Evening star. [volume] (Washington, D.C.) 1854-1972, 1935-09-12
STARS. MEN AND ATOMS
Notebook of Science Progress in Field,
Laboratory and Study.
ID
BY THOMAS r. HENRY.

The opoSsum, sole survivor in the
New World of primitive and very
ancient family, represents an overlooked
principle in evolution survival by
endurance.
How this clumsy. prosecuted race has
endured through millions of generations
in the midst of savage and hungry foes
is shown in a report just made to the
American Society of Mammalogists here
by DR.. j. D. Black of the University of
Kansas DR.. Black recently examined
closely the skeletons of 95 opossums in
the university museum-all killed in the
immediate vicinity.
Thirty-nine of them gave evidence of
broken bones that had completely
healed. One specimen had suffered, and
recovered from, breaks of both Scapulae
IL ribs two broken in three places, and
badly injured spine. Still another
gave evidence of having suffered at the
same time fractures of the jaw, the
scapulae, and nine ribs Many others
showed evidence of ribs and Scapulae
broken in several places. The ability to
survive such severe injurieS-they would
be fatal in any other animal either in
themselves or because the crippled con-
dition resulting from them would make
a creature an easy prey to its enemies
illustrates the importance of the opoS-
sums practice of playing dead.
The opossum represents an important
stage in the evolution of mammals
that of the marsupialS, or pouch bearers.
They presumably were quite widely dis
tributed over the earth at one time, be-
fore the emergence of the placental type
of mammals to which the human race
belongs, together with almost all other
known warm-blooded animals. They
may be the ancestors of the placentalS
or they may represent different line
of development from the ancestral rep
tiles. In any event, they are consid-
erably nearer the type of those ancient
egg-laying reptiles. They are just
step beyond the egg-laying stage.
When the placentals arose the mar
supials quickly disappeared from most
of the earth. They were not so well
adapted for survival in conflict with the
more advanced, efficient type of animal.
Only in Australia did they find a haven.
With single exception, they were the
only mammals there when the continent
first was discovered by white men. This
has led to the speculation that Australia
was cut off from the rest of the world
before the placental races were evolved.
or before they had attained such eff
cheney in the ways Of life as to enable
them to survive. There the marsupialS,
without competition, were able to sur
vive and differentiate into rich fauna of
the continent-of which the kangaroos
are the characteristic animals.
The one exception was in North and
South America in the person Of the lowly
opoSsum. All the meat-eating animals
which arose around the creature fed
upon it if they could catch it. 1t was
not very efficient in getting away from
a pursuer 1t developed no effective
armor, like the shell of the armadillo
or the quilts of the porcupine, with
which other weak animals managed to
survive 1t was not even very efficient
at hiding. When man arrived on the
scene with his bows and his guns, its
last Ravens, the treetops, lost their small
measure of security.
AL the cards were stacked against
the survival of the opossum, but 1t de-
veloped a means of its own to keep
tenacious hold on life while far more
efficient creatures-beset with new enc
mics and changing climates-were forced