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Animals

Classifying the tree of life

Monophyletic (Cladistics)

Paraphyletic (Linnaean Taxonomy)

Our branch

The primates •  Opposable thumb and big toe

–  assists in grasping and manipulation behaviors

–  adaptation to arboreal lifestyle •  Flat nails instead of claws, with

dermatoglyphs (fingerprints) on fingers and toes.

•  Hindlimb-dominated locomotion. •  Relative reduction in the olfactory

sensory system (smaller snouts) as compared to other mammalian orders.

•  Increased reliance on visual sensation. –  Forward-facing eyes

•  Tendency toward smaller litter size, longer gestation times, and extended period of juvenile growth.

•  Increased period of maternal investment and care.

•  Relatively large brains. •  Reduced number of teeth, with a

maximum of two incisors, one canine, three premolars, and three molars in each jaw quadrant.

Primate origins

65 MYA

Primate origins

•  Molecular clock: ~ 90 MYA •  Mass extinction event: ~ 65 MYA •  Earliest fossil: ~ 55 MYA

Dating methods

•  Uranium-Lead – Starting the clock: Zircon (ZrSiO4) incorporates

uranium during formation at high temperatures, but not lead.

– Ticking of the clock: Uranium-238 decays to Lead-208 (half-life = 4.47 billion years). Uranium-235 -> Lead-207 (half-life = 704 million years).

Dating methods

•  Potassium-argon –  Starting the clock: Gaseous argon escapes during

formation from molten rock, but potassium does not.

–  Ticking of the clock: Potassium-40 decays to Argon-40 (half-life: 1.26 billion years).

•  Argon-argon –  Sample irradiated with neutron from a reactor,

converting K-40 to Ar-39. Measure ratio of Ar-39 to Ar-40.

Dating methods

•  Molecular clock: – Starting the clock: speciation event – Ticking of the clock: mutation rate

Closest extant primate relatives

•  Scandentia (tree shrews)

•  Dermoptera (flying lemurs)

Proto-primates

•  Purgatorius – Montana deposits dated to about

65 MYA – Mouse-sized

•  Plesiadapiformes – Squirrel-like

Two main primate branches •  Prosimians (Lemurs, etc.)

–  More ‘primitive’ –  Lemurs –  Dwarf & mouse lemurs –  Lorises –  Galagos –  Aye-ayes

•  Anthropoids (Monkeys and apes) –  More derived –  New World monkeys –  Old World monkeys & apes

Nit-picky details •  Tarsiers cause all the problems

•  Strepsirrhines (basically prosimians) – Wet-nosed

•  Haplorrhines (basically tarsiers, monkeys, and apes) – Dry-nosed

Comparative analysis

•  Close relatives (based on the tree) •  Similar ecological niche

An example

An example