THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XIY. — The Armor of Stegosaurus ; by Richard S. 



Lull. 



[ Contributions from the Paleontological Laboratory of Yale University.,] 



I. Introductory. 



II. Character of armor. 



III. Morphology of the plates. 



IV. Position of the armor. 



I. Introductory. 



The American genus Stegosaurus, first made known to 

 science by Professor Marsh, includes the most bizarre and 

 grotesque of armored dinosaurs ; a group apparently quite 

 apart from the glyptodon-like Ankylosauridse with heavy mail 

 developed over the entire body, for in Stegosaurus the striking 

 armament was confined to certain regions and, so far as our 

 knowledge goes, but little developed elsewhere. 



Stegosaurus, while belonging to the Morrison, the beginning 

 of the Lower Cretaceous (Lull, this Journal, vol. xxix, p. 15), 

 was highly specialized and evidently represented a senile race, 

 and was, as Beecher has shown with other spinescent forms, on 

 the verge of extinction, for it shortly disappears entirely from 

 our records. 



II. Character of armor. 



The known armor of Stegosaurus includes five types of 

 structures, all dermal in origin, of which the first are the small, 

 rounded ossicles (gular plates) found in situ beneath the skull. 

 These form a continuous, pavement-like investiture protecting 

 the throat (fig. 1) and doubtless extending over a considerable 

 portion of the body as well, though not elsewhere preserved, 

 for it is unreasonable to suppose that an armored reptile would 

 have any portion of the skin bereft of scutes or scales of some 

 sort. These throat ossicles increase in size as one goes back- 



Am. Jour. Sci. — Fourth Series, Vol. XXIX, No. 171. — March, 1910. 

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