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Mesozoic (and Pleistocene) biomass issues
Man, go away from the office for a day, and suddenly everyone gets very
Okay, in any case, biomass issues are really significant for dinosaurian (and
any organisms!) biology. The two main factors involved
in per area biomass would be a) productivity of that environment and b) energy
flow up the trophic levels.
In the past there was a tendancy to assume productivity levels were the same in
the past as now. That is clearly incorrect. We have
various lines of geological information on changing atmospheric composition,
temperatures, water vs. land exposure, etc. at
different points in time (some better resolved than others). Recent work by
graduate student Sara Decherd (NCSU) and colleagues show
that plants which retain largely Mesozoic morphologies (such as gingko) have
elevated productivity rates (2-3x Holocene) in modelled
mid-Cretaceous atmospheres. So it might well be that plants were putting out
more energy per unit area per unit time than at
present. I won't even go into additional discussion about black shales here,
How about energy flow through the system? Well, let's just say that
bradymetabolism vs. tachymetabolism in dinosaurs remains a
matter for professional debate.
As for the Pleistocene: productivity rates in the polar regions may well have
been higher in the presence of mammoths. Dale Guthrie
and others have proposed a biome called the "mammoth steppe", based on the very
different pollen ratios and memberships in
Pleistocene Arctic regions to today. The model of this biome goes something
* Mammoths rip up the vegetation in the north, clearing up spots for
colonization of new plants.
* Mammoth droppings allow for the quick recycling of nutrients in the
* The combiination of these two above factors means that the nutrients
are not isolated into a solid tunda and permafrost, but
available for a higher diversity of plants, and thus a higher diversity of
animals. The latter themselves provide more dung and
continued high rates of nutrient recycling.
Then bad times happen to the mammoths and some other megafauna:
* Other animals are less well adapted to ripping up the vegetation mats.
* Less and less space is available for non-tundra type plants to
* Nutrients are less available (less dung), and animals starve or leave.
* Less biotic activity in the soil allows for establishment of
nutrient-poor dense tundra layers and of permafrost.
* Things suck for the North.
These issues are by no means agreed upon by all Quaternary workers, but I think
that they have a lot of merit.
Thomas R. Holtz, Jr.
Senior Lecturer, Vertebrate Paleontology
Department of Geology Director, Earth, Life & Time Program
University of Maryland College Park Scholars
Building 237, Room 1117
College Park, MD 20742
Phone: 301-405-4084 Email: firstname.lastname@example.org
Fax (Geol): 301-314-9661 Fax (CPS-ELT): 301-405-0796