Abstract Detail



Paleobotany

Pipo, M Laura [1], Iglesias, Ari [2], Bodnar, Josefina [3].

A new conifer taxon based on anatomically preserved leafy shoots from the Upper Cretaceous, James Ross Basin, Antarctic Peninsula.

Evolutionary history of conifers has been represented by taxa with different kind of leaves. As far as we know (mostly by studying the extant genera), the bigger leaves, broad, flattened and sometimes petiolate, are characterized by having multiple vascular strands. On the other hand, the smallest the leaf the less quantity of vascular strand there are, being almost all extant conifers with a single strand. Here we present a new conifer taxon with small leaves (brachyphyll) but with multiple vascular strands from the Santa Marta Formation (James Ross Island). The fossil samples are preserved in calcareous concretions from the Beta Member (early-mid Campanian) and correspond to plant remains transported by estuarine currents from the east continental margin of the Antarctic Peninsula. The permineralized remains have such excellent preservation that we can study fine anatomical details and 3D organic connections. Thin sections were studied using the cellulose-acetate peel technique, and cuticles were obtained by bulk maceration. Conifer remains are frequent in these concretions, consisting of leafy shoots and isolated leaves and seeds. So far we have differentiated almost 4 different foliage. The young shoots are approximately 10 mm in transverse section and have been preserved by up to 40 mm long. The adpressed leaves are in helically disposed, the blade is up to 10 mm long with rhomboidal section tending to triangular toward the apex. The distinctive characters that make this taxon unique are the presence of multiple vascular strands (from 8 at the base, to 1 at the leaf apex), multiple resin channels (one medial bigger, in abaxial position), and disorganized transfusion tissue. Leaf epidermis shows to be hypostomatic, with random distribution (not present at keel and margin areas), and not oriented stomata. Subsidiary cells consists of 4 (6-9) cells, with polar cells, Florin ring well developed. Polar extensions in guard cells are present. The adaxial side of the leaf is characterized by sinuous and buttressing epidermal cells. Among extant gondwanic families, there are two in which most of these characters are recognized: Araucariaceae and Podocarpaceae, both already known to have had an important role in the Cretaceous Antarctic forests. However, up to now, no anatomically preserved fossils are known having brachyphyll leaves with multiple veins.


1 - INIBIOMA, Quintral 1250, Bariloche, 8400, Argentina
2 - INIBIOMA, Quintral 1250, Bariloche, Rio Negro, 8400, Argentina
3 - La Plata National University , Paseo del bosque s/n, La Plata, Buenos Aires, 1900, Argentina

Keywords:
Cretaceous
Antarctica
conifer
anatomy
Leaf
Concretion
Gondwana
Cuticle
PeelĀ 
Araucariaceae
Podocarpaceae.

Presentation Type: Oral Paper
Number:
Abstract ID:116
Candidate for Awards:Isabel Cookson Award,Maynard F. Moseley Award


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