2 8 FOSSIL TURTLES OF NORTH AMERICA. 



History, volume xxi, 1905, page 167. Since the publication of that paper discovery 

 of new materials has shown that Anostelra belongs among the Dermatemydidae. 

 The family Bothremydidae, recognized in the present work, is represented in the 

 chart as springing from ancestral Pelomedusidae during the Lower Cretaceous. 

 It is wholly possible that Taphrosphys itself belongs to the Pelomedusidae, instead 

 of the Bothremydidas. It has been concluded that the stock that gave origin to the 

 Emydidse, and the Testudinidae ought to be brought into closer connection with the 

 Dermatemydida?. The Carettochelyidae also are represented as arising from the 

 Dermatemydidae. It is not improbable that they should have been regarded as 

 direct descendants of the Tretosternidae. 



The geological distribution of the families will be considered on a coming page. 



THE DERIVATION OF THE ORDER OF TURTLES. 



At the present day the most interesting and the most difficult questions that 

 confront the student of any group of animals or plants are : From what lower group 

 was this derived ? and: What are its relationships to kindred groups ? We must 

 here at least make the inquiry: From what lower order of reptiles have the turtles 

 been derived ? and the further inquiry: What are the relationships of this order to 

 other orders of reptiles ? The reply must be: We can not yet give definite answers 

 to these questions. 



Nevertheless, some progress appears to have been made toward framing answers 

 to these inquiries. It is quite generally agreed that the Cotylosauria or closely 

 related forms, known from remains occurring in Permian deposits, are the lowest, 

 the least differentiated, of all reptiles hitherto discovered, having themselves been 

 derived directly from the Stegocephalia. On this point see Baur (Anat. Anzeiger, 

 xn, 1896), Cope (Proc. Amer. Philos. Soc., xxx, 1892, p. 279), Osborn (Mem. 

 Amer. Mus. Nat. Hist., vm, 1903, p. 456), Woodward (Vert. Palaeontology, 1898, 

 p. 144), Broile (Palaeontographica, LI, 1904, p. 106). From the Cotylosauria, Baur 

 derived the turtles thru rhynchocephalian ancestors, animals not distantly related 

 to Sphenodon. Cope concluded (Proc. Amer. Philos. Soc., xxxv, 1896, p. 124) 

 that the cotylosaurian Otoccelidae, which he afterward removed to the order Chely- 

 dosauria (Syllabus of Lectures, 1898, pp. 54, 61), were the source of the turtles. 

 Osborn, as cited (p. 465), brings the line of descent of the turtles from the Coty- 

 losauria through the Anomodontia. Woodward, as cited (p. 170), calls attention to 

 the apparent relationships between the turtles and the Anomodontia, in which group 

 he includes the Cotylosauria and the Chelydosauria. Case has publisht a paper 

 (Jour. Geology, xm, 1905, p. 126) in which he describes a species of Diadectes. 

 In this communication he shows that the family of Diadectidae is to be transferred 

 to the Chelydosauria; and he demonstrates that there are many resemblances 

 between the skull of his specimens and that of turtles. He holds that we have in the 

 Diadectidae "forms veryclosely related to the ancestral stem of the turtles, which tell us 

 much regarding the development of the Testudinata directly from the Cotylosauria." 



The Cotylosauria and the closely related Chelydosauria indicate their eligibility 

 to stand as the ancestors of the turtles by the possession of a complete roof over the 

 temporal fossa, by the character, rare among reptiles, of having 18* presacral 

 vertebrae, by the existence of digits having the phalangeal formula, 2, 3, 3, 3, 3. 

 Case has shown that the claims of the Diadectidae for the honor of the ancestry of 

 the turtles are superior to those of the Cotylosauria, as limited by him, inasmuch as 



*Broili states that in Labtdosaurus hamatus there are at least 24 presacral vertebrae. 



