THE JURASSIC PERIOD. 



261 



believe that its jaws were furnished with teeth sunk in distinct 

 sockets, as is the case in no existing Bird. This conclusion, 

 at any rate, is rendered highly probable by the recent discovery 

 of "Toothed Birds" (Odontornithes) in the Cretaceous rocks 

 of North America. 



The Mammals of the Jurassic period are known to us by 

 a number of small forms which occur in the " Stonesfield 

 Slate" (Great Oolite) and in the Purbeck beds (Upper 

 Oolite). The remains of these are almost exclusively sepa- 

 rated halves of the lower jaw, and they indicate the existence 



Fig. 183. Lower jaw of Amphitherium ( Thylacotherium) Prevostii, 

 Stoneafleld Slate (Great Oolite.) 



during the Oolitic period in Europe of a number of small 

 "Pouched animals" (Marsupials). In the horizon of the 

 Stonesfield Slate four genera of these little Quadrupeds have 

 been described viz., Amphilestes, Amphitherium, Phascolo- 

 therium, and Stereognathus. In Amphitherium (fig. 183), the 

 molar teeth are furnished with small pointed eminences of 

 " cusps ; " and the animal was doubtless insectivorous. By 



Fig. 184 Oolitic Mammals. 1, Lower jaw and teeth of Phascolotherlum, Stones- 

 field Slate ; 2, Lower jaw and teeth of Amphttherium, Stonesfield Slate ; 3, Lower jaw 

 and teeth of Triconodon, Purbeck beds ; 4. Lower jaw and teeth of Plagiaulax, Pur- 

 beck beds. All the figures are of the natural size. 



Professor Owen, the highest living authority on the subject, 

 Amphitherium is believed to be a small Marsupial, most 

 nearly allied to the living Banded Ant-eater (Myrmecobius} of 

 Australia (fig. 158). Amphilestes and Phase -olotherium (fig. 



