Abstract
The new genus Gosavisiphon with the type-species Halimeda paucimedullaris SCHLAGINTWEIT & EBLI, 1998, tentatively referred to the Udoteaceae, is described from the Late Cretaceous (Middle/Late Cenomanian-Santonian) of the Branderfleck Formation and the Lower Gosau Subgroup of the Northern Calcareous Alps (Austria, Germany). It is a plurimillimetric to pluricentimetric marine, hard-substrate dwelling macroalga, with membraneous and partly fused plates and an internal siphonaceous construction but lacking a real medullary zone. Although some thallus details are still unknown, Gosavisiphon gen. nov. can, from a strictly morphological point of view, directly be compared with the Late Palaeozoic and Upper Triassic phylloid algae. Gosavisiphon gen. nov. is the first fossil record of a platy siphonal alga in the Cretaceous, since the Late Triassic Ivanovia triassica REID. The monotypic taxon is most probably endemic to the Northern Calcareous Alps where it dwelled in protected, terrestrially influenced lagoonal environments attaching to hard substrates, (metazoan skeletons, rudistid shells). Based on findings of the cylindrical Halimeda? aff. johnsoni PAL and another taxon described as Halimeda sp. with typically flattened ovate segments, some considerations on the segment-morphological phylogenetic evolution of Halimeda LAMOUROUX are provided. Halimeda species with discoidal-flattened segments, that can morphologically be compared with extant species, are not known prior to the Turonian. Forms possessing cylindrical segments date further back, but can not directly be compared morphologically with modern counterparts, thus placing doubts on the existence of long-lasting methusalemi species by uniting extant and fossil species, as proposed by both botanists and palaeontologists in recent times.
Highlights
In the area of the Northern Calcareous Alps (NCA), Late Jurassic to Early Cretaceous convergence and nappe stacking were followed by extensional exhumation and subaerial exposure of large parts of the orogen (e.g. RATSCHBACHER et al, 1989)
It represents a pluricentrimetric Cretaceous seaweed that is so far only known from the Upper Cretaceous of the Northern Calcareous Alps
For reasons of pragmatism and taxonomic simplification Gosavisiphon is tentatively placed in the family Udoteaceae and can be excluded as a candidate for the Halimedaceae
Summary
In the area of the Northern Calcareous Alps (NCA), Late Jurassic to Early Cretaceous convergence and nappe stacking were followed by extensional exhumation and subaerial exposure of large parts of the orogen (e.g. RATSCHBACHER et al, 1989). The Alpine Gosau Group can roughly be subdivided into a lower subgroup with neritic shelf lithologies, and an upper subgroup consisting of deeper water facies (WAGREICH & FAUPL, 1994) In the Lower Gosau Subgroup, calcareous algae, mainly Dasycladales and Halimedaceae, were reported from lagoonal limestones, rudistid limestones, and marly limestones, intercalated within marly successions of Middle Turonian to Upper Santonian age The alga Halimeda paucimedullaris was described by SCHLAGINTWEIT & EBLI (1998) from the Pletzachalm section in the Sonnwend Mountains, Tyrol. It occurs in the Lattengebirge (Salzburg), Weißwasser-Unterlausa (Lower Austria) and Pass Gschütt-Gosau New material from the Gosau of Gams, Styria, and the reinvestigation of material already published, especially that from the Hofergraben near Gosau, resulted in the recognition of morphological and microstructural details that differ sufficiently from the genus Halimeda LAMOUROUX, to warrant establishment of a new genus of the order Bryopsidales with the generic name Gosavisiphon gen. nov. and the new combination Gosavisiphon paucimedullaris (SCHLAGINTWEIT & EBLI), described in this paper
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