MESOZOIC – DINOSAUR I
Today, we’re going to do something different than we’ve done for every other lecture. We’re
going to talk about dinosaurs.
The remainder of this class is going to be divided between looking at the Mesozoic and the
Cenozoic, culminating in our world today.
We’re done with the Palaeozoic. The Mesozoic is the middle interval. It is broken down into
three time periods: the Triassic (248-206), the Jurassic (206-144), the Cretaceous (144-65). Thi
sis called teh age of dinosaurs. It is an interval of pronounced climate changes, and it is the
interval of the most dynamic plate tectonic activity in the phanerozoic. It is also the interval
where we see the origins of the most of the modern groups of animals wtaht we would recognize
The first interval, the Triassic 248-206 mya.
Here’s what we have. The Triassic is characterized by a couple of things: the breakup of Pangea
becomes important. We have the first occurrence of animals like turtles, frogs, modern groups of
fishes, and dinosaurs. We have hte beginning of whaat is called the mraine arms race.we have he
origin of ammals. We have the radiation of initial modern plants. At the end of the Permian, what
was previously during the laurentia and gondwana had formed together. Africa collided wit hte
east cost of NA...conglomeration of landmasses into single giant landmass called pangea. During
the Triassic, we see the intial fragmentation of pangea. It begins to break apart. We have the
intial opening of what is today teh north atlantic ocean, the gulf of mexico. How many people
know where the atlantic ocean is? Everyone knows. The ocean between ocean between Africa
and South America, and between Europe and North America. If you were to take all of the
continents today as puzzle piec, you could connect them altogether.
North America: single clarge continental land mass. The equator is considerably south relative to
its position today. Where was the equator during paleozoic: drunnning through tornoto. Now, the
NA landmass has oriented itself something akin to what we have today, even though it is
considereaably south. It is a single landmass, there is the appalachain mountain range along the
east, formed from the intial collision and formation of pangea. This land mass...NA relative to
Africa nad SA. We have the intial spepartion of this landmass into a northern landmass and a
southern landmass. The first separation occurs in the north atlantic. Europe and NA. We have the
separation of the margins of Africa and South America. What happens in plate tectonics when
two pieces of continental crust get pulled apart: ocean crust. It forms thin, dense, basalt crust. It
forms a low crust. The low spot will open up and flood as the continents move apart.
At the top, you have Evaporates aer rock deposits that are formed when you have the evaporation
of water. We have areas that have the solid residue of what happens when water is evaporated.
Has anyone been to the southwest part of the US (Grand Canyon). You get them when you drain
out and evaporate an ocean basin. So, as we begin to rift these continents apart, we form oceanic crust, adn we get periodic flooding of those areas from ocean waters as the continents move
We can see that by the distribution of the evaporate deposits.
So, we have this separation of pangea. What does this look like.
The cross section: you have basically the separation of two places as they move away from each
other. They don’t just break apart like a paper cut cuts your skin. Instead, teh crust is fairly rigid.
It breaks into a series of blocks. As these blocks break apart, some of them drop down a little bit.
Just lke blood out of a paper cut, magma material moves up and comes up to the surface,
expressed as volcanoes or basalt flows.
As these plates continue to move apart, you will have evaporates forming as ocnea water comes
in and ries out constantly. You’ll get ocean basins so well developed that you have continuous
ocean water there, and you form ocean environments. This is what is beginning to happen in the
Triassic. NA, Europe, and Africa separating from eac other.
You’ve also heard of petrified forest, AZ, Records Triassic forests. We have petrified logs,
thousands of them. You’re looking at a 230 million year old log lying on its side. These forests
are composed of plants of partly modern origin. We have confiers, we have cycads, we have the
gropu that goes onto form flowers and plants, and we have an abundance of lycopsids (but there
diversity has decreased). We’re see radiations of sea ferns and of conifers. There are no flowers.
There is no fruit. These reproductive structures have not evolved in the Triassic. Lots of cycads
and cone-bearing plants and lots of ginkos. What are ginkos. If you go farther south than
Ontario, you’ll run into these plants. They’re their own separate lineage. They have meaty seeds.
The seeds decompose in such a way that they smell exactly like vomit.
Alive ginkos and fossil ginkos.
Real trees and fossil logs.
There were no grasses at this time. The majority were ferns.
In marine environments whichi were devasted by the Permian extinction event, we have
recovery. Increasing diversity wit hmodern groups taking over. In teh paleozoic, there were
brachiopods, in the Mesozoic, you get molluscs and clams (of modern origin ) which dominate.
They diversity and radiate. We have trifea and corals. Corals today are primary reef builders.
Corals and reefs are engines of biodiversity. They are areas where large numbesr of species
evolve. At the end of the Permian, all the primitive corals that formed the reefs of the Permian go
extinct. You can se the big cliffs. Those are giant coral reefs in West Texas. They represent the
end of primitive corals. By the middle o the TRiasc, we see ocrals coming back, and they’re the
Echinoderms (deuderostomes related to us) these are sea urchins. They diversify. What is that at the bottom. That is the skeletal remains of an echinoderm.
You get a diversification of cephalopods (squid and octopus). That up there is the only living
shelled cephalopod in modern ecosystems. We have a big radiation of shelled molluscs. You’re
seeing coiled shells of a gropu of mollsuss called ammonites. They’er the most diverse Mesozoic
cephalopods. Biostratigraphy sues teh distribution through hthe rock reocord of fossios to
correlate different packages of rocks. Ammonites are one of the primary animals for correlating
marine rocks during hte Mesozoic. We have a lot of animals that evolve shells. Then, what we
have this evolution of shell-crushing predators: crustaceans (modern) diversify during hte
Mesozoic. There are arthropods and crustaceans going all the way back, but we get the modern
groups in the Mesozoic. They use massive, specialized shell-crushing claws. Harder, thicker
shells evolve in resistance to shell-crushing claws. It isn’t just the invertebrates. We get hte first
shell-crushing fishes. This is called a picnada. This happens in marine reptiles. Ther is a group
called placodonts. They’re related to lizards. This is a group of aquatic reptiles that evolve and
radiate out turing the Mesozoic and Triassic with big teeth. Specialized for Shallow marine sands
looking for shell fish.
Other marine radiations and reptiles. One of hte things that happens repeatedly in vertebrate
evolution is that tetrapods and amniotes (reptiles and mammals, and their common ancestors),
whih aer primitively terrestrial. There are repeated events where terrestrial animals evolve to life
in oceans. Whales are an example. Sealions and walruses. Polar Bears. Sea Cows. Any reptiles
that live in ocean environments. Sea snakes and marine aguanas. These animals are not hyper
special, but in the Mesozoic, we have radiation and domiatnion among vertebrates by reptiles. At
the top is a Sauropterygians. Then, there is the ichthyosaurs (fish lizard) at the bottom. This is
one of his favourite fossils. It is preserved in a way that. The tip of his mouth is there. There are
paddles, big rib cage going to the tail. These were marine animals that d