Lecture 13 Paleontology PDF

Molecular clock Some parts of the genome will accumulate changes (mutations) at a relatively steady rate The speed of accumulation depends on the part of DNA under study (some fast, some slow) The “clock” is calibrated using the fossil record (e.g. orangutan fossils h...

Molecular clock Some parts of the genome will accumulate changes (mutations) at a relatively steady rate The speed of accumulation depends on the part of DNA under study (some fast, some slow) The “clock” is calibrated using the fossil record (e.g. orangutan fossils have been securely dated for apes), or the accumulation of mutations over generations orangutan- like fossils  Molecular clock Orangutan Gorilla Bonobo Chimpanz Pongo pygmaeus Human Gorilla gorilla Pan paniscus Pan troglodyt Homo sapiens LCA 6-8 mya 14 mya -By using the known age of the orangutan split, plus info on orangutan DNA, we know the rate of mutations in certain parts of the ape genome - Count known differences in DNA between humans and chimps -The data indicates a date of the split between Pan and Homo at about 6-8 mya  Paleontology: Scientific study of Fossils: fossil organisms Preserved mineralized parts of organisms (shells, teeth, bone) Trace fossils left by organisms (indirect evidence) Coprolites and other remains More rarely: soft parts preserved as minerals Paleontology: Dating fossils Dating fossils Stratigraphy Relative dating: - Principle of superposition Absolute dating (chronometric) : - Radiometric dating The history of the Earth is recorded in its strata Principle of Superposition In a sequence of layered sedimentary rocks, any layer is older than the layer above it and younger than layers below it Early dating (19th century) This principle was sometimes used together with observations or guesses as to sediment buildup rate Paleontology: Dating fossils Absolute dating : -Radiometric dating Using the known half-life of radioactive isotopes in sediments  Paleontology: Dating fossils Radiometric dating Uranium series dating (U-Series) - 238 U Turns to lead (Pb) – Series of half-lives (several isotopes, 100 000s to billions yrs) Argon-Argon (40Ar-39Ar) dating is often used on volcanic rock - 1.25 billion y. half-life Ötzi, 5200y old  Patterns of Extinctions Background Extinctions “Normal” slow rate of extinction 96% of extinctions Mass Extinctions Global Extent Broad Range of Species Often rapid Big 5 - Mass Extinctions Five mass extinctions, effect on marine life. Some marking the end of geologic eras.  6 Mass th Extinction? 1,100 species extinct since 1600 Habitat loss Hunting Introduction of non-native species Previous mass extinctions: at least 5 mill y. to recover species diversity  Current rate of extinction = 100-1000X larger than background extinction  Plate tectonics and continental drift -Movement of continents (Pangea 250 mill y. ago) -Formation of mountain ranges –Leads to movement and separation of species -Can also explain some changes in climate 3.5 billion years ago: First evidence of cellular life  Root of the Tree of Life -Three domains rokaryotes(these occur first in the fossil record): Bacteria, Archae Eukaryotes: Eukarya Bacteria were present from earliest times Archaeans are often found in extreme environments, prokaryotes, but related to eukaryotes Prokaryotes typically have a cell wall outside the phospholipid plasma membrane  First cells must have been prokaryotic autotrophs Photoautotrophs produce energy from sunlight (using photosynthesis), whereas chemoautotrophs use simple compounds like ammonia NH3 Heterotrophs (like animals) obtain energy from already existing organic molecules, such  3.5 billion years ago: First evidence of The oldest known fossils cellular life are stromatolites = geological structures composed of many layers of photosynthetic cyanobacteria and sediment Date back to 3.5 billion years ago Prokaryotes were Earth’s sole inhabitants from 3.5 -  Around 2.5 billion years ago: Atmosphere gradually saturated with oxygen – Many oxygen- intolerant organisms died out or became confined to extreme environments (e.g. many archaeans) –Others adapted and used oxygen  Around 2.5 billion years ago: Atmosphere becomes saturated with oxygen Atmospheric oxygen (O2) is of biological origin. The early source of O2 was likely cyanobacteria O 2 produced by photosynthesis reacted with dissolved iron and precipitated out to form banded iron formations Ca 2 billion years ago: First eukaryotes  Ca 2 billion years ago: First eukaryotes Oldest eukaryote cells ca 2 billion y.a. Related to archaeans Nuclear membrane formed from infolding of plasma membrane Endosymbiosis : mitochondria and plastids such as chloroplasts were formerly small prokaryotes – engulfed by host cell Mitochondria and plastids have their own DNA and replicate in a way (With or without cell wall)  1.5 billion years ago: Multicellular eukaryotes  1.5 billion years ago: Multicellular Oldest known eukaryotes fossils of multicellular eukaryotes = tiny multicellular algae (photosynthetic protists) from around 1.5 billion years ago More diverse multicellular organisms do not occur until around 600 mill. y.a. (Precambrian)  Early animals Enigmatic Precambrian (Ediacaran) fossils Some are hard to identify as either animals or algae – but some have trace fossils Some are definitely the earliest animals ca 600 million years ago (no vertebrates)  Animals Earliest animals ca 600 million years ago, so a peculiar genetic mechanism must have evolved by then Homeotic genes containing a highly conserved 180-nucleotide “homeobox” are called Hox genes; always found in animals code for the body axis position in very different animals, and is one of the oldest animal synapomorphies (shared derived traits) The position of Hox genes along the chromosome is the same as the position of expression along the body axis  Paleozoic starts~550 million years ago: Cambrian explosion Many modern animal phyla suddenly appear Most of life is still in the seas, but some plants and invertebrates are found on land shortly after Palaeozoic Era (550-250 mya) –starts with the Cambrian “Cambrian explosion” ca 550 mya -First fossil chordates and vertebrates –Best preserved in Burgess Shale, Canada https://www.youtube.com/watch?v=EH9uDMBkR0k  Paleozoic starts~550 million years ago: Cambrian Many animal phyla explosion first appear in the Cambrian site of Burgess Shale Sudden appearance of fossils resembling modern phyla Provides the first evidence of predator- prey interactions More armor (shells, spikes) The chordates form a monophyletic taxon, with vertebrates being the most numerous group  Chordate shared derived characters: notochord, myotomes and others  Cambrian relatives of the vertebrates: Ancient Chordates  Chordates similar to the lancelet are known from the Cambrian 530 million y.a., Burgess Shale and China. (e.g. Pikaia, Haikouella)  These have the typical chordate features e.g. notochord, myotomes Pikaia gracilens Modern primitive cephalochordate (lancelet) Pikaia gracilens