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Nick Pharris says: "I think the strong and the weak points of the (mammal
and dinosaur) strategies most likely offset, and neither enjoyed much
differential success over the other."
But the mammals and dinosaurs were so different from each other, the
chances that they offset each other were infinitesimally small. This was
especially true if they were seperated in functional islands (see "Novel
The specificities of various niche adaptations are wonderful: a bat has an
advantage at night over birds, birds over bats in the day time. Why? At
night, the bat's senses are superior to birds'. In the day time,
however, because they are more agile fliers, the birds aree supreme.
This probably has to do with adaptations for weight. But how about this:
placentals can't compete because, when they are pregnant, they are too heavy.
Nick Pharris questions whether or not the lack of arms caused ratites to
have a limited niche.
The ratites are devoted to speed. This puts their body at such an angle
where arms are useless--or perhaps, inasmuch as they slow down the
animal, harmful. This is also seen in the atrophy of T-rex etc. Tyhe
bipedal lifestyle renders arms useless. A great exception to that rule
is humans. But we have arms we can use as incredibly adaptive tools,
i.e., they have free rotation in the shoulder joint, which, by the way,
evolved not for tool-use, but for swinging from branch to branch! Such
is the whimsy of evolution.