Gradualistic characean lineages in the Upper Cretaceous–Palaeocene of southern Europe

Abstract

Two charophyte lineages from the Upper Cretaceous–Palaeocene of southern Europe are described here, constituting a useful biostratigraphic tool for correlating non-marine stratigraphic sequences. The Peckichara pectinata lineage, ranging from the middle Campanian to the middle–upper Maastrichtian, consists of four successive gyrogonite morphotypes that displayed progressively more complex gyrogonite ornamentation and increasingly smaller gyrogonites with time. The Peckichara sertulata lineage, ranging from the middle Campanian to the Danian, consists of three morphotypes that followed a more common evolutionary trend, developing progressively larger gyrogonites without any changes in ornamentation. Intermediate forms between the successive morphotypes suggest that they corresponded to anagenetic varieties of the same evolutionary species rather than to separate species. The different trends observed appear to be palaeoenvironmentally controlled. The grades of the P. pectinata lineage first occurred in permanent lakes that later shifted to fluvial influenced floodplain ponds, this shift accounting for the reduction in gyrogonite size. By contrast, the P. sertulata lineage mainly occurred in permanent lakes, where stable palaeoenvironmental conditions enabled a steady rise in gyrogonite size to increase the space available for the zygote.

Keywords:

• Characeae
• charophytes
• macroevolution
• K/Pg boundary
• biometric analyses

Acknowledgements

We thank Dr. I. Soulié-Märsche (Institut des Sciences de l’Évolution, Université de Montpellier II, France) for the facilities provided for studying the L. Grambast collection. We acknowledge Dr. Josep Sanjuan (American University of Beirut-AUB), Dr. Ingeborg Soulié-Märsche (Université de Montpellier-II) and Dr. Bernard Gomez (Université Claude Bernard-Lyon 1) and the editor Gareth Dyke for their constructive observations during the peer-review process, which greatly improved the manuscript. Dr. C. Evans and Dr. T. Ahmed, Universitat de Barcelona, have corrected the English text.