562 MANUAL OF ZOOLOGY. 



Marsupials, Amphitherium and Phascolotherium, prove that the 

 Mammals were the same in order ; cones of Araucarian pines, 

 with tree-ferns and fronds of Cycads occur throughout the 

 Oolitic series ; spine-bearing fishes, like the Port-Jackson 

 Shark, are abundantly represented by genera such as Acrodus 

 and Strophodus; and, lastly, the genus Trigonia, now ex- 

 clusively Australian, is represented in the Stonesfield Slate by 

 species which differ little from those now existing. 



In the Middle Purbeck beds (Upper Oolite), where fourteen 

 species of Mammals are known to exist, it is probable that all 

 were Marsupial. All the Purbeck Mammalia were of small 

 size, the largest being no bigger than a pole-cat or hedgehog. 

 They form the genera Plagiaulax, Triconodon, and Galestes, of 

 which Plagiaulax is believed to be most nearly allied to the 

 living Kangaroo-rat (Hypsiprymnus) of Australia. 



In the Tertiary series of rocks Marsupials are of rare occur- 

 rence ; but an Opossum, closely allied to the existing American 

 forms, has been discovered in the Eocene Rocks of France 

 (Gypseous series of Montmartre), and has been named the 

 Didelphys gypsorum. 



The next occurrence of Marsupials is in the later Tertiary 

 (Pliocene) and in the Post-tertiary epoch ; and here they are 

 represented by some very remarkable forms. The remains in 

 question have been found in the bone-caves of Australia the 

 country in which Marsupials now abound above every other 

 part of the globe ; and they show that Australia, at no distant 

 geological period, possessed a Marsupial fauna, much re- 

 sembling that which it has at present, but comparatively of a 

 much more gigantic size. In the remains from the Australian 

 bone-caves almost all the most characteristic living Marsupials 

 of Australia and Van Diemen's Land are represented; but the 

 extinct forms are usually of much greater size. We have 

 Wombats, Phalangers, Flying Phalangers, and Kangaroos, with 

 carnivorous Marsupials resembling the recent Thylarinus and 

 Dasyurus. The two most remarkable of these extinct forms 

 are Diprotodon and Thylacoleo. In most essential respects 

 Diprotodon resembled the Kangaroos, the dentition, especially, 

 showing many points of affinity. The hind-limbs, however, of 

 Diprotodon were by no means so disproportionately long as in 

 the Kangaroos. In size Diprotodon must have many times 

 exceeded the largest of the living Kangaroos, since the skull 

 measures three feet in length (fig. 215.) Thylacoleo was a 

 carnivorous and predacious Marsupial, equally gigantic when 

 compared with living forms. Thylacoleo, in fact, must have 

 been, on a moderate estimate, at least as large as a Lion; 



