How To Use Ammonoid In A Sentence
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Other molluscs are present but less common, including bivalves, scaphopods, orthoconic cephalopods, tentaculitids, and small, indeterminate juvenile ammonoids.
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Outwardly indistinguishable from other ammonoids, clymeniids are distinguished internally by their dorsal siphuncle, contrasted to a ventral siphuncle in almost all other ammonoids.
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In summary, clymeniids fell well within the general range of Paleozoic ammonoid geometries, though most members of the Clymeniida tended toward an openly coiled shell with a low expansion rate.
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This kind of musculature was probably already developed in the cochleate ammonoids.
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According to these studies, allometric growth is particularly common in Carboniferous and Permian ammonoids.
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The Triassic ammonoids represent the phylogenetic bridge between Paleozoic and Jurassic ammonoids.
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Other mature modifications, such as change in the shape of the peristome, are also inconsistently observed in Paleozoic ammonoids.
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Ammonoids reflected changing environmental conditions by changing their fecundity, whereas in nautiloids a strong heritable differential occurred between genotypes.
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In these periods, the ammonoids became extremely diverse, but comparatively little is known about their Early and Middle Viséan ancestry.
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The sediments are noted for their rich ammonoid faunas, which allow detailed biostratigraphic subdivision and correlation.
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This study, which represents part of my Ph.D. thesis, could not have been performed without the thorough taxonomic work carried out by many Triassic ammonoid systematists that has provided the basis for this study.
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Some nautiloids display embryonic shells that match the dimensions of the ammonoids.
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All of these perrinitid-bearing ammonoid faunas are distributed along the active linear geosynclines and their adjacent areas, i.e., the ‘Open-Sea’ within basin and out shelf.
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Early ammonoids or goniatites may have simple zig-zag sutures, but they become increasingly complex from the Triassic to the Cretaceous.
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Ammonoids are descendants of the extinct, primitive coiled nautiloids and they are extinct relatives of modern squid, octopus, cuttlefish, and nautilus.
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The deposits immediately above the maximum flooding surface are thinly interbedded ammonoid-bearing cherts and lime mudstones.
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Ammonoids are descendants of the extinct, primitive coiled nautiloids and they are extinct relatives of modern squid, octopus, cuttlefish, and nautilus.
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During the prolonged debate over the boundary problem, further results on integrated magnetostratigraphy and ammonoid biostratigraphy were published, and additional palaeomagnetic measurements are in progress.
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Curiously, other Cisuralian ammonoid localities in Nevada have yielded abundant ammonoids but no additional representatives of Uraloceras.
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The taxonomically diverse goniatites dominated the Carboniferous-Permian ammonoid fauna.
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Another theory is that because ammonoids grew faster and had thinner shells, the shells were not as strong as those of the nautilus.
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Strong uniformity in Permian ammonoid biostratigraphy and provincialism between Xinjiang and Pamir is suggested.
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Both Permian perrinitid ammonoid areas are located within the transitional belt between the active geosyncline and the adjacent stable platform.
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Therefore, in terms of geological age determined by radiolarians and the ammonoid, this brachiopod fauna should be assigned to the latest Changhsingian.
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Most of these are from swimming organisms, such as ammonoids and nautiloid mollusks that lived just above the deep seafloor.
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Lewy demonstrated the similarity in breeding strategies between ammonoids and extant octopods.
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This unique succession of ammonoid assemblages allows unequivocal recognition of European substage-level chronostratigraphy across the mid-Carboniferous boundary interval in North America for the first time.
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The late Viséan was therefore the time in which the major Carboniferous ammonoid provinces were separated.
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It should be noted that the inner shell wall of ammonoids was lined by an organic membrane or pellicle, a porous sheet consisting of numerous interwoven organic fibers.
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In the Lower Devonian, ammonoids appeared, leaving us large limestone deposits from their shells.
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They are known to occur in abundance at only a few localities around the world and are entirely absent from some classic, highly diverse Permian ammonoid localities, such as the Urals in Russia and Kazakhstan.
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Bioclasts have mixed orientation, but large ammonoids and ramose corals are invariably concordant.
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They carried out the pelagic and stationary modes of breeding as the cochleate ammonoids.
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They also gave detailed descriptions of associated lithologies, noting that the coralline interval lies some tens of meters below the calcareous shale that contains ‘Paratrachyceras ammonoids’.
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Coiled shells, commonly of ammonoid cephalopods, nautiloids, or gastropods, have been given colloquial names such as rams' horns, snakestones, serpentstones, and conger eels.
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About this time the ammonoids began to take over from the nautiloids.
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The dorsal siphuncles of the Clymeniida tend to be larger than the ventral siphuncles of other ammonoid clades.
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The Permo-Triassic boundary is put below the bed of illite clay rock (the 34th bed of the Ermen Section, Fig. 1), because ammonoid Lytophiceras sp. is found at the superjacent bed.