742 Marvels of the Universe 
It is not here possible to do more than allude briefly to this seductive hypothesis which puts 
the descent of the vertebrates upon a higher plane than that occupied by the “ worms,” which 
have hitherto been accorded the distinction of being their primitive stock ; but it is quite clear that 
the theory in question, which has been most forcibly and ingeniously urged by Dr. Gaskell, invests 
these fishes of the Old Red Sandstone with quite a new interest. 
These, however, are not the only fishes that lived in that primeval period. There were others 
belonging to the existing orders, containing the sharks, the lung-fishes, and the gill-breathing 
fishes with bony skeletons, but those of the latter group were all of a lowly type more or less, 
serving to link the existing bony fishes with the lung-fishes. 
Now the lung-fishes are of peculiar interest, because it was from them that the higher vertebrates 
originated: first the amphibians, then the reptiles, and from the reptiles, the mammals and the 
birds. They are represented at the present day by only three types, one of which lives in 
FISHES OF THE OLD RED SANDSTONE. 
One of the armour-plated fishes remarkable for the peculiarly elongated snout. 
Australia ; another in South America, and the third in tropical Africa. They are thus a good 
illustration of the wide dispersal on the earth of many ancient but waning types. Some of 
the Old Red Sandstone lung-fishes, like Dipterus, were not so very different from the living 
Australian kind ; but others were so distinct as to be set aside in a special group by themselves. 
Coccasteus, shown in our illustration, is one of these. The special resemblance shown by 
Coccasteus to the latter lies in the investment of the fore part of the body, both above and 
below, by bony plates. The head, which carried a pair of large lateral eyes, was similarly 
protected above, and was movably jointed to the back plates. A Scotch species was only 
a little more than a foot long; but in North America there lived some huge examples akin 
to it, one of them, known as the Titan Fish, quite rivalling large existing sharks in size, if 
their computed length of about twenty-five feet be correct, while a smaller type, the Terrible 
Fish, perhaps ten feet long, must have been a predatory fish equalling the sharks in voracity, 
to judge from the size and sharpness of the teeth with which its jaws were armed. 
