Unidirectional shift in leaf morphology of coexisting species — a possible indicator of palaeoclimatic differences

Abstract

The pre-Neogene basement of the Pannonian domain is built up by a collage of terranes deriving from different parts of the Tethys, which finally accreted in the Late Oligocene–Early Miocene times. Combined stratigraphical, sedimentological, palaeomagnetic and tectonic investigations have revealed the palaeogeographic position of the Palaeogene Basin, including the Buda and Bükk tectonic units However, despite floristic similarities, the Buda and Bükk regions also show important physiognomic differences. In the vicinity of Budapest (Buda unit), the large size and width of leaves are conspicuous, whereas in Eger-Kiseged (Bükk unit), leaves are definitely smaller and narrower. In order to define the differences quantitatively, morphometrical measurements were adopted. The shape and size of leaf fossils were compared by means of a circular grid ( Hill, 1980). Leaves of 4 dominant species ( Sloanea elliptica (Andreánszky) Z. Kvaček & Hably, Engelhardia orsbergensis (Wessel & Weber) Jähnichen, Mai & Walther, Eotrigonobalanus furcinervis (Rossmässler) Walther & Kvaček, and Zizyphus zizyphoides (Unger) Weyland were the target of our study. The average leaf area is 1.4–2.3 times larger in the Buda tectonic unit (Budapest locality) than in the Bükk tectonic unit (Eger-Kiseged locality). Statistical tests proved highly significant differences between these values. Regarding the asymmetry of the leaf lamina, the four species differed considerably. Nevertheless, a significant difference between the two localities was shown only in one of them ( Sloanea elliptica). Consequently, a significant alteration of measures of asymmetry as a function of habitat conditions was not indicated. Smaller leaf area and significantly narrower leaf blade are possible indicators of drier climatic conditions in the Bükk unit.