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Re: attack on dinosaur--horrific video



"First, I am primarily interested in the ecological considerations of
 various 
strategies--regardless of their mass extinction impact...this interest 
doesn't go away and has fueled, I think, some interesting hypotheses:
 e.g., 
dinosaurs were big because they had to defend nests." -- bois

Probabilities are additive, and an equation that quantified the advantages of 
size would have a lot of terms in it; as nest defense would be but a presumably 
seasonal sub-term in the predator avoidance clause, and there are many 
situations where physical defense of the nest is moot, I don't see how it could 
be deemed a primary vector in size increase. 

Further, it is not clear to me that large size for either predator or prey is a 
likely advantage for nest predation. For predators, once talent is sufficient 
to breach the fortress of the eggshell, I would think large size would be a 
disadvantage, rather than the reverse. Large mosquitoes are easier to swat than 
small ... 

For prey, large size might also present tactical problems. I wonder how a herd 
of sauropod equivalents can defend a position against rat-sized creatures. The 
eggs would be doomed, either to crushing or ingestion.

On the extinction side, it is definitely interesting to speculate that since 
rodents probably first appeared near K/Pg, basal rodents may have found that 
incisors were the ideal tool for breaching eggs, and dinos (at least some 
species) may have found the combination of small size and prolificity 
overwhelming. I don't see it rising to best-fit cartoon status, though, much 
less falsifiable hypothesis, especially in the (apparent) absence of 
rodent-gnawed eggshell. 

[Clarification sidebar -- I don't use "cartoon" here as a derogatory term. I 
try to use it instead of "scenario" in my own musings to make it clear that I 
am NOT advancing a formal hypothesis. In other words, to make it clear that I 
am claiming (at that point) testability. Nor do I (obviously) agree w/ the 
"rule" that testable hypotheses, or observations leading thereto, are the only 
items fit for scientific discussion in the realm of 'biospheric history'. In 
the absence of a testable hypothesis, cartoons must be ranked by parsimony (due 
to the fact mutation/selection is the under-lying null), and the most 
parsimonious receives "best-fit" status. However, I have NEVER subsequently 
elevated (barring possible mis-speak), or advocated elevating, "best-fit 
cartoon" to "null hypothesis"! Even though some folks evidently assume that I 
did and/or would. Heh -- or as others, some of whom must not be quoted on DML, 
do indeed advocate doing.]

Don

PS -- I guess a sauropod herd could encircle a nest site, shoulder-to-shoulder 
and heads pointing inward, sweeping the sandy beach w/ lashing tails, while 
hoovering any rapacious hairy egg-suckers that make through the 'outer wall' 
(finally those necks and tails make perfect sense, lol). Hard to maintain 24/7, 
though. Even if they could keep it up "as long as they bloody well wanted to" 
... -- Don, again.

----- Original Message ----
From: john bois <jbois@verizon.net>
To: DML <dinosaur@usc.edu>
Sent: Sunday, November 25, 2007 11:45:36 AM
Subject: Re: attack on dinosaur--horrific video


----- Original Message ----- 
From: "David Marjanovic" <david.marjanovic@gmx.at>
To: "DML" <dinosaur@usc.edu>
Sent: Sunday, November 25, 2007 8:47 AM
Subject: Re: attack on dinosaur--horrific video

> I can't imagine the size difference between *Daspletosaurus* and 
> *Tyrannosaurus* can be explained by selection for nest defense.

Hadrosaurs gang up on D...T is selected...classic arms race.

> 2. We have fairly large eutherians in the Maastrichtian of North
 America. 
> Good. But we have just as large metatherians in the Campanian of
 North 
> America (and isn't there a "stagodontid" skull from Mongolia as
 well?). 
> You don't have any evidence to argue for a relaxation of size
 constraints!

Close relatives of the clades that adaptively radiated after the
 boundary 
increased in size before the boundary--their descendants have an
 observable 
major influence on the community structure of oviparous species via 
predation--again, not as a hypothesis for extinction at the K/T...but
 an 
influence, perhaps.  And, yes...perhaps not.

> You have tried to get around the third point below:
>
>>> If the answer lies somewhere in "very different creatures", then
 please
>>> elaborate.

> In the "Tertiary" of South America, there was a nice partition: the 
> herbivores were placentals (...or eutherians anyway... who knows),
 the 
> grapple-and-bite predators were sebecid crocodiles, the
 grapple-and-slash 
> predators were metatherians, and the pursuit-and-bite predators were 
> birds. This situation remained stable till 3.3 Ma ago, when an impact
 
> happened just off the coast of Argentina and the metatherian
 predators 
> died out, 300,000 years before they were replaced by placentals. (The
 
> sebecids are so rare that we can't tell when they died out.) There
 was a 
> carnivorous armadillo. Why didn't it stop digging and take over? Or
 why 
> didn't the monkeys take over in the Oligocene (the oldest known New
 World 
> monkey was rather terrestrial)?
>
> Sure, we have the dingo and the Tassie tiger as a probable case of 
> extinction by competition, but here we're talking about the skull
 base, 
> not about the reproductive system.

Look at the forest for a minute: Continental placental predators and 
herbivores--and whatever else--are invading/have invaded global
 terrestrial 
niches.  Rabbits, cats, rats, mice, dogs, pigs, goats--these animals
 are the 
subject of thousands of papers dealing mainly with how to ameliorate
 their 
influence.  Yes...there are other invasive animals, e.g.,  _Boiga
 boiga_, 
zebra muscles, Burmese python, etc. but their effects are somewhat
 local, 
not global...and not clade-wide.  Placentals enjoy a great diversity of
 
morphologies--probably a greater diversity than is available to, for 
example, marsupials.  It is a fact--ref. if needed--that marsupial
 embryos 
rush to develop craniofacial muscles and bone in order to be able to
 feed 
early...it is a fact that placentals spend this early phase developing 
neurosensory ability, i.e., laying down neurons.  Thus marsupials start
 late 
and are therefore at an ontological disadvantage in this respect.
  Also, 
limb morphology diversity is far less in marsupials because the front
 legs 
are already chaneled into being legs, not wings, not fins, not arms.
  Point 
is, ontogenic imperatives are a limit on morhological diversity in 
marsupials.  This is not going to go away for them.

> ...reliance on nest defense does nowhere near guarantee extinction.

Why has it not re-evolved in your view?  I mean, crocs are it, right?
  So, 
what is the probablity that nest defence strategy in terrestrial biomes
 has 
been eliminated by chance alone?  If it's a viable strategy, how come
 no one 
outside of crocs employs it?

>> They (crocs) are the exception...because they are exceptional: 
>> semi-aquatic niche
>> gives home-field advantage; they see at night (are practically 
>> nocturnal!!);
>
> Are you sure seeing at night isn't normal?

It's dark outside...at night.

>> many would-be predators don't like getting wet
>
> The eggs are not laid in water.

They are laid in swamps--many nests are accessible only by getting
 one's 
self wet.

>> or eaten (e.g., bird species
>> use tree above alligator nesting sites for protection against
 racoons);
>
> That's my point again.
>
>> silt river banks make poor burrows for predators;
>
> Predators are not required to have their own nests very close.

Yes...in fact, predators have to enter the crocs homefield...the one
 place 
where they are the only game in town.

>> predatory threat can only come
>>>from 180 degrees not 360;
>
> No, croc nests are not directly next to the water.

But a croc only has to scan 180 degrees--predators are not going to be 
accessing the nest from the water.  And to do this a croc can lie as
 still 
as a log waiting to ambush. This is an exceptionally effective strategy
 
whether animals are merely trying to get a drink of water or robbing a
 nest.

>> each of many hatchlings represent less reproductive effort than
>> dinosaur hatchlings (and are therefore more expendable).
>
> You are making this up. I submit that each croc hatchling represents 
> _more_ of an effort than just about any sauropod hatchling.

Croc eggs are smaller relative to parent than dinosaurs of the same
 size, 
right?

>> I view archosaur success as dependent on parental investment,
>> and that an interesting hypothesis is that this PI increased from
 crocs 
>> to
>> dinosaurs with its zenith in birds--but that relative to most birds,
 croc
>> babies are low maintenance.  This allows excess production of
 offspring 
>> to
>> offset intense predation.
>
> Yes, and this does not only apply to crocodiles. All known Mesozoic 
> dinosaur nests are very large.

Remembering that parental investment includes: yolk mass, incubation
 time, 
quality of incubation--e.g., brooding, post-hatchling care, and not
 just 
clutch-size.

> I still don't understand why you bother in the first place...Why
 bother to 
> work against the most parsimonious hypothesis as long as it isn't 
> falsified?

First, I am primarily interested in the ecological considerations of
 various 
strategies--regardless of their mass extinction impact...this interest 
doesn't go away and has fueled, I think, some interesting hypotheses:
 e.g., 
dinosaurs were big because they had to defend nests.

Second, I think extinctions are always very complex events.

Third--the only thing that is _falsifiable_ about your explanation, is
 the 
event itself.  The event happened.  But any specific cause of death for
 any 
clade, population, or individual is unfalsifiable.  Also, complex
 synergy 
remains equally parsimonious.