SQUALODONTS AND ZEUGLODONTS 1237 



saw-like manner. The squalodonts, which are found in Miocenne and Pliocene for- 

 mations, both in the Old and New World, clearly form one step between modern 

 Cetaceans and ordinary Mammals. And, so far as the structure of their teeth can 

 be relied upon, they appear to suggest a kinship between Cetaceans and Carnivores. 

 Very different from the above are the still earlier forms known as 

 zeuglodonts (genus Zeuglodon], which 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 rivaled the larger whales in point of size, while the Cauca- 

 sian species was not larger than an ordinary dolphin. 



The zeuglodonts had teeth of the same general type as those of the squalo- 

 donts, 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 differ- 

 ence 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 characteristics 

 of these zeuglodouts 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 

 armor of bony plates. 



