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Aalenian (Jurassic) to Berriasian (Cretaceous) chronostratigraphic zonation and guide ammonites of the Central Andes (Argentina, Chile, Peru)

Parent Horacio

Volumina Jurassica

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2022

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Vol. 20

1--46

EN

In the Central Andes there are developed two marine basins with an extensive Jurassic record: the Neuquén (or Central Andean) Basin and the Tarapacá Basin. Their Jurassic and Lower Cretaceous ammonite successions have been studied extensively for more than 150 years, producing detailed chronostratigraphic scales based on ammonite zones and biohorizons. The ammonite faunas include Andean lineages, and cosmopolitan, Tethyan, Caribbean, North American, and Indo-Madagascan elements. This paper presents the results of a revision of the zonation of the interval Aalenian-Berriasian. Before presenting the results, this paper emphasizes the distinction between, and the convenient nomenclature for, biozones, zones, standard zones, and biohorizons. The scissum Hz. (new) is introduced in the lower (-most?) Manflasensis Zone (Aalenian). The Rotundum Subzone (new) with base at the cf.-leptus Hz., is introduced for the upper part of the Rotundum Zone (Bajocian). The Gulisanoi Zone (Bathonian) is standardized by designation of the cf.-aspidoides Hz. (new) as its base. The Chacaymelehuensis Zone (new) with base at the “prahecquense” Hz. (new) is introduced for the Callovian. The Cubanensis Zone (Oxfordian) is introduced to replace nominally, or to rename, the inconveniently named “Passendorferia” Zone. The Tarapacaense Zone (Oxfordian) is standardized by designation of the tarapacaense Hz. (new) as its base. The Tithonian Malarguensis Zone (formerly subzone) is here emended and standardized by designation of the malarguensis Hz. as its base; this zone replaces the unviable Mendozanus Zone. The Zitteli Zone is standardized by designation of the widely recorded perlaevis Hz. as its base. The Fascipartita Subzone (Internispinosum Zone) is standardized by designation of the internispinosum-beta Hz. (new) as its base. The Alternans Zone is standardized by designation of the vetustum Hz. as its base, and the Koeneni Zone (uppermost Tithonian) by designation of the striolatus Hz. as its base.

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Late Cretaceous nautilid beaks from near-shore/shallow water deposits of the Bohemian Cretaceous Basin (Czech Republic)

Kostak M., Vodrazka R., Frank J., Mazuch M., Marek J.

Acta Geologica Polonica

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2010

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Vol. 60, no. 3

417-428

EN

More than 30 isolated nautilid jaws have been discovered in washed samples of late Cretaceous (turonian) nearshore/shallow water deposits located in the southern part of the Bohemian Cretaceous Basin (BCB). upper and lower jaws discovered in genetically-similar early turonian deposits are described in detail herein. the nautilid jaw apparatuses comprise rhyncholites (upper jaws) assigned to Nautilorhynchus simplex (Fritsch), and conchorhynchs (lower jaws) assigned to Conchorhynchus cretaceus Fritsch. some rhyncholites show signs of abrasion and corrosion, and may also form a substrate for sessile organisms. in one specimen, signs of acid digestion in the stomach of a predator were recognized. N. simplex is synonymized with "Rhyncholithus" bohemicus (till), "R". curvatus. (till), "R" rectus (till) and "R". curtus (till). the significant morphological variability observed in N. simplex is supported by biometric data. although the jaws were not found associated with body chambers, it is inferred from the extremely low nautilid biodiversity across the Cenomanian/turonian boundary interval in the BCB, and from the range and relative abundance of the only early turonian nautilid taxon present, that the jaws are probably referable to the genus Eutrephoceras hyatt and specifically to the common and long-ranging species E. sublaevigatum (d'Orbigny).

3

The erroneous distinction between tetrabranchiate and disbranchiate cephalopods

Lewy Z.

Acta Geologica Polonica

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2000

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Vol. 50, no. 1

169-174

EN

The informal subclass name Dibranchiata is still attributed to extant coleoids, referring to the possible taxonomic significance of the gill number cephalopods. Ammonoids and the dibranchiate octopods exhibit a remarkable similarity in breeding strategies and an ammonite shape of argonautid egg cases, suggesting close phylogenetic relationships in which octopods are nude ammonoids, and accordingly reflect the dibranchiate anatomy of ammonoids. All these cephalopods descended from the Paleozoic nautiloids, which are represented today by two genera with a tetrabranchiate gill structure and other anatomical features, which differ from those in extant coleoids. The physiology of extant nautiloids enables them to survive in waters with low oxygen content at a few hundred meters depth, toward where the nautiloids withdrew. The two pairs of gills, which occur in extant nautilids only, are suggested to rflect a minor anatomical modification to improwe respiration in low oxygen settings by the duplication of the cephalopod initial single pair of gills, and are thus of no taxonomic significance.