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Re: Sundry responses of Bois
Refuting John Bois' egg predation "explanation" for dinosaur extinction
seems to be a recurring activity hereabouts, so if any of this sounds like
stuff I've said before I apologize!
Lillegraven and Eberle comment in 1999 paper, that in the cross K/T strata
that they studied, the _only_ apparent change was the disappearance of
I am curious as to the extent, both temporally and geographically, of the
period covered by this paper. Surely these factors relate to a question of
the changes in the biota at the K/T - and to the question of what you are
trying to explain. Certainly it is true that we have no evidence that
every taxon that was around in the Cretaceous but gone by the Paleocene
actually survived up until the last moments of the K/T boundary. However,
this does not mean that all of the non-dinosaur taxa that disappeared died
out before the end of the period, or, conversely, that every line of
dinosaurs that disappeared during the Cretaceous survived until the last
moment in order to be overwhelmed by a catastrophe that struck them and
them alone. It strikes me that the phenomenon, or combination of
phenomena, that we are trying to explain is the biological changeover that
is more or less marked by the boundary, whether or not the events occurring
precisely at the boundary were even partially responsible. Therefore, the
question of what killed off the dinosaurs, especially if more than one
factor can be identified, should not be restricted specifically to the K/T
Viewed in this way, the criticism of John's explanation that it does not
extend to events during the final decline of the dinosaurs that led to the
extinction, at more or less the same time, of many other taxa is not
invalidated by the narrow conclusions of the paper he cites.
Since the hypothesis is dependent upon several subsidiary hypotheses, it
should be easy to falsify. These are: dinosaurs were relatively ineffective
at concealing their nests and depended instead on active nest defense;
This fits very nicely my distinction between a hypothesis and an educated
guess. As far as I can see there is absolutely no evidence one way or the
other on this point, even for those dinosaurs for which we have egg and
nest remains. There are many ways that an animal can conceal the location
of its nest, including some, such as cryptic color patterns on eggshells,
that are highly unlikely ever to turn up in fossil evidence. For example,
there are species of shorebirds, such as the Hooded Dotterel of southern
Australia, that lay their eggs in the open on sandy beaches. However, the
eggs are so cryptically colored that it is extremely difficult to detect
them, even at close range. This kind of "hiding in plain sight" would
simply be impossible to detect from fossil evidence. Therefore, I submit
that not only is there no evidence in support of John's claim, but that
there is unlikely ever to be, and therefore that it is not testable.
observable morphological changes in mammals increased the pool of
potential predators on nests and hatchlings;
As others have pointed out, there appears to be no evidence of this either,
and in fact there does not appear to be away of identifying such a change
should it have happened. If this is true, then this hypothesis, too, is
changes in birds increased the pool of potential predators on nests
I would be curious to know what John is talking about here. Egg predators
among birds include, at least among living species, a very wide range of
creatures including jays, toucans, Egyptian Vultures (which use tools to
break ostrich eggs, another aspect of their behavior that would be unlikely
to fossilize) and other birds. There are no, to my knowledge, specialized
egg predators among birds. Therefore I would not be at all sure how to
identify the kind of morphological change that John is talking
about. Further, most bird fossils are of limb elements. Skulls are quite
rare in the fossil record, and therefore the chief area where you might
expect to find adaptations for egg-eating is the area least likely to
provide us with evidence.
such adaptations increased the competiveness of
neornithines and also resulted in the gradual domination of
neornithines over enantiornithines toward the K/T;
Frankly, I do not think we have any idea why the neornithines supplanted
the enantiornithines, and I have certainly never seen any suggestion of a
specific morphological change that gave modern birds the edge. Again, I
would like to know what John is talking about here.
mammals and birds
today and throughout the Cenozoic have limited the evolution and
distribution of large egg layers;
As we have discussed many times before on this list, with many contrary
examples, this statement is at best only partially true. Even if it were
entirely true, it is equally true that many living egg-laying animals have
found ways to get around this problem, either by altering their nesting
behavior or by nesting in inaccessible places. I see no reason why the
dinosaurs should not have been able to do the same, especially as they had
tens of millions of years of coexistence with egg predators of one sort or
another to get things right.
successful large egg layers depend on
grass (a concealing medium which did not exist at the K/T), or
This statement does not apply to many successful species of ground-nesting
birds and reptiles today which are neither inhabitants of grassland or of
wetland areas, including many tortoises and birds like the ostrich, which,
despite John's claim to the contrary, nests quite successfully in areas of
near-desert which could only by the greatest stretch of the imagination
wetlands and grass are more effective mammal insulators than
I see no evidence of this whatever. There are a number of successful
wetland-dwelling mammals from many different lineages, including predators
as large as the tiger and a small as a water shrew. As for grasslands,
anyone who has taken a trip to the African savannas would have a hard time
understanding that such areas are mammal-poor.
post K/T dinosaurs will be found.
Surely a prediction of future events cannot be used as evidence for a
Therefore, from the above, I must conclude that if John's principal
hypothesis depends on the subsidiary hypotheses he has stated, everyone of
which is either unsupported by available evidence or incapable of
verification from the fossil record, then the principal hypothesis itself
is by definition unsupportable.
If someone discovered big terrestrial egg
layers and mammals (particularly placentals) living in harmony--without
having to hide, I would run away
As it has been repeatedly pointed out that this is indeed the case for
ostriches and emus, both of which coexist with potential nest predators and
often nest in open, completely unconcealed situations, I am inclined to
doubt this promise.
But the egg laying way of life really does appear to be heavily
constrained by predation.
There is certainly no question that any animal, whether it lays eggs or
not, may be highly vulnerable at the reproductive stage. However, a
constraint is not an eliminating factor. That dinosaurs suffered from nest
predation would seem to be so obvious as to almost not require
verification; that they were so incapable of defending themselves against
nest predators that this factor became the primary or sole contribution to
their final extinction is a very different kind of claim indeed, and one
that is not obvious in the least.
This is at least an hypothesis worthy of
Perhaps, but I do not think it is worthy very much examination. This is
because, to put it simply, there is no compelling evidence supporting it
and it is highly unlikely that any such evidence will be forthcoming in the
This proposition is being actively studied in
It may well be that the number of Island birds were wiped out by introduced
nest predators such as rats, but in every case that I can think of the
introduced animals could also have killed adults (including incubating
adults - something that may welll have a greater effect than clutch
loss). This is highly unlikely to have been the case for Tyrannosaurus
rex! Further, all of these examples were the result of human-caused
introductions into extremely isolated ecosystems over a very narrow time
frame, and I'm not all sure that analogous events could have happened on a
worldwide scale in the past.
Specifically, extant egg-eaters show no particular egg eating adaptations.
There is actually one striking exception to this. The egg-eating snakes of
Africa have very specific adaptations to their diet, including the loss of
teeth and the presence of projecting spikes on the vertebrae that assist in
cracking the eggshell.
Firstly, most large turtles
lay in very out of the way places probably trying to minimize predation.
Actually this statement does not seem to match what is known about the
biology of sea turtles. There are a number of factors involved in the
selection of nesting beaches by sea turtles, but most of these are physical
factors such as the width of the beach, the slope of the sand, and other
aspects of beach structure that seem to be related more to the need to keep
nests from being washed away by the sea and to any need to avoid
predators. Sea turtles certainly take steps to prevent their nests from
being discovered, such as sweeping sand over the nest site with their
flippers, but this is not the same thing as nesting in "out of the way
places." There are many sea turtle beaches in continental areas where nest
predators certainly occur, and in fact it is well-documented that predators
on hatchlings take a large toll on the babies as they emerge from their
nest burrows. And yet sea turtles have survived with very limited
morphological change since the Jurassic.
The nests of many species of megapodes, in addition, are huge mounds that
are almost impossible to ignore in the right kind of habitat. This
includes the three Australian species, which co-exist with nest predators.
Such an analysis supports my hypothesis. The vast majority of survivors
employed strategies of stealth rather than defense.
To repeat, we haven't the faintest idea to what extent dinosaurs relied on
concealment to protect their eggs. This is another statement that simply
cannot be tested.
If Australia is both geologically and
taxonomically different, we should not be surprised to see differences in
the success and/or failure of different strategies. I realize this says
little about my hypothesis.
In fact, I would describe this statement as little more than wishful
thinking. Although there are certainly some unique adaptations among
Australian animals and plants -- as is true for every other biota I can
think of -- one of the most remarkable things about evolution in Australia
has been the extent to which it has resulted in convergence. It would
appear that Australia is a better example of the degree to which different
evolutionary lines can produce very similar strategies that it is of the
1. The biggest birds in recent history were found on islands depauperate of
carnivorous fauna. It is widely accepted that the "cause" of the
evolution of huge Moa on New Zealand is the absence of mammals.
Yes, but not the kind of mammals you are talking about. The evolution of
moas was probably influenced far more by the absence of herbivorous
browsers and grazers, to which the moas could supply ecological
replacements, then it was by the absence of predators. As for the other
lines of giant birds, not one arose in an area without mammalian
predators. In fact, the extremely large size and thick eggshells of the
elephant birds of Madagascar might possibly have been an antipredator response.
Zealand bird species with close relatives in Australia have longer
incubation times than their continental counterparts. This suggests that
predation pressure has an effect on the evolution of life history
strategies and that this pressure is different on different land
I see no reason to conclude this. Longer incubation times might just as
easily be the result of differences in climate or food availability.
3. The largest and most diverse big bird faunas of Australia came after the
evolution of grass--a very effective concealing medium.
Considering that grasses did not really become predominant anywhere in the
world until the Miocene, and this period Was also the one in which there
was probably the greatest radiation of oscine songbirds, which are the most
diverse group of birds today, I do not see how this statement applies any
more to Australia than it does to anywhere else in the world. Further, if
the spread of grasslands was really correlated with the success of
ground-nesting birds, I would have expected to see, not a radiation of
songbirds, but of other more terrestrial groups, during that period. As it
stands, I know of no evidence from the fossil record or anywhere else to
support John's claim.
5. Australia possesses the largest forest-nesting bird--the cassowary.
Which lives in an area inhabited by bandicoots, daysures, and other
potential egg predators.
Only if the parent doesn't give it away by its presence. My hypothesis
depends upon either nest attendance by most dinosaurs, or improved ability
in finding buried eggs. I would argue that it is very hard for a big
dinosaur to conceal anything.
I would argue that it is extremely easy if the dinosaur doesn't hang
around, or adopts behavior that makes it very difficult to locate the
precise site of the nest within the area where it spends most of its
time. Deer, which include some quite large animals, seem quite capable of
concealing their fawns during much of the day while their foraging. I do
not see why dinosaurs could not have had similar behaviors.
I claim that there is an upper limit in
size of parent for most
locations for the success of the lay-and-leave strategy, and that the
distribution of turtle species of different sizes supports that.
The largest living turtle, the leatherback, adopts -- as all turtles do --
a lay-and-leave strategy. In fact, since I know of no turtle that does
not, I do not see what turtle size has to do with this point.
Sand supports less vegetation and affords less concealment, i.e., a
large dinosaur leaves a large signature.
Once again, this should also apply to sea turtles, which appear quite
capable of concealing their nests.
would also add leash laws, predator extirpation and the behavior of Canada
Geese, viz., they are unlike Snow Geese which show high fidelity to nest
in Northern Canada.
Snow Geese, by the way, nest in areas where their nests are neither
concealed nor safe from egg predators such as the Arctic Fox.
Ronald I. Orenstein Phone: (905) 820-7886
International Wildlife Coalition Fax/Modem: (905) 569-0116
1825 Shady Creek Court
Mississauga, Ontario, Canada L5L 3W2 mailto:email@example.com