POLYPROTODONTS 



front of the fore limbs, a trace of the primitive lateral 

 membrane being left in what is called in those animals 

 the metapatagium. There is a kind of a hint that 

 in the earliest known bird, Archczopteryx, a lateral 

 feathered membrane existed besides the special patagium 

 with its feathers in front of the fore limb. A remarkable 

 fact about these small flying phalangers is that the 

 power of flight appears to have been independently 

 produced more than once in the group. For we find 

 several types of them each of which is separately re- 

 lated to a non-flying form ; we suppose, therefore, 

 that each has been evolved separately. The same 

 conclusion can be come to with regard to the flying 

 squirrels, real squirrels that is to say, for the marsupials 

 which we are now considering are sometimes termed 

 flying squirrels. In Sciuropterus and Anomalurus, of 

 which the former is often to be seen at the Zoo, we 

 have parachuted squirrels not nearly akin to each 

 other, and therefore possibly to be derived from different 

 forms of merely arboreal squirrels. The carnivorous 

 polyprotodont marsupials have not as yet produced 

 any flying forms. 



THE TASMANIAN WOLF OR THYLACINE 



This wolf-like creature is not a wolf but a repre- 

 sentative of the polyprotodont section of the marsupials, 

 called polyprotodont because the lower incisors are 

 numerous instead of reduced to two as in the vegetable- 

 feeding diprotodonts. The thylacine and its polypro- 

 todont allies show another feature, not found in any 

 other mammals, except the whales, and that is that the 

 total number of the teeth exceed the normal forty- four. 

 This is the original number of teeth, as it appears, in 

 the higher mammals, as testified to by various extinct 

 forms ; from this perfection of tooth numbers most 

 living mammals have degenerated. Another feature 



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