JURASSIC FAUNA. 167 



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Turning to the flora, we find it to be sharply defined from that 



of any of the Paleozoic periods, although in the abundance of ferns, 

 many of them of ancient type, and in the absence of the higher 

 forms of plants, it shows an interesting correspondence. Its most 

 marked feature is furnished by the group of the Cycads, of which 

 there are numerous genera recognised, and the pines, whose nearest 

 allies appear to be the southern araucarias. The earliest undoubted 

 representatives of endogens are found in the deposits of this age, 

 some of them clearly indicating a close relationship with the Aus- 

 tralian screw-pines (Pandanus). No positive traces of exogenous 

 plants other than conifers have as yet been determined, but it is by 

 no means improbable that they already existed. 



Comparing the fauna and flora of the Jurassic period with the 

 existing fauna and flora of any portion of the earth's surface, w T e 

 remark a striking similarity to the conditions presented on the 

 Australian continent. Here, at the present day, is the home of 

 the marsupials, of the Port-Jackson shark, which had its Jurassic 

 representatives in genera like Acrodus, Hybodus, and Strophodus, 

 and of Ceratodus among the lung-fishes, a form which, though of 

 more ancient date, also had its habitat in the seas of the Jurassic 

 period. Only along the Australian coast do we meet at the present 

 time with the lamellibranchiate genus Trigonia, one of the most 

 characteristic and abundant of the Jurassic mollusks. As regards 

 the flora, a no less striking correspondence is apparent. On the 

 Australian land-surface flourish a considerable variety of ferns, tree- 

 ferns, and cycadaceous plants ; likewise, the Araucaria type of 

 Conifer; and here, principally, do we find the singular plants al- 

 ready referred to as screw-pines (Pandani). Australia is, in fact, 

 that portion of the earth's surface which, as far as its faunal and 

 floral characteristics are concerned, has undergone the least modi- 

 fication since the Jurassic period, and, indeed, it may be said that 

 the present fauna and flora of the continent became differentiated 

 during the interval between the Triassic and Jurassic periods, al- 

 though, as has already been seen, some of the distinctive types date 

 from a more ancient epoch. The retention of an ancient type of 

 fauna and flora clearly indicates that the continent had retained its 

 isolated position through a period probably extending as far back 

 as the Mesozoic era ; otherwise, if connection with some other 

 continental land-mass had, existed ftt some subsequent period, it 



