quatic--the predaceous kinds equalled
or exceeded the largest of the herbivorous sorts. The difference is
striking, and it does not seem likely that it is merely accidental.

The explanation lies probably in the fact that the large herbivorous
mammals are much more intelligent and active, and would be able to use
their weapons of defense so as to defy the attacks of relatively slow
moving giant beasts of prey, as they do also the more active but less
powerful assaults of smaller ones. The elephant or the rhinoceros is
in fact practically immune from the attacks of carnivora, and would
still be so were the carnivora to increase in size. The large modern
carnivora prey upon herbivores of medium or smaller size, which they
are active enough to surprise or run down. Carnivora of much larger
size would be too slow and heavy in movements to catch small prey,
while the larger herbivores by intelligent use of their defensive
weapons could still fend them off successfully. In consequence giant
carnivores would find no field for action in the Cenozoic world, and
hence they have not been evolved.

But the giant herbivorous dinosaurs, well armed or well defended
though they were, had not the intelligence to use those weapons
effectively under all circumstances. Thus they might be successfully
attacked, at least sometimes, by the powerful although slow moving
Megalosaurians.

The suggestion has also been made that these giant carnivores were
carrion-eaters rather than truly predaceous. The hypothesis can hardly
be effectively supported nor attacked. It is presented as a possible
alternate.

_Albertosaurus._ Closely allied to the _Tyrannosaurus_ but smaller,
about equal in size to _Allosaurus_, was the _Albertosaurus_ of the
Edmonton formation in Canada. It is somewhat older than the Tyrannosaur
although still of the late Cretacic period, and may have been ancestral
to it. A fine series of limbs and feet as also skull, tail, etc., are
in the Museum's collections. At or about this time carnivorous
dinosaurs of slightly smaller size are known to have inhabited New
Jersey; a fragmentary skeleton of one secured by Professor Cope in 1869
was described as _Laelaps_ (=_Dryptosaurus_).[10]

_Ornitholestes._ In contrast with the _Allosaurus_ and _Tyrannosaurus_
this skeleton represents the smaller and more agile carnivorous
dinosaurs which preyed upon the lesser herbivorous reptiles of the
period. These little dinosaurs were probably co