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.     

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.     

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.     

Sectorial expansion and shell morphogenesis in molluscs

Checa, A. 1991 01 15: Sectorial expansion and shell morphogenesis in molluses. Lethaia . Vol. 24, pp. 97–114. Oslo. ISSN 0024–1164.
Any coiled shell can be described as a series of independent helicospirals that join homologous points along the shell surface. The cross-section is therefore seen as a set of points. obtained at its intersection with the helicospirals. Any cross-sectional sector contained between two adjacent points is capable of expanding or contracting during the development and a differential parameter ( L'/L ) has been devised to quantify this expansion rate. The morphometrics so obtained is here called sectorial expansion analysis. This analysis and other related procedures have been applied on cross-sections and apertures in selected Molluxa with the aim of evaluating the incidence of sectorial expansions on shell shape. Those parameters affecting whorl expansion rate and whorl overlapping may be directly modified by sectorial expansions. Changes in the mode of coiling (curvature and torsion) often, but not always, involve sectorial expansions, perhaps as a constructional feature. This approach reveals the advantages and drawbacks of the present analysis as compared to previous theoretical models. Sectorial expansion. morphogenesis. ornamentation, septal suture, coiled shell, gastropods, bivalues. ammonites .     

Sutural amplitude of ammonite shells as a paleoenvironmental indicator

The Sutural Amplitude Index (SAI), obtained by measuring the maximum height of sutural elements and the length of the suture pattern on ammonoid shells, provides a useful indicator of relative habitat depth for ammonoids with similar shell morphotypes. A higher SAI indicates greater septal support for the shell wall against implosion under increased hydrostatic pressures in deeper waters. Relating the sutural amplitude indices of ammonites found in a well-studied depositional basin, such as the Cretaceous Western Interior Seaway, to morphotype distributions illustrates the utility of this index in bathymetric interpretations. □ Ammonoidea, sutures, Sutural Amplitude Index, Cretaceous, Greenhorn Cyclothem. Western Interior.     

Fractal analysis of the Orce skull sutures

Methods of fractal geometry (Mandelbrot, 1983) are used here to analyse the relative complexity of the sagittal and lambdoid sutures visible in the skull fragment formed by parts of an occipital squame and parietals found in a sealed deposit at the early Lower Pleistocene site of Venta Micena (Orce, Granada, Spain), generally regarded as human bone but occasionally suggested as belonging to an equid. For comparison with the fossil, corresponding sutures of various primates (hominids, pongids and cercopithecids) and two other groups of mammals (equids and ruminants) were analysed using the computer program FRACTAL-D (Slice, 1989) in order to determine their fractal dimensions as a measure of differential sutural design complexity. The results show that the fractal dimension of the Venta Micena skull sutures lies within the range of variation for infant specimens of both modern and Plio-Pleistocene hominids. Sutural complexity in young pongids and cercopithecids overlaps the range of fractal dimensions found in hominids, whereas values obtained from equids and ruminants are significantly greater than those for all the primates analysed here. Therefore, in terms of fractal dimension measures of relative complexity, the sutures preserved in the Venta Micena fossil could not have belonged to an equid (pace Agusti & Moyà-Sola, 1987); rather, its fractal dimension is consistent with the attribution of the fossil to an infant of Homo sp.     

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.     

Floral biology,reciprocal herkogamy and breeding system in four Psychotria species (Rubiaceae) in Brazil

Distylous species have two floral morphs with reciprocal positions of sexual whorls, functioning to promote cross‐pollination. Additionally, most distylous species have an incompatibility system linked to the discrete variation of anthers and stigmas. Here we provide new data on heterostyly, reproductive biology and pollination in four Psychotria spp. from the Cerrado Region (Brazil). Psychotria deflexa, P. nitidula and P. trichophoroides fitted the distylous morphological syndrome, whereas P. prunifolia was monomorphic and self‐compatible. Reciprocity varied across species, with the upper whorl of anthers and stigmas being more reciprocal than the lower whorl. Psychotria nitidula has a heteromorphic incompatibility system, whereas P. deflexa and P. trichophoroides showed partial self‐compatibility. Psychotria prunifolia and P. trichophoroides were visited by large bees and exhibited lower reproductive efficacy than P. nitidula and P. deflexa, which are visited by wasps and small bees. Our results provide new evidence that the morphological distylous syndrome does not always co‐occur with heteromorphic incompatibility and additional mechanisms (e.g. disassortative pollen transfer) may operate to maintain the polymorphism and isoplethy of species with different incompatibility system.     

Reappraisal of the latest Albian (Mortoniceras fallax Zone) cephalopod fauna from the classical Salazac locality (Gard,southeastern France)

The Salazac locality (Gard, southeastern France) is renowned for the richness of its cephalopod fauna (especially ammonites) from the Mortoniceras fallax Zone (uppermost Albian, Lower Cretaceous). However, most ammonite species have paradoxically been scarcely illustrated up to now. Furthermore, the rare assessments of ammonite taxonomic diversity are presumably inaccurate, as they either result from a drastic typological approach or could not benefit from the most recent advances in modern concepts of ammonoid intraspecific and ontogenetic variations. In this work, we document an original cephalopod assemblage from Salazac represented by abundant, well-preserved specimens (564 studied ammonites, including ca. 50% of heteromorphs) constituting a high diversity. The sample size and quality of this new material allowed some extensive morphological and biometric analyses whenever possible (i.e., for subdatasets in which a significant number of measurements is available) and to thoroughly assess intraspecific and ontogenetic variations for a few species. This led to determine the diagnostic value of various shell characters commonly used to characterize both well-documented and poorly-defined species. In particular, we show that a significant part of the variation in the number of ribs per whorl within the heteromorphic genera Mariella and Turrilitoides is directly related to shell size and that the strength of tubercles covaries negatively with the number of ribs in Mariella, therefore challenging the diagnostic value of these characters. We further suggest that rib density covaries with whorl shape in Mariella, following Buckman’s first rule of covariation. In total, one species of nautilid and 38 taxa (25 genera) of ammonites are described, among which five species are documented from Salazac for the first time. In turn, this study provides valuable data for future phylogenetic, biostratigraphical, biogeographical and broad-scale diversity studies.     

Septal implosion in Late Carboniferous coiled nautiloids from Ohio

Mapes, R.H. & McComas, G.A. 2010: Septal implosion in Late Carboniferous coiled nautiloids from Ohio. Lethaia, 10.1111/j.1502–3931.2009.00213.x More than 200 relatively mature coiled nautiloid specimens, assigned to Metacoceras mcchesneyi, were recovered from an Upper Carboniferous shale in northeastern Ohio. Twenty‐seven undistorted specimens reveal that the septa in every specimen were collapsed and/or telescoped. This septal collapse without external shell distortion could only have been accomplished by limited implosion due to excessive pressure. Analysis of the fossils, sediment and the depositional environment indicate that after burial, the nautiloid cameral spaces were probably filled with both liquid and gas, and the body chamber was filled with semi‐solid thixotropic mud. To prevent conch collapse at the time of septal implosion, the thixotropic mud filling the nautiloid body chamber acted as a liquid at the time of stress release during septal failure. The stress was produced by combined lithostatic and hydrostatic pressures, which fluidized the unlithified thixotropic mud that flowed from the body chamber into the phragmocone during septal collapse. After the septal implosion and when flowage ceased, the thixotropic mud quickly resolidified into a solid state providing internal conch support that prevented the collapse of the conch. □Carboniferous, nautiloids, septal implosion, taphonomy, thixotropic mud.     

Sclerochronological study of the gigantic inoceramids Sphenoceramus schmidti and S. sachalinensis from Hokkaido,northern Japan

Here, we present the first sclerochronological investigation of shells of the gigantic inoceramids Sphenoceramus schmidti and S. sachalinensis from the middle Campanian cold seep carbonate‐bearing strata of the Yezo Basin in Hokkaido (northern Japan). Stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotope values were measured in the aragonitic and calcitic shell layers of both species and compared to those of other co‐occurring benthic (mainly bivalves and gastropods) and demersal molluscs (ammonites). Sedimentological and stable isotope data suggest that these bivalves lived near cold seeps and were exposed to high H₂S level in the seawater. The inoceramid shells exhibited higher δ¹³C and lower δ¹⁸O values than the coeval non‐cold seep molluscs. We ascribed the anomalous isotopic pattern to a combination of vital and environmental effects determined by the hosting of chemosymbionts and the exposure to warm interstitial waters. Inoceramid δ¹³C minima coincided with growth lines and likely reflect changes in nutrient supply by the chemosymbionts. Absolute temperatures estimated from δ¹⁸O values of Sphenoceramus schmidti and S. sachalinensis were, on average, ca. 4–5°C warmer than those reconstructed for the non‐seepage environment (19.3 ± 0.7°C). Short‐term δ¹⁸O fluctuations of the inoceramid material indicate local temperature ranges of up to 5.2°C, that is four times larger than those reconstructed from the benthic and demersal fauna (1.3°C). In general, our data suggest that the stable carbon and oxygen isotope values of the studied Sphenoceramus spp. were strongly affected by short‐term fluctuations in seepage activity and do not reflect seasonal fluctuations.     

Evidence for seasonal variation in δ13C and δ18O profiles of Baculites and implications for growth rate

The life histories of ammonites and the life strategies they employed are difficult to assess without robust modern analogues but placing constraints on ammonite growth rates provides a fundamental first step to understanding this abundant, but poorly understood, fossil group. Here we interpret periodic variations in carbon and oxygen stable isotope profiles from Campanian and Maastrichtian ammonites (Baculites) as seasonally driven and use these records to determine their rate of shell precipitation. Several of these samples are housed in museums and were originally prepared using sealants for display and preservation but testing of these sealants indicated no alteration of the isotopic values of treated carbonate. Diagenetic alteration, as determined by shell microstructure, affected the preservation of isotopic signals, resulting in the loss of seasonal variation in less well‐preserved specimens, and the δ¹³C signal is more robust than δ¹⁸O. The periodicity of isotopic profiles from Baculites shells presented here suggest that these organisms grew at rapid rates (c. 340 mm per year), which may imply an r‐type life strategy in which the animals reach maturity quickly, spawn large quantities of progeny, and die at a young age. Because of the potential mobility of Baculites, reconstructing palaeoenvironmental conditions from these isotopic records is challenging and should be conducted cautiously. Unfortunately, well‐preserved Baculites shells much longer than 350 mm are rarely recovered, which complicates the statistical treatment of potential periodicity in isotopic profiles.     

Shell structure of helically coiled microconchids from the Middle Triassic (Anisian) of Germany

Microconchid affinity of helically coiled tubes of Microconchus aberrans (Hohenstein, 1913) from the early Anisian of southern Germany is supported by an SEM study of shell structure. There are probable pseudopunctae in the shell of M. aberrans. Helically coiled and some substrate-cemented planispiral microconchids have similar microlamellar tube structures in the Triassic. The structure of the morphologically aberrant M. aberrans is characteristic of Palaeozoic to Middle Triassic microconchids. Allochthonous tube fragments of M. aberrans in the Wellenkalk presumably originate from a microconchid biostrome.     

Dendritic field structure of the large ganglion cells in the retina of <Emphasis Type="Italic">Pholidapus dybowskii</Emphasis> Steindachner, 1880 (Pisces: Perciformes: Stichaeidae)

This paper deals with the dendritic field structure of three large ganglion cell types in the retina of a marine teleost, Pholidapus dybowskii. Cells were retrograde labeled with horseradish peroxidase applied to lesioned fibers of the optic nerve. Their morphology was studied in wholemounted retinae. Dendritic fields of α_ab cells were more complex. Their structural complexity measured using Kolmogorov and information fractal dimensions exceeded significantly those of α_a and biplexiform cells. The latter two types exhibited no significant differences in complexity and spatial heterogeneity of dendritic field. The cell types studied differed dramatically in the relationships between fractal and nonfractal parameters of their dendritic arbors. The functional and evolutionary implications of the dendritic field structure of retinal ganglion cells are discussed.     

New aspects in ammonoid mode of life and their distribution

The intensively debated functional morphology and mode of distribution of ammonites can be clarified and explained when ammonoids are regarded as conch-bearing octopods. The terminal body chambers of some ammonites were modified into a floating egg case, widely dispersing the hatchlings along the course of oceanic and long-shore currents. Hatchlings from eggs attached to a substrate lived and bred in the same region, developing indigenous evolutionary lineages. Females became sexually mature after 1–3 years of age, breeding only once, dispatching numerous eggs at a time. This contributed to the high evolutionary rate of ammonoids. Due to ammonoid short longevity, growth was rapid and septa were frequently precipitated. Ammonite internal molds exhibit small scars of adductor muscles, which could rapidly detach and reattach during septa secretion. The resultant weak hold between the conch and the body was compensated by the septal marginal fluting in the form of backward expanding lobes, into which the soft tissue penetrated, stiffening when needed. Increased suture complexity (unrelated to buoyancy regulation or diving ability) reflects a better hold between the body and the buoyant conch, hence a more successful functioning. The complex network of mantle muscle fibers could also form the template for septa precipitation. The high intelligence and learning ability of extant octopods can explain ammonoids’ adaptation to diverse niches, successfully coping with ecological changes and threats (hence evolution) in contrast to the associated nautiloids. Post-mortal drift of the empty conch was minor due to rapid sinking of shells of dead ammonoids, for which ammonites are good biogeographic indicators.     

Fractal dimensions of metropolitan area road networks and the impacts on the urban built environment

The fractal dimension of road networks emerges as a measure of the complexity of road transport infrastructures. In this study, we measured fractal dimensions of both the geometric form (i.e., the layout of the roads) and structure hierarchy (i.e., the connections among roads) of the major road networks in the largest 95 U.S. metro areas. We explained the causes of the variances in these fractal dimensions, especially the one for structure hierarchy. Further, we hypothesized the impacts of these fractal dimensions on the urban built environment and validated our hypotheses using path analysis. We found that a larger geometric fractal dimension (D_g) shows a more uniform distribution of roads over the metro area, which provides the accessibility to suburban areas and incentives to low-density development. A larger structural fractal dimension (D_s) indicates the highly-connected roads (e.g., highways) tend to join to other highly-connected roads so that most roads can be reached by a small number of neighboring roads (i.e., the small-world phenomenon). As D_s increases and the small-world effect become more significant, daily vehicle miles traveled per capita (DVMT/Cap) decline. However, D_s should be kept low in order to reduce the DVMT/Cap as population size increases. We consider that the low D_s can contribute to more mixed, polycentric and more uniform on an urban area-wide basis. Overall, higher D_g and D_s of the major road network in a metro area leads to higher per capita carbon emissions of transport, and lower quality of life as population increases. In the end, we conclude that fractal dimensions can provide valuable insight into the nature of the transportation land use nexus.     

Enzymatic activity of palmitoyl‐protein thioesterase‐1 in serum from schizophrenia significantly associates with schizophrenia diagnosis scales

Genome‐wide association studies have confirmed that schizophrenia is an inheritable multiple‐gene mental disorder. Longitudinal studies about depression, first episode psychosis (FEP) and acute psychotic relapse have mostly searched for brain imaging biomarkers and inflammatory markers from the blood. However, to the best of our knowledge, the association between enzymatic activities with diagnosis or prediction of treatment response in people with schizophrenia has barely been validated. Under the Longitudinal Study of National Mental Health Work Plan (2015‐2020), we have studied a subsample of approximately 36 individuals from the cohort with data on palmitoyl‐protein thioesterase‐1 enzymatic activity from FEP and performed a bivariate correlation analysis with psychiatric assessment scores. After adjusting for sex, age, body mass index (BMI) and total serum protein, our data demonstrated that PPT1 enzymatic activity is significantly associated with schizophrenia and its Positive and Negative Syndrome Scale (PANSS) scores. This longitudinal study compared the PPT1 enzymatic activity in FEP schizophrenia patients and healthy volunteers, and the former exhibited a significant 1.5‐fold increase in PPT1 enzymatic levels (1.79 mmol/L/h/mL, and 1.18 mmol/L/h/mL; P < 0.05; 95% CI, 2.3‐2.9 and 1.4‐1.8). The higher PPT1 enzymatic levels in FEP schizophrenia patients were positively associated with larger PANSS scaling scores (r = 0.32, P = 0.0079 for positive scaling; r = 0.41, P = 0.0006 for negative scaling; r = 0.45, P = 0.0001 for general scaling; and r = 0.34, P = 0.0048 for PNASS‐S scaling). Higher enzymatic PPT1 in FEP schizophrenia patients is significantly associated with increased PANSS scaling values, indicating more serious rates of developing psychosis. Enzymatic activity of PPT1 may provide an important new view for schizophrenia disorders.     

Functional implications of dicynodont cranial suture morphology

Cranial suture morphology of Lystrosaurus and the generalized dicynodont Oudenodon was investigated to determine the strain environment during mastication, which in turn may indicate a difference in cranial function between the two taxa. Finite element (FE) analysis indicated that less strain accumulated in the cranium of Lystrosaurus during orthal bite simulations than in Oudenodon. Despite the overall difference in strain magnitude, moderate to high FE‐predicted strain accumulated in similar areas of the cranium of both taxa. The suture morphology in these cranial regions of Lystrosaurus and Oudenodon was investigated further by examination of histological sections and supplemented by observations of serial sections and computed tomography (CT) scans. The predominant type of strain from selected blocks of finite elements that contain sutures was determined, enabling comparison of suture morphology to strain type. Drawing from strain‐suture correlations established in extant taxa, the observed patterns of sutural morphology for both dicynodonts were used to deduce cranial function. The moderate to high compressive and tensile strain experienced by the infraorbital bar, zygomatic arch, and postorbital bar of Oudenodon and Lystrosaurus may have been decreased by small adjustive movements at the scarf sutures in those regions. Disparities in cranial suture morphology between the two taxa may reflect differences in cranial function. For instance, the tongue and groove morphology of the postorbital‐parietal suture in Oudenodon could have withstood the higher FE‐predicted tensile strain in the posterior skull roof. The scarf premaxilla‐nasal suture of Lystrosaurus provided an additional region of sutural mobility in the anterior surface of the snout, suggesting that Lystrosaurus may have employed a different biting regime than Oudenodon. The morphology of several sutures sampled in this study correlated with the FE‐predicted strain, although other cranial functional hypotheses remain to be tested. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Growth trajectories of some major ammonoid sub‐clades revealed by serial grinding tomography data

Molluscs such as ammonoids record their growth in their accretionary shells, making them ideal for the study of evolutionary changes in ontogeny through time. Standard methods usually focus on two‐dimensional data and do not quantify empirical changes in shell and chamber volumes through ontogeny, which can possibly be important to disentangle phylogeny, interspecific variation and palaeobiology of these extinct cephalopods. Tomographic and computational methods offer the opportunity to empirically study volumetric changes in shell and chamber volumes through ontogeny of major ammonoid sub‐clades in three dimensions (3‐D). Here, we document (1) the growth of chamber and septal volumes through ontogeny and (2) differences in ontogenetic changes between species from each of three major sub‐clades of Palaeozoic ammonoids throughout their early phylogeny. The data used are three‐dimensional reconstructions of specimens that have been subjected to grinding tomography. The following species were studied: the agoniatitid Fidelites clariondi and anarcestid Diallagites lenticulifer (Middle Devonian) and the Early Carboniferous goniatitid Goniatites multiliratus. Chamber and septum volumes were plotted against the septum number and the shell diameter (proxies for growth) in the three species; although differences are small, the trajectories are more similar among the most derived Diallagites and Goniatites compared with the more widely umbilicate Fidelites. Our comparisons show a good correlation between the 3‐D and the 2‐D measurements. In all three species, both volumes follow exponential trends with deviations in very early ontogeny (resolution artefacts) and near maturity (mature modifications in shell growth). Additionally, we analyse the intraspecific differences in the volume data between two specimens of Normannites (Middle Jurassic).