THE TRIASSIC PERIOD. 223 
which is the fact that the animal possessed the power of 
walking, temporarily at least, on its hind-legs, which were 
much longer and stronger than the fore- limbs, and which 
were sometimes furnished with no more than three toes. 
As the bones and teeth of Deinosaurs have been found in 
the Triassic deposits of North America, it may be regarded as 
certain that some of the bipedal tracks originally ascribed to 
Birds must have really been produced by these Reptiles. It 
seems at the same time almost a certainty that others of the 
three-toed impressions of the Connecticut sandstones were in 
truth produced by Birds, since it is doubtful if the bipedal 
mode of progression was more than an occasional thing 
amongst the Deinosaurs, and the greater number of the 
many known tracks exhibit no impressions of fore - feet. 
Upon the whole, therefore, we may, with much probability, 
conclude that the great class of Birds (Aves) was in existence 
in the Triassic period. If this be so, not only must there 
have been quite a number of different forms, but some of 
them must have been of very large size. Thus the largest 
footprints hitherto discovered in the Connecticut sandstones 
are 22 inches long and 12 inches wide, with a proportionate 
length of stride. These measurements indicate a foot four 
times as large as that of the African Ostrich ; and the animal 
which produced them—whether a Bird or a Deinosaur—must 
have been of colossal dimensions. 
Finally, the Trias completes the tale of the great classes of 
the Vertebrate sub-kingdom by presenting us with remains of 
the first known of the true Quadrupeds or JZammalia. ‘These 
are at present only known by their teeth, or, in one instance, 
by one of the halves of the lower jaw ; and these indicate 
minute Quadrupeds, which present greater affinities with the 
little Banded Ant-eater (AZyrmecobius fasciatus, fig. 158) of 
Australia than with any other living form. If this conjecture 
Jit Wp 
Fig. 157.—a@, Molar tooth of 
Microlestes antiguus, magni- 
— ; fied; 4, Crown of the same, 
Fig. 156.—Lower jaw of Dromatheriunt sylvestre. magnified still further. ‘Trias, 
Trias, North Carolina. (After Emmons.) Germany. 
be correct, these ancient Mammals belonged to the order of 
the Marsupials or Pouched Quadrupeds (A@arsupialia), which 
