The Rise Of Mesozoic Biosphere Flashcards
What was the Early Triassic land environment like?
Pangea, harsh, hot, deserts
No ice at poles
Evidence: rocks, ventifacts, calcretes
What was the Early Triassic ocean environment like?
Analysis of oxygen isotopes taken from conodonts showed rapid warming to about 36°C, peaking at around 252.1 MA. There is a cooling following the main extinction and then a second rise in temperature around 250.7 MA. Temperatures rose to even 40°C.
How were oxygen isotopes used to determine environment?
Isotopes used: 16-O and 18-O.
Water with 18-O is heaviest, water with 16-O is lightest. During cold periods, there’s less energy to evaporate 18-O water. Clouds are enriched with 16-O water. Some of that 16-O water will remain trapped on land in ice sheets leading to an enrichment of 18-O water in the ocean. This will continue until warmer conditions melt the 16-O rich ice, return the water to the ocean, hence driving the 16-O/18-O ratio back in favour of 16-O. These changes will be reflected in shells of marine animals that use oxygen to produce CaCO3 shells.
What are disaster taxa?
Creatures after an extinction that are high in abundance but low in diversity.
Describe Lystrosaurus.
Disaster taxa of Early Triassic. Member of group of reptiles called dicynodonts and a wider group of reptiles called therapsids. No evidence of teeth, but it is thought to have a beak and tusks. Moved backwards and forwards using its jaw for food. Possible able burrower due to sturdy bones in fore limbs.
What plants were present during Early Triassic?
Smaller herbaceous forms like seed ferns and perhaps conifer. Changed rivers from mainly meandering to chaotic braided.
What was life like in the oceans during the Early Triassic?
Disaster taxa like brachiopod Lingula and bivalve Claraia. No corals, only stromatolites.
What was the geography of the Early Triassic like?
Majority of life was at higher altitudes (near the poles) and there was barely any life near the equator (opposite of what we see today).
Describe the Lilliputian Effect.
In response to rising temperatures, the creatures have smaller adult sizes and increased juvenile mortality rate.
What was driving the impoverished Early Triassic?
Increase in temperature pushed organisms beyond their tolerance. Increased temperature caused other problems like reduced oxygen in oceans and rise of H2S due to sulfur loving bacteria. Increased CO2 led to acidic sea water.
Why did the extinction last so long?
Possible that Siberian Traps was active and releasing CO2. Possible destabilization of methane hydrates that further warmed planet.
When did the biota start to recover?
During Middle and Late Triassic, numbers and diversity increased.
Describe the recovery of corals and reefs.
By Middle Triassic, reef gap ended. During Paleozoic, reef builders were rugose and tabulate corals. When they became extinct, so did creatures that lived around them. 10 Ma after extinction stony corals came back and Middle Triassic was when scleractinian corals appear.
Describe brachiopods.
Resemble clams, but are are from a different group called lophophorates. They feed using a lophophore, a ring of ciliate tentacles that are used to capture materials. Prior to Permian extinction, they were common, but never again would they dominate.
Describe bivalves and gastropods.
They are mollusks. Bivalves are clams and gastropods are snails. They both recovered and diversified and dominated during the Mesozoic and Cenozoic.
