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Tytuł:
Septal neck-siphuncular complex in Stolleyites (Ammonoidea),Triassic, Svalbard
Autorzy:
Kulicki, Cyprian
Powiązania:
https://bibliotekanauki.pl/articles/2052710.pdf
Data publikacji:
1994
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
Arctic
Edgeöya
Triassic
paleontology (Ammonoidea)
Źródło:
Polish Polar Research; 1994, 15, 1-2; 37-49
0138-0338
2081-8262
Pojawia się w:
Polish Polar Research
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The origin of ammonoid locomotion
Autorzy:
Klug, C
Korn, D.
Powiązania:
https://bibliotekanauki.pl/articles/21156.pdf
Data publikacji:
2004
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
phylogenesis
Bactritida
ontogenesis
Ammonoidea
conch
coiling
Devonian
paleontology
locomotion
ammonoid
Opis:
Evolution of the coiled ammonoid conch from the uncoiled bactritid conch was probably coupled with changes in manoeuvrability and swimming velocity. The gradual transformation of uncoiled to coiled ammonoid conchs has essential functional consequences. The radical change in conch geometry during phylogeny but also in ontogeny of early ammonoids implies a shift of the aperture from an original roughly downward, via a downward oblique and an upward oblique to an upward orientation, presuming a neutrally buoyant condition of the ammonoid animal. Similar trends were reconstructed for the three main ammonoid lineages in the Middle Devonian, the agoniatitid, the anarcestid, and the tornoceratid lineages. This allowed an increase in manoeuvrability and in the maximum horizontal swimming speed.
Źródło:
Acta Palaeontologica Polonica; 2004, 49, 2
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Terminal Maastrichtian ammonites from Turkmenistan, Central Asia
Autorzy:
Machalski, M.
Jagt, J.W.M.
Alekseev, A.S.
Jagt-Yazykova, E.A.
Powiązania:
https://bibliotekanauki.pl/articles/20971.pdf
Data publikacji:
2012
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
paleontology
Maastrichtian
ammonite
Turkmenistan
Central Asia
Ammonoidea
extinction
paleobiogeography
Cretaceous
Paleogene
Opis:
A complete uppermost Maastrichtian–Danian succession in the Sumbar River section, western Kopet Dagh (southwest Turkmenistan, Central Asia), constitutes one of the few instances in the world where the fossil record of the last ammonites can be directly positioned with respect to the iridium−rich, impact−related clay layer, which defines the Cretaceous–Paleogene (K–Pg) boundary. Two ammonite taxa, Baculites cf. vertebralis and Hoploscaphites constrictus johnjagti, range up to a level directly beneath the K–Pg boundary clay in the Sumbar River section. Thus, these two forms probably survived until the very end of the Maastrichtian in the western Kopet Dagh area. The terminal Maastrichtian ammonite records from the Sumbar River area represent the southeasternmost occurrences of these essentially Boreal taxa.
Źródło:
Acta Palaeontologica Polonica; 2012, 57, 4
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The last Cretaceous ammonites in Latin America
Autorzy:
Stinnesbeck, W.
Ifrim, C.
Salazar, C.
Powiązania:
https://bibliotekanauki.pl/articles/20513.pdf
Data publikacji:
2012
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
paleontology
Cretaceous
ammonite
Latin America
Ammonoidea
Paleogene
Maastrichtian
Chile
Argentina
South America
Opis:
Sections yielding late Maastrichtian ammonite assemblages are rare in Latin America and precise biostratigraphic correlation with European type sections remains difficult. In all, the extinction pattern of ammonites appears to differ between sites in southern high latitudes and those in the tropics to subtropics. In austral sections of Chile, and possibly also in southern Argentina, diverse assemblages range throughout most of the substage and then show a gradual decline prior to the Cretaceous–Paleogene (K–Pg) boundary. Further north, in northeast Brazil, only two genera (Diplomoceras, Pachydiscus) range into the uppermost Maastrichtian, but disappear within the last 0.3 Ma of the Cretaceous. In tropical sections of Columbia and Mexico, the decline of ammonites started earlier and Sphenodiscus is the last ammonite known to occur in the late Maastrichtian. In all sections revised here the disappearance of ammonites was completed prior to the end of the Maastrichtian and was thus independent of the asteroid impact at, or near, the end of the Cretaceous.
Źródło:
Acta Palaeontologica Polonica; 2012, 57, 4
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Double alignments of ammonoid aptychi from the Lower Cretaceous of Southeast France: Result of a post-mortem transport or bromalites?
Autorzy:
Reboulet, S
Rard, A.
Powiązania:
https://bibliotekanauki.pl/articles/21005.pdf
Data publikacji:
2008
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Cretaceous
Valanginian
predation
coprolite
ammonoid
paleontology
taphonomy
France
aptychus
Ammonoidea
Lower Cretaceous
Opis:
A new preservation of aptychi is described from the Valanginian limestone−marl alternations of the Vergol section (Drôme), located in the Vocontian Basin (SE France). Aptychi are arranged into two parallel rows which are generally 50 mm in length and separated by 4 mm. The alignments are very often made by entire aptychi (around 10 mm in length), oriented following their harmonic margin. Aptychi show the outside of valve to the viewer: they are convex−up. This fossilization of aptychi is successively interpreted as the result of post−mortem transport by bottom currents (taphonomicresedimentation process) or the residues (bromalites: fossilized regurgitation, gastric and intestinal contents, excrement) from the digestive tract of an ammonoid−eater (biological processes). Both the parallel rows of aptychi are more likely interpreted as a coprolite (fossil faeces) and they could be considered as both halves (hemi−cylindrical in shape) of the same cylindrical coprolite which would have been separated in two parts (following the long axis) just after the animal defecated. Considering this hypothesis, a discussion is proposed on the hypothetical ammonoid−eater responsible for them.
Źródło:
Acta Palaeontologica Polonica; 2008, 53, 2
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Size-shape relationships in the Mesozoic planispiral ammonites
Autorzy:
Parent, H.
Greco, A.F.
Bejas, M.
Powiązania:
https://bibliotekanauki.pl/articles/19942.pdf
Data publikacji:
2010
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
size-shape relationship
Mesozoic
planispiral ammonite
ammonite
Ammonoidea
shell
Cephalopoda
paleontology
marine fossil
Opis:
Ammonites are of outstanding importance in dating events of the Mesozoic and in the study of mechanisms, modes and timing of evolutionary processes. These applications rely on a detailed understanding of their morphology and the modes of variation. It has been known for a long time that their shape is composed of a number of highly correlated features. A new model, called the ADA−model, is introduced for the study of shell morphology (size and shape). The new model is based on classic dimensions which are stable parameters throughout ontogeny, giving very close agreement between pre− dictions and actual observations. It was applied in the exploration of the morphospace occupied by the planispirally coiled and the regularly uncoiled Mesozoic Ammonoidea, based on two new reduced morphospaces introduced for the analysis. Results obtained expose close relationships between size and shape, and general patterns in the ammonite shell morphol− ogy and morphogenesis. (i) The relative apertural height of the whorl section relative to the diameter of the shell (H₂/D) is involved in definition of size and shape. (ii) This same dimension shows a strong tendency to be H₂/D = 0.3. (iii) There are some geometrically possible shell shapes (or morphotypes) which seem to have not been developed since they are not known in the current record. Assuming the known ranges of protoconch size and whorl number as constraints, the ADA−model strongly suggests that these morphotypes have not been developed for the too large or too small sizes the shells would have attained, well outside of the actual size range of the planispirally coiled Ammonoidea. (iv) The law of covariation is shown to be a general pattern within the planispiral ammonites which describes structured variation of the shell shape. (v) A large fraction of the non−structured variation seems originate in the lack of correlation between the rela− tive umbilical diameter and width of the whorl section.
Źródło:
Acta Palaeontologica Polonica; 2010, 55, 1
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
The Barremian heteromorph ammonite Dissimilites from northern Italy: Taxonomy and evolutionary implications
Autorzy:
Lukeneder, A.
Lukeneder, S.
Powiązania:
https://bibliotekanauki.pl/articles/22570.pdf
Data publikacji:
2014
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
paleontology
Ammonoidea
Acrioceratidae
Barremian
Cretaceous
heteromorph ammonite
Dissimilites
Italy
taxonomy
evolution
Alps Mountains
Opis:
A new acrioceratid ammonite, Dissimilites intermedius sp. nov., from the Barremian (Lower Cretaceous) of the Puez area (Dolomites, northern Italy) is described. Dissimilites intermedius sp. nov. is an intermediate form between D. dissimilis and D. trinodosum. The new species combines the ribbing style of D. dissimilis (bifurcating with intercalating single ribs) with the tuberculation style of D. trinodosum (trituberculation on entire shell). The shallow-helical spire, entirely comprising single ribs intercalated by trituberculated main ribs, is similar to the one of the assumed ancestor Acrioceras, whereas the increasing curvation of the younger forms resembles similar patterns observed in the descendant Toxoceratoides. These characters support the hypothesis of a direct evolutionary lineage from Acrioceras via Dissimilites to Toxoceratoides. D. intermedius sp. nov. ranges from the upper Lower Barremian (Moutoniceras moutonianum Zone) to the lower Upper Barremian (Toxancyloceras vandenheckii Zone). The new species allows to better understand the evolution of the genus Dissimilites. The genus appears within the Nicklesia pulchella Zone represented by D. duboise, which most likely evolved into D. dissimilis. In the Kotetishvilia compressissima Zone, two morphological forms developed: smaller forms very similar to Acrioceras and forms with very long shaft and juvenile spire like in D. intermedius sp. nov. The latter most likely gave rise to D. subalternatus and D. trinodosum in the M. moutonianum Zone, forms which were probably ancestral to the genus Toxoceratoides.
Źródło:
Acta Palaeontologica Polonica; 2014, 59, 3
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Dimorphism in tetragonitid ammonoid Tetragonites minimus from the Upper Cretaceous in Hokkaido, Northern Japan
Autorzy:
Aiba, D.
Powiązania:
https://bibliotekanauki.pl/articles/31341368.pdf
Data publikacji:
2022
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
paleontology
dimorphism
tetragonitid
ammonoid
Ammonoidea
Tetragonidae
Tetragonites minimus
Cretaceous
Upper Cretaceous
Hokkaido
Japan
Źródło:
Acta Palaeontologica Polonica; 2022, 67, 4; 949-961
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Differential preservation of the Upper Cretaceous ammonoid Anagaudryceras limatum with corrugated shell in Central Hokkaido, Japan
Autorzy:
Wani, R
Powiązania:
https://bibliotekanauki.pl/articles/21872.pdf
Data publikacji:
2007
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Hokkaido
fossil record
Japan
Ammonoidea
Cretaceous
Upper Cretaceous
paleoecology
Anagaudryceras limatum
corrugation
paleontology
ammonoid
Opis:
The taphonomy of the Upper Cretaceous ammonite Anagaudryceras limatum differs from associated ammonites in the same horizon. This differential taphonomy is reconstructed based on fragmentation patterns and structural property of the corrugated shells of their body chamber parts. The characteristic preservation of isolated body chamber parts with corrugations is commonly observed in A. limatum from the upper Turonian of the Oyubari area, central Hokkaido, Japan. This preservation probably results from the differential internal structural properties of the hollow body chamber and septated phragmocone as well as the peculiar corrugation on body chamber of the present species: (1) fracturing along the corrugations against bending force is easier than flat material, because of the concentration of force on the tops or bottoms of corrugations, and (2) high durability against compressive forces. The separated body chamber parts were resistant to being squashed and broke into pieces due to the durability of corrugations against compressive force. The statistic test on the fossil assemblage suggests that selective destruction did not affect the fidelity of species composition and relative abundance of the studied fossil assemblage. Molluscan death assemblages in marine systems consistently show strong fidelity to relative abundances in the live community, suggesting that there was an Anagaudryceras−dominant ammonoid community during the late Turonian in the Oyubari area.
Źródło:
Acta Palaeontologica Polonica; 2007, 52, 1
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Devonian pearls and ammonoid-endoparasite co-evolution
Autorzy:
De Baets, K.
Klug, C.
Korn, D.
Powiązania:
https://bibliotekanauki.pl/articles/23478.pdf
Data publikacji:
2011
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Algeria
Ammonoidea
Devonian
Germany
Morocco
Trematoda
paleontology
parasite
pearl
evolution
terminology
distribution
ammonoid
endoparasite
Opis:
Raised shell projections on the inner shell walls that form pits on the internal moulds of Devonian ammonoids have been known for several decades. New specimens from Morocco reveal novel details of these structures; most, if not all, of which consist of a capsule of ammonoid shell that covers tiny tubes attached to the outer (= lateral or ventral) shell wall from the inside. In accordance with comparable Recent occurrences of similar structures in molluscs, we use the term “pearls” for these structures and the pits they form on the internal moulds. The nature of these encapsulated tubes is described and discussed. Because of the presence of these tubes inside the pearls, pearl arrangement, and their similarity to Recent mollusc occurrences, the tubes are interpreted as traces of parasitoses. The pearls and pits were grouped into five types based on differences in morphology, size, and arrangement. Then, having used these traits to perform a simple cladistic analysis, the resulting cladogram was compared to the phylogeny of ammonoids. Based on this comparison, it appears likely that the parasites underwent a co−evolution with the ammonoids, which lasted 10 to 15 Ma. Patterns of evolutionary events include co−speciation, “drowning on arrival” (end of parasite lineage near base of a new host clade), and “missing the boat” (parasite lineage does not adapt to a new host clade, thus not evolving a new parasite clade). Because of the lack of fossilised soft tissue, only speculations can be made about the systematic affiliation of the parasites, their life−cycle, infection strategy, and ecological framework. Some co−occurring bivalves also have pits reminiscent to structures caused by trematodes in Recent forms. Based on the available information, the tubes are interpreted as artefacts of trematode infestations, which, if correct, would extend the fossil record of parasitic trematodes into the Early Devonian.
Źródło:
Acta Palaeontologica Polonica; 2011, 56, 1
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Sublethal injuries in Early Devonian cephalopod shells from Morocco
Autorzy:
Klug, C.
Powiązania:
https://bibliotekanauki.pl/articles/22322.pdf
Data publikacji:
2007
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Ammonoidea
Bactritoidea
Devonian
Early Devonian
Gnathostomata
Morocco
cephalopod
paleontology
shell
predation
life mode
ectocochleate cephalopod
Opis:
Internal moulds of the relatively small− to moderate−size shells of Early Devonian ectocochleate cephalopods (typically <150 mm diameter) occasionally display traces of repaired shell damage. Presumably, these animals with their highly specialized buoyancy device, the phragmocone, lived in the water column. It is uncertain as to how the shells of these animals were damaged; one likely cause would be predatory attacks but the identity of the perpetrator remains uncertain. So far, no remains of arthropods capable of breaking or cutting shells have been found in the fossiliferous outcrops of this age in the Anti−Atlas (Morocco). The only macrovertebrate remains of this age are of acanthodian and placoderm fish which probably lived a more or less benthonic life style. Additionally, a fish attack on these cephalopods would probably have destroyed most of the thin−shelled conch and killed the animal. Most of the repaired shell breaks are triangular in shape which is characteristic for cephalopod bite marks. Additionally, the paired arrangement of the fractures in over 70 bactritoids supports the hypothesis that it was a cephalopod attacking another cephalopod. It cannot be excluded with certainty that occasional vertebrate attacks left traces on their shells. Fossil evidence indicates that the development of tightly coiled conchs was a rapid evolutionary event in the Ammonoidea in the Early Devonian; however, the evolution of coiling is probably not directly related to predation pressures because the ratio of injured to healthy specimens is roughly the same in Zlíchovian bactritoids with orthoconic and ammonoids with coiled shells.
Źródło:
Acta Palaeontologica Polonica; 2007, 52, 4
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
New Lower Kimmeridgian ataxioceratin ammonite from the eastern Iberian Chain, Spain: Systematic, biogeographic, and biostratigraphic relevance
Autorzy:
Moliner, L.
Oloriz, F.
Powiązania:
https://bibliotekanauki.pl/articles/20591.pdf
Data publikacji:
2010
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Lower Kimmeridgian
ataxioceratin ammonite
ammonite
Spain
systematics
biogeography
biostratigraphy
paleontology
Ammonoidea
Ataxioceratinae
Geyericeras
Jurassic
Late Jurassic
Opis:
New ammonites collected bed−by−bed from the upper part of Ataxioceras hypselocyclum Chronozone deposits in the eastern Iberian Chain are described as Geyericeras gen. nov. The new genus includes microand macroconchiate Ataxioceratinae of small size, with moderate to loose coiling and subpolyplocoid ribs, a character crucial for its identification. Key points for the comparative identification of Geyericeras gen. nov. are: (i) microconchiate Geyericerasshow morphological convergence with evolute specimens of the stratigraphically older genus Schneidia [m]; (ii) contemporary Ataxioceratinae genera such as Ardescia [m, M] and Lithacosphinctes [m, M] did not develop subpolyplocoid ribbing; (iii) smoothing of sculpture combined with short primary ribs are not realized in Geyericeras gen. nov. [M] and can be therefore used to separate the new genus from Ataxioceras[M]; and (iv) smaller shells, and weaker and less dense ribbing with no parabolic structures differentiate Geyericeras gen. nov. [m, M] from Parataxioceras[m, M], as well as the type of subpolyplocoid ribs seen among microconchiate specimens of these two genera. The new species Geyericeras aragoniense sp. nov. is the index and guide fossil for identification of a biohorizon occurring below the first occurrence of the genus Crussoliceras in the eastern Iberian Chain.
Źródło:
Acta Palaeontologica Polonica; 2010, 55, 1
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Hydrodynamically controlled anagenetic evolution of Famennian goniatites from Poland
Autorzy:
Niechwedowicz, M
Trammer, J.
Powiązania:
https://bibliotekanauki.pl/articles/22390.pdf
Data publikacji:
2007
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
environment change
Famennian
hydrodynamics
Ammonoidea
Polska
Devonian
evolution
Holy Cross Mountains
Tornoceratidae
paleontology
fossil animal
ammonoid
Opis:
This paper reports on the evolution of ammonoids belonging to the family Tornoceratidae from the Devonian of Janczyce in the Holy Cross Mountains, Poland. Steady and gradual changes in conch morphology of the goniatite lineage Phoenixites frechi–Tornoceras subacutum–T. sublentiforme occurred in concert with water shallowing during the deposition of the Lower Famennian cephalopod limestone. Biometric analysis of ammonoid conch and facies analysis of the cephalopod limestones have been applied to assess the possible relationship between shell geometry and environmental changes. Results show that ratios of whorl width / diameter as well as whorl width / whorl height decreased, while distance from the venter to the greatest whorl width / diameter increased with time, thereby reducing hydrodynamic drag of the shells, probably in response to increasing water turbulence. The interpretation presented here is in agreement with similar cases from the literature. However, this kind of environmentally controlled evolution has hitherto been recognized only in Jurassic and Cretaceous ammonoids. Conch morphology may be considered as an indicator of palaeobathymetry.
Źródło:
Acta Palaeontologica Polonica; 2007, 52, 1
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Emergence and collapse of the Frasnian conodont and ammonoid communities in the Holy Cross Mountains, Poland
Autorzy:
Dzik, J
Powiązania:
https://bibliotekanauki.pl/articles/21673.pdf
Data publikacji:
2002
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
Ammonoidea
paleobiology
Conodonta
Polska
collapse
population variability
conodont
community
Frasnian
change
Devonian
evolution
Holy Cross Mountains
paleontology
ammonoid
Opis:
The dominant factor in faunal succession of conodonts in the Frasnian of Poland is the apparent immigration of species originating allopatrically in other regions. Each immigration event usually changes the population variability of a local species (character displacement). Only a few lineages show their phyletic evolution within the studied area. Attempts to distinguish conodont species on the basis of platform element shape failed in some of the latest Frasnian palmatolepidids. Even at the apparatus−based generic level, certain ramiform elements of the apparatus appear much more diagnostic than the platforms. Correlative value of the late Frasnian palmatolepidids of unknown apparatus structure is thus questionable. The evolution of platform elements in Ancyrodella offers a more solid basis for age determination although their great population variability makes resolution rather low and requires the population approach. The panderodontids Belodella(?) tenuiserrata sp., B. minutidentata sp. nov., B. robustidentata sp. nov., prioniodontid Icriodus kielcensis sp. nov., enigmatic monospecific Playfordiidae fam. nov., prioniodinids Dyminodina planidentata gen. et sp. nov., D. anterodenticulata sp. nov., D. kovalensis sp. nov., Pluckidina kielcensis gen. et sp. nov., P. slupiensis sp. nov., P. robustipegmata sp. nov., and P. lagoviensis sp. nov., derived polygnathid Avignathus bifurcatus sp. nov., probably secondarily simplified polygnathid Nicollidina gen. nov., and palmatolepidids Kielcelepis gen. nov., Lagovilepis gen. nov. and Klapperilepis gen. nov. are proposed.
Źródło:
Acta Palaeontologica Polonica; 2002, 47, 4
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Dorsal shell wall in ammonoids
Autorzy:
Kulicki, C
Tanabe, K.
Landman, N.H.
Mapes, R.H.
Powiązania:
https://bibliotekanauki.pl/articles/20686.pdf
Data publikacji:
2001
Wydawca:
Polska Akademia Nauk. Instytut Paleobiologii PAN
Tematy:
dorsal wall
Ammonoidea
biomineralization
dorsal shell
Sibirites
body organ
Aconeceras
shell wall
paleontology
ultrastructure
wrinkle layer
ammonoid
paleozoology
Subolenekites
Opis:
In ammonoids, a soft body organ (possibly a supracephalicmantle fold), extending from the conch aperture secreted aragonitic wrinkles, forming a layer on the surface of the preceding whorl. The dorsal shell wall consists of the outer and inner components which were deposited sequentially, beginning at the aperture of the living chamber inwards. The dorsal wall attains its full thickness near the last septum. The outer component is visible in the apertural region and is smooth or wrinkled; it is called the wrinkled layer in the latter case. The wrinkles may be continuous, interrupted, or form isolated patches arranged in rows. The wrinkles are usually triangular in cross section. A further stage of dorsal wall development involves filling in the space between the apices of triangles, and then adding one or more inner prismatic layers from the inside of the living chamber. This pattern occurs at least in the postembryonic stage of all genera studied, belonging to five suborders of Ammonoidea ranging from Late Carboniferousto Late Cretaceous. In many genera, the outer component of the dorsal shell wall exhibits remarkable ontogenetic change in its ultrastructure and microornament. It may be compared with the black film of Recent Nautilus shells with respect to place of formation. The outer component of the ammonoid dorsal shell wall is regarded as a product of organic secretion and carbonate precipitation in the area of the supracephalic mantle fold.
U planispiralnie skręconych amonoidów, u których ścianka grzbietowa styka się bezpośrednio ze ścianką poprzedniego skrętu, mamy do czynienia z modyfikacją strukturalną ścianki grzbietowej w obszarze styku obu ścianek. Wymienione modyfikacje dotyczą w głównej mierze zewnętrznego składnika ścianki grzbietowej tzw. wrinkle-layer, położonego bezpośrednio na peryostrakum poprzedniego skrętu. Strefa zmarszczek (wrinkle-layer) znana była początkowo jedynie u amonoidów paleozoicznych, dopiero Senior (1971) i Kulicki (1979) odnotowali jej występowanie u amonoidów mezozoicznych. Na podstawie przebadanego materiału obejmującego 12 rodzajów należących do pięciu podrzędów Ammonoidea i występujących od późnego paleozoiku do późnej kredy nie stwierdzono występowania strefy zmarszczek poza ścianką grzbietową. Podobne suuktury, obserwowane u paleozoicznych amonoidów w ściankach bocznej i brzusznej nosza nazwę „Ritzstreifen” i nie są homologiczne do zmarszczek „wrinkle-layer”. Typowa zmarszczka „wrinkle-layer” w przekroju podłuznym zbudowana jest z elementu centralnego, organicznego lub organo-mineralnego, oraz pryzmatycznych warstewek, w których długie osie pryzm są prostopadłe do boków trójkąta skierowanych do wnętrza komory mieszkalnej. Obok typowych elementów strefy zmarszczek, opisano tzw. elementy dwurożne o zarysie okrągłym, lub owalnym u triasowych rodzajów Subolenekites i Sibirites, a także u wczesnokredowego Aconeceras. Te elementy były błędnie interpretowane (Doguzhaeva & Mutvei 1986) jako pory związane z przyczepami miękkich tkanek płaszcza do muszli. Typowa strefa zmarszczek wytwarzana przez fałd nadgłowowy płaszcza, została stwierdzona we wszystkich badanych podrzędach za wyjątkiem Phylloceratina. W wymienionym rzędzie opisano powszechnie występujące rytmiczne modyfikacje peryostrakum wbudowywane do ścianki grzbietowej. We wczesnych stadiach rozwojowych modyfikacje te mogą przypominać elementy strefy zmarszczek, lecz ich pochodzenie i budowa są różne.
Źródło:
Acta Palaeontologica Polonica; 2001, 46, 1
0567-7920
Pojawia się w:
Acta Palaeontologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 18

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