chapter 4 opener skeletal remains of the pliocene hominin australopithecus afarensis evolution and...

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Chapter 4 Opener Skeletal remains of the Pliocene hominin Australopithecus afarensis Evolution and the fossil record Today: phyletic evolution or anagenesis

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Chapter 4 Opener Skeletal remains of the Pliocene hominin Australopithecus afarensis

Evolution and thefossil record

Today: phyleticevolution or anagenesis

Dates to remember

• Age of• Earth and solar system: 4.6 bya• Earliest fossils of living things: 3.5 bya• Earliest fossils of animals: 800 mya

Figure 4.1 Plate tectonic processes

Plate tectonics: provides topographicand geographic heterogeneityBut may eradicate fossils

5-10 cm/yr

Absolute dating fossils• Radiometric dating• based on rates of radioactive decay

– one element into an isotope or into a different element

• 1. Rates constant and independent of environmental factors

• 2. Rates of decay are known• 3. therefore, amount of decay from a parent

element (or isotope) into a daughter element (or isotope) = a geologic clock.

Potassium/Argon clock

• Decay of 40K produces 40Ar

• Igneous rocks; e.g. derived from volcanic activity

• Heat drives off previously accumulated Argon gas

• Sets the “clock” to zero• As rock cools and solidifies, 40K continues to

decay to 40Ar which is trapped inside the rock.

• To date the rock, it is reheated and the amount of 40Ar is measured.

• The ratio of 40K to 40Ar permits dating the rock.• 40K has a half-life of 1.3 billion years.• In 1.3 billion years, 1/2 of the original 40K will

have been converted to 40Ar • In 2.6 billion years, 1/4 of the original 40K will

remain.

Fossils found in sedimentary rocks, so relative dating of fossils

1. Determine ratio of parent isotope to daughter isotope.2. Convert ratio to number of half- lives elapsed. 3. Multiply number of elapsed half- lives X number of years it takes for a half-life to elapse 4. This is the age estimate of that rock.

Radiometric Dating

Geologic Time: What you should know

Divisions based on shifts in distinctive floras and faunas

Figure 4.6 (A) Lineage leading from basal sarcopterygian fishes to early tetrapods. (B) Articulated skeleton of Tiktaalik. (C) The pectoral fin, or forelimb, of Tiktaalik

Marjorie Latimer: Curator, East London Natural History Museum, South Africa1938

Latimeria chalumnaeJ. L. B. Smith

Second specimen: 1952

Extant coelacanths

Africa

Indonesia 1997

Figure 4.7 Birds are extant theropod dinosaurs

Figure 4.8 Skeletal features of (A) Archaeopteryx, (B) a modern bird, and (C) a dromaeosaurid theropod dinosaur, Deinonychus

Figure 4.9 Feathered dinosaurs

Figure 4.10 The origin of mammals (Part 1)

Figure 4.10 Skulls of some stages in origin of mammals (Part 2)

Dentary-squamosalarticulation.Last remnantsof an articular-quadratearticulation

Figure 4.11 Fossil evidence of evolution of cetaceans from terrestrial artiodactyl ancestors

Figure 4.12 Stages in the evolution of the cetacean ear, adapted for directional hearing in water

A sequence of 60 bases from the beta-casein gene = 60 characters

Characters:(a) informativeCharacter 166

(b) uninformative1. no variatione.g., character 1422. occur only onceautapomorphye.g., character 192

(c) conflictingphylogeneticsignals e.g., 162 and 177

Homoplasy

Genetic resolution?

SINES and LINESRetrotransposableinterspersed elements

RNA intermediateContains info forreverse transcriptase

Resolution of whale phylogeny:

Figure 4.15 Chimpanzee and some fossil hominins NOT TO SAME SCALE

Figure 4.13 Estimated body weights (A) and brain volumes (B) of fossil hominins

Figure 4.14 The approximate temporal extent of named hominin taxa in the fossil record

Figure 4.19 Three models of evolution, as applied to a hypothetical set of fossils

Figure 4.21 Punctuated equilibria: phylogeny and temporal distribution of a lineage of bryozoans