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THE 



ATURALIST [Vol. XLIV 



regard to the Sauropoda. For although admitting that 

 they were in general bipedal and walked with the body 

 clear of the ground, he finds himself compelled, in the 

 logical development of his theories, to assign them a 

 widely straddling walk. This compels him to explain the 

 observed tracks of 1 guanodon, which are not straddling, 

 as being an unusual mode of progression associated with 

 slow walking, but that if the animal had been running it 

 would have had a wider trackway. So far as the re- 

 viewer's observations extend, the faster an animal is 

 walking or running the more it is inclined to plant the 

 feet close to the median line of its trackway, and the less 

 likely to waddle — this is assuredly true of our own gait, 

 and probably holds good with any bipedal animal. The 

 stronger evidence derived from the numberless tracks of 

 the Connecticut Valley Triassic, Dr. Hay would explain 

 by supposing that these tracks were made, not by dino- 

 saurs which we know existed, but by birds of whose ex- 

 istence at that time we have no evidence. 



But Lull has shown that not only do many of these 

 tracks correspond precisely and in detail with the recon- 

 structed hind feet of carnivorous dinosaurs, but the oc- 

 casional impressions of the fore feet, the pubes and the 

 tail, correspond equally well. A disputed hypothesis in 

 regard to the amount of straddling in their gait is hardly 

 sufficient ground to question the accepted view that these 

 tracks were made by dinosaurs. 



It is indeed quite reasonable to suppose that ancestors 

 of the birds, more or less closely related to the dinosaurs, 

 were living during the Triassic. But the extreme rarity 

 of bird remains during the whole Mesozoic, and the fact 

 that, with the exception of Arrhaopt^njx, the better 



ground for supposing that the normal habitat of Mesozoic 



to the higher and drier uplands, remote from the river- 

 tat of the heavy and bulky dinosaurs, and which the 



