a 
Se Te a a FT eee Ral a i em eR nee eT fe ee Eee Sige a ee 
ere 
a 
5) 
or Toothed Birds of North America. 265 
posterior limbs, a specialization here seen for the first time in 
aquatic birds, recent or fossil. Those who have observed a 
Penguin or a Loon swimming beneath the water know what a 
useless these members may appear to be on land. Not only 
do the wings, in such a case, assist in the forward movement 
through the water, but they are of much service in steering. 
A Penguin, when in swift sub-aqueous flight, can turn around, 
by the aid of its wings, while moving twice its length. Hespe- 
rornis had no such aid, but the legs and feet were far superior, 
for swimming and diving, to those of the Penguins, not merely 
in power, but in the more perfect adaptive mechanism. This 
was doubtless the main reason why the posterior limbs of 
Hesperornis became so predominant. 
“The tail of Hesperornis was clearly of great service in its 
aquatic life. In the number of vertebre and length, it ex- 
ceeds nearly all known birds, and it is unique in its widely 
expanded transverse processes, and in its depressed, horizontal, 
Plough-share bone. his broad horizontal tail reminds one of 
that of the beaver, and was undoubtedly of great assistance in 
steering and in diving. Whether it was, like the beaver's tail, 
destitute of feathers, or, like the tail of Plotus, was furnished 
With long stiff feathers, so as to act as a rudder, cannot at 
present be determined with certainty, although the latter view 
seems more probable. That Hesperornis was provided with 
d 
feathers of some kind, we can hardly doubt.” 
Figure 5.—Caudal vertebrae of Hesperornis regalis, Marsh; seen from above, in 
Position ; two-thirds natural size. 
Pre powers of Struthious birds. The latter, from his studies 
e 
. Myolog: : 
ee these birds could never have possessed the power of flight. The 
