SAUROPODA 325 



sealevcl, with sluggish bayous separated hy nuiiicrous islands clothed in 

 a dense tropical vegetation. h\ these iastnesses the creatures would he 

 enniparatively safe from their carnivorous enemies, while in tlie ipiiel 

 waters they would iijid support for their huge bodies both against the 

 burden imposed l)y gravity and the wai'nijig pangs of hunger. 



Their structure of tooth, claw, and body ])oints conclusively to a ear- 

 ni\oi'ous ancesti'Y, and Ilueiie sees in the dinosaur I'hilcosdiiriis. fi'oni 

 I be (iei'iuan Keuper, a possible ancestral form. The change o\' habitat 

 may well ha\e been due to the growing burden of the llesh, which also 

 may have caused the dietary change. AMtliin some families of modern 

 reptiles, notably the Iguanida?, most of which are insectivorous, some are 

 also herbivorous and their range of habitat is equally broad, as they are 

 arboreal, terrestrial, burrowing, semi-aquatic, and one, Amhlyrhynclius, 

 is even semi-marine ! Hence the conjectured change of habit and habitat 

 on the part of the Sauropoda is not without modern parallel. 



Stegosauria 



The tStegosaurs are the armored dinosaurs Ijclonging to a dift'erent sub-' 

 order, all of which are characterized, with a single known exception, by 

 having the mouth toothless in front, but doubtless armed by a more or 

 less turtle-like prehensile beak. The dental battery, which reached a re- 

 markable degree of perfection in some of the latest types, is confined to 

 the rear pcn'tion of the jaws and is amply lltted tor the mastication of 

 herbaceous food. The Stegosaurs were quadrupedal, though, as DoUo 

 has shown, they doubtless descended from a bi|)edal ancestry, which the 

 increasing w^eight of armor caused to reassume the four-footed gait of 

 still more remote forebears. The armor takes the form of crocodile-like 

 scutes, which in certain portions of the body tended to form l)road pr.;- 

 tective shields through coalescence. In Stegosaurus, the aberrant genus 

 which has determined the name of the group, the median fore and aft 

 keel ot' the dorsal scutes has hypertrophied enormously, giving rise to the 

 huge upstanding jdates diagnostic of the genus. Other dermal elements 

 took the foriii of s|)ines, Ixinie by SI I'ljusdnrus en the distal end of the 

 tail, by other genera nwv dixci's poilions dj' the fi'anu', although I do not 

 know that the e\ idence for llieii' alleged |)o>ition is always clear. 



Of the habits of 1 be Stegosaui's we know little: tlic teeth in known 

 types, iiotabK in S/rf/n.^aiiriis itself, ai'e i-elati\ely leeblc coiii|iai'ei| witii 

 those of the arniorless iy|ie and with those of the I'eratopsia : hence the 

 infei'ence is that their food must ha\e liceii of a nci'v succulent ciiaracter 

 ami of sullicieiit abundance to maintain the Itulk of a creature whose sub- 

 stance was two or three times that of an elephant. 



