Lecture 27: The Phanerozoic Bioshpere Flashcards
-The Cambrian Explosion -Major Evolutionary Milestones -Mass Extinctions
What happened in The Cambrian Explosion?
Most major animal phyla appeared abruptly in the fossil records, and apparently without obvious precursors.
-It lasted for about 30 million years and resulted in the rapid appearance of most modern animal phyla.
What are examples of cambrian fauna?
Sponges, predatory worms, molluscs, brachiopods, archaeocyathids (1st reef-building organism), and arthropods (trilobites).
What are the three accepted explanations for the Cambrian Explosion?
1) Environmental changes
2) Developmental changes
3) Ecological changes
What environmental changes could have led to the Cambrian Explosion?
Oxygen and calcium levels in the ocean increasing.
- Oxygen could lead to more complex life forms to evolve
- Calcium would make it possible for marine organisms to build skeletons and shells.
What is the Great Unconformity?
It represents a long period of time of weathering between Precambrian and Cambrian strata.
What are the two reasons for the sudden developmental changes?
- It took time for animals to form Hox genes
- Horizontal gene transfer
What are Hox genes?
Genes that control how different regions of the embryo develop into specific organs.
-Control basic body form
What is Horizontal gene transfer
The process whereby genetic material is transferred between organisms.
-Has also been identified as a possible factor in the acquisition of the biochemical capability of biomineralization.
How would end-Ediacaran mass extinction be an ecological factor for the Cambrian Explosion?
Explains why the Ediacaran fauna disappeared and mass extinctions are often followed by adaptive radiations.
How would would the evolution of eyes be an ecological factor for the Cambrian Explosion?
Prey would need new defences against predation, such as the evolution of amour and spines.
How would evolution of predators be an ecological factor for the Cambrian Explosion?
As predators evolved, prey would also need to grow bigger and develop greater mobility or biomineralized to prevent being eaten.
How would large zooplankton be an ecological factor for the Cambrian Explosion?
Fecal pellets get formed and deposited on the seafloor, thus providing a new energy source.
-Opened the door to more burrowing animals
What is a lagerstatte?
It is a fossil site exhibiting extraordinary preservation and often fauna or floral diversity.
How does fossil records of soft tissue help paleontologists?
They allow them to examine the internal anatomy of animals.
What is so important about the Burgess Shale?
An entire community of marine organisms became preserved, allowing scientists to observe an entire ecosystem from 508 million years ago.
What are epifaunal?
Animals that live on the surface of the seafloor.
What are infaunal?
Animals that burrow into sediment.
What marked the late Cambrian and Ordovician?
A tripling in global biodiversity.
-Including new trilobites, brachiopods, bivalves, bryozoans and coralline animals.
What are classified as Bivalves?
Clams, mussels, scallops and oysters
What are classified as Gastropods?
Snails, slugs, conchs, and limpets
What are classified as Cephalopods?
Squid, cuttlefish, octopus, and nautilus
What is the difference between nautiloid cephalopods and ammonoid cephalopods?
Nautiloid- have straight or gently undulating sutures
Ammonoid- have complex sutures
What are Arthropods?
They are a phylum of invertebrates that include insects, spiders, crustaceans, and a host of other animals that possess exterior skeletons.
Which arthropods were important during the Paleozoic?
Trilobites and eurypterids
What are vertebrates?
Animals that have a segmented backbone composed of individual vertebrae.
What are the two groups of vertebrates?
1) Non-amniotic vertebrates
2) Amniotic vertebrates
What are non-amniotic vertebrates?
Fish and amphibians must be in the water (or at least wet) to reproduce. Their eggs are exposed - lack a covering.
What are amniotic vertebrates?
All higher vertebrates that have evolved internal fertilization and amniotic egg (enclosed egg).
What is so important about amniotic vertebrates?
There form of reproduction allows them to exploit diverse terrestrial environments away from water bodies.
What are the two earliest vertebrates?
- Pikaia, a worm-like animal with a dorsal nerve cord and muscles that run down the side of the body
- Myllokunmingia, oldest fish
What are a few biological innovations that facilitated the widespread divergence of fish?
- Many species developed some form of armour
- The evolution of the jaw
- The evolution of bony fish. Played a key role in the eventual evolution of tetrapods.
- Some developed muscular lobe-fins and a pair of opening in the roof of the mouth that led to external nostrils. Eventually passed on to primitive lungs
What changes in amphibians came with the shift from water to land?
1) Limb bones and skeletal structures were modified to help hold their bodies above ground.
2) The spinal column was transformed into a more sturdy structure.
3) The organs for hearing underwater needed to adapt to hearing in the air.
What are tetrapods?
The first amphibians.
What are amniotes?
Reptiles that first appeared in the Pennsylvanian and who developed the amniotic egg.
When did the oldest bird appear and what did it look like?
It appeared in the Jurassic and possessed a jaw with teeth and a lizard-like tail. It resembled a dinosaur, except for its fossilized feathers.
When did the earliest mammals evolve?
During the Late Triassic. They were fairly small until after the Mesozoic.
What did plants evolve from?
Stromatolites formed from cyanobacteria which eventually become algae.
What was the first form of reproduction for plants?
Seedless
- Spore-bearing plants
- Became to abundant in swamps that they eventually formed some of Earth’s largest coal deposits
What was the second form of reproduction for plants?
Naked seed-producing, pollinating, but non-flowering plants (gymnosperms).
-Did not require moist environments so they expanded their habitat and dominated the supercontinent, Pangea.
What was the third form of reproduction for plants?
Self-enclosed seed-producing plants
-Plants with both seeds and flowers (angiosperms)
How did all three of the early Paleozoic plants alter the environment?
They facilitated soil formation and provided food and shelter for emerging land animals. They also paved the way for the evolution of large trees.
What are two events that led to mass extinctions?
1) Meteorite impacts
2) Volcanic eruptions
What are the two major extinctions?
1) Permian-Triassic. Most severe in Earth’s history
2) Cretaceous-Tertiary. Loss of dinosaurs and many other plant and animal species
What percentage of marine and land animals perished in the Permian extinction?
90% of marine species
70% of land animals
What caused the Permian extinction?
- Huge amount of volcanic activity
- Extra carbon dioxide would have led to global warming
- Dust would have blocked out the sun causing prolonged nuclear winters
- Sulfate reduction took place in the water column which would have killed the aerobic organisms.
What caused the Cretaceous extinction?
The impact of the large meteorite colliding with the Earth in Mexico.
- Dust would have blocked out the sun killing the plants which killed the animals
- Vapourized surrounding rock and oceans
How many species were wiped out during the Cretaceous extinction?
1/4 of all known species.
What evidence do paleontologists have that explains the cause of the Cretaceous extinction?
- The abrupt manner of the extinctions
- A layer of clay found around the world that contains iridium that only occurs naturally in the Earth’s mantle and core. The only other source would have to be extraterrestrial.
What is another possible cause of the Cretaceous extinction?
Massive outpouring of flood basalts, known as the Deccan Traps.
-Could have led to the same environmental changes like the end of the Permian.
