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Re: Segregated vs age-mixed sauropod herds
> Not sure how we'd define complexity, but in any case, there is a great deal
> of variation in parental care among vertebrates, and especially among those
> that have rather large brains and higher cognitive functions.
Very true...but how about we just look at physical (not behavioral)
parental investment. Lactation is a significant development which goes
directly to the benefit of the baby. It required sisgnificant genetic
change to acquire relevant anatomical accomodation...it is more
complex than, for example, regurgitating food into your child's mouth,
i.e., the food has to be broken down, absorbed, reformulated, then
delivered through some bodily faucet. Pre-lactation, egg-laying
mammals (does monotreme "milk" contain lactose?), fed their babies for
sure, but isn't it fair to say milk is an amazing formula for rapid
neonate development, containing antibodies, etc., etc., and that this
contributes to the reproductive success of the lactator...that it has
adaptive value which is probably why it is highly conserved.
> It is just as
> easy to produce anecdotal evidence suggesting that parental care has
> relatively little patterning, and/or that it has almost no relationship to
> time or phylogenetic position.
The pattern above seems like a progression on an evolutionary scale.
Is there one that goes in the opposite direction? Presumably, it would
be possible to give up lactation if, in some environment, it paid to
do it more cheaply. I mean, couldn't it be possible that a mammal
would find greater reproductive success in some other environment by
delivering and leaving the babies to fend for themselves? And yet this
hasn't happened, right? This suggests (to me) that there is something
intrinsically valuable in bringing baby up to a more developed form
before pitching it onto the world stage. Is this just my mammal bias?
Same thing with birds...behavior now. From stem reptiles to
theropods...comparing lizards and turtles to today's theropods...do
you believe extinct relatives of lizards and turtles fussed around
their young, built elaborate nests, provisioned the young with as many
varied and _complex_ behaviors as birds do today?...and no
backtracking here as well (OK...a megapode species that nests in
volcanic soil...but most megapodes are like fastidious bakers,
constantly testing the nest environment). And incubation...it's
expensive in terms of energy use and predation risk...yet birds don't
give it up...certainly one reason for this is that they have already
invested so much in terms of yolk volume (another trend)...One would
think if these traits weren't valuable you would see some
hedging...some reversion to the primitive (in the cladistic sense)
> I'm also not sure why we'd expect the
> potential for care to go more with titanosaurs than sea turtles (titanosaurs
> were not large-brained animals), nor am I clear on why we should expect that
> any animal that *can* provide care, hypothetically, actually will or did so.
Large yolk volume, incubation, and lactation are, judging by their
almost universal retention, highly valuable traits. These animals can
and _do_ provide that investment. The only question is: where do
turtles and titanosaurs fit on that continuum?
> ÂOverall, you've identified that parental care is common in crown group
> birds, crocodilians, and mammals. ÂNo arguments there, but I don't get the
> "trend" you're arguing for.
I'm arguing that the crown groups are the (current) end of that continuum.