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Wetmore, Alexander, 1886-, et al. / Warm-blooded vertebrates
(1931)

Chapter IV: ancestors and ancestry,   pp. 39-49 PDF (4.1 MB)


Page 39


CHAPTER IV
ANCESTORS AND ANCESTRY
THE fossil record of the birds of past geologic ages is a
broken one. In contrast with the approximately 25,000
living species known, we have record of only 8o0 fossil
species, not including the few of forms which still survive
and whose bones are preserved in deposits of the Ice Age.
Our knowledge of many fossil species is limited to frag-
ments of a single bone; and from this we must attempt to
build up a sketchy picture of the entire animal, basing it,
of course, on parallelism with existing species-a procedure
which is justified by the established fact that adaptation
for flight has restricted form in birds to narrow limits of
variation.
Considering the number of living species and the abun-
dance of individuals in each species it is strange that fossil
bird records are so scarce. Estimates of abundance can
not be very exact, but statistics of birds shot as game may
give us some idea of the unquestionable magnitude of
their number. Dr. Joseph Grinnell states that during the
winter of i90-Ioi five companies engaged in the handling
of game in San Francisco sold i85,867 wild ducks of eleven
or more species. According to figures obtained by Dr.
J. C. Phillips more than 283,ooo wild ducks of nine or
more species were sold in New Orleans in the winter of
I9I3-14. These figures cover the traffic in only two cities.
The Game Commission of Minnesota estimated the num-
ber of ducks killed in that State in i919 as I,804,000, and
in i920 as ii80,000. From these and other figures Phillips
estimates the ducks shot annually in the United States at
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