6 4 
CETACEANS. 
X 
Zeuglodonts. 
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 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 zeuglodonts 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. 
