28 FOSSIL TURTLES OF NORTH AMERICA. 
History, volume xx1, 1905, page 167. Since the publication of that paper discovery 
of new materials has shown that Anosteira belongs among the Dermatemydide. 
The family Bothremydide, recognized in the present work, is represented in the 
chart as springing from ancestral Pelomeduside during the Lower Cretaceous. 
It is wholly possible that Taphrosphys itself belongs to the Pelomedusidz, instead 
of the Bothremydide. It has been concluded that the stock that gave origin to the 
Emydidz, and the Vestudinidz ought to be brought into closer connection with the 
Dermatemydide. The Carettochelyida also are represented as arising from the 
Dermatemydide. It is not improbable that they should have been regarded as 
direct descendants of the Tretosternide. 
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, 
x11, 1896), Cope (Proc. Amer. Philos. Soc., xxx, 1892, p. 279), Osborn (Mem. 
Amer. Mus. Nat. Hist., vitt, 1903, p. 450), Woodward (Vert. Paleontology, 1898, 
p. 144), Broile (Paleontographica, L1, 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 Otoccelida, 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, x11, 1905, p. 126) in which he describes a species of Diadectes. 
In this communication he shows that the family of Diadectidz 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 
Diadectidze “forms very closely 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 
vertebra, by the existence of digits having the phalangeal formula, 2, 3, 3, 3, 3- 
Case has shown that the claims of the Diadectidz 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 Labidosaurus hamatus there are at least 24 presacral vertebra. 
