64 



CETACEAXS. 



Zeuglodonts. 



Very different from the above are the still earlier forms known 

 as zeuglodonts (genus Zeuglodon), wliich appear to be mainly or 

 entirely confined to the Eocene Tertiary, and have been obtained from regions 

 as far asunder as North America, Western Europe, the Caucasus, and Australia and 

 New Zealand. So different, indeed, were these animals from all existing Cetaceans, 

 that it has even been doubted whether they can be included within the limits of 

 the same order. Some of them rivalled the larger whales in point of size, while 

 the Caucasian species was not larger than an ordinary dolphin. 



The zeuglodonts had teeth of the same general type as those of the squalodonts, 

 but those of the cheek-series were fewer in number, the premolars and molars 

 together being apparently only five on each side. The skull differs from that of 

 ordinary Cetaceans in having elongated nasal bones, and the cavity of the nose 

 placed more forwardly, as well as in certain other features ; all these points of 

 difference being in the direction of ordinary mammals. Unfortunately, we know 

 but very little of the structure of the limbs. The humerus, or bone of the upper 

 arm, is, however, proportionately much longer than in modern Cetaceans, although 

 it has flattened articular surfaces at its lower end, showing that the bones of the 

 fore-arm had scarcely any free motion, and thus indicating that the fore- limbs 

 were modified into flippers. So far as they can be determined, the general 

 characters of these zeuglodmit^ are such as we should expect to find in an 

 ancestral group of Cetaceans : but it is remarkable that the body appears to have 

 been protected by an armour of bony plates. 



