of phosphatized siphuncles were discovered in four specimens of a Permian prolecanitid ammonoid Akmilleria electraensis (Plummer and Scott) from Buck Mountain, Nevada. These structures occur as truncated segments within the siphuncular tube. The outer surface of the siphuncle is sculptured by numerous equally spaced longitudinal ridges and furrows; the ridges represent an infolded basement membrane of epithelial cells which corresponds to the distal ends of individual canaliculi between epithelial cells. In cross-section, the siphuncle of A. electraensis consists of a large central vein, possibly two pairs of arteries, porous connective tissue with reticulate hemocoelic spaces, and a thin epithelium. In the presence of two pairs of arteries and porous connective tissue, the siphuncle of A. electraensis is more like that of Nautilus pompilius than that of Spirula spirula, which has nine arteries and dense connective tissue. However, Nautilus possesses relatively smaller and more numerous epithelial cells around the siphuncle than does Akmilleria. These observations strongly suggest that the siphuncular epithelium of Akmilleria served as the salt-­concentrating organ for buoyancy regulation of the living animal, just as in Nautilus and Spirula.     

Major trends in the evolution of Permian ammonoids

The phylogeny of major families of Permian ammonoids is analyzed. The evolution of most families followed a typical scenario with distinct stages of early evolution, diversification, and decline. A smaller group followed a different evolutionary narrative, with indistinct stages. The former group includes families with both simple and complex morphology and a wide range of variation. The nature and trends in the evolution of the families may change depending on their phylogenetic stage. The Early Permian (Asselian), the second half of the Artinskian, and the beginning of the Middle Permian were marked by the most significant evolutionary changes. The Late Permian was the time of the decline of Paleozoic ammonoid orders and of the onset of the evolution of the Mesozoic order Ceratitida.     

Role of heterochronies in the morphogenesis of paleozoic ammonoids

Various types of evolutionary changes related to shifts in the appearance or order of formation of characters, i.e., heterochronies are shown. The most common such changes in Paleozoic ammonoids was the appearance of mosaic forms combining conservative and advanced characters resulting from recapitulation and paedomorphosis. These phenomena are related to certain phylogenetic stages in each group: the growth stage predominantly showed recapitulations; the diversification stage showed the appearance of many mosaic forms; the decline stage commonly shows paedomorphosis connected with retardation.