CONCLUSION 117 



there appear Pareiasaurians, a considerable variety of Dinocephalians, many Thero- 

 cephalians, a few Anomodonts, the only known Dromasaurians, and a temnospon- 

 dylous amphibian. Where this great collection of forms came from is of course 

 unknown. They can hardly have originated in South Africa, because though the 

 lower Permian beds are lithologically exactly similar to those of later Karroo times, 

 they are almost entirely unfossiliferous. 



"It seems to me, however, probable from the general resemblance of the African 

 fauna to the North American Permian, that both have come from the common 

 source, which I believe must have lived in the northern part of South America. 

 After the invasion of North America in Upper Carboniferous times, all connections 

 between North and South America ceased for a very long period. The near relatives 

 of the ancestors of the North American Permian forms left in South America evolved 

 on quite other lines. For long they were probably confined to the Brazilian region 

 owing to the cold prevailing in the South, but ultimately they spread down and 

 across the South Atlantic into Africa, where they, for the most part, arrived during 

 Middle Permian times. 



"If this conclusion be correct we may regard the American and South African 

 Permian faunas as derived from a common origin, but having evolved in quite 

 different directions. The American types undergo many curious specializations; 

 the African, or more preferably the South Atlantic type, is chiefly remarkable for 

 the great development of the limbs. The Pareiasaurians, the Dinocephalians, the 

 Therocephalians and the Anomodonts have all developed powerful limbs, and not 

 improbably all independently of each other." 



These conclusions of Broom are contrary to the opinion which has prevailed 

 among American workers on the Permian reptiles. They have held that the Ameri- 

 can Cotylosauria and Pelycosauria are distinct and indigenous. Broom's summary 

 of evidence only cites as common characters the most primitive features, which all 

 date from the time when the reptiles separated from the amphibians. Such a 

 relationship of the two groups must be admitted, but it can only be very remote. 

 The strikingly similar general appearance of the groups as a whole, which appeals 

 to every observer at first glance, is very probably due to the parallel development 

 of very plastic groups in a similar environment. Such characters as follow the lines 

 of development in each group seem to indicate wide diff^erences. 



The Cotylosauria is still regarded as the most primitive order of reptiles, though 

 far from occupying the direct relationship to the Stegocephaha formerly assumed. 

 It is a very large and comprehensive order, of world-wide distribution, containing 

 several highly specialized suborders. The table of comparable characters (pages 

 63-66) shows how widely separated were some of its members. Though some forms, 

 as Seymouria and perhaps Stephanos pond ylus, approach very close to the Stegoce- 

 phalia in the character of skull, they are widely separated from them in other 

 characters. It now appears we must turn to some of the small and less well-known 

 Cotylosauria to find the probable connecting link between the reptiles and amphib- 

 ians. It may well be that none of the forms now known will turn out to be the 

 connecting form, but the most hopeful path leads in the direction of some of the 

 smaller forms, such as Gymnarthus, now placed provisionally among the amphibians. 



The primitive form seems to have been a small creature with a low, flat skull 

 containing all the bones of the Stegocephalian skull and without an epiotic notch. 

 The quadrate was covered and the parasphenoid bone was reduced to a rostrum 



