Do NOT write on this paper. Return this paper at the end of the class period!
Extinction Hypothesis A – Mammal Competition
SOURCE # 1 : What Killed the Dinosaurs? - an online resource accessed at
http://www.pbs.org/wgbh/evolution/extinction/dinosaurs/low_bandwidth.html
@2001 WGBH Educational Foundation and Clear Blue Sky Productions, Inc. All Rights Reserved
Hypothesis: Mammal Competition
Extinction implies that the species that perish are poorly adapted to a changing set of conditions.
Faced with an evolving group of competing organisms -- the mammals -- perhaps dinosaurs were driven
to extinction by competition. Packs of small mammals would have competed with dinosaurs for food.
And carnivorous mammals would have preyed on dinosaur eggs. Not only did mammals likely compete
with dinosaurs for resources, many species survived the end-Cretaceous extinction and subsequently
came to dominate Earth.
Evidence for the Mammal Competition Hypothesis
 Fossil Record
A gradual decline in the number of dinosaur species would likely mirror an equally
gradual cause of their ultimate extinction. Conversely, a sudden "now you see them,
now you don't" end to the dinosaurs implies a catastrophic cause. Depending on
location and interpretation, the fossil record seems to say different things. While
mammals certainly prospered on the heels of the dinosaur extinction, it is unclear
whether mammals and dinosaurs experienced little competition or if they regularly
challenged each other for limited resources.
SOURCE # 2 : Guide to the Dinosaurs of Colorado? - an online resource accessed at
http://webspinners.com/dlblanc/paleo/dino-colo/index.php
A resource of the Morrison Museum in Colorado Written by Donald L. Blanchard @2004
Egg Predation by Mammals:
Were there Cretaceous mammals that would have found a nest full of tasty dinosaur eggs an irresistible
treat? Undoubtedly there were. Could new species of mammals have evolved at the end of the
Cretaceous Period that were even more efficient egg stealers than their predecessors? Quite possibly.
Could mammals have eaten ALL the dinosaur eggs (or at least enough of them to cause dinosaurs to
become extinct)? No way! Could early mammals have caused all of the mass extinction that occurred at
the K/T boundary? Don't be absurd.
First of all, mammals, or at least their immediate ancestors, the synapsids, sometimes called "mammallike reptiles," considerably predated the dinosaurs. Dinosaurs competed with, and evolved along side of,
mammals or near-mammals for all of their 150+ million years of existence. It is difficult to imagine that
dinosaurs would have survived for so long if they couldn't defend their nests from predators. Dinosaur
nests have been found in numerous locations, and in at least one case (Maiasaura in Montana),
evidence was found suggesting parental care and feeding of the hatchlings.
Secondly, dinosaurs, at least in the case cited above, appear to have nested in large rookeries, with
many nests together, each separated by about one adult dinosaur-length. This undoubtedly made
predation more difficult, as a predator would have to run the gamut of many dinosaur feet to get to any
but the outermost nests.
The notion of mammals causing the extinction of dinosaurs is mammalian chauvinism, by members of
one mammalian species (mankind) who want to think that their ancestors somehow triumphed over the
"terrible lizards" after all. This position is difficult to defend when dinosaurs were so successful in their
competition with mammals for the entire time that dinosaurs lived. (It could also be pointed out that
this theory fails all the criteria for a successful mass extinction theory, by not even addressing the
marine species that disappeared at the K/T boundary, or any other mass extinction event.)