68 THIRD GENERAL MEETING. 



THIRD GENERAL MEETING. 



Thursday, August 25//^. 



A General Meeting of the Congress was held at 10.30 a.m. to 

 discuss tJie Origin of Mammals. 



The President having taken the Chair, introduced Prof. Hubrecht, 

 who had been appointed Chairman for this discussion. Prof. 

 Hubrecht having sketched briefly the lines which the discussion 

 should follow, called on Prof Seeley, of whose remarks the follow- 

 ing is an abstract. 



When certain fossil reptiles proved to have some bones of the 

 skeleton almost identical with those of birds, reptiles and birds were 

 united in a division of Vertebrates named Sauropsida. Similarly 

 when other extinct reptiles showed forms of bones and teeth which 

 were almost indistinguishable from those of mammals, the lower 

 mammalia and Anomodontia were thrown together into a group 

 named Theropsida. The Iguanodont reptiles have been regarded as 

 ancestors of birds, and Theriodont reptiles have been regarded as 

 ancestors of mammals. 



The imperfection of the evidence has favoured differences of 

 interpretation. 



When Theriodesmus was described, the mammalian resemblances 

 of the bones appeared to prove it a mammal; but after Pareiasaurus 

 was found, there was proof that Theriodesmus approached still 

 closer to that genus in its limbs ; and therefore was no mammal but 

 a reptile. In the same way when the imperfect skull of Tritylodon 

 was described, its molar teeth were so similar to those of mammals 

 and so unlike any known reptiles that the animal was accepted 

 as a mammal. Subsequently the group of Gomphodont reptiles, 

 represented by several genera, was found with teeth as complicated 

 as those of Tritylodon, and skull structures which are regarded as 

 reptilian. So that Tritylodon also is now classed among reptiles. 



Few skeletons of these extinct reptiles are known, Pareiasau- 

 rus is nearly complete. Dicynodonts are fairly complete, Cyno- 

 gnathus wants nearly the whole of the limbs. These and other 

 skeletons show different affinities in different parts of the skeleton ; 

 and from the skull of Pareiasaurus and Dicynodon no indication 

 could be inferred of mammalian resemblances seen in other parts 

 of their skeletons. This difference between skull and skeleton in 

 affinity is in harmony with other fossil reptiles, since no one could 

 have inferred from the skull of Iguanodon the bird-like characters 

 of its pelvis and hind limb. 



