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Re: Sundry responses of Bois




On Mon, 29 May 2000 KiernanCR@aol.com wrote:

> John Bois wrote:
>> This assumes that without an extra-terrestrial event, the paleo biota
>> should remain in unpunctuated equilibrium.<<
> 
> No, it doesn't, actually. 
> 
> It's fairly obvious that populations are dynamic enough phenomena, without 
> the aid of cataclysmic extraterrestrial influences. Predation does occur and 
> it is relevant to the process of natural selection. However, that said, 
> demonstrating that egg-eating mammals played a role in the extinction of 
> non-avian dinosaurs is another matter. As I said, I don't think anyone here 
> will argue that there were not Maestrichtian mammals that ate dinosaur eggs, 
> but that's a long, long way from their being a potential factor in 
> dinosaurian extinction.

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

> Why suspect mammals as the agent? It seems rather arbitrary. For example, why 
> not varanoid lizards? We know that extant varanids are ovivorous, and the 
> varanoids experienced their first success in the Late Cretaceous (hence they 
> lack the much longer, problematic coexistence with dinosaurs that mammals 
> exhibit). If ovivory was the culprit, don't varanoids make a better 
> candidate? And if not, why?

Yes.  Varanids must also be considered.  But my argument is that the guild
membership increased such that the predation load became overwhelming.  As
you know, most oviparous--especially large oviparous creatures--suffer
very high predation.

>> 1. small dinosaurs disappear towards the
>> end...
 
> What do you mean by "small."? Has anyone ever demonstrated that smaller 
> dinosaurs posed more of a threat to mammals than larger dinosaurs? There are 
> fairly large carnivorous mammals today (such as wolves) that prey on fairly 
> small mammals (such as lemmings). Maestrichtian troodontids surely would have 
> found even lemming-sized mammals fair game.

I would consider a wolf-sized dinosaur small.  And while large dinosaurs
may have snacked on small mammals occasionally, they were more likely to
subsist on larger fare.  A very conservative hypothesis is that small
dinosaurs, lizards, birds, and mammals existed in a robustly connected
food web.

> And why do larger mammals pose a greater threat to nesting dinosaurs?

Mechanical advantage in moving, rolling, knocking, digging eggs.

> >>In addition to size increase, dentition diversity increases.<<
> 
> Can you demonstarte a connection between more complex mammalian teeth and 
> ovivory?

No.  But inasmuch as most egg eaters are omnivorous, the increase in
omnivorous dentition over specialized insectivorous dentition increases
the likelyhood of involvement.  And, it demonstrates ecological change,
i.e., things were different at the end of the Cretaceous than at the
beginning.
 
> Eggs are easy things to break into, even relatively large eggs. Complex teeth 
> simply aren't a prerequisite. I'll cite varanoids again. Very good 
> egg-eaters; very simple teeth.

Agreed.

 >>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.<<

> ???? Quote Lillegraven and Eberle to this effect. I'm certain they were not 
> making a generalization about the whole K/T transition. Unless I've somehow 
> missed all those Paleocene ammonites and rudistids . . . 

I'm sorry.  I made that clear elsewhere in the same post.  I certainly did
not mean to imply this.  Still, the tone of their paper in this part is
one of surprise:  "Indeed the very concept of 'mass extinction'
applies to only part of the total picture.  The nature and extent of
faunal change in the Ferris Formation differed greatly from one taxanomic
group to another.  By far, the most important locally documented change
among vertebrate assemblages at and soon after the boundary involved
non-avian dinosaurs and (the invasion of) condylarthran mammals."

> >>I, and many paleontologists, find the Alvarez
> explanation of dinosaur extinction very unsatisfying.<<
> 
> Why? Whether it's true or not, the model satisfies the criteria that would 
> have to be satisfied to explain such a global event.

We need convincing as to the proximate mechanisms, the individual deaths
in valleys, riversides, arctic regions, etc.

>>My claim that an important
> synergistic effect was predation is controversial.  But I'm not sure why.<<
> 
> Because there's no evidence to support your claim. I'm not being flippant. 
> It's just that simple.

We are talking about reproductive failure, right?  Or does the Alvarez
model posit a clean wiping out of all non-avian dinosaurs without
regard to their reproduction?  I mean, it is in these details that the
Alvarez model has no clothes.  Predation--and nest and hatchling
predation-- is a prime determinant of the structure of all known
ecologies.  It must be considered in paleo-ecologies as well.  I mean, if
nesting non-avian dinosaurs were laboring under some kind of environmental
stress, the first thing that would happen is that traditional predators
would take advantage of that.  The egg is, after all, a real energetic
bonanza!

>>If someone discovered big terrestrial egg layers and mammals (particularly 
> placentals) living in harmony--without having to hide, I would run away
> forever. <<
> 
> I'm uncertain as to why marsupials make poorer egg-eaters than placentals, 
> but . . .

So am I.  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.

> what about the phorusrhacids and diatrymatids? They coexisted with 
> far larger mammals than those that tyrannosaurs and ceratopsians would have 
> had to contend with. And while I'm sure these large birds probably did have 
> eggs eaten by mammals (and reptiles, for that matter) - almost all birds do - 
> there seems little reason to suspect ovivory as a casual factor in their 
> eventual extinction.

My hypothesis is that the phororhacids were protected by grasslands--in
the same way that ostriches are (for concealment); and that diatrymids
(now called something else) were wetland creatures.  They became extinct
at different times on different continents; but both extinctions happened
at the time of disappearance of wetlands.  And, they were ducks, right?

> If your hypothesis is correct, why were the 
> phorusrhacids ever able to *become* dominant predators, after the blow dealt 
> to the dinosaurs by the Maestrichtian egg-eaters?

Because the evolution of the grassland biome provided a habitat for this
body form that survive nest and hatchling predation.  The model I'm
referring to is the ostrich.  Simply, there nests are very difficult to
find.  They nest in a territory of 2km sq. and they cannot be seen until
you are within 10m.

> And why do we exclude crocodilians...

Perhaps they enjoy a habitat-specific advantage over terrestrial
layers.  That is, nest predators are more likely to become dinner
themselves because the crocs are so perfectly adapted to their
niche.  Take a big Nile croc.  Situate its nest in the middle of the
Serengeti.  Do you think that nest would survive jackals, hyenas, lions?

> and turtles from the threat of
> extinction 
> by ovivory?...
> ...and even larger predatory mammals have access to the beaches where 
> sea turtles lay eggs. 

If you are arguing that predation does not limit the distribution of large
turtles, you must also explain the non-random distribution of nesting
sites, and the nonrandom distribution of body size.  Its the moa all over
again.  Large tortoises can exist only where there are no mammals
(Galapagos).  These factors are so consistent, one _must_ come up with an
hypothesis to explain them.  Nest predation is one hypothesis.  What is
another?  Also, turtles do have an advantage over nesting dinosaurs in
that they do not attend their nests (an important part of my hypothesis is
that non-avian dinosaurs did attend nests--there is some support for
that, but not that they did so universally).

> And what about _Megalania prisca_ in Australia? How did it survive to become 
> a top-level predator with so many marsupial egg-eaters, not to mention murid 
> rodents?

Can you suggest a reason?

> You can't protect your hypothesis by pleading special cases for these obvious 
> problems.

The strength of _evolution by natural selection_ is its ability to address
special cases--islands, etc.  I must try to protect it.  If you or anyone
else has an hypothesis for this phenomenon--the greater number of large
egg layers in Australia--we should hear it.  I am offering one hypothesis,
viz., the distribution of large oviparous species is different in
Australia because the distribution of egg-eating species is
different.  This is not some whacky hypothesis.  If memory serves,
E.O. Wilson supports it.  I just don't see this as an "obvious
problem".  True, explaining historical speciation is an obvious
problem.  But, within the context of currently known data, there is plenty
of room for my hypothesis.

> >>As far as I know, the "out-dated" version was rather perfunctory (mammals
> eat dino eggs).  My version has many more bells and whistles.  In any case,
> age of an hypothesis is only relevant if new information has made it
> illogical.<<
> 
> The earlier version of this idea was largely based on a) a need to explain 
> the disappearance of dinosaurs, b) a mistaken view of dinosaurs as 
> "reptiles", and c) the idea that mammals are innately "superior" to 
> dinosaurs.

I reject them all except a).  We need to explain this.  Alvarez does not.

> As the evidence of a cosmological and/or cataclysmic geological agent/s grows 
> more weighty, the need to search for other causes diminishes, especially 
> causes as far-fetched as sudden, worldwide predation by Maestrichtain 
> egg-eating mammals.

My hypothesis does not claim "sudden, worldwide
predation...".  Nevertheless, you are crediting the bolide simply because
this was a rare event and was timed to certain known extinctions.  But
what statistical method are you using that can determine which has the
greater probability of occuring at any given time: a large impact; or the
evolution of mammals to the point where they could impact
dinosaurs.  Bolide strikes happen all the time, the evolution of the
placenta (for example) may be a once-in-a-universe event.  It seems to me
that you may be biasing the bolide just because the phenomenon placenta is
familiar to you but the bolide is not; when, in fact, the reverse is
probably true!

> In short (again), you have no new evidence to present (or you aren't 
> presenting it). 

I am not presenting new evidence, just trying to place existing evidence
into a coherent framework.  Our failure to address the issues without
reasonable hypotheses is...a failure.  I'm not picking on you Caitlin, for
I am grateful for the reasoned challenges you make, but there is another
side to science other than attacking known hypotheses: it is to present
alternate hypotheses.  I am aware that many of my own hypotheses exist
thanks to the rarity of data.  But let's have some alternate hypotheses
which explain the following: non-random distribution of large egg layers
in Oz.  Non-random distribution of very large egg layers on mammals-free
islands.  Non-random distribution of large egg layers in either grasslands
(emu, ostrich), or semi aquatic niche (crocs).  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").

> We have a set of explanations that already work far better 
> than your hypothesis (whether they're the truth or not).

I don't see _any_ explanations.  Whether or not my hypothesis is viable,
at some point those who advocate the bolide as a cause must tell us what
the mechanism was.  The fact that this does not seem to be an important
requirement may be an indication that the hypothesis is not that robust.

> Therefore, there is 
> no need to take this idea, of extinction via egg predation, off the shelf and 
> dust it off for reconsideration.

Well, I obviously disagree, but I thank you for a chance to get into the
particulars.
John Bois.