Chapter 4 Opener Skeletal remains of the Pliocene hominin Australopithecus afarensis Evolution and the fossil record Today: phyletic evolution 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 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 40 K produces 40 Ar 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, 40 K continues to decay to 40 Ar which is trapped inside the rock.

To date the rock, it is reheated and the amount of 40 Ar is measured. The ratio of 40 K to 40 Ar permits dating the rock. 40 K has a half-life of 1.3 billion years. In 1.3 billion years, 1/2 of the original 40 K will have been converted to 40 Ar In 2.6 billion years, 1/4 of the original 40 K 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 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

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 occur only once autapomorphy e.g., character 192 (c) conflicting phylogenetic signals e.g., 162 and 177 Homoplasy Genetic resolution?

SINES and LINES Retrotransposable interspersed elements RNA intermediate Contains info for reverse 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