G106 Final Spring 24 TAMU
Principle of Horizontally: all rock layers are originally laid down (deposited) horizontally and can later be deformed
Principle of uniformity: geological events of the past must be explained by means of the same causes now in operation (charles lyell)
Principle of Stratigraphy: law of superposition, law of original horizontality, law of cross-cutting relationships, and law of lateral continuity
Burgess Shale: window into the Cambiran and is full of fossils
Conditions for fossil preservation:
Ice
Amber
Low oxygen conditions
Organism has hard parts
Lives in marine environments
Wide geographic range
Large and easily recognizable
Conditions of special preservation are met
Lecture 13 - Permo-Triassic Extinction and Mesozoic Recovery
Most profound change in the history of Phanerozoic life
Synapsids and Sauropsids
Synapsids are one of the two major groups of animals that evolved from basal amniotes, the other being the sauropsids (reptiles, dinos, birds)
Pennsylvanian: evolution of the amniotic egg in tetrapods
Major evolutionary innovation that allowed tetrapods to live in drier areas away from water (not reliant on aquatic habits for reproduction anymore)
Early Evolutionary split in amniotes into:
Synapsids (mammals and early relatives)
They actually got off to a great start in the permian period
Pelycosaurs(dimetrodon)
Why the sail on its back?
Body temperature regulation? (perhaps related to initial evolution of warm-bloodedness in mammals?)
Mating display?
Make organisms look bigger in the eyes of predators?
Therapsids
Many mammal-like qualities:
Legs vertically under body
Feet parallel with body
Whiskers
FATE OF PERMIAN SYNAPSIDS
Many synapsid groups went extinct at the end of the Permian Period
The therapsid lineage survived into the Mesozoic and eventially gave rise to the crown group of mammals
Sauropsids became dominant land vertebrates after the extinction
Mesozoic = “Age of Reptiles”
Sauropsids (reptiles and birds)
What happened at the end of the Permian Period?
Three “Evolutionary Faunas”
Largest extinction event in Earth history
96% of marine species lost
70% of terrestrial vertebrate species lost
Complete devastation and reorganization of ecosystems
End of the reign of the Paleozoic Fauna
Beginning of the dominance of Modern Fauna
Seemingly related to Siberian Traps Large Igneous Province (LIP)
Massive, continuous volcanic eruptions for 2 million years
3 million square miles of basalt exposed in siberia
Large igneous provinces (LIP) thought to be related to periodic mantle plumes
Devastating effect on global ecosystems
How can volcanism cause extinction?
Release of massive amounts of CO2 into the atmosphere. This can cause:
Direct CO2: toxicity to organisms (hypercapnia)
Rapid, intense global warming
Pulse of intense terrestrial weathering, delivering massive amounts of nutrients to the oceans, ultimately driving global ocean anoxia
Buildup of toxic hydrogen sulfide in anoxic oceans + degassing hydrogen sulfide to the atmosphere
Ocean acidification
Losers:
Our Paleozoic darlings: brachiopods (96% losses), crinoids (98% losses), bryozoans (79% losses), tabulate and rugose coral (extinct), trilobites (extinct)
Permian synapsids (early mammal relatives)
Late paleozoic rain forests: a coal gap is found in the Early Triassic Period
Winners:
The modern marine faina: bihalves (clams, oysters, mussels, etc), gastropods(snails), echinoids (starfish, sea urchins, sand dollars), scleratinian coral
Ray-finned fish
Terrestrial sauropsids (Mesozoic “Age of Reptiles”)
Triassic Recovery
Post- extinction recovery was very slow:
Global levels of biodiversity remained low until the Late Triassic Period
Terrestrial vertebrate communities took 30 million years to recover to pre-extinction levels of diversity!
Toxic, anoxic oceans persisted well into the Triassic Period
Hot, dry conditions persisted on land; equatorial latitudes were uninhabitable
O2 in the atmosphere reached a Phanerozoic low, high CO2 conditions persisted
Pangea as a contributing factor?
Extreme aridity in the interior of the supercontinent Pangea
Mesozoic Reptiles
The sauropsid lineage was highly successful in both terrestrial and marine environments during the Mesozoic Era
This include these main groups:
Extant:
Turtles, crocodilians and their early relatives (pseudosuchia), saurischian(lizard-hipped) dinosaurs (including birds), lizards and snakes
Extinct:
Pterosaurs, ornithischian (bird-hipped) dinosaurs, pleiosaurs, icthyosaurs, mosasaurs
Pseudosuchia (crocodilians and their ancestors) achieved a great diversity during the Mesozoic Era
Mesozoic Pseudosuchia achieved a HUGe diversity of sizes, shapes, and lifestyles (much more than today)
Up to 40ft long weighted up to 8 tons
Some with longer legs → could run fast
Were dominant during Triassic Period, before the rise of dinosaurs
Turtles and their early ancestors
Early turtle ancestors appeared in the Triassic Period
Long standing debate as to whether turtles belong to the anapsid of the diapsid group of sauropsids
All modern turtles look like snapsids with no temporal openings in their skull
Recent finds of triassic turtle ancestors suggest that they are actually diapsids that have since lost the temporal openings in their skulls
Ichthyosaurs
Sauropsid lineage that returned to marine environments
Superficially resembled dolphins, although dolphins are synapsids
TOP MARINE PREDATORS FROM THE TRIASSIC TO EARLY CRETACEOUS PERIODS
Plesiosaurs
Predatory marine sauropsids
Common during the Jurrasic and Cretaceous Periods
“Loch ness monster”
Mosasaurs
Another group of Mesozoic marine sauropsids
Became top marine predators towards the end of the Cretaceous period
Other Miscellaneous Groups
Eupodophis (cretaceous snake)
Jurassic iguana-like lizards
Pterosaurs
Flying sauropsids from Late Triassic to Late Cretaceous Periods
Wing membranes stretched from ankles to dramatically lengthened 4th finger on the hand
Dinosaurs appeared during the Late Triassic Period
Separated into 2 main groups based on the bone structure of their hips:
Ornithischian (bird-hipped) and Saurischian (lizard-hipped)
Ornithischian (bird-hipped) dinosaurs
Exclusively herbivorous
Common groups: ceratopsians, stegosaurs, ankylosaurs
Hadrosaurs
Saurischian (lizard-hipped)
Both herbivores and carnivores
Sauropods (quadrupedal and herbivorous)
Brachiosaurus
Diplodocus
Theropods (bipedal and carnivorous)
Allosaurus
Tyrannosaurus
Velociraptor
Traditional views of theropods have been completely revised in the last 20 years
Zhenyuanlong (velociraptor relative) with feathers!
Sinornithosaurus (feathered theropod dinosaur from the early Cretaceous period)
Many theropod dinosaurs may have had feathers and been warm-blooded
AVES = Birds (specialized group of theropod dinosaurs that arose in the Late Jurassic or Cretaceous Periods)
Lecture 14: The Mesozoic World
Plant Evolution:
Lycopod forest of the Late Paleozoic Era were hit hard by the Permo-Triassic extinction
Gymnospers became the dominant trees during the Triassic and Jurassic Periods
Pollinated by wind. Their seeds are exposed, rather than being enclosed within fruits
Types of gymnosperms include: Cycads, Ginkgoes, Conifers
Cycads: seeds without true flowers
Mesozoic could be called “Age of Cycads”
Cycads appeared during Triassic Period and grew to be tall trees during Jurassic Period
They experienced a marked decline during Late Cretaceous Period, and only a few species survived to the present, including the Sago Palm, a common house plant
Ginkgoes
Naked, fleshy seeds
Appeared during Late Paleozoic Era
The oldest genus of tree that is still living
Fossil ginkgoes more than 200 million years old are nearly identical to living ginkgoes
Conifers
Appeared during Late Paleozoic Era, declined during permian Period, and expanded again during Mesozoic Era
Six groups of conifers were present during Jurassic and Cretaceous Periods, including large numbers of pines
Angiosperms (flowering plants) appear during the Late Cretaceous Period
Diversified while the gymnosperms declined during Late Cretaceous Period
Angiosperms provide many examples of coevolution with Mesozoic insects, dinosaurs, mammals, and birds
Insects depended on the plants for food, and the plants depended on the insects for pollination
Plant differences evolved due to competition for pollinators
Dominate the plant kingdom today, accounting for ~88% of all plants on Earth
Pangea built by continent- continent collision in the Late Paleozoic Era
Final step int he evolution of the Appalachian mountain range
Pangea breakup and opening of the Atlantic Ocean began during the Triassic Period
Late Triassic (220 Ma): rift basins and deposition of lake sediments in eastern North America
Early Jurassic (200 Ma): Early rifting of the Atlantic Ocean
CAMP (Central atlantic Magmatic Province) 201Ma: Large set of magmaic events associated with the opening of the Atlantic Ocean
Triassic-Jurassic Mass Extinction:
4th of the “big five” Phanerozoic extinctions, and probably the most poorly understood
Likely related to emplacement of the Central Atlantic Magmatic Province, but exact mechanism is unclear
Triassic-Jurassic extinction marked a change in dominance among archosaur groups:
The Pseudosuchia (crocodiles and their ancestors) dominated in the Triassic Period
The dinosaur side of the archosaur tree thrived beginning in the Jurassic Period
Other groups Affected
Non- amniotes (amphibians) were strongly affected
Diversity of Triassic amphibians dwindled substantially
Amphibian crown groups (frogs, salamanders, etc) diversified in the Jurassic Period
Very similar story for synapsids:
Therapsids (who survived the end-permian extinction) diversified again in the Triassic Period
Many groups were lost at the end-Triassic extinction and the mammal crown group diversified in the Jurassic Period
- Early Cretaceous (120 Ma): Large Scale mountain-building begins in the Rockies
- Late Cretaceous (90Ma): Time of incredibly high sea levels (200m higher than today!) and warm climates. Western interior seaway covered much of western North America
Tropical plant and crocodile fossils found north of the Arctic Circle
Mean temperature of greater than 10 deg. C at the North Pole (Mean temp of Fairfax today = 12.5 deg C)
Strange colonia clams called rudists build huge reefs during the Cretaceous Period
Mesozoic Era also saw a huge change in the types of plankton in the oceans
Prior to Mesozoic Era, the dominant phytoplankton were organic-walled: cyanobacteria, green algae, arcitarchs, dinoflagellates
Phytoplankton with mineralized skeletons became dominant during Mesozoic:
Cocolithophores
Appeared during Early Jurassic Period
Calcium Carbonate disks arranged into spherical structures
So abundant during Cretaceous Period that they formed extensive chalk deposits (e.g. White Cliffs of Dover)
Extremely small (0.001 to 0.015 mm). An electron microscope must be used to view them
Silicoglagellates & Diatoms
Secrete hard parts made of silica
Appeared during the Cretaceous Period
Dominant in both marine and freshwater systems today
Resulting evolution of larger zooplankton
Planktonic foraminifera (calcium carbonate and planktonic radiolarians (silica) diversified during the Mesozoic Era
Evolution of calcareous phytoplankton and zooplantok altered the global carbon cycle
Lecture 15: The End-Cretaceous Catastrophe
Final big 5 extinction: The Cretaceous-Palogene mass extinction.
Preferential extinction for groups dependent on photosynthesis
Groups on seafloor largely unaffected
Groups in surface water that relied on phytoplankton were devastated
Unlike other extinctions, plants severely affected
57% of North American plants extinct
Major changes in pollen assemblage
Spike in ferns (comes after everything else dies)
Large swimming predators like mosasaurs and plesiosaurs were completed eliminated
Flying sauropsids (pterosaurs) went completely extinct
Only extinction that affect large terrestrial insects
Amphibians in freshwater habitats that relied on detritus fared well
All non avian dinosaurs completed extinct, birds were the only dinosaurs that survived
Bottom line:
Organisms that relied on plants for food were screwed
In extinctions events, organisms that the top of the food chain most vulnerable because they rely on the food chain below
Smaller organisms that eat anything have advantage
Mesozoic Mammals
Originally thought to be an afterthought in the mesozoic era.
Turns out to be more abundant
Small, badger sized, omnivore with diverse food source
R. robustus = 1 meter-long early cretaceous mammal with dinosaur remain in its stomach
Docodonts such as this mostly fed on insects
Teeth morphology are important synapomorphies of Mesozoic mammals
Mammals were clearly well-adapted to survive the extinction
Geologist bred to reject catastrophism for centuries
Cretaceous-Paleogene extinction was fundamentally different
Extinction was abrupt
Not associated with long term climate change or biogeochemical event
Large volcanic province did erupt (deccan traps in india) but timing doesn’t seem right
Original Idea
Iridium (Ir) is an element that is found in very low abundance on Earth but raining down continuously from space
Alveraz father and son duo thought they could measure Ir in a continuous set of sedimentary rocks and use known rate of Ir rain down to estimate rate of accumulation
Found astronomical levels of Ir in one particular layer, which just happens to be at the the Cretaceous-Paleogene boundary
Great idea, testable, fundamentally against the gradualist point of view
Evidence of meteorite impact
Large spike in iridium found globally at the K-Pg boundary
Shocked quartz found in global deposits that span the K-Pg boundary (quartz crystals that have sustained damage from due to extreme impact pressure)
Tiny glass spherules known as microtektites found in global deposits at K-Pg boundary
The Chicxulub crater in Mexico
Chicxulub Crater
93 miles wide and 12 miles deep
Carbonaceous chondrite struck shallow in shallow ocean off the coast of Mexico
Meteorite was at least 7 miles in diameter (may have been 50 miles in diameter)
Generated an explosion equivalent to at least 20 billion Hiroshima bombs (maybe 900 billion bombs)
Currently buried under 2,000 ft of sediment
Tektites from crater itself produced an extremely precise radiometric age date of 66,038,000 +- 11,00 years which is the date of the K-Pg boundary
Effects
Initial air blast flattens forest in large surrounding areas
Megatsunamis up to 100 meters tall
Shock wave triggers global earthquake and volcanic eruptions
Extreme heat potentially caused global forest fires (spike in ferns and widespread deposition of soot and coal)
Forest fire and direct strike of meteorite into limestone and sulfate deposits generated large pulse of CO2 and sulfuric acid into the atmosphere (causing acid rain and ocean acidification)
Dust clouds blocked the sun and for decades, causing impact winter and blocking light for photosynthesis (loss of photosynthesis felt throughout the food chain)
Lecture 16: The Cenozoic Era
Chicxulub Crater
Gravity anomaly beneath the
Location of modern cenotes (deep sinkholes) surrounding the subsurface crater
Mesozoic mammals
Morganucidib (early mammal relative) for the Late Triassic Period
Castorocauda = semi-aquatic mammal relative from the Jurassicc Period
It has long been thought that mammals were tiny afterhoughts in the Mesozoic Era compared to dinosaurs
Recent research suggests, however, that mammals were more abundant than previously thought
They did, however, remain small (mostly badger-sized at most) and were omnivores with diverse food sources
Cenozoic mammals
Mammals underwent a major adaptive radiation during the Paleogene Period
Even though avian dinosaurs (birds) also thrived during the Cenozoic era (continuing to today), mammals took over as the dominant large terrestrial vertebrates, replacing non-avian dinosaurs after the K-Pg extinction
Includes 3 main groups monotremes (lay eggs), marsupials (pouch), placentals (embryonic development in mother’s body)
Monotremes and marsupials exist in select habitats today, but placentals are by far the most dominant group globally
Modern monotremes (duck-billed platypus, spiny anteater)
Major groups that diversified in the Cenozoic Era: Insectivora (shrew), Edentates (armadillo, tree sloth), Rodent (squirrel, mouse, rat, beaver), rabbits, bats, carnivores, ungulates (horse, cow, sheep, goat, elephant, whale, ie mammals w hooves)
Perissodactyls: odd number of toes on each foot
Artiodactyls: even number of toes on each foot
Close evolutionary relationship to cetateans (whales)
Proboscidean: mammals with trunks
Cenozoic Climate
The cenozoic era was characterized by progressive cooling and falling of sea level compared to the very warm Cretaceous Period
Short-term warming events include the Paleocene-Eocene Thermal Maximum (PETM) and Early Eocene Climatic Optimum
Progressive trend was towards cooling and glaciation, however Antarctic ice sheets starting forming by the Oligocene and northern hemisphere glaciation was prominent by the Pliocene
Cenozoic climates aslo got progressively drier, which led to expansion of grasslands (uplift of the Himalayas had major effects on global climate
Lecture 17: The Cenozoic Era (Cont)
Tectonic effects on climate
India-Eurasia collision and the uplift of the Himalayas and Tibetan Plateau exposed fresh rocks to chemical weathering
Chemical weathering is a sink for atmospheric CO2, thus promoting global cooling
Opening of the Drake Passage around Antarctica around 40 Ma isolated Antarctica from heat transport from the equator, thus causing ice sheets to form
Ice sheets then reflect more sunlight to space (ice-albedo effect) further promoting global cooling
The supercontinent cycle controls climate on the scale of 100’s of millions of years
Periods of supercontinent assembly and stability are associated with cooling
Periods of supercontinent breakup are associated with warming
Closing of the isthmus of Panama around 2.8 Ma diverted moisture to the North Atlantic (the Gulf Stream), thus promoting Northern Hemisphere glaciation
Other Cenozoic tectonic/global event
Large lakes created oil shales int he green River Basin, Wyoming
Crustal extension created the Basin and Range Province of the American SW
The Sierra Nevada and costal ranges were raised in Western North America
Volcanic fissure eruptions occurred, creating the Columbia Plateau in Washington, Idaho, and Oregon
Tectonic effects on the biosphere
Closing of the Isthus of Panama around 2.8 Ma separated marine population in the Atlantic and Pacific, but connected terrestrial populations between North and South America
Marsupials moved northward
Placentals moved southward
Placentals began to outcompete marsupials in both North and South America
Hoofed marsupials, as well as ground sloths and glyptodonts went extinct
Placentals came to dominate in the Americas, which continues today
C4 Photosynthesis evolves as a response
C4 Photosynthesis is more efficient at concentrating CO2, while retaining water
Well adapted for the low CO2 and arid conditions of the Late Cenozoic Era
C4 plants fix carbon very differently, so that they have very different carbon isotope ratios than C3 plants
Isotope records show a major shift in soil and teeth carbon towards C4 plants during the Miocene Epoch
Grasses are C4 plants and did exist on Earth until very recently
Declining CO2, increased aridity, and increased seasonality of precipitation led to a global expansion of grasslands over forests beginning in the Miocene Epoch
These climate conditions also favored increased frequency of forest fires, which favors grasses over forests because grasses are better adapted to withstand frequent fires
Co-evolution of grasses and mammals
Miocene shift from forest-dwelling and woodland mammals to mammals better adapted for open prairies and savannahs
Modern forms of grazing ungulates (giraffes, hippos, cattle) diversified during the Miocene Epoch
Fundamental changes in mammalian tooth structures to eat silica- rich grass
Evolutionary split btwn chimpanzees and early hominds also occurred during Miocene Epoch
Standing upright, having flexible diets, and developing complex social structures is a fundamental adaptation to life on grasslands and savannahs
Fascinating co-evolution of global tectonics, climate, and the biosphere
Orbital effects on Climate
Natural variations in Earth’s orbital parameters (Milankovitch cycles) exert strong controls on global climate over short timescales
Humans as a force for global change
Pleistocene megafauna of North America experience large-scale extinction coincident with the arrival of humans
The “6th extinction” that continues through today
Lecture 18: Approaching the Modern Day
The Cenozoic
The past 65 million years
Considered the age of the mammals
Placentals
Diversified in the Cenozoic, major groups are:
Insectavora (shrew, European hedgehog?)
Edentate (armadillo, tree sloth)
Rodents (squirrel, rat, beaver)
Rabbits
Bats
Carnivores
Ungulates (horse, cows, whales)
Climate
The era is categorized by progressive cooling and falling sea levels compared to the previous (Cretaceous) period
C4 Photosynthesis
A type of photosynthesis that evolved during this time
More efficient at concentrating CO2 without as much water loss
Allowed plants to be well adapted to the changed environment
Co-evolution of grasses and mammals
There was a shift in mammals where they went from being better suited to forests to better suited to grasslands/prairies/open spaces
Occurred during the Miocene Epoch
Co-evolution of grasses and hominoids
Evolutionary split between shrimps and hominoids also occurred in the Miocene
Orbital Effects on Climate
Milankovitch cycles-the earth’s orbit changes over time in a cycle
Eccentricity is the degree to which Earth's orbit approximates a circle
The cycle lasts about 100,000 years
Obliquity is the tilt of the earth on its axis
Cycle lasts about 41,000 years
Precession-is the northern hemisphere tilted towards or away from the sun at aphelion?
Aphelion-point in a planet’s orbit when it is furthest from the sun
Changes every ~19,000 and ~23,000 years
All cause changes in the amount of solar radiation the earth receives which impacts the climate
We know of these changes through the rock record because things like changes in the magnetic fields are recorded
The most recent ice age was only 10,000 years ago
Other Cenozoic/Tectonic Events
Large lakes created oil shales in the Green River Basin, Wyoming
Crustal extension created the Basin and Range Province of the American SW
The Sierra Nevada and coastal ranges were raised in Western North America
Volcanic fissure eruptions occurred, creating the Columbia Plateau in Washington, Idaho, and Oregon
Human Evolution
Evidence for bipedalism in Australopithecus dates back to 3.5 Ma during the Pliocene Epoch
The genus Homo dates back to ~2.5 Ma during the early Pleistocene Epoch, including Homo Erectus (oldest ~1.8 Ma) and its early ancestors
Also known to use tools
Neanderthals appeared in europe (~28,000 years ago)
Homo Sapiens in Africa (oldest ~195,000 years ago)
Humans crossed the Bering Land Bridge sometime between 10,000 and 30,000 years ago (came to america)
Large fauna in the area go extinct with this introduction of humans (ie wooly mammoths) and this extinction is still continuing today
Sea levels were lower during the last ice age and migration routes may have existed along the coast or in between the laurentide and cordilleran ice sheets
Early humans in north america gave rise to clovis culture
Pleistocene megafauna of north america experience large scale extinction coincidental with arrival of humans
6th extinction that continue through today
Pulse of CO2 to the atmosphere on short timescale is a cause of major concern
Rising sea levels, ocean acidification, ocean deoxygenation
Basic geology relies on uniformitarianism: “present is the key to the past”
Three evolutionary faunas
A theme and a warning
Many mass extinction events of the phanerozoic are associated with rapid climate change