EVOLUTIONARY SIGNIFICANCE OF FLORISTIC CHANGES IN THE NORTHERN-HEMISPHERE DURING THE LATE CRETACEOUS AND PALEOGENE, WITH PARTICULAR REFERENCE TO CENTRAL-EUROPE

Documented changes in the composition of the vegetation of Central Eur ope during the Late Cretaceous and Palaeogene are compared with those for other parts of the Northern Hemisphere in order to test the validi ty of the supposed global bioevents at the Cretaceous-Tertiary (K/T) a nd Eocene-Oligocene boundaries. Many heterosporous plant species, know n mainly from megaspores, became extinct by the end of the Cretaceous. Most of the plants with which the enigmatic ''mesofossils'' Spermatit es and Costatheca were associated also disappeared towards the end of this period. On the other hand, the angiosperms seem to have evolved w ithout significant interruption at either the K/T or the Eocene-Oligoc ene transitions. Although there were many extinctions during the Late Cretaceous among certain groups, the plants concerned appear to have b een continually replaced by other taxa. Recent studies of fruit and se ed assemblages from Central and Western Europe have revealed 270 speci es of angiosperms and some conifers belonging to 28 families. Of the 1 3 genera recovered from Maastrichtian deposits, 11 occur in the Palaeo cene and are partly represented by the same species. Although the vege tation may have been damaged by the kinds of catastrophic events that are suggested to have taken place at the K/T boundary, such as a bolid e impact or an episode of major volcanism, the effects are likely to h ave been only temporary (a few years) and not necessarily on a global scale. Overall, the palaeobotanical evidence suggests that there were continuous rather than abrupt changes in the composition and physiogno my of the vegetation throughout the Late Cretaceous and Early Tertiary . The changes that took place during the Eocene and Oligocene correspo nd to stepwise climatic deterioration. The uppermost Eocene-lowermost Oligocene transition was connected with subhumid to semi-arid summer s easons which resulted in the disintegration of forest cover and increa sed migration of terrestrial vertebrates. A lowering of mean January t emperatures during the Oligocene led to the ''withdrawal'' or extincti on of some palaeotropical elements and immigration of deciduous trees into Central Europe in several waves, the most pronounced of which was in the middle Oligocene.