360 AN IXTRODUCTION TO THE STUDY OF FOSSILS 



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oda) includes forms 

 which were hghtly 

 built, walking bird-like 

 upon their toes, with 

 short fore legs and 

 long hind ones, hollow 

 limb bones, and sharp 

 carnivorous teeth. 

 The union of the ischia 

 extended backwards 

 and downwards, form- 

 ing a kind of third foot 

 when the animal rested 

 upon his hind legs (Fig. 

 153). One of these, 

 Anchisaurus, has been 

 found only in the 

 Triassic sandstones of 

 the Connecticut Valley 

 and is doubtless re- 

 sponsible for many of 

 the three-toed tracks 

 so numerous upon 

 these old muddy sands. 

 Another branch 

 iSaiiropoda) includes 

 massively built herbi- 

 vores, walking semi- 

 flatfooted, with fore 

 and hind legs more 

 nearly equal in length, 

 and with limb bones 

 apparently solid. 

 Some of the Jurassic 

 forms were, so far as 



