GEOL 104 Dinosaurs: A Natural History
Fall Semester 2006
Eat or be Eaten: Dinosaur Paleoecology
Ecology is NOT what most people think it is!
It is not environmental activism. Instead:
- Ecology is the scientific study of the factors which control the abundance and
distribution of organisms.
Therefore, ecology isn't about saving the whales, but it WILL tell us something about HOW to
save the whales...
Paleoecology is attempting to reconstruct the ecology of extinct forms.
Some aspects about paleoecology:
- Ecological niche: the "way of life" of a particular taxon
- Species ranges: how large an area did a particular species occupy at a given
point in time (very difficult for most dinosaurs, as they are known from very few specimens)
- Trophic relationships: aka "who eats who". Often restored as a food web
- Can get some good idea about carnivores vs. herbivores, but difficult to establish
exactly which carnivores ate which herbivores, and which herbivores ate which plants.
Bakker used his interpretations of trophic relationships to try and determine the
thermophysiology of dinosaurs and other extinct forms. His technique:
- In modern endothermic communities very few predators compared to many herbivores
(tachymetabolic predators require a lot of food, so only a few can survive in a given
- Bradymetabolic predators require a lot less food, so same amount of potential food
can support many bradymetabolic predators.
- In order to calculate P/P ratios, Bakker had to consider the different sizes of the
various populations. Used biomass (# kgs or tons of flesh) rather than number of
- Found that modern populations had P/P ratios of 0.5 – 4 %
- Looking at fossil record, found:
- 1st Radiation (Basal synapsids): 25 – 30%, much higher than modern populations. Most
paleontologists have accepted this as a cold-blooded community
- 2nd Radiation (Therapsids): 10 – 20%, seemingly between endo- and ectothermic
- 3rd Radiation (Pseudosuchians): 10 – 20%, as in 2nd
- 4th Radiation (Dinosaurs): 0.5 – 3.5%, as in modern endotherms!
- 5th Radiation (Mammals): 0.5 – 4.5%, known endotherms
- How do you know the dinosaur mass estimates are correct?
- How do you know that the numbers accurately sample fossil populations?
- At least 1st and 5th Radiation populations seem to match expectations (but new finds
from Germany may show almost mammal-like levels for upland 1st Radiation communities!)
- How do you know which dinosaurs ate which?
- At best can only give the thermal physiology of predators!
- For herbivores would need a Herbivore Biomass – Plant Productivity ratio
- Some preliminary evidence suggests that MORE herbivores per acreage in dinosaur
populations than in modern or fossil mammal populations
So, P/P ratios are problematic, at best.
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Last modified: 14 July 2006