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Re: giant toothed bird-species or genus that lasts 50 million yrs?
Yes, but what I am trying to ask is would an "Apatosaurus firstuvus"
as a species last 10's of millions of years before "secundus" came
around - or a species very closely related such as eastern and
diamondback rattlers - not rattlesnakes as a whole or a very large
genus. It would seem at first glance there would be a
die-off/replacement of another species within the same genus?
First of all, genera don't exist outside our heads, and the term
"species" unites lots of different things that have pretty much nothing
Second, below a maximum set by the mutation rate, the rate of
morphological evolution depends on natural selection, which is
determined by the environment. If the environment changes so that a new
phenotype has advantages over an old one, morphological evolution will
be fast -- that's caused directional selection. If the environment does
not change, morphological evolution will be very slow -- basically, an
optimum phenotype will be approached or found, and all deviations of it
will cause disadvantages or be neutral -- that's called stabilizing
selection. Neutral changes can still spread through a population just by
chance (that's called drift), but this is a slow process (except in
small populations); and the stronger stabilizing selection is, the fewer
phenotypic changes will be neutral.