The Descent of Man

and Platyrrhine monkeys, with their subgroups,
have all proceeded from some one extremely
ancient progenitor. The early descendants
of this progenitor, before they had diverged
to any considerable extent from each other,
would still have formed a single natural group;
but some of the species or incipient genera
would have already begun to indicate by their
diverging characters the future distinctive
marks of the Catarrhine and Platyrrhine divisions.
Hence the members of this supposed
ancient group would not have been so uniform
in their dentition, or in the structure of their
nostrils, as are the existing Catarrhine monkeys
in one way and the Platyrrhines in another
way, but would have resembled in this respect
the allied Lemuridae, which differ greatly from
each other in the form of their muzzles (15.
Messrs. Murie and Mivart on the Lemuroidea,
'Transactions, Zoological Society,' vol. vii, 1869,
p. 5.), and to an extraordinary degree in their
dentition.