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Life span and growth rate of Middle Jurassic mesohibolitid belemnites deduced from rostrum microincrements

Wierzbowski H.

Volumina Jurassica

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2013

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Vol. 11, no. 1

1--18

EN

The microincrements of nine Middle Jurassic mesohibolitid belemnite rostra (Hibolithes jurensis, Pachybelemnopsis fusiformis and Pachybelemnopsis “subhastatus”) were analysed to measure the ontogenic age and growth rate of the belemnites. The microincrements are interpreted to have been formed daily based on analogy with extant coleoid cephalopods and the frequency of circadian rhythms in animal activity. The mesohibolitid belemnites are found to have had a short life span of ca. 1 year. The short life span of the belemnites studied is similar to the life span of modern coleoids (squids, cuttlefishes and common octopuses). It restricts the utility of belemnite rostra as a proxy for average secular seawater temperatures and chemistry. Short-lived cycles (2–8 days) in the belemnite growth rate are linked to variations in the metabolic activity of these animals. Minor diagenetic alteration revealed by the dull cathodoluminescence of some rostra is found to have no effect on the preservation of the growth rings.

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Large-sized ammonites of the genus Calliphylloceras in the Middle Oxfordian of the Polish Jura Chain

Kin A.

Volumina Jurassica

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2006

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Vol. 4, no. 1

236-237

EN

In the Middle Oxfordian (Plicatilis Zone: Patturatensis and Ouatius subzones) of the Polish Jura Chain, the present author found 12 large-sized phylloceratid specimens assigned the genus Calliphylloceras. Maximal diameter of the biggest specimen (nearly complete one coming from the Przybynów locality at Częstochowa) equals 730 mm. Genus Calliphylloceras is a characteristic element of the Mediterranean Province. In the Submediterranean Province comprising the area of the Polish Jura Chain, discoveries of such forms belong to rarities. Presence of phylloceratids, characterized by their large sizes, in the area of this province could have been caused by the postmortem drift of the shells. In contrast to the shells of small individuals, the large ones (>200 mm) had greater chance to be far transported in the sea (assuming postmortem phenomenon). The range of postmortem drift was connected with longer time-span of the buoyancy gases release, during ammonite soft-tissue decomposition. Empty phragmocone cameras were then successively filled with water, but before ammonite shell became sinking they could drifted of hundreds of kilometers. Genus Calliphylloceras is characterized by its largest shell diameters of all Jurassic representatives of the family Phylloceratidae. The occurrence of phylloceratid shells in deposits of Middle Oxfordian (especially of the Plicatilis Zone) both of “normal” sizes, as well as gigantic ones indicates free communication between the Mediterranean and Submediterranean provinces in the area of southern Poland.

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The ammonites of the family Perisphinctidae from the Plicatilis Zone (lower Middle Oxfordian) of the Polish Jura Chain (Central Poland); their taxonomy,phylogeny and biostratigraphy

Głowniak E.

Acta Geologica Polonica

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2002

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Vol. 52, nr 3

307-364

EN

The Plicatilis Zone of the Submediterranean Middle Oxfordian is redefined and subdivided into three subzones; the Paturattensis Subzone, the Ouatius Subzone and the Arkelli Subzone. Their boundaries are defined by the appearance of the successive perisphinctid species referred to a Kranaosphinctes-Otosphinctes lineage. Correlation with other lower Middle Oxfordian zonations is provided. Classification of the studied ammonites is based on the morphological variability in the successive perisphinctid assemblages. The species are assigned to three genera: Perisphinctes, Liosphinctes and Neumannia gen. nov. Microconchs of Neumannia gen. nov. and of Perisphinctes trifidus (SOWERBY) are described for the first time. The type species of the subgenus Arisphinctes, P. ariprepes (BUCKMAN) is reassigned to the subgenus Kranaosphinctes BUCKMAN, and thus Arisphinctes is treated as a younger synonym of Kranaosphinctes; Perisphinctes plicatilis (SOWERBY) and Perisphinctes laevipickeringius ARKELL are reinterpreted and reassigned to the genus Liosphinctes BUCKMAN. Two new chronosubspecies, Perisphinctes ouatius ouatoides and Perisphinctes arkelli wysokae of the subgenus Otosphinctes, are described. The Kranaosphinctes-Otosphinctes lineage gives rise to the Perisphinctes-Dichotomosphinctes lineage at the boundary between the Plicatilis and Transversarium zones. The two other lineages, one of P. trifidus (a possible offshoot from the Kranaosphinctes-Otosphinctes lineage), and the other of the genus Liosphinctes, disappear in the upper Arkelli Subzone of the Plicatilis Zone. Mediterranean roots for all of the three lineages are suggested. The fourth lineage, of Neumannia gen. nov., appears in the upper Arkelli Subzone of the Plicatilis Zone as a consequence of an immigration event from the Mediterranean area.

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The Platysphinctes immigration event in the Middle Oxfordian of the Polish Jura Chain (Central Poland)

Głowniak E.

Acta Geologica Polonica

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2000

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Vol. 50, no. 1

143-160

EN

Ammonites of the subgenus Platysphinctes, represented by the species Perisphinctes (Platysphinctes) perplanatus (TINTANT, 1961), both microconchs, were recently found in the Middle Oxfordian of the Częstochowa Upland (Polish Jura Chain, Central Poland). Their appearance marks an invasion of ammonites of Mediterranean affinities into the Submediterranean Province. This episode is represented in the studied succession by a distinct horizon, named herein the Platysphinctes event - horizon, that is located in the upper part of the newly erected Arkelli Subzone of the Plicatilis Zone. An emended description of Perisphinctes (Platysphinctes) perplanatus and a description of a new species, Perisphinctes (Otosphinctes) arkelli sp. nov. are provided