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An extinct cephalopod mollusk of the subclass Ammonoidea of the Devonian to Cretaceous Periods, having a straight or coiled chambered shell characterized by more or less intricate suture patterns where the septa between individual chambers join the outer shell wall.


any of the extinct group of sea-dwelling cephalopod molluscs with coiled and chambered shells


(ˈæm əˌnɔɪd)

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Noun1.ammonoid - one of the coiled chambered fossil shells of extinct mollusksammonoid - one of the coiled chambered fossil shells of extinct mollusks
fossil - the remains (or an impression) of a plant or animal that existed in a past geological age and that has been excavated from the soil
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The stratigraphically valuable invertebrates, ammonoids, are missing in those deposits, and conodonts are very rare, being represented by a shallow-water polygnathid assemblage.
The age of the studied stratigraphic units is controversial due mainly to the scarcity or even lack of ammonoids and other pelagic fossils commonly used for establishing the chronostratigraphic ages in Global Time Scales (see Gradstein et al.
Geochronological constraints on postextinction recovery of the ammonoids and carbon cycle perturbations during the Early Jurassic.
The first section illustrates the differences between nautilids and ammonoids in respect to shell shape, ornamentation, body chamber, phragmocone, septa, the siphuncle and buoyancy regulation, apparatus, radula and diet, arms and tentacles, eyes, development, mode of life, reproduction, dimorphism, stability, swimming, pathology and teratology, taphonomy, biostratigraphy, mass extinctions, and more.
London, December 22 ( ANI ): Marine animal groups like ammonoids and conodonts already peaked three or four million years earlier, namely still during the Ear-ly Triassic, researchers say.
They collected abundant fusulinaceans and ammonoids, which they identified to establish a biostratigraphic framework for the upper Paleozoic and Mesozoic sequences.
The exact correlation with the subboreal standard zonation based on ammonoids (GRAMANN et al.
The warm climate and floods of the Devonian period produced fishes, ammonoids, and reefs but it also accommodated two of the biggest mass extinction events ever.
Coprolites containing ammonoids from the Devonian of New York.
Analysis of heteromorph ammonoids by differential geometry.
Conodonts also exhibit a broader distribution than Permian ammonoids because they are the only stratigraphically important Permian fossil group that is little affected by provincialism.