218 TEN years' progress in vertebrate paleontology 



suborder, and placed therein Dermochelys. Knowlton (48) published 

 a paper on the turtles that have. been referred to the Judith Eiver beds. 

 He insisted that while 16 species had been credited to the formation, a 

 considerably smaller number have, according to strict evidence, been 

 found there. 



The questions most important that have been discussed by students of 

 chelonology are those concerning the origin of the order, the relation of 

 Dermochelys to the other sea turtles, and hence the division of the order 

 into suborders. The views of certain authors as to the origin of the 

 Testudinata have been briefly noted above. These animals are regarded 

 as having been derived (a) from the Pleisosaurs, (b) from the Cotylo- 

 saurs, or (c) from some Anomodont-like form. Osborn has held that 

 they came from the Cotylosaurs through the Anomodonts. In his "Fos- 

 sil Turtles of N'orth America" the writer accepted the view that the 

 order here under consideration sprang from the Cot3dosaurs, especially 

 from some form like Otocoelus, which was supposed to be a Cotylosaur. 

 Williston (40) now declares Otocoelus to be an Amphibian. Further- 

 more, the results of his investigations on the Cotjdosaurs make it impos- 

 sible for the writer to accept any longer the idea that the turtles were 

 derived from them, and he is inclined to betake himself to the camp of 

 the advocates of the Anomodonts. 



As regards the origin of the mosaic armor of Dermochelys, Wieland 

 (10), who has done excellent work on fossil turtles, has endeavored to 

 fortify his position by referring to certain elements found in Archelon. 

 In this genus he found a row of thin plates along the mid-dorsal region 

 overlying the proximal ends of the costal plates and probably concealing 

 the neural plates; also apparently some unusual plates at the outer ends 

 of the ribs. These he regards as elements secondarily acquired, fore- 

 shadowing the mosaic of Dermochelys. The present writer may possibly 

 be pardoned for briefly discussing Wieland's conclusions. Let it be ad- 

 mitted that those dorsal and marginal plates are present, which, how- 

 ever, is not absolutely proved; are they remnants of a disappearing 

 armor or the beginnings of a new one ? Why Wieland accepts the latter 

 opinion is difficult to see', unless he knows that Archelon with these ele- 

 ments is the descendant of Protostega, which he thinks did not have 

 them. It would constitute a similar case if we were to affirm that the 

 supramarginal horny scutes of Macrochelys are a new acquisition, be- 

 cause they are not found in Chelydra, so far as we know, an older form. 

 Nor is it certain that the supraneurals were not present in Protostega. 

 They were probably present in P. advena, and Cope found that the costal 

 plates of P. gigas projected so far toward the midline that he thought 



