Wednesday, March 20, 2013
Non-avian dinosaurs go extinct along with 50-70% of all living species.
Mammals survive and begin to diversify (lots of empty niche space after KT extinction…)
After the extinction, a mammal adaptive radiation!
Q: What other mammals are primates most closely related to?
• Our closest living non-primate relatives: Colugos (Flying Lemurs) and Tree Shrews
(Order Scandentia) … first predicted by Linnaeus.
Order Primates + Order Scandentia + Order Dermoptera = Euarchonta
• Our next closest relatives are Bunnies (order Lagomorpha) and Rodents (Order
o Euarchonta + Order Rodentia + Order Lagomorpha = Euarchontoglires
These relationships suggest something interesting about WHERE primates originated.
o Tree shrews and flying lemurs (living and fossil) are found ONLY in southeast
o Earliest fossil rodents and rabbits are found in East Asia
• MAYBE an East Asia origin for primates?
o Unfortunately, the fossil record from the earliest epoch (Names bits of time that
we use as short hand when we talk about things) following the K-T extinction
(Paleocene) in E & SE Asia not great…
o Paleocene mammal fossil record in Northern Hemisphere much better
Where you find the earliest possible primates
Earliest possible primate fossils
o N. American, Europe, Asia.
o Oldest: 65 million years old
• Why from N. America, Europe and Asia?
o Sea levels change and contents move
o Species could disperse overland across 3 continents: Holarctic distribution
• Primarily from the Paleocene epoch
• Ecologically diverse group
• EX: Diets: insectivorous, folivorous, frugivorous, nectarivorous)
• Most primative:
• Latest Cretaceous to Paleocene- N. America
• Why traditionally grouped with primates?
o Remarkable molar similarities between some Paleocene plesiadapiforms and
define primates from the Eocene
• Are these molar similarities evidence for common ancestry, of the product of homoplasy
(due to similar diet)?? o Palaechthon
• Relatively unspecialized/primitive plesiadapiform
• Middle Paleocene
• N. America
• Molar teeth relatively primate-like BUT anterior teeth specialized-not very
• Orbits small and directed laterally (sideways). Orbits NOT encircles by
bone (no postorbital bar)
Large infraorbital canal for maxillary nerve (sensory to snout) Snout
probably had many vibrissae / good tactile abilities
• Only THREE premolars (true for ALL plesiadapiforms except Purgatorius.)
Earliest definite primates (Eocene) had FOUR premolars
•Reconstruction of Palaechthon's Ecology
Small, specialized insectivore like hedgehog
o Small laterally-facing eyes and sensitive snout
o Not very primate-like…
Highly specialized anterior teeth (like most plesiadapiforms)
o Orbits like Palaechthon.
o Bottom line:
• Cranial anatomy of most plesiadapiforms is more reminiscent of rodent
than a primate.
o Hands and feet: Mosr plesiadapiforms had claws and non-grasping hands/feet
• Arboreal locomotion similar to squirrel.
o One known exception:
o Recently describes skeleton from 56 Ma
o Grasping hands and feet w/long digits
o Nail on big toe instead of claw (other digits do have claws)
Q: Common ancestry or similar ecology?
•Probably similar ecology and parallelism (skull and teeth too specialized)
•Grasping hands and feet and nail on big tow have evolved in parallel in other groups…
The Big Picture
•Plesiadapiforms DON'T have most of the features that distinguish living primates.
•In some respects (ex. Premolar number, anterior teeth) they are TOO SPECIALIZED to
have given rise to later definite primates
Q: What happened to them?
•Most extinct by the end of Paleocene
•None survive past the Eocene
•At the same time rodents are diversifying… Coincidence?
•The warmest epoch of the Cenozoic.
Oxygen Isotope Record
•The warm Eocene meant a widespread tropical forests • Paleocene Eocene Thermal Maximum: hottest global temp. Single warmest instant in
• Carbon Isotope Excursion: indicates a massive release of Carbon into biosphere. HUGE
possibility that it is related to continental drift.
• Leads to pulse of mammalian dispersal across high latitude land bridges connecting
• Reason earliest define fossil primates appear abruptly at the very beginning of the
• Oldest definite fossil primate: Teilhardina asiatica China; earliest Eocene.
• Other closely related species arise on other continents.
• Primates that appear in holartic continents at beginning of Eocene belong to 2 groups:
• Notharcuts: molars w/well-developed shearing creasts: floivory (frugivory)