[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

100% goose-free responses (longish and eggy, though)



I said:
>>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;

Ron replied:

>...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.

Egg-shell crypticity may or may not have been used by non-avian dinosaurs.
However, if eggs were buried, or if hadrosaur-sized parents attended nests
(both of which are known), this may not be all that relevant.  But if
parents attended nests (testable), the nests were easier to find than extant
nesters simply because big things are easier to find.  Ostriches are very
good at hiding, but they depend on a medium which did not exist, i.e.,
grass.  And, there is likely an upper limit to the size an animal can be if
it wants to remain hidden, even in the biome that supports the very largest
extant dinosaur body plan (ostrich).

I said:
>>observable morphological changes in mammals increased the pool of
>>potential predators on nests and hatchlings;

Ron replied:
>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.

Again, a change in dentition has been observed.  Dental diversification
increases in the latter part of the Cretaceous: from specialized
insectivorous to omnivorous types.  Since most/all nest predators today are
omnivores, this change does represent an increase in _potential_ nest
predators.  This is a fact.  And, rather than pointing out what others have
pointed out, if you want to refute this, you should tackle it head on.  No
one else has!  I am not arguing that such changes did lead to increased
predation pressure, only that the fossil record indicates an increased
potential for it.  I agree that we will probably never know if mammals and
birds did prey on Cretaceous nests.  Nevertheless, an increase in potential
predators is indicated.

I said:
>>...observable morphological changes in birds increased the pool of
>>potential predators on nests and hatchlings;

Ron replied:
>I would be curious to know what John is talking about here.

And:

>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.

And:

>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.

You are forgetting that most predation by birds on ratites is on
chicks, not eggs.  Relative to mammals, chicks are a much smaller proportion
of adult size.  This makes them highly susceptible.

The issue of enantiornithine/neornithine competition/predation is an
interesting enough question in itself without its resolution impacting my
ideas.  If it is ever resolved, the answer surely will involve more than
bills.  When I say adaptations I am not referring only to bill adaptations
(though these may be important).  Something happened in the genome of
neornithines to enhance their survival relative to enantiornithines.
Improved flight characteristics, enhanced neuronal capacity--leading to
greater flexibility of behavioral response, claw structure, all could have
been critical in effecting this change.  If something along these lines lead
to their dominance over enantiornithines, a thoroughly reasonable
proposition is that it impacted non-avians as well.  This is especially
likely because hatchling dinosaurs were not much bigger than the biggest
chicks today (which suffer tremendous predation from birds of prey). Is
there ever going to be a site as forthcoming about this issue as the China
fossils are about bird origins?  If so, I would look for limb changes and
skull changes for an indication.  It could be something as simple as
vertical takeoff ability.  And, although we will most likely never have
direct evidence of bird predation on hatchlings, morphological changes may
permit us to infer an increased likelihood of such predation.

I said:
>>mammals and birds today and throughout the Cenozoic have limited the
>>evolution and distribution of large egg layers;

Ron replied:
>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.

This is the negative equivalent of the dinosaurian senescence idea.  But it
is equally unsupportable.  Creatures don't always "get things right".
Indeed, if animals did there would be no point in looking at the fossil
record: it would have remained unchanged since species got things right.  As
it exists, however, it is full of things that got things wrong.  The
argument here is whether dinosaurs were affected by normal biological
pressures.  Saying: No, because they got things right, amounts to little
more than gainsaying.

I said:
>>successful large egg layers depend on grass (a concealing medium which
>>did not exist at the K/T), wetlands and grass are more effective mammal
>>insulators than other biomes;

Ron replied:
>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.

Grasslands indeed shelter ostriches on the African savannah.(argued in
"Harmonious depredations" post).  By "insulators" I meant insulating
oviparous species from predation.  I certainly don't mean that mammals
cannot exist in these biomes.  But current understanding of endangered
wetland species follows the general principle that contraction of wetland
habitat increases mammalian predator access and, therefore, nest failure
rates in waterfowl (Picman 1998, Pasitschniak-Arts and Messier 1995,
Sanchez-Lafuente et al. 1998).  This suggests that wetlands are an effective
refuge from predation.  In addition, predator density is lower in wetlands
vs. uplands in waterfowl habitat--and nesting success greater (don't have
paper on hand--can cite if needed).

I said:
>>  post K/T dinosaurs will be found.

>Surely a prediction of future events cannot be used as evidence for an
>hypothesis!

This is fair.  I should have said: The hypothesis is that dinosaurs did not
become extinct at the same instant across the world.  One prediction from
that is that post K/T dinos will be found.  Another one would be extinction
rates should vary from one location to another.  I believe there is evidence
for the latter.

I said:
>>  But the egg laying way of life really does appear to be heavily
>>constrained by predation.

Ron replied:
>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.

This must be considered from taxon to taxon.  Certainly, over geological
time, constraints have eliminated species.  Indeed, I could claim that
extant large oviparous species have been eliminated from the majority of
biomes.

Regarding: "any animal, whether it lays eggs or not, may be highly
vulnerable at the reproductive stage."  This is obvious.  But it ignores
the critical points of my argument: eggs are stationary; oviparous
offspring are smaller relative to adult size than mammal offspring--they
are, therefore, vulnerable to a greater range of predators; and the
biggest oviparous animals have the smallest relative offspring size.  Any
given egg baby stands a higher chance of being preyed upon than any given
neonate.  Yes, oviparous species may compensate by having more
babies.  But clutch size is finite.  This is especially true if it costs
large species a greater share of their daily energy budget to make an egg
than small oviparous species--I have a paper which claims that.

Ron said:
>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.

Agreed.

Ron said:
>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 than it is of the
>reverse.

Such as, what?  A marsupial horse, monkey, human, cow, pig, hippopotamus?
Convergence is a wonderful thing.  But it says nothing about the relative
talents of the respective mammals.

>>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.

This is definitely the minority view.  Most cite absence of predation as the
prime factor here (e.g., Romer 1964, Fuller 1987, Quammen 1996, Diamond
1998)

>...the extremely large size and thick eggshells of the elephant birds of
>Madagascar might possibly have been an anti-predator response.

Can you suggest a likely predator on elephant bird adults?  Are there any
papers on the possible ecology of this extinct bird?  This is yet another
area crying out for research.

>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.

I thought that was my argument!

>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.

I don't follow.  If "the question of what killed off the dinosaurs should
not be restricted specifically to the K/T event." How could anyone's
explanation "extend to events during the final decline of the dinosaurs"?

>>  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.

I don't see how this is relevant.  What you say is true, of course.  But
why would you eliminate predation as a concern--unless you had evidence of
immunity.  Indeed, predation is a serious concern for researchers into this
subject (e.g., Wood and Bjorndal 2000).  A testable hypothesis is that some
species imprint on beaches that have similar abiotic characteristics but
have relatively lower predator access/density than other beaches.

>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.

Predation is cumulative.  A species which suffers high predation upon
hatching, probably should avoid high levels of predation during incubation.
This is commonsense, right?  After that, it's data we need.

>>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.

Not true.  Mammals have no trouble finding beach nests.  This is especially
true immediately after laying when aromatic cloacal fluids are present.

>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.

What do you mean by "coexist"?  I imagine bunnies and mice sipping tea
under colorful toadstools.  And Mrs. Megapode comes up to Mr. Renard and
invites him for a hand of Canasta.  Since non co-existence is a broad
assumption of my hypothesis, it needs to be specifically rebutted.  Do
megapodes only exist in Australia because Australian predators are nice,
because they're stupid, because they're too well fed, because they are
conservationists, because they don't like eggs?  Or is it because
Megapodes nest in incredibly dry areas, nest in low predator density,
etc,?  What, exactly, are you arguing?

>>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.

No. The above statement is about extant animals.  And it can be tested--by
simple observation.  The vast majority--indeed, I would argue ALL
oviparous species except crocs--employ strategies of remote laying or
concealment. Mammals "hide" baby within.

>>The largest and most diverse big bird faunas of Australia came after the
>>evolution of grass--a very effective concealing medium.

>...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.

Radiations of large ground-nesting birds are paltry.  But, such as they are,
they did occur around the time of grass.  This is true for emu,
phororhacids, ostriches.  Isn't this true?

>>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.

It's _very_ different.  Fawns are fully competent in avoiding most
predators in a relatively short time.  A dinosaur must keep up this
stealth for 2+ months, during which time the clutch cannot relocate--and
relocation is a crucial mammal predator-avoidance tactic!--And then the
tiny hatchling is vulnerable for an additional period until its grown
sufficiently to avoid a critical percentage of predators.  And even small
differences in size can be critical.  For example, in Alaskan Forests,
size of nest was correlated with predation: thrush-size suffering higher
levels than warbler-sized nests (Willson and Gende 2000).


>Snow Geese, by the way, nest in areas where their nests are neither
>concealed nor safe from egg predators such as the Arctic Fox.

Is it Snow geese whose populations plummeted when furriers populated
previously immune islands with Arctic fox, and whose populations have
rebounded with their elimination?  This is one of the great success stories
in conservation.  My hypothesis is, of course, that geese fly to this region
due to lower predation--that this is an important adaptive value of their
migrations.  And, while some geese take advantage of explosive summer
productivity, others arrive with fat stores and eat little.  Indeed, it is
hard to make the case that productivity in Arctic is higher than the birdís
wintering grounds.

In response to a post that asked with incredulity why nest predation ought
to be considered at all among all the other factors, I said:

>>I disagree.  Anything that affects the reproductive success of another
>>animal must _a priori_ be considered a potential factor.

>Saying that any factor that could possibly affect reproductive output must
>be considered as a potential cause of extinction says nothing whatever
>about whether one factor is likely to have been more important than
>another.  You could make exactly the same argument for a massive outbreak
>of sunspots

The effect of sunspots on the evolution and structure of communities is
unknown.  Predation, and specifically, predation on offspring, is a primary
structuring agent.  Predators are "the usual suspects".  Would
you-the-detective give equal time to any and every consideration?

>>Yet, varying abilities in placental vs. marsupial body plans remains a
>>subject of modern research.  And a reasonable assumption is that the two
>>taxa are not equally gifted in this regard.

>Once again, why?  Both the placental and marsupial body plans have
>produced a very wide range of mammalian types, with extensive convergence.
>As others have pointed out, the North American opossum is a superlative
>egg predator.  I see absolutely no reason to assume that marsupials and
>placentals, taken as a whole, differ in this area.

Practically no research has been done in varying ability with nest
predation.  However, cats hear higher frequency than any marsupial so far
tested.  Most placentals have bigger brain mass/body mass ratio than most
marsupials.  In embryo, the placental focuses on brain development while the
marsupial, in preparation for attachment to nipple, focuses on cranio/facial
muscle and skeletal development.  Marsupial forelimb development is
restricted due to need to develop an efficient tool for dragging embryo to
pouch.  They are very different.  To assume they have equal gifts in any
niche is stretching the notion of convergence beyond reason.  Please don't
construe me as saying marsupials are inferior in any way.  I know for a fact
that possums and sugar-gliders are awesome.

>>Take a big Nile croc.  Situate its nest in the middle of the Serengeti.
>>Do you think that nest would survive jackals, hyenas, lions?

>Crocodiles do nest in the middle of the Serengeti, though admittedly along
>rivers.  Do you think that jackals, hyenas, and lions are incapable of
>walking down to a river bank in search of a meal?

I think they have serious qualms about doing so.  The croc enjoys a
home-field advantage.  Predators are extremely wary of ambush predation,
right?  Out in the open this is not such a threat.  I mean, the carnivores
can use speed and agility to advantage in a way they could not near the
river's edge--for starters, their escape route is reduced by about a half
(they can't run away in the river direction).

>>Large tortoises can exist only where there are no mammals(Galapagos).

>This is not true.  The following is taken from Pritchard's Encyclopedia of
>Turtles:

OK.  I need to research this further!  Is each tortoise a special case?  Do
predators not exist for local populations?  Does tortoise lay-and-leave
strategy provide a critical margin of stealth?  Or do predators give them a
free pass?

>>   the lack of re-evolution of non-avian dinosaur body form and the
>>ability of mammals to fill this vacant niche (this _must_ require a
>>better hypothesis than "chance").

>What, exactly, do you mean by non-avian dinosaur body form?  I would argue
>that the ostrich, for example, does indeed represent the re-evolution of
>at least one such form, barring only the retention of highly modified
>wing and tail structures.

I agree.  But there is such a dramatic reduction in diversity and size.  The
question is: Why, if the dinosaur body form is so successful, doesn't it
reestablish itself as the dominant form in the large-animal niche?  My
answer to that is that it should.  I would say T. rex would kick Serengeti
butt if brought back to life.  So, why hasn't it, or, rather, something
like it, been brought back to life?  I think you must be able to at least
suggest an hypothesis for that lack of phenomenon--or, scrap the notion of
convergence!

>  Further, it seems worth mentioning that the phorusracids may have
>represented a re-evolution of the predatory dinosaur form, and that the
>last of these successfully invaded North America where it survived until
>the Pleistocene.

And, across South America, died out after a placental mammal invasion!
And, depended upon grass.  And, didn't reach anywhere near past glory days
in size.

>>But let's have some alternate hypotheses which explain the following:
>>non-random distribution of large egg layers in Oz.

>First of all, I do not see that the distribution of these animals is any
>less random in Australia than anyplace else, especially if you compare
>areas with similar temperature and moisture regimes.

I apologize.  I was unclear.  I meant that there are more, bigger, oviparous
species in the recent evolutionary history of Australia as compared with
other continents.  In this sense it is non-random.

>>  Non-random distribution of very large egg layers on mammals-free
>>islands.

>To some extent this may be an artifact of the spread of human beings.  As
>noted above with respect to tortoises, many of these animals were more
>widely distributed a comparatively short geologic time ago.also, we
>should remember that Madagascar, which had both giant flightless birds
>and giant tortoises not that long ago, is hardly a mammal-free island.

But it is depauperate, having neither felids nor canids.  And, it is an
island, meaning guild composition must be less diverse (smaller land masses
support fewer species).  But I agree this is a challenge for my hypothesis.
Is anyone on the list from Madagascar?

>>Australia possesses the largest forest-nesting bird--the cassowary.

>Which lives in an area inhabited by bandicoots, daysures, and other
>potential egg predators.

With whom they play regular games of Canasta.  But seriously, here is
another area where _nothing_ is known.  There has never been a
description/monograph on the Cassowary.  My hypothesis is that predator
density and/or predator search ability is lower here than anywhere else on
the planet; that this allows the existence of a niche which is truly unique!
Again, what are the alternate hypotheses?

>>   Non-random distribution of large egg layers in either grasslands
>>(emu, ostrich), or semi aquatic niche (crocs).

>Once again, this may be an artifact of recent extinctions.  The Madagascar
>elephant birds were apparently forest dwellers, for example, and there
>were certainly animals in Madagascar that could have acted as predators
>on eggs or newly hatched young.

Barring dromornithids (not recent), the Elephant bird is the only other
species.  This is hardly, then, an artifact.  How about dromornithids?

Stan Friesan said:
>I would really like to see any animal try and steal eggs from a Troodon!
>(Assuming it didn't hide its nests, that is).  Such an attempt is likely
>to end up with the would-be thief becoming the dinner.

Caracara hawks fear rheas.  But they sit just out of reach waiting for an
unattended chick.  They do not have to do battle with the rhea in order to
eat its babies.  Similarly, nests may be unattended for periods.  Also,
borrowing a valid argument from the bolide idea, if Troodon's prey are
gone, so is Troodon.

>And, killing of incubating/gravid females is indeed often more deleterious
>to a population than killing the young (including eggs).

Yes.  But this appears not to be an issue in extant ratites.  During 
Bertram's (1992) entire study period, no instances of adult predation were
observed.  This is contrasted with 90-95% predation to one year old for eggs
and chicks.

Literature cited:

Bertram, B.C.R  1992.  The Ostrich Communal Nesting System.  Princeton
University Press, Princeton, NJ.

Diamond, J.1998.  Guns, Germs, and Steel: The Fates of Human Societies.
W.W. Norton & Co., New York.

Pasitschniak-Arts, M. and F. Messier.  1995.  Risk of predation on
waterfowl
nests in theCanadian prairies: effects of habitat edges and agricultural
practices. Oikos 73:347-355.

Picman, J. 1988.  Experimental study of predation on eggs of ground-nesting
birds: effects of habitat and nest distribution. Condor 90:124-131

Quammen, D.  1996.  The Song of the Dodo. Scribner Pub., New York.

Romer, A.S.  1964.  Vertebrate Paleontology. The University of Chicago
Press, Chicago. p .257-272.

Sanchez-Lafuente, A.M., J.M. Alcantara, and M. Romero. 1998. Nest-site
selection and nest predation in the purple swamphen. J. Field Ornithol.
69:563-576.

Willson, M.F., and Gende. 2000 Nesting Success of Forest Birdsin S.E. Alaska
and Adjacent Canada. The Condor.102:314-325

Wood, D.W., and K.A. Bjorndal 2000, Relation of Temperature, Moisture,
Salinity, and Slope to Nest Site Selection in Loggerhead Sea Turtles.
Copeia 2000(1)119-128