There are several extant species which exhibit this intermediate format - somewhere
between ground predator and primate. Examples of these are the Raccoon (Procyon lotor),
Kinkajou (Potosflavus), and Madagascan Fossa and so viability of this way of life
is evident. In time, perhaps millions of years, selection for features which are
essentially primate-like will come about in these animals. This is because primate
characteristics and forms are the best suited for the maximum exploitation of arboreal
Let us have a closer look at some of these modern intermediates.
The Raccoon (Procyon lotor)
Our pioneering rainforest dog, at the stage described above, could have had traits
similar to the raccoon. They are quite capable of climbing up into trees. They are
relatively small (around 30 inches in length) and some aspects of ‘primatisation’
are already present. These include the five fingered and manipulative hands and
the long and narrow hind feet (plantigrade) which rest flat on the ground - as in
all primates. Diet is omnivorous and mainly relates to resources found in trees including
fruit, eggs, nuts, insects and rodents. However, the raccoon could only develop into
a monkey and not an ape because it lacks the brain architecture required to produce
an intelligent ape.
The Kinkajou (Potos flavus)
Kinkajous are of a similar size to the raccoon. They are more dedicated to life in
the rainforest canopy than the racoon which roams at ground level too. Hence, as
one would expect, they are endowed with characteristics which are more monkey-like.
They have shorter snouts, forward facing eyes, rounded ear lobes, and a prehensile
tail. They also have, the primate-like long fingered hands and long feet.
The brain morphology of the kinkajou is comparable with that of the raccoon - and
so it could be that they are just further along the path of primatisation than raccoons.
Kinkajous and raccoons are classed as ‘small bears’ - the Procyonids in the Order
Carnivora. Being omnivorous they are intermediate between monkeys (mainly leaf-eating)
and true carnivores. Perhaps the kinkajou will reach true monkey-ness when it’s diet
matches that of monkeys.
A Closer Look at Primatisation
In the diagrams below the skeleton of a dog illustrates the long carpals and tarsals
of the digitigrade form. Dogs, like many other mammals and birds stand on their toes.
Primates and some mammals like the raccoons and kinkajous, mentioned above, have
short carpals and tarsals and are described as plantigrade.
In the process of primatisation, the carpals and tarsals are reduced to form long
flat feet and hands. I have digitally modified the original dog skeleton to show
this in the next illustration.
I have also orientated the skeleton into an upright stance, rotating the cranium
to a position at right-angles to the vertebral column. The other skulls depicted
show the stages of the foreshortening of the snout. To complete the primatisation
process I have removed the tail vertebrae and depicted the vestigial tail (pigostyle).