Why is the fossil record incomplete? It takes the right conditions at the right time in the right place. - some organisms are simply not likely to yield fossils - sedimentation does not occur in all habitats - fossils must survive geological events and weather the elements for millions of years before discovery

Process of Fossilization After remains are buried by sediments: Compression/impression/casts/molds:impressions or casts made before decomposition (like footprints). (2) Permineralized fossils: precipitation of minerals in cells before decomposition. Or Occasionally: (1) Unaltered remains: Frozen , amber embedded, peat bogs.

permineralized fossils amber cast Impression fossil

Fossil Record is Biased Fossilization is higher for organisms that are: Durable and likely to be buried in an anoxic environment (low land or marine habitats) Also, there is temporal and geographic bias: Probability that an organism will be fossilized depends on the geographical area and historical time.

Fossils and associated rocks contain Radiometric Dating Fossils and associated rocks contain reactive elements that decay at known rates Half-life Uranium235 --> Lead235 = 7 x 108 years Carbon14 --> Nitrogen14 = 5730 years Parent Atom Daughter Atom

Radioisotope Decay Time (half-lives) 1 2 3 Surviving Parent Atoms Accumulating Daughter Atoms 1 2 3 1/1 1/3 1/7 1. Find fossil 2. Determine ratio of parent to daughter atoms 3. Determine number of elapsed half-lives 4. Estimate age of fossil

Try this problem You are using C14 (half-life = 5730 years) radioisotope dating to determine the age of rocks associated with a fossil. The percentage of daughter isotope atoms (N14)) is 87.5%. What is the age of the fossil? 17,190 yrs

There are Good Examples of Macroevolution in the Fossil Record Sarcopterygii --> Ichthyostega --> Amphibia see also (Figure 4.6) Gradualism : (e.g. limbs are intermediate) Mosaic evolution: (limbs evolved faster than braincase, tail fin, tooth structure

Other Examples From Book To Review (Chapter 4) Origin of Birds Archaeopteryx is but one of many fossils Origin of Mammals - Gradual evolution of “reptilian” skull and jaw Origin of Cetacea A series of fossils have recently been discovered showing adaptation to aquatic life Origin of Hominins We are the lone survivors of an otherwise extinct radiation of bipedal African hominids

Vertebrates Hair Mammary Glands Amniotic Egg Endothermy Four Limbs Cartilagenous Fish Hagfish, Lampreys Bony Fish Amphibians Mammals Birds Reptiles Hair Mammary Glands Amniotic Egg Endothermy Four Limbs Terrestrial Phase Bony Skeleton Swim Bladder Skull Backbone Paired Fins Jaws

Mammals Hair, mammary glands Most advanced nervous system Learning important to survival Warm blooded Humans are mammals

Humans are primate mammals Class Mammalia Order Primates Prosimians (e.g. lemurs) Tarsiers Anthropoids (e.g. monkeys, hominoids)

Lemur Tarsier Macaque

Primates : Humble Beginning Rabbit Shrew Shrew-like Ancestor

Homininae : African Great Apes Major Primate Groups Family Hominidae Old World Monkeys Orangutan Chimp Human Tarsiiformes Gibbons Gorilla Lemurs New World Monkeys Homininae : African Great Apes and Humans Hominidea : Great Apes and Humans Hominoidea : Apes and Humans

What Features Are Associated With Primate Evolution? I. Sensory Adaptations Protected, forward looking eyes with stereoscopic vision Improved sight : more detail even in low light Reduction of olfactory structures

What Features Are Associated With Primate Evolution? II. Adaptations for tree-climbing and insectivory Freely moving limbs and digits Long mobile digits capable of grasping Retention of tail as organ of balance Evolution of upright body posture and extensive head rotation Increased body size Evolution of nervous system to give precise and rapid control of movement

Major Primate Groups Hasegawa et al. 1987 Orangutan Chimp Human Family Hominidae Old World Monkeys Orangutan Chimp Human Tarsiiformes Gibbons Gorilla Lemurs New World Monkeys 25 mya 12 mya 6 mya Hasegawa et al. 1987 5 mya 38 mya Estimated Divergence Times

What Traits Do Humans and Apes Share? Larger Brain Absence of a tail More erect posture Greater flexibility of hips, ankles, wrist, thumb DNA sequence similarity

Gorilla Chimpanzee Human Horai et al (1995) Proc. Nat Acad Sci. 92:532-536. Mito DNA (complete sequences) Kim and Takenaka (1996) A. J. Phys. Anth. 100:301-309 Y-chromosome DNA Ruvolo (1997) Mol Biol Evol 10:1115-1135. Examined 14 different DNA data sets Satta et al (2000) Mol. Phyl. Evol 14:259-275. Autosomal DNA (45 genes, 47,000 bp of DNA) Paabo (2003) Nature 421:409-412. Review of human and chimp/ape genomes.

Common Ancestor of Chimp/Human Knuckle-walker? Broad-fruit based diet May have hunted May have used tools May have had complex social relationships: (e.g.warfare, cannabalism, sharing, teaching, compassion)

Our Understanding of Human Evolution is Primarily Based on Fossils