80 
Records of the Geological Survey of India. 
[VOL. X. 
The genus Merycopotamus is not introduced into Professor Kowalevsky s table; there 
can, however, be no doubt but that since its teeth are very markedly selenodont, the genus 
would be placed somewhere near the Antliracotlieridce (or Hyopotamidce, for the family is 
known by both names) and entirely apart from the Hippopotamidw. In his Memoir on the 
Osteology of the Hyopotamidte, published in the “ Philosophical Transactions” for 1873, 
Professor Kowalevsky refers to the genus Merycopotamus at page 25 as belonging to 
a group nearly related to Hyopotamus, though it seems probable that the Professor 
would place the two genera In distinct families, owing to the upper molars of the Indian 
genus having only four cusps or cones on the masticating surface, while those of the 
European genera carry five. Whatever be the exact family position of the Indian genus, 
it is perfectly clear that according to Kowalevsky’s plan of evolution there can have been 
no connection between the original stocks of Hippopotamus and Merycopotamus since 
the lower Eocene period. 
I have already noticed in my former paper the very remarkable similarity in the form 
of the mandibles of Hippopotamus and Merycopotamus ; and I think every one must admit 
that these two genera must have descended from some common ancestor which had a some¬ 
what similarly shaped mandible. Now, neither of these two genera is known in the fossil 
state from strata older than the Siwalik period; while no other Pig-like animal, either 
recent or fossil, has a similarly shaped lower jaw, though there is a very slight rudiment 
of the descending process in the American Peccari and Hyopotamus; it is further a very 
noteworthy fact, that the lower jaw of the Siwalik Hippopotamus (as is well shewn in 
PL 61 of the “ Fauna Antiqua Sivalensis”) which is the oldest known species of the genus, 
is very much more like that of Merycopotamus than is the lower jaw of the living 
species; indeed, except in the matter of size and of the form of the teeth, the jaws of the 
two Indian forms are almost indistinguishable. If the common ancestor of these two 
genera had lived as far hack as the lower Eocene period, it is extremely strange that the 
remarkable configuration of the lower jaw should have persisted in these two isolated genera 
np to the Siwalik period, and that there are no traces of any fossil forms with similarly 
shaped lower jaws which lived between the Eocene and Siwalik periods; it is therefore 
probable that the hypothetical ancestor of these two genera lived subsequently to the 
Eocene period; and that the Bunodonta and Selenodonta are more closely connected than 
Kowalevsky supposes. 
With regard to this hypothetical ancestor, we may notice that Merycopotamus exhibits 
such affinities to the older Hyopotamoids of Europe, now known for the first time in India, 
that it is almost certain that the ancestral form must have been selenodont or hemi-seleno- 
dont, and that, consequently, Hippopotamus is descended from a selenodont and not from 
a bunodont ancestor. In favour of this view we may note the very significant fact that, 
in tracing back the affinities of Hippopotamus, Professor Kowalevsky has not been able 
to place a single genus between it and the primitive bunodonts of tbe early Eocene. If 
this view be true, the bunodont teeth of Hippopotamus are an instance of reversion to 
an older type; in confirmation of this view we may notice that the pig-like animals with 
selenodont teeth, like Merycopotamus, Hyopotamus and Or codon, have all disappeared 
from the earth, and evidently belonged to a typo which was not suitable to persist 
in that condition ; this type is admitted to have been modified into the true Ruminants, 
and it is quite likely that another branch of it may have reverted to the bunodont 
type. It seems to be probable that the more specialised selenodont type of tooth, though 
advantageous to the true Ruminants, was not suitable to those animals which retained 
the general organisation of the Pigs, and that these animals either were further modi- 
