Re: Impacts and ETs

[David Marjanovic <david.marjanovic@gmx.at>]

> A relationship exists between the number of neurons possessed and the
> cognitive ability of an organism.

Who says?

I mean, of course it sounds logical, but it has never been tested. Even the 
number of neurons _per total body mass_, which comes closer even though it 
sounds less logical, does not seem to correlate 1 : 1 with any measure of 
intelligence.

> Still, while demonstrations of parrot and crow intelligence are
> wildly impressive, they don't compare with human cognition...as far
> as we can test it, anyway.

Well... that parrot is learning to read, with a brain the size of... perhaps 
one of your eyes.

> Neurons are the most expensive (energetically) tissue to create.

I don't know. They are, however, the most expensive one to maintain.

> Other organisms
> must make harder choices...e.g., marsupials must devote embryonic energy
> to developing jaw and musculature for climbing and sucking at an early
> age.  Like some chromosomal conditions in humans, there are some very
> smart marsupials...but, by an large, they are limited by this ontological
> demand!  For an egg layer, the longer one tends a nest in one location,
> the longer that nest is at risk.  This provides a pressure to vacate.
> And, after hatching, a long period of precociality adds even more
> of the same pressure.  Hatchlings that fly or run immediately must be
> under the same
> developmental pressure as marsupials, i.e., physiological choices favoring
> locomotion/coordination must be made.
> I think this leaves archosaurs with only one option: develop safety and
> ontological leisure time _in utero_.

I'm not so sure that vivipary is automatically safer than ovipary. An 
immobile nest may well be at a similar risk as a mobility-impaired pregnant 
female. I've already mentioned how marsupials get around this constraint.
       Now consider the trademark misfeature of vertebrates: the birth 
canal passes through the pelvis. We've reached the limit. We can't evolve 
larger brains at birth anymore. Marsupials have no such limit. The pouch is 
not constrained by bones.

> I know we've talked about this before...but I can't remember why--or if
> there are good hypotheses--why this was not done as far as we know in
> archosaurs.

The embryos of archosaurs... or at least birds... take the calcium they need 
from the eggshell. Other animals store it in the yolk. I can imagine that 
this makes archosaurs without eggshells impossible.

> The one I do remember goes like this: lizards and other
> _small_ reptiles have evolved similar structures independently and
> repeatedly.  But archosaurs were too big

I don't need to mention hummingbirds. Your average tiny croc --  
Atoposauridae, for instance -- suffices.