Cretaceous angiosperms

[StephanPickering@cs.com]

       Like late Jurassic/early Cretaceous dinosaur taxonomy, there is no consensus in the literature re: the radiation of angiosperms during the same period. Pollen grains are known from the Valanginian/Hauterivian, and during the Barremain/Aptian evolution of angiosperms was apparently quite gradual, increasing in complexity and numbers of genera throughout the Albian/Cenomanian. By the time of the K/T Bolide impact, angiosperms were 75% of land plants, and this is crucial: a concomitant change in herbivorous dinosaur diets must have been taking place. However, throughout the Cretaceous, angiosperms originated in, and did not spread far from, ecohabitats lacking in stability. Scott Wing and Lisa Boucher, in a major 1998 study, state that known morphologies of wood, leaves, and seed from the Cretaceous point to angiosperms "as herbs to small trees with earl!
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successional strategy. The diversification of flowering plants in the Cretaceous represents the evolution of a highly speciose clade of weeds, but not necessarily a major change in global vegetation". As gymnosperms were being displaced, were there dinosaur clades dying out from starvation? What dinosaurs were eating the basal angiosperms? Was seed dispersal and pollination intertwined with dinosaur and pterosaur feces, i.e., a pterosaur flying far from one area would defecate in another, thus propogating a new generation of seedlings? Were basal angiosperms, and their offspring by the late Cretaceous, poisonous to some dinosaurs and not to others? 
       A second avenue of dinosaur research can possibly be gleaned from another avenue. The fossil record, as outlined above, is (forgive the play on words) evolving. DNA sequential data, however, points to something else: 75% of all known angiosperm families, using a three gene data base, indicates angiosperms arose 179-158mya, early/middle Jurassic; eudicots (most of today's genera, e.g., ice plants, lettuce, sunflowers, potatoes, coffee, ivy, rosids, hamamelids, and the asterids [= nearly 75000 genera]) appearing in late Jurassic/early Cretaceous 147-131 mya. I am indebted here to Niklas Wikstrom, Vincent Savolainen, M.W. Chase, 2001, "Evolution of the angiosperms: calibrating the family tree", Proceedings Roy. Soc London 268B:2211-2220.
       The fossil record of dinosaur transitions (extinctions of clades>mutations>new genera) could be linked to botanical changes in biosystems. Biodiversity after extinctions -- let us say, dinosaur populations dying because their metabolisms could not survive because of a decrease in available gymnosperms, perhaps not able to consume and digest angiosperms of unknown kinds -- is not rapid. Jack Sepkoski's 1982 paper on 3500 marine families was the basis for an eye-opening study (it was when I first read it  when published) in 1986 by Jack Seposki and David Raup related to what I am curious about: the 1986 paper points to periodicity of known extinctiion events in the fossil record, i.e., a number of  large extinction events is scattered throughout the fossil record. Some of the extinction events were gradual, but some were devastating on unimaginable scales. James Kirchner, using Jack Sepkoski's analyses, has in two papers!
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one published in 2000 with Anne Weil, the newest paper published this month, January 2002) pointed to interpolations (Mr Kirchner is using spectral analysis) one can derive. After an extinction event, biodiversity is again accomplished, ten million years later. If, however, and I am hypothesizing an example, one asteroid hits, say Nebraska, and another hits Oregon, ten million years may not be enough for dinosaur populations to survive because entire ecological regions -- plants, non-dinosaurs, insects, etc. -- would have been damaged perhaps irreparably. Habitats would not be the same, perhaps would be smaller, and (again I am just speculating) perhaps angiosperms were the plants better able to aggressively spread in such unstable regions more than gymnosperms. As James Kirchner seems to be saying, perhaps biotic genomes have inner speedometers, as it were, and biodiversity can only occur within certain frameworks.