Power scaling of ammonitic suture patterns from Cretaceous Ancyloceratina: constraints on septal/sutural complexity

The spatial scaling of 77 hemisutures from 65 species of Cretaceous heteromorphic ammonites was quantified with the fractal box‐counting method. Fractal dimensions within Baculites compressus did not significantly differ between adult hemisutures; however, the juvenile suture of this species did exhibit a significantly lower fractal dimension. This suggests that variation in sutural complexity between explicitly adult ontogenetic stages may not contribute to significant noise in comparisons between other species/morphotypes. High‐spired, three‐dimensionally coiled heteromorphs with a larger degree of septal asymmetry exhibit higher fractal dimensions in outer whorl hemisutures than inner whorl hemisutures due to their elongation and improved space occupation over a larger whorl surface. Three‐dimensionally coiled ammonites also have higher fractal dimensions on average (mean D_b = 1.45) with respect to their 2‐D coiled counterparts (mean D_b = 1.38). All ammonites in this study exhibit a positive trend between sutural complexity and shell size (proxied by whorl height). These relationships suggest that septal frilling is constrained by shell morphology and whorl section geometry during septal morphogenesis. This, in turn, influences the scaling, space‐filling properties and scaling limits of ammonitic suture patterns. Sutural/septal complexity is also found to positively influence the amount of liquid retained in marginal septal recesses. However, as these septa approach larger scales, less cameral liquid is retained per septal mass. This may further explain the positive relationship between sutural complexity and shell size.     

Shell features, main colonized environments, and fractal analysis of sutures in Late Jurassic ammonites

A precise approach to the quantification of relationships between suture complexity, as measured by fractal analysis (step-line procedure), the architecture of shells, and the main colonized environments, has been made in a set of Late Jurassic ammonites ( N =507). Statistically significant differences between fractal-dimension ( D _f) mean values of evolute and involute shells are interpreted as caused by differences in the surface:volume ( S:V ) ratio. Suture complexity is also related to the shape of whorl section. The lowest D _f values correspond to subcircular whorl sections (low S:V ratio) and the highest ones to acute sections (high S:V ratio). The shape of flanks shows correlation with suture complexity. The highest values of D _f are found in planulate shells and the lowest ones in whorl cross sections with convex flanks. Highly significant differences appear between D _f mean values from unsculptured shells and those from ammonites with ribs and/or tubercles of medium to large size. Multivariate analysis shows a combined variation of shell features and suture complexity, resulting in a heterogeneous distribution of D _f values within the ammonite morphospace, mainly according to structural (shell architecture) and ornamental (sculpture strength rather than density) factors. Finally, the data obtained on relationships between suture complexity and the colonized environments (epicontinental vs. epioceanic inhabitants) suggest that suture complexity is not primarily related to bathymetry, and/or that no major differences in habitat depths existed between epicontinental and epioceanic ammonites.     

Morphostructural constraints and phylogenetic overprint on sutural frilling in Late Jurassic ammonites

The functional significance of frilled septa and complex sutures in ammonoids has generated ongoing debate. The 'classic' hypothesis envisages ammonoid shells and septa as designed for resisting ambient hydrostatic pressure, complex sutures being the evidence of strength in shells for colonization of deep habitats. Here we address the 'suture problem', focusing on the analysis and interpretation of variables in our database of Late Jurassic ammonites not included in previous studies, such as whorl height ( W h ), whorl shape ( S ), shell coiling ( WD ), taxonomic grouping and basic planispiral shell shape. The results indicate that sutural complexity, as measured by the fractal dimension ( D f ) value of the suture line, is positively correlated with W h , and that the sutures of oceanic shells tend to provide, for a given W h value, lower D f estimates than do those of neritic shells. No general trend of increase in sutural complexity was noted for specimens recovered from swell areas belonging to oceanic fringes with respect to those that inhabited epicontinental shelves. In fact, Perisphinctoidea, the clade best represented in the database analysed, shows a higher D f mean value in neritic species than in epioceanic ones. Significant differences in sutural complexity were detected for groups of ammonites classified according to shell shapes ( WD , S ). Oxycones and discocones, streamlined potential swimmers, show the highest D f mean values, while spherocones and cadicones, which were presumably vertical vagrants, present the lowest ones. This indicates that sutural complexity was more related to shell geometry than to bathymetry.     

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.     

Breeding latitude and timing of spring migration in songbirds crossing the Gulf of Mexico

Each spring, millions of songbirds migrate across the Gulf of Mexico on their way to breeding sites in North America. Data from radar and migration monitoring stations have revealed broad patterns in the spatial and temporal course of trans-Gulf migration. Unfortunately, we have limited information on where these birds have previously spent the winter and where they are migrating to breed. Here we measure stable-hydrogen isotopes in feathers (δD_f) to infer the breeding latitude of five species of songbirds – hooded warblers Wilsonia citrina , American redstarts Setophaga ruticilla , black-and-white warblers Mniotilta varia , ovenbirds Seiurus aurocapilla , and northern waterthrushes S. noveboracensis – that were captured at a stopover site along the coast of southwestern Louisiana in spring 2004. Values of δD_f across all species ranged from −163 to −35‰ (n=212), and within most species the range was consistent with the latitudinal extent of known breeding sites in central and eastern North America. Individuals that arrived first along the northern Gulf coast had δD_f values indicative of southerly breeding sites in hooded warblers, American redstarts, black-and-white warblers, and ovenbirds, but no relationship was found between passage timing and δD_f for northern waterthrushes. Our findings suggest that spring passage is often timed to coincide with the emergence of suitable conditions on breeding areas, with southern breeding birds migrating first.     

Mechanical significance of ammonoid septa with complex sutures

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.     

Taphonomy and ichnology of cephalopod shells in a Maastrichtian chalk from Western Australia

The post-mortem history of a prolific Maastrichtian ammonite and nautiloid fauna preserved as phosphatic steinkerns in chalk of the upper Miria Formation of Western Australia is described. Sediment infilling of phragmocones, required for their fossilisation, was accomplished by means of perforations in the shell wall induced by the activity of abundant endoliths. These include borings ascribed to clionid sponges (Entobia), thallophytes, polychaete worms (including Caulostrepis and probable Maeandropolydora), phoronids (Talpina and Gnathichnus) and others of conjectural origin. Sediment infilling by this mechanism is considered to be more applicable to the taphonomy of phragmocones in general than sediment entry through the siphuncle and to be indicative of low sedimentation rates for the hosting strata. Nonheteromorph ammonites, and the nautiloid Cimomia, are preserved almost exclusively as phragmocones in the upper Miria Formation, and are numerically subordinate to the heteromorph Eubaculites which, together with Glyptoxoceras, is preserved predominantly as body chambers. This phragmocone/body chamber preservational contrast is attributed to the influence of shell shape on pre-burial mechanical abrasion. The apparent dominance of Eubaculites is considered to be largely a preservational artifact and ascribed to the ease with which body chambers were infilled, and thereby favoured for steinkern formation, relative to phragmocones. Phragmocones, or parts thereof. not filled with sediment were eliminated from the fossil record by diagenetic aragonite dissolution. Many ammonites with open umbilici have the early whorls missing. This we attribute to the trapping of sediment in the umbilicus prior to burial, preventing endolith attack whereby the early whorls avoided a sediment infilling. However, the protected inner whorls of involute ammonites and Cimomia, which have closed umbilici, and the inner whorls of evolute ammonites where a cemented umbilical plug supported the mouldic cavity left by shell dissolution, were preserved and were commonly infilled with calcite spar later in diagenesis. The dearth of cephalopod fossils in chalk underlying the upper Miria Formation is ascribed to diagenesis in which aragonite dissolution was not preceded by cementation.     

Preferential predatory peeling: Ammonoid vs. nautiloid shells from the Upper Carboniferous of Texas,USA

Narrow groove-like excavations on ammonoid and coiled nautiloid shells are rare in Upper Carboniferous units from Texas, USA. The morphological characteristics of the excavation grooves typically are confined to the ventral and ventrolateral parts of the outer whorl of the shell, are narrower than the length, and have irregular edges where small segments or chips of shells have been removed. Analysis of these features reveals a statistically significant preferential occurrence on ammonoids (1.195% of ca. 3515 specimens) as compared to coiled nautiloids (0.506% of ca. 2965 specimens). The ammonoids typically have longer excavations that penetrate the phragmocone more frequently than those observed in the coiled nautiloids. The groove-like excavations were probably formed by the removal and peeling of shell material by one or more predatory or scavenging arthropods to obtain organic material (tissue and membranes) within the ammonoid and nautiloid body chambers and phragmocones. The excavations probably occurred when the cephalopod was alive (i.e., the cause of death) or shortly after the cephalopod's death. There is no evidence that the excavations are related to sheltering by the excavating organism.     

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.     

The role of suture complexity in diminishing strain and stress in ammonoid phragmocones

Several hypotheses have been put forward to explain the sinuosity and complexity of suture lines in Ammonoidea. At present, the two principal opponent views maintain either that high complexity was a requisite to reinforce the shell in response to hydrostatic pressure, or that complexity augmented the attachment area for muscles. By using finite element calculations and analytical estimates of simplified ammonoid shell geometries, it is shown that complex suture lines reduced dramatically the strain and the stress in the phragmocone. The calculations lend support to the hypothesis that high sinuosity is an evolutionary response to external pressure. Additionally, it is found that without complex septa, the inward deformation of an ammonoid with thin shell would cause it to shrink in response to pressure and to lose buoyancy by a non-negligible amount.     

Sutural complexity and bathymetry in ammonites: fact or artifact?

The widespread assumption that sutural complexity in ammonites is mainly proportional to water depth is revisited. Fractal analysis has been used for the precise morphometric evaluation of sutural complexity in 131 Upper Jurassic ammonites. Suture lines belonging to twelve families have been analyzed, account being taken of shell structure (coiling, shape of whorl section), sculpture and paleoenvironments. Fractal dimensions obtained in epicontinental and epioceanic ammonites show the unlikelihood of precise relationships between suture complexity and depth, and/or the absence of major differences in habitat depth if bathymetry played any significant role in the configuration of intricate septa. Suture complexity appears to be better related to shell structural types. □ Fractal analysis, ammonite sutures, Upper Jurassic.     

The A-mode sutural ontogeny in prolecanitid ammonoids

The generally accepted theory of a U-mode sutural ontogeny of prolecanitid ammonoids and their descendants is refuted. The basic suture formula of the order Prolecanitida is E A L U I (not E L U₂ U₁ I), resembling that of derived members of the suborder Tornoceratina (their phylogenetic ancestors), and of the suborder Goniatitina. During phylogeny of the prolecanitids, secondary umbilical lobes are introduced and lead to multilobate forms. In early ceratites, the original L lobe disappeared, and an increase in sutural elements took place by the introduction of supplementary U lobes. Consequently, sutural nomenclature of Permian ceratites and Mesozoic ammonoids has to be modified.     

Correlation among dominance status, metabolic rate and otolith size in masu salmon

In spatial competition between individuals, neither fish sex nor body mass affected dominance status in masu salmon Oncorhynchus masou . In contrast, resting metabolic rate ( M _R) was significantly correlated with dominance status, indicating that a high metabolic rate can increase the dominance rank of juvenile salmon. Whole animal growth rate was significantly correlated with M _R, but not with initial body weight. This suggests that the body size of masu salmon is not a cause, but rather a consequence, of dominance status which is closely related to M _R. The increment width between otolith daily rings was also significantly correlated with M _R. Thus, the size of the Otolith may indicate the degree of M _R.     

Response to conspecific and heterospecific alarm cues by pumpkinseeds in simple and complex habitats: field verification of an ontogenetic shift

Three focal size classes [small (<40 mm, standard length, L _S), medium (40–80 mm L _S) and large (>80 mm L _S)] of pumpkinseed Lepomis gibbosus were exposed to conspecific or one of three heterospecific chemical alarm cues under one of three levels of habitat complexity (low, intermediate and high). Under low and intermediate habitat complexities, pumpkinseeds <80 mm L _S exhibited a significant antipredator response when exposed to the chemical alarm cues of heterospecific prey guild members (largemouth bass Micropterus salmonides and hypoxanthine‐3‐ N ‐oxide, the putative Ostariophysan alarm 'pheromone'), while pumpkinseeds >80 mm L _S exhibited a foraging response. Under highly complex habitats, pumpkinseeds of all three size classes exhibited an antipredator response. Moreover, under all three habitat conditions, pumpkinseeds of all size classes exhibited an antipredator response to conspecific alarm cues. There was no change in behaviour under any treatment combination in response to an allopatric heterospecific control (swordtails Xiphophorus helleri ). These results provide the first field verification of the size dependent use of chemical alarm cues by centrarchids and demonstrate that microhabitat complexity significantly influences the threat‐sensitive use of these cues.     

Can ribs and septa provide an alternative standard for age in ammonite ontogenetic studies?

In ammonites, the time between two successive septal secretions is assumed to be almost stable during growth within homogeneous sets with regard to phylogeny and morphology. The number of septa (included in the adult phragmocone) is proposed as an alternative standard for age. At each moment of growth, the rate of shell secretion can be directly estimated by the measure of shell length between two septa. Equivalent results are obtained for ribs whose formation is also dependent on an almost stable rhythmical process. Results obtained from septa and size used as age standards are compared in the example of Liparoceratidae-Amaltheidae evolution. The two standards provide estimations of age which diverge from more than 1 to 2. For example, some small species previously seen as progenetic are now classified as dwarfed. These results emphasize the risk of using size as the only standard of age. Alternative standards not only in ammonites but also in other animal groups should be investigated.     

Taphonomic differentiation of Oxfordian ammonites from the Cracow Upland, Poland

Taphonomic analysis of Lower and Middle Oxfordian ammonites from the Cracow Upland, southern Poland (localities at Pod???e, Zalas, M?ynka) revealed differences in ammonite preservation. The studied ammonites, usually termed as external and internal moulds, show a more complex state of preservation. In the Middle Oxfordian glauconitic marls, ammonites are preserved as internal moulds with neomorphic calcite shells showing relics of the original internal structure. In the Middle Oxfordian platy peloidal limestones, ammonites are preserved mostly as external moulds, without septal suture, however under microscope might show relics of internal whorls and septa and/or subtle differences in sediment filling phragmocone chambers. In sponge–microbial bioherms and biostromes, ammonite internal moulds have shells, which in contrast to ammonites from glauconitic marls are not strictly neomorphic ones, but originated by shell dissolution and subsequent filling of moldic porosity by calcite cement. In sponge–microbial nodular limestones, the ammonites are strongly deformed and the outer wall is usually removed by dissolution under pressure. Other important taphonomic differences include the rate of compaction (highest in platy limestones), sedimentary infillings, microborings, encrustations and preservation of siphuncular tubes. The majority of the ammonites appear to be phragmocones; aptychi in all facies are rare. Siphuncular tubes are fossilized exclusively in oppeliids, only in specimens from glauconitic marls and platy limestones, although their other taphonomic attributes are different. Tubes seem to have fossilized due to microbially mediated phosphatization that could be favoured by a set of parameters which operated rather at the scale of ammonoid carcasses: closed, poorly oxygenated conditions, and reduced pH. Taphonomic processes were controlled by the sedimentary environment (fragmentation, sedimentary filling, phosphatization of siphuncular tubes), as well as by early and late diagenesis (neomorphic transformation, dissolution, cementation, compaction) influenced by lithology.     

Observations on the shell morphology of two species of cockle Cerastoderma edule and C. glaucum

Aspects of the shell morphology of the cockles Cerastoderma edule (L.) and C. glaucum (Poiret) collected from the R. Crouch and R. Roach (Essex, England) are considered with reference to interpretation of the environment of sub-fossil assemblages. Discrimination between the two cockle species is best achieved by assessment of qualitative shell characters, quantitative measurements being of rather limited value. Factors influencing shell rib-number differ in the two species of Cerastoderma; within a common environment C. glaucum has fewer ribs than C. edule . Mean rib-number of C. edule is directly related to salinity over the colonized salinity range 20–36.5%₀ whilst in C. glaucum rib-number is lowest in both low (<10%₀) and high (>35%₀) salinity environments, being maximal where salinities between 20–30%₀ occur. Internal shell pigmentation may be absent in C. glaucum from low salinity environments. Magnesium content of whole shells is similar in the two cockle species from a mixed population. In both cockles, however, the prismatic layer contained more magnesium than the nacreous shell layer. The most useful molluscan indicators of brackish water lagoon environments are C. glaucum and Hydrobia ventrosa; these species being absent from areas of only limited wave action. C. edule may be associated with marine or estuarine molluscan indicators.     

Composition and ontogeny ofDictyoconites (aulacocerida,cephalopoda)

Dictyoconites from the middle Triassic Cassian Formation is a characteristic representative of the Aulacocerida. Embryonic development and construction of the phragmocone is like that of Jurassic belemnites. The siphuncular tube is double-walled with a long retrochoanitic mineralized septal neck continuing into an organic tube. The extended decoupling zone resembles that ofSpirula. Characteristic ofDictyoconites are the tubular »living chamber« and two layered deposits of the muscular mantle on the phragmocone. The Triassic coleoid was a slender squid with visceral mass and mantle cavity encapsuled in shell and the whole conch covered by muscular mantle extending in two lateral apical fins attached to the aragonitic rostrum.     

河北秦皇岛地区奥陶纪奇壁角石科分子的发现及意义

奇壁角石科（Ａｌｌｏｔｒｉｏｃｅｒａｔｉｄａｅ）分子在我华北东部属首次发现。它产于马家沟组下部。界于Ｄｅｆｏｒｍｏｎ－ｃｅｒａｓ－Ｐｅｒｉｐａｔｏｃｅｒａｓ与Ｐｏｌｙｄｅｓｍｉａ－Ｗｕｔｉｎｏｃｅｒａｓ－Ｅｏｓｉｏｔｅｌｕｓ组合带之间偏下。奇壁角石科是Ｆｌｏｗｅｒ,Ｒ．Ｈ．１９９５年创立的,至今科内已建立６属１３种和３个相似种。但以往所描述标本绝大多数仅保存有部分内体管,对其它特征所知甚少。文中描