Transcript Evolution, 2e

Chapter 4 Opener Skeletal remains of the Pliocene hominin Australopithecus afarensis
Evolution and the
fossil record
Today: phyletic
evolution or
anagenesis
Dates to remember
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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 topographic
and geographic heterogeneity
But 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
Radiometric Dating
1. Determine ratio of parent
isotope to daughter isotope.
2. Convert ratio to number of halflives elapsed.
3. Multiply number of elapsed halflives X number of years it takes for
a half-life to elapse
4. This is the age estimate of that
rock.
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 Africa
1938
Latimeria chalumnae
J. 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-squamosal
articulation.Last remnants
of an articular-quadrate
articulation
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
Genetic resolution?
A sequence of 60 bases from the beta-casein gene = 60 characters
Characters:
(a) informative
Character 166
(b) uninformative
1. no variation
e.g., character 142
2. occur only once
autapomorphy
e.g., character 192
(c) conflicting
phylogenetic
signals
e.g., 162 and 177
Homoplasy
Resolution of whale phylogeny:
SINES and LINES
Retrotransposable
interspersed elements
RNA intermediate
Contains info for
reverse transcriptase
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