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copes law

        Seems to me that at least part of this might have something to do
with the nature of mass extinction. Big animals were hit especially hard
by the KT event. With all those niches open for big things, of course
mammal lineages would tend to increase in size.  Whether a similar pattern
is observed in other extinctions or local extinctions, I don't know. It
might just be that big animals are more vulnerable to extinction. There
are fewer of them which means that they have less genetic variation, less
chance of surviving in high-mortality events, and repopulate more slowly. 
        It would be interesting to know if bigger species are more
vulnerable to extinction. Many big animals have seen significant reduction
in numbers through part or all of their ranges- bison, cheetahs, tigers,
wolves, elephants, rhinos, sea otter, elephant seal, condor, most big
species of whales. Certainly the big animals really bought it hard in the
last extinctions. Of course, we pay more attention to the plight of a
rhino than that of a mouse or a beetle. There are probably many more
endangered small species, what would be good to know is whether a higher
percentage of big animals are endangered or go extinct. Of course, humans
are implicated in most or all of these events, so the application of
recent times to prehistory may not work. 
        Of course, all this SOUNDS logical. But the sun going round the
earth sounds logical without any tests. Science isn't about finding an
explanation which appears to fit the facts, it's about testing it and
seeing if it really is the one explanation which fits the facts. 
        There are tons of other factors, too. Speciation rates, not just
extinction rates, global cooling and the tendency for size to increase
with temperature reductions, the start of huge open grasslands and steppes
which support some very large animals like plains deer (Irish Elk) and
mammoths and grazing horses (much bigger than their browsing ancestors),
and who knows how many other factors could be at work even if this
observation of Cope's is correct. And while there are plenty of examples
to support him, one would have to show that these are more frequent than
the counterexample.