Tuesday, December 4, 2012

Plant Wars



Over at one of my favorite blogs- The Dragon's Tales - they highlight a new study which provides a model for angiosperm spread during the Cretaceous. For your convenience I will copy and paste the abstract below.




Rise to dominance of angiosperm pioneers in European Cretaceous environments

Authors:

1. Clément Coiffard (a)
2. Bernard Gomez (b,*)
3. Véronique Daviero-Gomez (b)
4. David L. Dilcher (c,*)

Affiliations:

a. Museum für Naturkunde, Leibniz Institut für Evolutions und Biodiversitätsforschung, Invalidenstrasse 43, D-10115 Berlin, Germany

b. Centre National de la Recherche Scientifique Unité Mixte de Recherche 5276, Laboratoire de Géologie de Lyon–Terre, Planètes, Environnement, Université Lyon 1 (Claude Bernard), F-69622 Villeurbanne Cedex, France

c. Department of Geology, Indiana University, Bloomington, IN 47405-7005

*. To whom correspondence may be addressed. E-mail: dilcher@indiana.edu or bernard.gomez@univ-lyon1.fr.

Abstract:

The majority of environments are dominated by flowering plants today, but it is uncertain how this dominance originated. This increase in angiosperm diversity happened during the Cretaceous period (ca. 145–65 Ma) and led to replacement and often extinction of gymnosperms and ferns. We propose a scenario for the rise to dominance of the angiosperms from the Barremian (ca. 130 Ma) to the Campanian (ca. 84 Ma) based on the European megafossil plant record. These megafossil data demonstrate that angiosperms migrated into new environments in three phases: (i) Barremian (ca. 130–125 Ma) freshwater lake-related wetlands; (ii) Aptian–Albian (ca. 125–100 Ma) understory floodplains (excluding levees and back swamps); and (iii) Cenomanian–Campanian (ca. 100–84 Ma) natural levees, back swamps, and coastal swamps. This scenario allows for the measured evolution of angiosperms in time and space synthesizing changes in the physical environment with concomitant changes in the biological environment. This view of angiosperm radiation in three phases reconciles previous scenarios based on the North American record. The Cretaceous plant record that can be observed in Europe is exceptional in many ways. (i) Angiosperms are well preserved from the Barremian to the Maastrichtian (ca. 65 Ma). (ii) Deposits are well constrained and dated stratigraphically. (iii) They encompass a full range of environments. (iv) European paleobotany provides many detailed studies of Cretaceous floras for analysis. These factors make a robust dataset for the study of angiosperm evolution from the Barremian to the Campanian that can be traced through various ecosystems and related to other plant groups occupying the same niches.


From what I gather the dominance of angiosperms in freshwater environments starting in the Barremian was the first step in a series of conquests into floodplains, back swamps and coastal wetlands. And it raises the question, was domination of freshwater environments pivotal for the conquest of subsequent habitats? Is this a recurring theme in plant evolution that new groups proliferate in freshwater habitats before subsequent expansion?



Despite the increase in diversity of angiosperms several other studies suggest that gymnosperms, despite   loss of diversity, maintained high biomass in Cretaceous North America. Wing (1993) notes an in situ paleobotanical deposit from the mid-Maastrichtian that, although rich in angiosperm diversity, is still dominated by gymnopserms and pteridophytes in terms of biomass. In a review of the subject of angiosperm spread during the Cretaceous (Wing & Boucher, 1998) argue that early angiosperms were "ruderal" plants- that is plants that gained footholds in disturbed habitats. In this paper Wing argues that conifers and pteridophytes (ferns, other spore forming plants) enjoyed a type of "ecological incumbency" in less disturbed habitats where fast growth and spread were not limiting factors. Species diversity of a clade is decoupled from ecological dominance in this scenario, Wing posits. This pattern, he argues, is consistant with the prevailing dominance of gymnosperms in higher latitudes into the late Cretaceous while angiosperms gained ground relatively quicker in the lower latitudes with higher solar radiation- allowing faster growth.

Are the contentions of Wing at odds with the new study of do they substantiate each other? Was the switch from gymnosperm dominance to angiosperm dominance essentially a Mesozoic or Cenozoic affair? Did dinosaurs somehow play a role in all of this? Insects?




The Big Cedar Ridge documents in situ volcanically preserved vegetation from the Late Cretaceous. Three dominant communities became apparent. Angiosperms dominated the streamside thickets but, with the exception of one type of palm, were secondary to gymnosperms in other habitats.

Big Cedar Ridge fern "peatland" (c) Mary Parrish

Big Cedar Ridge Palmetto/Fern scrubland (c) Mary Parrish


Big Cedar Ridge streamside vegetation (c) Mary Parrish

Cheers!



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