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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
non-avian dinosaurs.

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 events.


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 not testable.


 observable morphological
changes in birds increased the pool of potential predators on nests
and hatchlings;

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
wetlands;

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 called grasslands.


wetlands and grass are more effective mammal insulators than
other biomes;

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 hypothesis!


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
forever.

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
examination.

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 future.


 This proposition is being actively studied in
birdland.

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 reverse.


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.


  Also, New
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
masses.

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.


 I
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
sites
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:ornstn@home.com