The leaf of Glossopteris: character?s restatement to allow a cluster analysis based on the morphography

COTUREL, ELIANA P.

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

The Permian flora of Gondwana is portrayed by the presence of Glossopteris, a genus of tongueshaped, entire leaves. This genus includes almost one hundred species, leading several authors to think about an artificially over-represented diversity at the species level. A major problem comes from the fact that leaves are mostly represented as impressions, showing few useful characters for taxonomic discrimination. Permineralizations and cuticle preservation increase the number of characters available for taxonomic analysis, but few studies are able to determine natural taxa combining different preservation types. Several authors have pointed-out different useful characters in taxa discrimination, but classifications still allow subjective interpretations, with no clear limits between species. However, the abundance and morphological variability of Glossopteris allow the searching of new approaches to solve the problem of its classification. I propose herein the use of software classification tools and the reassessment of leaf characters in order to group them based on their similarities. The ultimate objective of this method is to create a parataxonomy that could be used world-wide, and reduce the number of potential artificial species. The first appointed character I have considered is the course of secondary veins. This character has been defined by: (i) the angle of departure from the midvein, (ii) the general course of veins, and (iii) the angle of contact of the veins with the leaf margin. To compare (i)-(iii) together as a same unit, I have: 1) standardized the leaves to remove the differences caused by size, 2) reinterpreted the veins as a curve, and 3) obtained the formula that describes the curve in the standardized interval between the midvein and the margin. This allowed me to get a full characterization of the veins, and compare the positions of different veins in a coordinate axis point by point. Other standardized characters were the density of secondary veins and the types of intersection between veins. The comparison was made using distance coefficients, resulting in several morphogroups. These morphogroups are in part correlated with the already known species. The improvement of the analysis with a larger dataset, may result in a grouping that could be useful for paleoecological, systematic and biostratigraphic studies.