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Re: What did Spinosaurus eat? New species of Lepidotes found
On 2/25/2011 12:13 PM, Dan Chure wrote:
By "committed to nesting" do you mean nesting behavior as in caring for
young or a building physical nest? There are some pretty minimalist
nest in the avian world and the Fair Tern just lays an egg in the fork
of a tree branch. Cowbirds lay their eggs in other bird species nests.
You are right, bird nesting behavior is variable in the sense that nests
come in many styles. The phrase was poorly chosen.
The eggs themselves are what I was referencing. They all seem to have a
great deal in common.
Afaik, they all need to exchange water vapor and gases with the
atmosphere more or less constantly, and with extremely narrow tolerances
relative to rates of exchange.
E.g., an egg optimized to a sealevel environment may not hatch at higher
altitudes, due to changes in the density of the surrounding atmosphere.
This explains why individual chickens, and I assume other birds, can
adjust the porosity of their eggs in response to a change in altitude.
That's right -- if you move from Denver to LA, your pet chicken will
begin to lay eggs that have more porous shells. I do not have an exact
ref at hand, but Cynthia Carey and others have published regarding this
Bird eggs also have a narrow viable temp range combined w/ an incubation
period that is variable but seems a significant time and energy
investment to the adults. There are no species (afaik) that show any
signs of retention of the egg inside the mother while the embryo
develops (corrections appreciated).
This mandates at minimum a degree of terrestrial competence in adult
females. It all seems limiting in terms of lifestyle, energy and habitat
-- even when care of hatchlings is not considered.
The core assumption was that avian and non-avian dinosaur eggs are
functionally analogous -- I was basically wondering why there is not
more evidence in the record of other pathways evolving (e.g., live
birth) in the multitudes of dino's, living and dead.