GEOGRAPHIC AND GEOLOGIC DISTRIBUTIOX 327 



inffs, the ranse including western and eastern N"orth America, J*]ng1an(U 

 nortliern France and Portugal, East Africa and Madagascar, India and 

 far ]*atagonia. Geologically they appear suddenly in widely remote lo- 

 calities as though "living forms, limb'd and full grown, out of the ground 

 uprose," the earliest types l^eing in rocks of early Middle Jurassic 

 (Bath(mian) age. This sudden apparition, of course, implies a long, as 

 vet undiscovered, antecedent evolution. In ever im-reasing numbers 

 Siuir()|H)da a])pear with the passing of Jurassic time, until with the dawn- 

 ing of the Comanchian the full inflorescence of the race is attained, and 

 not long after, geologically speaking, the huge forms are l)lotted out ; for, 

 as Hatcher has shown, they were so absolutely dependent on one peculiar 

 type of habitat that, with their great size and consequent slow maturity 

 and rate of increase, very slight geologic changes would bring about their 

 extinction. 



8TEG0SAURIA 



The armored dinosaurs are confined almost without exception to the 

 northern hemisphere, but recent developments at Tendaguru, East Africa, 

 have brought to light immense numbers of "Stegosaurs," the estimated 

 number of bones in but two quarries being no less than 1,850 ! These 

 represent apparently two species of an undetermined genus, small and 

 highly spinescent ; but we are not yet made aware of their exact relation- 

 ship with others of the gToup. With this notable exception, the armored 

 dinosaurs are unknown from the southern land-masses. Geologically the 

 range is from the Lias to the close of Mesozoic time; Stegosaurus itself, 

 however, represents an aberrant, short-lived race of late Jurassic and 

 probably early Comanchian ( AFori'ison) age. 



THREE VISTAH OF DINOSAURIAN SOCIETIES 



During the Upper Jurassic and tlie (*omanchiau we are given three 

 vistas of dinosaurian societies in which the profusion of animals makes 

 fairly accurate anatomical conipai'ison in some instances possible. These 

 are the American Morrison of Wyoming, Colorado, South Dakota, and 

 Utah; the Tendagurn of German East Africa; and the late Jurassic, and 

 especially the W'ealden. of l-^igland and northern France. Of these the 

 greatest variety of Saiiio[)od genera and species are known from the 

 Morrison, including live families from which no fewer than in genera 

 and 23 species have heen described, ranging from more or less generalized 

 to highly specialized types. Of these families certain are exclusively 

 American, some have representatives in Europe, while others include the 

 dinosaurs of Tendaguru, there being, so far as my researches have taught 

 XXIV— Bull. Geol. Soc. Am., Vol. 26, 1014 



