ANCESTRY OF THYLACINES 
admirably adapted for the protection of young born in the imperfect and 
helpless condition characteristic of all the marsupials, is hard to divine.” 
Beddard’s “‘Mammalia” 8” (pages 14-18) should be consulted for fuller 
treatment of this subject. 
The origin of the pouch, as an advantageous feature, is probably 
due to the arboreal habits which are believed 2° to have been character- 
istic of all the ancestral marsupials, the coming down to earth (assumption 
of terrestrial habits) being a comparatively modern matter affecting only 
certain groups of this class. 
In regard to the early history of this group, Dr. W. D. 
Matthew writes me as follows: — 
“Recent studies by W. J. Sinclair have shown that the thylacine, 
although now found only in Australia and Tasmania, is the last survivor 
of a group of carnivorous marsupials which inhabited South America during 
the Tertiary period, and took the place in that continent of the true Car- 
nivora of the northern world. Since none of these animals, living or ex- 
tinct, has been found in any of the northern continents, it appears most 
reasonable to suppose that the thylacines reached Australia from South 
America (or vice versa) through a former land connection by way of the 
Antarctic regions, an hypothesis supported by many other resemblances 
between the animals and plants, recent and extinct, of the three southern 
continents. About the middle of the Tertiary period Africa became con- 
nected with Europe, and at a later epoch South America with North Amer- 
ica, the south polar land connections having in the meanwhile sunk below 
the ocean. The more active, powerful, and intelligent carnivorous ani- 
mals of the northern world were thus enabled to extend their range into 
the southern continents, and soon displaced and destroyed all their mar- 
supial predecessors in those regions, while Australia, still separated by 
ocean from the northern land masses, retained its ancient population of 
marsupial carnivores.” 
The true opossums are a family (Didelphide) related to 
the dasyures, but never represented in Australia. It is the low- 
est family in rank of organization and the one most 
ancient in lineage, for it seems to have become well 
established in the Cretaceous, and widely distributed throughout 
the northern world during that and the Eocene periods. No 
other marsupial group, so far as known, approaches this in 
2L 513 
Opossums. 
