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1.
The trace elemental composition of calcified larval hard parts may serve as useful tags of natal origin for invertebrate population studies. We examine whether the trace metal barium (Ba) deposits into the calcium carbonate matrix of molluscan larval statolith and protoconch in proportion to seawater Ba concentration at two temperatures (11.5 and 17°C). We also examine strontium (Sr) uptake as a function of temperature. Using encapsulated larvae of the marine gastropod, Kelletia kelletii, reared in the laboratory under controlled conditions, we demonstrate a significant inverse effect of temperature and a positive effect of seawater Ba/Ca ratio on Ba incorporation into larval carbonates. Ba/Ca partition coefficients (DBa) in protoconch were 1.13 at 11.4°C and 0.88 at 17.1°C, while DBa in larval statolith measured 1.58 at 11.4°C and 1.29 at 17.1°C. Strontium incorporation into statoliths is also inversely affected by temperature, but there was a significant positive effect of temperature on Sr incorporation into protoconch. These data suggest larval statoliths and protoconchs can meaningfully record variation in seawater physical and chemical properties, and, hence, have potential as natural tags of natal origin.  相似文献   

2.
The southernmost occurrence of the early Maastrichtian larger benthic foraminifera (LBF) in Tethys is known from the Kallankuruchchi Formation in the Cauvery Basin, SE India, represented by Lepidorbitoides-Siderolites assemblages. The systematics, age and paleobiogeography of Lepidorbitoides here have as yet remained unresolved due to lack of information particularly on the nepionic arrangement, whereas their links with the Western Tethyan and Caribbean biogeographic domains were speculated. Lepidorbitoides, studied from the same level in seven samples in two separate areas, invariably possess quadriserial nepionts and adauxiliary chamberlets, whose mean number ranges from 3.79 to 4.67. The ratio between the sample means of the internal diameter of deuteroconch and protoconch varies between 1.72 and 1.86. The equatorial layer in the early stage consists of arcuate chambers with basal stolons, and ogival-to spatulate chamberlets with annular and oblique stolons in the later stages. These features are consistent with the phylogenetically advanced members of the Western Tethyan Lepidorbitoides lineage, such as L. minor (Schlumberger) and L. socialis (Leymerie), and all samples were assigned to the transitional development stages of these species based on the morphometry. The taxonomic status of some Lepidorbitoides species, originally described from the Kallankuruchchi Formation and widely adopted in previous works, such as L. blanfordi (Rao) and L. inornata (Rao), are not justified. We extend the geographic range of Western Tethyan Lepidorbitoides to southern India.  相似文献   

3.
Early Cambrian univalve molluscs are predominantly represented by microscopic forms (body length of 1–3 mm), preserved mainly as phosphatised internal moulds with limited definable features. Macromolluscs (≥ 5 mm) are generally rare, occur in low abundance and are poorly preserved, often lacking apical features and ornament which hinders taxonomic assessment. New and previously undescribed material from lower Cambrian Hawker Group carbonates of the Flinders Ranges in South Australia includes four new taxa, Minastirithella silivreni gen. et sp. nov., Galeacalvus coronarius gen. et sp. nov., Helcionella histosia sp. nov., and Ilsanella enallaxa sp. nov. Three-dimensional silicified shell material preserved with intact apices offers new insight into protoconch morphology, growth habit (isometric vs. allometric) and developmental mode. This material supports previous suggestions that some micromollusc taxa may in fact be early ontogenetic stages (juveniles) of larger macroscopic taxa; such that the millimetric size range of helcionelloids conforms to the dimensions of earliest apical portion in some macromolluscs documented herein. However, taphonomic limitations associated with phosphatisation show that the morphology (especially height vs. width) of the apex can greatly influence the probability of steinkern formation and preservation potential for both micro- and macro-scale helcionelloids. Artificial inflation in the appearance of millimetric helcionelloids with an optimal morphology for phosphatisation is thus directly linked to taphonomic biases in the fossil record.  相似文献   

4.
The John Martin Reservoir tracksites from the Dakota Group of Bent County, in southeastern Colorado form part of the mid Cretaceous Dinosaur Freeway characterized by abundant ornithopod footprints (Caririchnium). Over 350 tracks (331 Caririchnium, 1 Magnoavipes, 22 crocodiles, and a few pterosaurs) were discovered at 10 new tracksites. All tracks were found as natural casts, including Caririchnium trackways that were still in-situ, parallel and regularly spaced, suggesting gregarious behavior. Most crocodile tracks are swimming tracks that consist of three or four scratch marks also with parallel orientations in many cases. A few pterosaur tracks consist of pes footprints and scratch marks suggesting swimming or floating activity in shallow water. This is the first pterosaur evidence from the Dakota Group. The Caririchnium size structure from John Martin Reservoir is consistent with the size structure tendency of the whole Dinosaur Freeway, which shows larger track size in the north. This tendency could be interpreted as evidence for more than one ornithopod species spread out across the Dinosaur Freeway. The alternative, that there was one ornithopod species that migrated north and south seasonally is less likely. The John Martin paleoecosystem is interpreted from the track evidence as a well-vegetated coastal plain environment with many ornithopods and a few theropods on land, crocodiles in the water, and pterosaurs in the skies and on the water.  相似文献   

5.
Abundant Buchiidae (Bivalvia) from the Upper Volgian-Lower Valanginian sediments of the Northern Sikhote-Alin (Russian Far East) were studied in the key section at right bank of the Amur River opposite to Komsomolsk-on Amur. The analysis of the Buchiidae stratigraphic distribution in the section allowed us to reveal the sequence of Buchia-bearing beds: this is well correlated with the Buchia zonal scales of many Arctic regions. Here, from the base upward, there have been recognized the following: beds with Buchia terebratuloides, beds with B. unschensis and B. terebratuloides, beds with B. volgensis, and beds with B. inflata and B. keyserlingi. The beds with B. unschensis and B. terebratuloides also yielded the Berriasian ammonite Pseudosubplanites? sp. of Tethyan affinity. The obtained paleontological data confirm the occurrence of a large syncline in the studied section. The data also permit one to refine the age spans of the local stratigraphic units.  相似文献   

6.
The Bathonian ammonite assemblages have been previously poorly recorded in Kutch. The present study has unearthed a rich array of ammonite taxa ranging from the Middle to Upper Bathonian. While Oxycerites Rollier (1909) is a new record from Kutch, the oldest occurrence of Choffatia Siemiradzki (1898) has been found from the Middle Bathonian horizon. Oxycerites cf. orbis (Giebel) is a zonal index of the Late Bathonian in other areas and thus facilitates interprovincial correlation. Besides, palaeobiogeographic and stratigraphic distribution of many species have been modified based on new information. For example, macrocephalitin species, i.e., Kamptokephalites cf. etheridgei Spath (1928), Macrocephalites bifurcatus transient intermedius Spath (1928), M. cf. mantataranus Boehm (1912) were previously known from West Pacific, Indonesia have been now found in Kutch. Gracilisphinctes Buckman (1920) has been previously known to occur during the Middle Bathonian time, the present work extends its stratigraphic distribution up to the definite Upper Bathonian horizon. Procerites hians (Waagen) an endemic species in Kutch previously known from the Upper Bathonian beds, its stratigraphic range has been extended down to the Middle Bathonian.Detail taxonomy of the newly obtained taxa has been done and in many cases sexual dimorphism has been recognized.  相似文献   

7.
Fish communities found in the marine, brackish, and freshwater shallows of the Clarence River (New South Wales, Australia) were sampled over a 12-mo period to compare communities inhabiting bare and vegetated substrata. A total of 26,107 fish representing 57 species and 36 families was collected biomonthly suing a 6-mm mesh siene. Permanent residents (i.e., species found throughout the year) were primarily gobies (Gobiidae) and gudgeons (Eleotridae). Juveniles of many species found as adults in other parts of the river were seasonally abundant in the shallows. Most numerous was a small ambassid, the glassy perchlet (Ambassis jacksoniensis), the majority of which was collected from marine and brackish regions of the river. Firetail gudgeons (Hypseleotris compressus) were caught in highest numbers at the freshwater sites. Cluster analysis suggested that fish communities in widely separated vegetated sites were more similar to each other than to those in adjacent bare sites. Shallow vegetated (Zostera capricorni) habitats in the marine region of the river had greatest diversity and highest abundances of fish, particularly during recruitment periods. At these times, juveniles of many commercially important species were captured, including yellowfin bream (Acanthopagrus australis), sea mullet (Mugil cephalus), flat-tail mullet (Liza agentea), tarwhine (Rhabdosargus sarba), luderick (Girella tricuspidata), silver biddy (Gerres subfasciatus), and sand whiting (Sillago ciliata). The vegetated (Vallisneria gigantea) sites in the brackish region also had significantly more species and individuals during recruitment periods (spring) than bare sites. Although freshwater vegetated sites consistently had more individuals than freshwater bare sites, there were no significant differences in species richness between vegetated and bare habitats. The need to conservatively manage shallow-water fish habitats is stressed. *** DIRECT SUPPORT *** A01BY073 00004  相似文献   

8.
Four juvenile specimens referable to Pinacosaurus grangeri (Ankylosauria: Dinosauria) are described from the Campanian (Upper Cretaceous) locality Bayan Mandahu in northern Inner Mongolia Autonomous Region (People’s Republic of China). All the specimens preserve the skulls as well as, in some cases, mandibles, postcrania, and osteoderm. They are not taphonomically deformed by expanding matrix distortion, unlike many Gobi specimens, including the holotype of P. grangeri. Bayan Mandahu is also the type locality for Pinacosaurus mephistocephalus. The proximity in space and time of these two closely related species warrants a generic and specific revision for Pinacosaurus. The distinction of the two species is based on characters of the squamosal dermal elaborations, cranial roof posterior to the orbits, premaxillary notch, and distal margin of the ilium. Although a relatively well-represented ankylosaur taxon, the phylogenetic position of Pinacosaurus has not been unequivocally resolved. A new analysis recovers Pinacosaurus as the most basal member of the Ankylosaurinae.  相似文献   

9.
Microhardness (H) and fracture toughness (K 1C) have been studied for the main varieties of shock-resistant cryptocrystalline fluorite, a natural ceramic widespread at the Suran deposit. Suran cryptocrystalline fluorite (SCF) is characterized by high fracture toughness (K 1C), which is 2–5 times higher than K 1C of common fluorite monocrystals. The relationship between K 1C and microhardness H is complex and nonlinear. The SCF varieties from the sellaite-fluorite orebody are distinguished by the highest K 1C = 1.9–2.3 MPa m1/2, which exceeds K 1C = 0.84 MPa m1/2 of porcelain-like fluorite from the main fluorite orebody. Qualitative and quantitative variations of structural point defects in the studied samples exert a much stronger effect on microhardness than on fracture toughness, which mainly depends on the size of crystallites, their mutual crystallographic orientation, and the structure of intergranular boundaries, i.e., on the parameters seemingly related to recrystallization and/or twinning of fluorite. In general, the nature of the Suran deposit of fluorite ceramic with unusual physicomechanical properties remains a geological puzzle in many respects.  相似文献   

10.
Species richness and abundance of seagrass-associated fauna are often positively correlated with seagrass biomass and structure complexity of the habitat. We found that while shoot density and plant biomass were greater in interior portions of turtle grass (Thalassia testudinum) beds than at edges, mean faunal density was significantly greater at edges than interior sites during 1994. This pattern was also observed in 1995, although differences were not significant. The four numerically dominant taxonomic groups showed varying degrees of elevated densitities at edges ofT. testudinum beds. Peracarids and polychaetes had significantly greater densities at edges oft. testudinum beds, while both decapods and gastropods showed dramatic temporal variability in density, with reversals in density between edge and interior occurring during the course of the study. This within-habitat variability in abundance may reflect both active accumulation of fauna at edges and settlement shadows for species with pelagic larvae. Active accumulation of highly mobile taxa seeking refuge in seagrass beds may explain the differences in density between edge and interior ofT. testudinum patches for peracarids in 1994 and in 1995. Active accumulation at edges may also explain differeces in density for some decapod taxa. Chauges in gastropod densities between habitats may reflect larval settlement patterns. Results showed a distinct settlement shadow for the gastropodCaecum nitidum whose densities (primarily second stage protoconch) increased by more than an order of magnitude in 1994. Settlement shadows and post-settlement processes may also explain density differences of polychaetes between the edge and interior ofT. testudinum patches. The differences in faunal densities between edge and interior habitat resulted in habitat specific differences in secondary production among the major taxonomic groups. On four of five dates in 1994 and in 1995, secondary production was greater at edge than interior locations. These unexpected results suggest that differences in faunal densities and secondary production between edges and interiors of seagrass patches represent a potentially vital link in seagrass trophic dynamics. If this elevated secondary production leads to increases in trophic transfer, then edges may serve as a significant trophic conduit to higher-level consumers in this system.  相似文献   

11.
A model of 4He accumulation in a confined aquifer is presented which includes in situ production and a crustal degassing flux of 4He into the bottom of a confined aquifer. The model is consistent with the measurements of 4He concentration in the Great Artesian Basin, Australia (Torgersen and Clarke, 1985) and also with the measurements of 4He concentration in the Auob Sandstone of Namibia (Heaton, 1981). The measured value of the crustal degassing flux of 4He from these two areas is comparable with the 4He degassing flux calculated from the atmospheric budget of 4He (Wasserburget al., 1963; Ozima and Podosek, 1983). A literature review suggests that a crustal degassing 4He source may account for the 4He accumulation in many other groundwater systems. It is concluded from the literature review, the detailed modelling of 4He accumulation in GAB and the Auob Sandstone, and the atmospheric budget that crustal degassing of 4He may be a common and widespread phenomena.  相似文献   

12.
The Middle Triassic fossil reptile localities near Bayreuth (Bavaria, southern Germany) consist of shallow marine autochthonous glauconitic marls and terebratulid-rich tempestite carbonates of the newly defined Bindlach and Hegnabrunn formations. Single bones and incomplete skeletons of marine reptiles have been recorded in bone beds within in the Illyrian and Fassanian stages. These include the remains of the sauropterygians Neusticosaurus sp., Lariosaurus cf. buzzii [1], Nothosaurus mirabilis [2], Paranothosaurus giganteus [2], Placodus gigas [3], Cyamodus rostratus [4], Cyamodus münsteri [5], Pistosaurus longaevus [6], and ichthyosaursOmphalosaurus sp., and Shastasaurus sp. or proterosaur Tanystrophaeus conspicuus [7]. New skeletal reconstructions are based on the osteological analysis of three dimensionally preserved bones and skeletal remains. The large number of marine endemic placodont macroalgae feeders (P. gigas) in the Bayreuth sites coincides with the presence of invertebrate palaeocommunities that are characteristic of macroalgae meadow paleoenvironments. Most of the reptile species and genera from the Bayreuth localities also occur in beds of similar ages from the Monte San Giorgio (Switzerland/Italy) or Perledo (Italy) lagoonal areas. Ichthyosaurs and pistosaurs were adapted for open marine conditions, and may have migrated from the Panthalassa Oceans into the shallow marine Germanic Basin to reproduce, whereas placodonts and many other sauropterygians seem to have lived permanently in those shallow marine habitats, with large squamates and thecodont or smaller archosaurs in coastal areas.  相似文献   

13.
The Paleocene-Eocene transition is one of the most remarkable Cenozoic periods coinciding with the global thermal maximum (PETM). Based on the complex biostratigraphic analysis of diatoms, silicoflagellates, and dinocysts, this global event is revealed in three sections of the Middle Trans-Urals region (Kamyshlov, Korkino, Chumlyak) represented by marine biosiliceous sediments of the Serov and Irbit formations. The interval of the Trinacra ventriculosa-Hemiaulus proteus-Coscinodiscus uralensis diatom zones is marked by the appearance of new genera Moisseevia, Solium, Fenestrella, Craspedodiscus, Podosira, Pseudotriceratium, intense radiations of Grunoweiella and Coscinodiscus, and development of extreme morphotypes among silicoflagellates. The defined diatom assemblages differ slightly from their coeval counterparts from the Middle Volga region, which casts doubt upon the assumed stable water exchange between these basins. On the contrary, the dinocyst assemblages are lacking zonal index species (Appectodinium homomorphum, A. augustum) and Apectodinium acme characteristic of the transitional Paleocene-Eocene strata in many worldwide localities. The facies settings of his period with intense vertical mixing and relatively low temperatures and salinity are characterized by the dominant role of dinocysts belonging to the genera Areoligera, Deflandrea, Spiniferites, and Operculodinium.  相似文献   

14.
The Cretaceous sections of the eastern Caucasus contain rich in organic matter (OM) sediments corresponding to the late Cenomanian Oceanic Anoxic Event 2. They are marked by positive δ13C and negative δ18O isotopic anomalies, which are characteristic for this level in many areas of the world. The sediments exhibit distinct cyclic patterns reflected in an alternation of black OM-rich and gray more calcareous layers. The rocks are enriched with many chemical elements, although concentrations of some of them (Mo, Se) are lower than in typical sediments of anoxic basins. It is inferred that anoxic environments in the paleobasin were unstable and locally developed. Nannofossil assemblages from OAE 2 sediments are dominated by the highly resistant eurytropic taxon Watznaueria accompanied by common cool-water Eprolithus and rare warm-water Rhagodiscus representatives, which implies the development of environments unfavorable for the normal marine nannoflora and short-term cooling in the basin during OAE 2. The OM-rich sediments were deposited against the background of the rapid eustatic transgression due to a significant increase in productivity of phytoplankton in the paleobasin. The OAE 2 duration is estimated to be approximately 400 ka.  相似文献   

15.
Cymrite, BaAl2Si2O8 · nH2O, is a rare mineral formed during low-grade dynamothermal metamorphism (T = 250–300°C, P = 1–3 kbar). Cymrite has been described from many metasedimentary ores and hydrothermal rocks. In carbonatites, it has been found for the first time. Cymrite has been identified in the Kovdor and Seblyavr massifs, Kola Peninsula. In Kovdor, this mineral has been described from one of the hydrothermal veins cutting the pyroxenite-melilitite-ijolite complex at the Phlogopite deposit; cymrite is associated with thomsonite, calcite, and stivensite. In the Seblyavr pluton, cymrite occurs in thin veins of calcite carbonatite that cut pyroxenite contacting with ijolite. Cymrite from the Seblyavr pluton is associated with calcite, natrolite, pyrite, and chalcopyrite. The mineral is optically negative and uniaxial, with extinction parallel to elongation; ω ～ 1.607(1). According to X-ray diffraction data, cymrite from Seblyavr is monoclinic, space group P1m1; unit-cell dimensions are: a = 5.33, b = 36.96, c = 7.66 Å, β = 90°, V = 1510.55 Å3. According to the results of IR spectroscopy, in the series of samples from different massifs (in the running order Kovdor-Voishor-Seblyavr), the double-layer deformation is enhanced and accompanied by a decrease in the Si-O-Si angle and weakening of hydrogen bonds of interlayer water. The empirical formulas of cymrite calculated from electron microprobe analyses are Ba0.93–0.95Ca0.01–0.02K0.00–0.05Na0.02–0.04Al1.97–2.01Si1.99–2.03O8(H2O) and Ba1.00–1.02Ca0.00–0.01Sr0.00–0.01Fe0.00–0.01Al1.94–2.00Si1.98–2.03O8(H2O) at Seblyavr and Kovdor, respectively. Cymrite from the carbonatite massifs of the Kola Peninsula was formed under hydrothermal conditions at low temperature (200–300°C), high activity of Ba and Si, and high water pressure. At Kovdor, the mineral crystallized directly from the residual solution enriched in Ba. The sequence of mineral deposition is as follows: thomsonite-cymrite-calcite-stevensite. Cymrite from the Seblyavr pluton is a product of hydrothermal alteration of primary Na-K-Ba silicates of ijolite: nepheline, feldspar, and probably celsian. Natrolite replaces cymrite indicating high alkalinity of late hydrothermal fluids.  相似文献   

16.
To aid interpreting the source area of charcoal in lake-sediment records, we compare charcoal deposition from an experimental fire to predictions from a particle dispersal model. This provides both a theoretical framework for understanding how lake sediments reflect fire history and a foundation for simulating sediment-charcoal records. The dispersal model captures the two-dimensional patterns in the empirical data (predicted vs. observed r2 = 0.67, p < 0.001). We further develop the model to calculate the potential charcoal source area (PCSA) for several classes of fires. Results suggest that (1) variations in airborne charcoal deposition can be explained largely by the size of PCSAs relative to fire sizes and (2) macroscopic charcoal travels many kilometers, longer than suggested by dispersal data from experimental fires but consistent with dispersal data from uncontrolled fires.  相似文献   

17.
The Mellin transform is a mathematical tool which has been applied in many areas of Mathematics, Physics and Engineering. Its application in Geophysics is in the computation of solution of potential problems for the determination of the mass as well as the depth to the basement of some solid mineral deposits. In this study, the Mellin transform is used to determine the depth to the top (h) and the depth to the bottom (H) of the basement of a profile of an anomalous magnetic body. Ibuji, the study area is located in Ifedore Local Government area of Ondo state, Nigeria, underlain by Precambrian complex rocks and bounded by geographical co-ordinate of Easting 5°00t’00″ to 5°4t’30″ and Northing 7°24t’00″ to 7°27t’36″. The magnetic anomaly profile due to a two- dimensional body(vertical thin sheet)over magnetic spring of the study area was digitised and the values of magnetic amplitude (nT) with respect to its horizontal distance (say interval of 5 m) obtained from the digitized profile was then used in the computation of Mellin transform using Matlab programs. In order to determine the depths H and h, the amplitudes were considered at three arbitrary point (s = ¼, ½ and ¾) such that, (0 < s < 1), where s is a complex variable of real positive integer. The value obtained for H was 47.95 m, which compared favourably with the result obtained using other methods. Meanwhile, the value obtained for h has a convergence restriction, whereby, at lower values of s, there is divergence, while at higher values of s, (about 0.9), the result converges and h was obtained to be 32.56 m. The Ibuji magnetic anomaly was therefore analysed to have a depth to the bottom (H) of 47.95 m and depth to the top of 32.56 m using this mathematical tool.  相似文献   

18.
Auger electron spectra (AES) of sulfides are interpreted using published photoelectron spectra, sulfurK β X-ray emission spectra (XES) and Multiple ScatteringX α calculations on metal-sulfide molecular clusters and using newly measured spectra for ZnS, Cu2S and MoS2. For compounds without appreciable metald-sulfur 3p interactions, only one sulfur LVV peak or a closely spaced doublet is observed. For those with substantial metald-sulfur 3p interactions additional peaks occur, with peaks at lower electron kinetic energy arising from ejection of electrons from orbitals more tightly bound than theS3p, and those with higher kinetic energy arising from electrons in less tightly bound orbitals. Thus, for many sulfide minerals, the sulfur LVV Auger Spectrum is essentially a self-convolution of the valence band density of states weighted by the amount of S3p character, and can be predicted from a knowledge of the sulfurK β X-ray emission spectra and the X-ray photoelectron spectra.  相似文献   

19.
The potential significance of the contributions of long chain iso and anteiso monomethyl alkanes (LC MMAs) from plants of the Lamiaceae, a family that includes many culinary and aromatic herbs of cultural value, to sediments and soil has been evaluated by analyzing 21 specimens from 16 species of Lamiaceae from different environmental settings in Hubei Province, central China, and comparing the results with those from tobacco plants, which are established to be rich in these compounds. Odd numbered iso-alkanes (i-C25 to i-C36) and even numbered anteiso-alkanes (a-C25 to a-C36) are abundant in the Lamiaceae (1.9-23.2% and 0.9-23.8% of total alkanes, respectively). The proportions of LC MMAs are relatively high and comparable to those in the tobacco plant. However, chain lengths in the Lamiaceae are longer than those in tobacco plants and compound-specific δ13C values are more negative than in the tobacco plants, potentially allowing distinction of their different origins. The results imply that Lamiaceae, in addition to some other land plants, can be important sources of LC iso- and anteiso-alkanes in sediments and soils.  相似文献   

20.
The fossil record of Nautilida in carbonate facies is skewed towards moulds (steinkerns) in various states of preservation, which complicates assessment of the original shell ornament of many taxa. As a remarkable exception, moulds of Epicymatoceras vaelsense from upper Campanian and lower Maastrichtian (Upper Cretaceous) siliceous limestones (opoka) in Poland retain details of the original shell ornament, allowing conclusions on the original structure of the shell wall, systematic position and hatching size of this nautilid to be drawn. Both external and internal moulds are present in the material studied, which are referred to as taphomorph 1 and 2, respectively. Based on morphology and inferred taphonomy, it is proposed that the external ribbing of E. vaelsense was originally composed of overlapping, tile-shaped lamellae of the outer prismatic layer, a character recently suggested to be a synapomorphy for the cymatoceratid clade. The diameter of the embryonic conch of E. vaelsense is estimated to have been around 30 mm, which is near the maximum range of hatching size recorded for Cretaceous and younger nautilids. On the basis of the inferred shell structure of E. vaelsense, it is speculated that living individuals of this nautilid were covered by a dense periostracal cover similar to that of Recent Allonautilus scrobiculatus. This study demonstrates that nautilid moulds may provide a better source of palaeontological data than conventionally accepted.  相似文献   

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