PROF. OvSBORN ON THE ORIGIN OF MAMMALS. 419 



of reptilian type. The second point may be met by supposing that 

 at the time the Marsupio-placcntals were given ofif, the Thcrio- 

 dontia conserved a number of Amphibian characters, which were at 

 the time or subsequently lost. 



The problem of most immediate concern, however, is whether 

 the Theriodontia are actually the long sought Promammalia of 

 Haeckel, Hypotheria of Huxley, or Sauromammalia of Baur, or 

 whether they present a fresh instance of extensive parallelism due 

 to the assumption of habits analogous to those of Mammalia. 

 Professor Seeley has just presented the latter view', and it is 

 certainly true that none of the known Theriodonts fill the characters 

 outlined above as those we must look for in the Promammal or 

 Eutherian stem, for they are all too large and too specialized. 



There are however grounds for the more sanguine former view, 

 that the Theriodontia are the Hypotheria or Promammalia, because 

 it appears that within the order may well have existed some small 

 insectivorous types, far less specialized in tooth structure than either 

 the carnivorous Cynodonts or herbivorous Gomphodonts, 'as one 

 of those conservative spurs of adaptive radiation which form the 

 focus of a new progressive type. 



The problem will therefore be settled by additional discovery 

 and knowledge of the skeletal structure of the diverse types which 

 undoubtedly composed this remarkable group. 



^ "Anomodonts are not the parents of Mammals, but a collateral and closely related 

 group. The common parent of both may be sought in rocks older than Permian, per- 

 haps in Silurian or Devonian strata." Abstract of Discussion, p. 70. 



