Fossil Primates 1
Dr. Bill Sellars In the last lecture I tried to give you an
outline of primate taxonomy and how humans fit into the taxonomic
framework. The next two lectures attempt to fit humans into the
evolutionary framework of the primates. Today's lecture concentrates on
the evolutionary period from just before the Palaeocene (about 70 mya)
to the end of the Miocene (about 5 mya). Tomorrow's lecture will follow
on and look at the early hominins in the Pliocene (5 mya) and the
Pleistocene (1.5 mya) stopping before the Holocene (10,000 ya)
What I'll be presenting is a simplified story of early primate
evolution. The fossil record is really very patchy, and although the
reconstructions look nice, some are based on rather scanty information.
So this is very much conjecture, and will be different in different
books. The arguments about which is more likely to be correct rage all
The oldest fossil that anyone considers to be primate-like is
a animal called
Purgatorius ceratops, which consists of a single tooth found in
late-Cretaceous rocks in Montana. This is dated to approximately 70 mya.
This is what it looks like based on a fossil mandible!
primate-like animal with a reasonable fossil record is
Plesiadapis, which is often considered the first prosimian.
However, it has recently be re-evaluated in light of new fossil finds
and is maybe best considered to not to be a primate, but a form of
Dermoptoran (Colugo, or flying lemur).
Here is a list of Plesiadapis
* Long tail
* Agile limbs
* Claws, not
* Rodent-like jaws and teeth
* Eyes at side of head
* Long snout
* No post-orbital bar
Only the first two
features would indicate a primate affinity. There are other mammal
fragments that date to the Palaeocene that just might be ancestral
primate material, but until some more complete fossils are found, it is
best to remain sceptical about claims of primates from this period.
The first unequivocal primates occur about 50 mya. There are
two main groups identified: Adapiformes which are usually considered to
be ancestral to modern Strepsirhines; Tarsiiformes which are (mostly)
considered to be early Haplorhines.
Adapids are the main group of
early Adapiformes. They are clearly primate-like with:
facing eyes (binocular vision)
* Post-orbital bar
* Reduced snout
* Vertical incisors
an Adapid where we have a particularly good skeleton, has:
* Nails, not claws
* Opposable thumb and big-toes
* Flexible limbs
* Long tail
* Supple back
very clearly prosimian-like.
Omomyids are the best examples of
early Tarsiiformes. For example
Rooneyia or Necrolemur. These early Tarsiiformes have
some features to associate them with later anthropoids, including:
* Short face
* Big eyes
* Narrow gap between eyes
* Tubular ectotympanic bone
And in some respects,
they are more similar to anthropoids than extant tarsiiformes:
or 126.96.36.199 dental formula (188.8.131.52 in modern tarsiers)
But to add
to the confusion, they have a tubular ectotympanic bone, like extant
anthropoids, but early anthropoids have a ring-like ectotympanic bone.
The distinction between Catarrhines and Platyrrhines occurred
sometime in the Oligocene. However, there is a distinct shortage of
fossils (isn't there always). Branisella is a good example of a
New World Monkey. The African fossils from this period are almost all
from the El Fayum valley in Egypt. The example here is Apidium.
There are a number of questions concerning New World Monkeys. South
America was an island continent at this period, so where did they come
from? Rafting or island hopping have been suggested. Also, primates die
out in North America... Generalisations about Oligocene NWM are
difficult to make because of a severe shortage of specimens. There is
some indication that they may not have yet achieved full orbital closure
and have more laterally directed orbits than extant species, but this is
The considerably better fossils from El Fayum allow us
to be more definite about early OWMs:
* Orbital closure is almost
* Fused mandibular symphysis
* Absence of
stapedial artery and canal
* Lacrimal bone within orbit
a number of ancestral features are still retained in some species:
* Smaller brains than extant OWMs
* Ectotympanic ring
In the Miocene, we see the rise of Hominoids. Early on, there
is a split between Cercopithecoids and Hominoids with the appearance on
animals such as
Proconsul (again a remarkable fossil) about 18 mya. This animal
is classified as a Dryopithecin - one of the three sub-families of the
This split is characterized by the following features (of
* Y-5 Molar pattern
* Loss of tail
* Mobile shoulder and elbow (for suspension)
Proconsul has a long monkey-like trunk as opposed to the short trunks of
In the early Miocene, there were a great many
Hominoids, but later on the Cercopithecoids seem to have largely taken
over. Except for humans, Cercopithecoids are certainly much more
successful today than Hominoids.
NOTE: as an aside, many
authorities class the Hominids as starting with the Australopithecines.
However, current thinking puts this as just a anthropocentric bias - the
group containing Homo and
Australopithecus has been down-graded from a family to a
subfamily, Hominins. So, the family Hominids includes the three
sub-families: Dryopithecins (all now extinct); Pogins (great apes);
Hominins (human-like animals). Lesser apes are considered to have
branched off the Hominid line earlier on to produce the family of
However, the nomenclature for the early hominoids is
fairly uncertain. This is best expressed by describing the ancestral
gibbon forms as "small bodied hominoids" and the ancestral great ape
forms as "large bodied hominoids". This latter group can be further
split into Asian forms leading to the orang-utans and the African forms
leading to the chimps, gorillas and the hominins.
5 mya we'll stop here with the appearance of the Australopithecines...
Draw up summary tree.
This page is maintained by Steve Paxton