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The Barremian heteromorph ammonite Dissimilites from northern Italy: Taxonomy and evolutionary implications

100%

Lukeneder A., Lukeneder S.

Acta Palaeontologica Polonica

2014

tom 59

nr 3

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.

Spatiotemporal signals and palaeoenvironments of endemic molluscan assemblages in the marine system of the Sarmatian Paratethys

80%

Lukeneder S., Zuschin M., Harzhauser M., Mandic O.

Acta Palaeontologica Polonica

2011

tom 56

nr 4

The present study is the first quantitative comparison of Sarmatian mollusc assemblages from the Central and Eastern Paratethys seas. The assemblages (47,840 shells, 32 samples, 84 species) derive from eight Middle and Upper Miocene localities covering an interval from 12.7–11.0 Ma, when a highly endemic mollusc fauna flourished in the entire Paratethys. Cluster analysis of samples yields two major clusters: one composed of late Sarmatian (Bessarabian) collections and the other composed of early Sarmatian (Volhynian) collections. The Volhynian cluster includes two subclusters: the first reflects a strong stratigraphic signal because it combines samples from the Mohrensternia Zone of the Vienna Basin and the western Ukraine. The second combines samples from the Upper Ervilia Zone of the Vienna Basin with samples from the Mohrensternia Zone of the Vienna Basin and Romania. Cluster analysis of species indicates that the sample clusters represent different palaeoenvironments with distinct molluscan assemblages: The Volhynian wellagitated shore is characterized by the Granulolabium–Venerupis–Ervilia biofacies, the Volhynian muddy foreshore by the Granulolabium–Mohrensternia–Ervilia biofacies, and the Bessarabian shallow to medium deep sublittoral by the Hydrobia–Venerupis–Pseudamnicola biofacies. Although not all biozones and regions of the Sarmatian Sea are covered, we suggest that these biofacies cover a wide range of possible assemblage compositions of Sarmatian nearshore and shallow−water assemblages.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

2 Lukeneder S.

1 Harzhauser M.

1 Lukeneder A.

1 Mandic O.

1 Zuschin M.

1 2014

1 2011

Wyniki wyszukiwania

The Barremian heteromorph ammonite Dissimilites from northern Italy: Taxonomy and evolutionary implications

Spatiotemporal signals and palaeoenvironments of endemic molluscan assemblages in the marine system of the Sarmatian Paratethys