Lect 13 Flashcards
Global conditions: Triassic
• 252 Million years ago, directly following end- Permian mass extinction (worst one)
• Pangaea still largely intact (middle of it very dry and warm= deserts)
• Temperatures were high initially, then fluctuated
• CO2 highest at the end of the Triassic
• Ended with mass extinction
Fossils provide support to tectonic plates
Some small pockets of fossils of inverts, reptiles, early mammal like ancestors only found in eastern edges of South America today and the western edges of Africa.
Global conditions: Jurassic
• Pangaea split into Laurasia (northern) and Gondwana (southern), separated by Tethys Sea
• Temperatures dropped slightly during middle of Jurassic
• CO2 levels steady
Beginnings of the break ups of Pangaea, broke up North and South
Seaways between were sites of evolution for inverts and verts, like 2ndaryly marine tetrapods
Global conditions: Cretaceous
• Laurasia split into North America and Eurasia
• Gondwana split into South America, Africa, Australia, India, and Antarctica
• Atlantic Ocean formed and sea levels were ~200m higher
• Temperatures rose again, temperate conditions to polar regions; climate fluctuated at end (little to no ice or snow)
• CO2 fell at mid-Cretaceous
India collide with Asia and get Himalayan
Had swallow ocean ways that would flood the continents or continental shelf.
How we are able to find aquatic fossils in places very far away from water today.
Triassic
• Diversity low after end-Permian extinction (biggest one), recovery slow
• Diversity remained low around equator, higher in temperate regions (lot of niches left open after extinction. Diversity didn’t bloom everywhere all at once tho)
• Synapsids (mammalian ancestors) abundant early, replaced by dinosaurs (weren’t exactly mammals yet but give rise to them)
• Rhynchocephalia, Testudines, pterosaurs evolve
“Rink-cho-ser-phalia”
tropical rainforest = lots
Desserts = low niches
Jurassic
• Dinosaurs diversify rapidly, some getting very large
• Stegosaurs and sauropods
• Mammals become omnivorous (were 1st insectivores)
• Squamata and modern Lissamphibia evolve
• Stem birds, such as Archaeopteryx appear (from meat eating Dino’s)
Cretaceous
• Dinosaurs diversify further
• Hadrosaurs (duck-billed dino) and ceratopsians abundant
• Basal birds diversify
• Serpentes, Crocodylia, all three clades of mammals evolved
Pterosaurs
• pteron = “wing”, sauros = “lizard”
• First vertebrates to achieve powered flight
• Convergence with birds
• Reduction/loss of teeth
• Reduced bony tail
• Keeled sternum (extends away from spine —> protrusions provide structures for attachment of muscles used for flight)
• Pelvic girdle strongly fused to spine (but not censtracrum like in birds)
• Hollow bones (bits do go across on the inside tho)
Pterosaur morphology
• Wing (patagium) supported by elongated 4th digit
(More like bats membrane. Weight of wings and forces of flight too)
• Different jaw structures associated with different diets
(Live around ocean —> fish. May have been like pelican. Some teeth —> eat meat. Some omnivores)
• Many had crests on their heads (help prevent roll when flying and/or communicate within species)
• Body covered with pycnofibers – a hair-like insulating fuzz (still not fur,feathers, or hair. Might have been for display reasons)
Up to debate if endo or ecto.
Are amniotic —> keratin structures
Huge range in size
If fossil record correct could be very large and still have powered flight, which is insane given 1 could be as large as a giraffe)
Marine fauna
Fishes
• Oceanic productivity high, leading to robust communities
- Multiple shallow seaways flooded continents
• Acanthopterygians diversify
• Sharks increase in size
Break up of land —> more erosion on land —> goes to water —> more minerals and nutrients in water
Also make shallow water —> more sunlight —> more life can be supported in water
Secondarily marine reptiles
Lineages that have returned to life in water.
14 clades of saurosipda attempted to return but only 5 were most successful
Ichthyosauria: Evolved during Triassic, went extinct during Cretaceous. (Dorsal fin, 4 fins kept or Hind limbs reduced. Dolphin or shark like, homoceral tail)
Sauropterygia: Evolved during Triassic, went extinct at end of Cretaceous (few diff subclades with diff degreees of water relations)
• Placodonts: not specialized for swimming life; had crushing teeth (bony growth in skin, not attached like shell on turtle)
• Plesiosaurs: Long-necked elasmosaurs and large-headed pliosaurs (some had short necks and large heads. Limb locomotion not axial locomotion. 1st thought to be filter feeding, had hoop shaped jaw and teeth bent inwards to mouth)
- Propulsion from flippers
Thalattosuchians: Evolved during Jurassic, went extinct during Cretaceous
- Lineages of aquatic crocodiles
Mosasauroidea: Evolved during Cretaceous, went extinct at end of Cretaceous (shortest range of time on earth, 30 mil years ish)
- Related to snakes
- Diversified rapidly
Testudines: Sea turtles evolved during Jurassic (some got massive but those went extinct)
Extinctions
End-Triassic mass extinction
• Likely caused by volcanism associated with the breakup of Pangaea (releases magma underneath water too)
• Volcanic gasses changed chemistry of atmosphere and oceans
• Killed animals or collapsed ecosystems (food webs collapse too)
Anoxia—> oxygen content is low
Euxina —> oxygen and sulfur mix, even more toxic
Also acidification in ocean
Evidence this extinction was worse in the oceans
Extinctions
End-Cretaceous mass extinction
• 43% of tetrapod families went extinct
(More damaging in end-Triassic)
3 common traits.
Organisms usually have 1 of them
• Mid-sized, fossorial (burrow underground), or semi- aquatic vertebrates fared best (resources on land and water)
• No arboreal birds survived (medium birds are secondaryly evolved)
• Turtles and crocodiles hit lightly (b/c semi aquatic)
• Amphibians (semi-aquatic) and lepidosaurs (very small) not hit worse than background extinction
• Fishes fared well
(Turn over and background extinction. A few lineage but not many)
Extinctions
End-Cretaceous extinction causes
• Deccan Trap volcanism in India
• Sea levels fell
- Changed ocean chemistry
- Reduced area of marine habitats
• Chicxulub asteroid impact
- Tsunamis, wildfires
- Debris and soot in atmosphere reduced sunlight, led to global cooling (6-8°C)
Has good support
Element found all around world is low but asteroids have more, layers found at end-Cretaceous had a high level of it
Both might have been working together
Key Concepts
• Pangaea broke first into Laurasia and Gondwana, eventually into modern continents.
• Terrestrial fauna included pterosaurs, dinosaurs, and the evolution of modern tetrapod clades.
• Marine fauna included multiple attempts of re-invasion of the seas, but ichthyosaurs, plesiosaurs, thalattosaurs, mosasaurs, and turtles were most successful.
• The Triassic and Cretaceous periods were both marked by extinctions, the end-Cretaceous extinction saw the death of non-avian dinosaurs, pterosaurs, and non-turtle marine reptiles.
