D. Mesozoic Life Flashcards
When did complex metazoan life evolve?
about 600 million years ago
Summarize the Permian Triassic mass extinction
The Permian – Triassic mass extinction is the greatest catastrophe the biosphere has faced since complex metazoan life evolved about 600 million years ago. A cascading series of events, probably triggered by extensive volcanic activity in Siberia, would see the development of runaway global warming and the extinction of vast swathes of the biosphere. Some estimates suggest that around 96% of all species on the plant became extinct in a geological snap of the fingers.
What features from the Early Triassic indicate the climate?
In Lesson 10 (Mesozoic Climate) we learned that the Early Triassic climate was harsh. Hot, arid deserts covered most of the interior of the supercontinent. Evidence of this is found in the rocks, where evaporites are common as are red desert sandstones. In addition to evidence from the rocks, other telling features from the Early Triassic include ventifacts and calcretes. These rock features also point toward hot, arid conditions. In fact it is possible that this may have been the hottest, most arid time since life began to proliferate 600 million years ago! There was likely no ice at the poles… in fact it is possible that the poles might have been relatively temperate, meaning forests and a more diverse fauna of animals could survive.
From what organism did we analyze oxygen isotopes in Mesozoic (Early Triassic)? How do the sea temperatures back then compare to today?
Analysis of oxygen isotopes taken from conodonts (the mouth parts of a worm-like chordate) paint a disturbing picture of the temperature change during the Early Triassic.
Research in equatorial deposits from South China spans the period covering the extinction at the end of the Permian and continue into the Early Triassic. These results show a 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. This happened during a stage of the Early Triassic called the Late Smithian, when temperature in the water column rose again to about 38°C, perhaps even exceeding 40°C at the surface in equatorial regions. As a comparison we can consider sea surface temperatures today which don’t really get above 30°C at the equator. (Note that in the Geological Time Scale there are two stages recognized in the Early Triassic, the Induan and the Olenekian. The Olenekian is sometimes divided into two stages instead, called the Smithian and the Spathian.)
What are the two stages recognized in the Early Triassic temperature-wise?
the Induan and the Olenekian
(Olenekian can be divided into the Smithian and the Spathian stages)
What are disaster taxa?
Creatures that live after disasters; high in abundance, meaning there were a high number of individuals, but they were of low diversity, meaning there were a low number of different types of species.
Describe the Lystrosaurus
A disaster taxa
A strange shovel faced animal, a member of a group of reptiles called dicynodonts (pair of dog-like tooth tusks); belonged to wider group of reptiles called therapsids (mammal-like reptiles) which are important in the evolution of mammals.
Evolved during the Permian.
Lystrosaurus most abundant during Early Triassic (251-247 Ma), making up over 90% of the terrestrial vertebrate species on Earth.
Features: shovel-like face, twinned tusks (maybe to dig up food like roots and tubers), likely a herbivor (no evidence of teeth but has turtle-like beak)
Jaw moved backwards and forwards (grind down plant material), didn’t move up/down or side to side
Has a semi-sprawling gait; legs stick out like croc or gecko
Sturdy fore limb bones suggest powerful muscle, maybe could burrow, maybe lived in burrows
These features may have allowed it to survive through hard times.
It is a generalist
Did generalists or specialists live through the Early Triassic? Why?
Generalists overall. Because the times were tough.
What kind of plants were there in Early Triassic?
Forests were not as common on the desert planet. When plants were present on land, they would often be dominated by smaller herbaceous forms like Pleuromeia and Dicroidium (types of seed ferns) and perhaps by a few species of conifer.
Describe the change in land between Permian and Early Triassic. What is a possible explanation for this change?
Forests were not as common on the desert planet. When plants were present on land, they would often be dominated by smaller herbaceous forms like Pleuromeia and Dicroidium (types of seed ferns) and perhaps by a few species of conifer.
This may also explain why we see a transition from mainly meandering river systems in the Permian with banks stabilized by plants, to the common occurrence of a more chaotic braided system in the Early Triassic. This is a signal that plant communities have retreated and along with them their ability to stabilize the river channels.
Give examples of disaster taxa in oceans
Lingula is a burrowing brachiopod that is still extant today. Claraia is a scallop like bivalve.
Describe the ocean fauna in Early Triassic.
There were no corals. In fact just like the coal gap on land, there is a similar coral gap in the oceans, with coral reefs not returning to the planet until about 10 million years after the start of the Triassic. The only reef like structures at this time were stromatolites. These are columns of cemented sediment created by mats of microbes. Stromatolites were common before predators evolved in the Cambrian. Since then, they are limited to the periods following mass extinction events, other than a few isolated communities that manage to survive in unusual environments where grazers are kept in check.
When do stromatolite populations dwindle and when do they increase?
Dwindle when grazers are plenty, increase after mass extinction events (less predators)
Stromatolites were common before predators evolved in the Cambrian. Since then, they are limited to the periods following mass extinction events, other than a few isolated communities that manage to survive in unusual environments where grazers are kept in check.
What is strange wrt diversity in the Early Triassic?
Basically there is a geographical pattern to the impoverishment of the taxa in the Early Triassic in both marine and terrestrial environments that is opposite to what we would expect based on today. During the Early Triassic a disturbing gap in fossils occurs at the equator. The equator had become a dead zone!
In the ocean, no life around the equator except for invertebrates like sessile mollusks and stromatolite reefs. Likewise on the land, majority of fauna surviving the extinction moved to the poles.
Thus in Early Triassic the biodiversity has flipped, was opposite vs what we have today.
Describe the pattern of modern biodiversity in the globe
When we look at the diversity of the biota today, we find a consistent pattern of highest biodiversity at the equator, decreasing as you move toward the poles.
Describe the Lilliput Effect
The Lilliput Effect, which includes smaller adult size and increased juvenile mortality rate, is seen to occur as a response to rising temperatures. Together these characteristics result in a fossil record that is composed of smaller individuals. This probably also explains why trace fossils only record the presence of small organisms that were not really burrowing very deeply at this time.
Many of the taxa during Early Triassic times were very small.
What is pushing organisms to the poles during the Early Triassic? (Lowering biodiversity)
It would appear that the increase in temperature during the Early Triassic (especially at the equator) is pushing organisms beyond their thermal tolerance. For many plants that temperature is about 35°C, with few being able to survive over 40°C. This also explains why active creatures like fish, marine reptiles and cephalopods are absent or rare at the equator. The more active you are the more active your metabolism and the more active your metabolism the greater your demand for oxygen.
But also many other causes like reducing oxygen conditions in various parts of the ocean, resulting in rise in euxinic conditions (H2S) by sulfur loving bacteria that made seawater acidic, which was problematic for creatures that have calcium carbonate shells/skeletons (e.g. corals, bivalve Claria). They would only secrete very thin shells.
Why did the low biodiversity climate/ environment in Early Triassic last so long?
We don’t know for sure yet.
In most extinctions the biosphere is well on the way to recovery within a few hundred thousand years whereas in the Permian things were still pretty awful up to 5 – 7 million years into the Triassic. In fact the only reason we are probably not registering another mass extinction at this time is that there is very little left to become extinct!
Not only due to rising temps and acidic waters, but also possible the Siberian Traps were still active and releasing CO2, which may be responsible for increased warming at end of the Smithian. But evidence is not yet found.
When did Earth’s biota start to recover from the Early Triassic?
During the Middle and Late Triassic, in both the continental and marine realms, the numbers and diversities of lineages increased significantly. This general overall increase in the numbers of lineages continued into the Early Jurassic. In addition, there is a major increase in ecological associations as well.
When did long term reef development initiate once more?
Middle Triassic
How long did the reef gap last? (i.e. absence of long term reef developments)
From the end-Permian and into the Early Triassic
Describe the main Paleozoic reef builders. What were some minor reef formations after the P-T boundary?
The main Paleozoic reef builders were the rugose and tabulate corals. They supported much of the oceanic biodiversity, but were driven to extinction during the end-Permian extinction. When they became extinct, so did many of the invertebrates and vertebrates that lived in and around them. Although there is evidence of some minor reef formation about 1.5 million years after the P-T boundary (by sponges and serpulid worms), it is not really till around 10 Ma after the extinction that stony corals really start to make a comeback and it is not until the Middle Triassic that we see the scleractinian corals appear in earnest. It is these scleractinian corals that are still the main reef forming metazoans today.
Before the Permian extinction what kind of shells would you find commonly washed up on shore?
Brachiopods, likely. They dominated the ocean floor during the Paleozoic.
What are brachiopods? Do they belong to the same group as clams?
Brachiopods superficially resemble clams, but they belong to a very different group of animals called the lophophorates. Brachiopods feed using a lophophore which is a ring of ciliate tentacles that they used to capture material suspended in the water column.
After the Permian extinction, by the Middle Triassic, what kind of shells would you most commonly find?
Mollusks.
Mollusks like bivalves (clams) and gastropods (snails) recovered and diversified.
(Note: Brachiopods did survive but didn’t dominate anymore)
What kind of land vertebrates popped up in Middle Triassic to Early Jurassic?
Archosaurs.
E.g.: The group “Rauisuchia” were like crocs with long (tucked under body) legs, apex predators of land.
E.g. 2: Dinos. But they only emerged not dominated the Triassic.
Archosaurs would dominate above therapsid reptiles (e.g. lystrosaurus).
Describe the Coelophysis and its features. Also how it lived.
A Triassic dino. A slender bipedal carnivore, about 3 m (9.8 ft) long. It was very common in the southwestern United States but it has been found worldwide. Coelophysis was probably an agile runner. Its forward facing eyes giving stereoscopic vision and a good view of the road ahead that included good depth perception.
What were the first vertebrates that could fly?
Archosaurs. During the later Triassic, they evolved to fly.
Describe the burst of diversification following the Permian extinction in a couple of sentences.
Lots of vertebrates diversified- archosaurs popped up and dominated (specifically the croc-like land predator, the Rauisuchia). Expansion of both terrestrial and freshwater vertebrate.
How did the earliest mammals likely evolve? Is there a clear distinction between the last mammal-like non mammals and the true mammals?
It is likely that some of the earliest mammals evolved (during the burst of diversification following the Permian extinction) from some of those mammal-like reptiles (therapsids like Lystrosaurus) that had been so common in the Permian and earlier Triassic.
No. It is difficult to distinguish between the last of the therapsids (that were starting to look like mammals) and true mammals, but Late Triassic animals like Megazostrodon are certainly starting to look very mammalian.
What is accepted as being one of the earliest mammals?
Megazostrodon - a Late Triassic animal
Describe the Luoping fossil site in China showing long recovery of life from the largest extinction in Earth’s history:
What does the site date?
How do we know we’re looking at a fully recovered ecosystem?
How many fossils are there?
What kind of predators are found?
What do the fossils tell us about?
Only 1 / 10 species survived the Permian mass extinction (worst extinction)
Dates from Middle Triassic.
We know it’s a fully recovered ecosystem cuz of the diversity of the predators (fish and reptiles) which is much greater than Early Triassic. Also, the high complexity of the of food web has bottom of food chains dominated by later Triassic marine fauna like crustaceans fishes and bivalves.
There are 20,000 fossils found at the site.
Just as important is the ‘debut’ of top predators – such as the long-snouted bony fish Saurichthys, the ichthyosaur Mixosaurus, the sauropterygian Nothosaurus and the prolacertiform Dinocephalosaurus – that fed on fishes and small predatory reptiles.
The fossils tell us about the recovery and development of marine ecosystems after the end-Permian mass extinction.
