202 TEN years' progress in vertebrate paleontology 



The upper of the two temporal openings occurs between the squamosal 

 and the prosquamosal and postorbital, the lower between the latter and 

 the jugal and quadratojugal. It has been shown that, with the exception 

 of Pantylus, no Cotylosaur has more than two bones below the parietal in 

 the temporal region, the squamosal and the prosquamosal or quadrato- 

 jugal. It is evident that the two openings could not have oiiginated in 

 such forms. Pantylus has the three bones, and the two openings might 

 have appeared in such a form, but Pantylus is one of the most specialized 

 of the Cot3'losaurs and can not be placed in an ancestral position. If the 

 theory of the primitive double-arched condition is to prevail, it must be 

 supported by the discovery of a generalized Cotylosaur with the bones, as 

 in Pantylus. N'o such form is known and there is an enormous hiatus in 

 the evidence. At present it seems more probable that Pantylus is a spe- 

 cialized departure from the primitive stock, with but two bones in the 

 temporal region. 



On the other hand, it has been contended that the Pelycosaurs are two 

 arched forms of the assumed primitive stock; this has been seriously 

 questioned by Broom and von Huene, and it must be admitted that some 

 Pelycosaurs are single arched, and that in Dimetrodon, even, the evidence 

 is not conclusive. Last summer a joint expedition from the universities 

 of Chicago and Michigan into Xew Mexico recovered a nearly complete 

 skeleton of Ophiacodon, a primitive Pelycosaur, in which the two tem- 

 poral openings are distinctly present. It may be that the weight of evi- 

 dence is on the return swing toward the original theory. 



The inadequacy of the theory has led to the formulation by Broom and 

 von Huene of somewhat complicated and tentative theories to account 

 for the different t}'pes of skull structure as independent developments 

 from the Cotylosaurs. These have not yet been worked into definite form. 

 More evidence is the great desideratum, and our achievements in this 

 line are not inconsiderable. The confusion resulting from pioneer work 

 in America has been in large measure, I hope, cleared up. Broom has 

 performed a like service for the South African forms. Thevenin is busy 

 with the French forms. The collections of the University of Chicago in 

 the last ten years have been wonderfully rich. The American Museum 

 has added much to its original material. The expedition of last summer 

 into New Mexico brought back much of value, which, added to that which 

 has long lain forgotten in the Yale ^luseum, throws a flood of light on 

 the fauna of a new locality. Moody is busy on a monograph of the fossil 

 amphibians of North America. Broom is still actively collecting, and 

 Doctor Watson, of the University of Manchester, in England, has started 

 on a collecting trip to South Africa. 



