hi everyone today we're going to be going over the
cenozoic era so like all the other time interval lectures we've done i start by showing you this
timeline to remind you where we're at now in geologic history we started with the pre-cambrian
which goes from the haitian to the archaean to the proterozoic then we went to the paleozoic era
last we did the mesozoic and now we're finally at the cenozoic era this is the most recent era in
earth's history and is still going on right now and that is why i put humans as the main event
for this era however there are a lot of other things that went on during this era early on
and are still going on now and we're going to go over the major geologic and biological events
that occurred in the cenozoic first to start with geological events we can look at the evolution
of cenozoic paleogeography or the movement of the continents we left off the cretaceous the
last period of the mesozoic with the continents almost in their current configuration except
india was still moving up to collide with asia and hadn't done so yet and australia and antarctica
were still kind of locked together and hadn't really separated much yet so these were the main
two movements but basically the configuration of continents finalized itself during the cenozoic so
now let's look at what's happening at the surface throughout the cenozoic and how it led to our
current tectonic situation throughout the globe as well as the current mountain belts that we
have at our surface today so here is the current configuration of lithospheric plates on earth
today and where they are colliding with each other during the cenozoic most of the world's geologic
features were formed or are still being formed including the himalayas the alps the andes the
san andreas fault the grand canyon and the north american rocky mountains to start with we're going
to talk about the tectonics that were occurring at the courtyard mobile belt throughout the cenozoic
and what's occurring now at that mobile belt we talked about how the courtyard mobile belt is at
the western margin of the us and in the last video over the mesozoic we talked about how the nevadan
and severe orogenies occurred in the mesozoic and we talked about how the laramie orogeny began in
the mesozoic but then continued until the eoc the laramie orogeny was the last major origin event
contributing to the development of the cortier and mobile belt before a change in stress occurred
basically the laramite orogeny was the subduction of the farallon plate an oceanic slab that
subducted under north america at a very shallow angle causing deformation further inland of the
trench and then by the eocene the subduction got to the point where the mid-ocean range of
the farallon plate had reached the trench however that was the point at which subduction ceased
and this is because the mid-ocean ridge wasn't dense enough to subduct and therefore the stress
changed from compressional to shear and that was because transform motion began causing the san
andreas fault instead of continuing compressional subduction and currently today the remnants of
the farallon plate that hadn't subducted yet called the wandifuga plate and the couscous plate
are still subducting under north america as seen in this map however the shift in stress regime
in the eocene did cause a lot more than i want to talk about before we move on to more recent
events so let's talk about the basin and range deformation during the eachine when the transition
of compressional to shear stress began the stress further inland throughout western north america
became extensional and this caused base and range deformation basically all the compressional
deformation that had occurred further inland due to the fairlawn plate subduction at a low
angle that had just switched from compressional to extensional causing all the compressional fold
and thrusty formation to become basin and range deformation where extensional normal faulting and
horsts and gravins formed horses and gravins are basically in this lower picture we can see that
the robins are dropped down blocks due to normal faults on either side of a graven and forests are
the blocks that don't drop down or even uplifted in some cases so along with the extinction during
this time and in this area we also had rifting occur in north america however these two specific
instances i'll be talking about were much later for example the real grande rift began around five
to ten million years ago and this rifting is shown in the right picture where we have the yellow
blobs and then we have the rio grande river in the rift valley we also had around the same time
as this rift the rifting between baja california and mexico causing the gulf of california to
open up which is shown here so moving on to original activity outside of north america this is
a map showing in purple the alpine and himalayan moba belts the courtyard mobile belt and the
indian mobile belt we just talked about the coordinate mobile belt and the deformation it
caused in north america during cenozoic however let's now turn our attention to outside of north
america for example the himalayan the alpine and the andean oragenies the himalayan orogeny began
around the eocene when india collided with asia and is continued today as india continues to
push toward asia the alpine orogeny also began by the eocene as africa began colliding with
europe closing the tethosc and forming the mediterranean black and caspian seas if you
don't remember what the tethosc was remember when we went over the continental configurations
during the mesozoic right after pnga formed during the latest paleozoic we had pangea break up back
into laurasia and gondwanaland forming the tethosc in between these two continental masses and
this tethosc remained in between europe and africa until africa closed that gap and the
remnants of the tethoscape are the mediterranean black and caspian seas now the andean orogeny is
caused by the subduction of the nazca plate under south america and continues today as well and
another thing that all of the ocean continent subduction zones are famous for on earth today
is something called the ring of fire the ring of fire is defined by strong earthquakes and
intense volcanic activity that occurs along ocean continent subduction zones along the margins of
the pacific ocean now to just give a brief summary of the geologic events that we just discussed
let's put them all along the timeline of the cenozoic era the cenozoic era has epochs paleocene
eocene oligocene myosin pliocene pleistocene and holocene and these epochs go from 65 million years
ago at the end of the mesozoic to now at the end of the holocene at zero million years ago as we
are in the holocene currently so going from right to left we have the andean orogeny beginning
in the earliest paleocene the ring of fire also beginning to form around this time as well
due to subduction zones such as the andean the himalayan orogeny beginning in the eocene the
laramite orogeny ending in the eocene remember it started in the late mesozoic the alpine orogeny
beginning also in the eocene the san andreas fault forming due to the end of the laramie subduction
and beginning of shear stress the beginning of the basin range extension the beginning of central
america subduction the beginning of the rio grande rift zone and the ring of fire the himalayas
the alps the san andreas and the basin range continue in their original activity today so
now before i get to the biological events that occurred in the cenozoic let's just talk about the
climate a little bit the climate in the cenozoic began pretty hot and the paleocene-eocene boundary
is marked by a thermal maximum meaning a really hot period around 55 million years ago however the
rest of the cenozoic era up until today has been marked by pretty intense cooling associated with
continental fragmentation and then we had our most recent ice age happening around 2.6 million years
ago in the pleistocene and ever since then things have been warming up again and now of course we're
adding on to that but besides that these are the transitions of the cenozoic in terms of climate we
have the eocene warm period with high sea level we had the pleistocene way later with the ice age
and now we have the present with ice caps but more temper temperatures and sea level throughout
most of the globe now moving to cenozoic life the citizen is referred to in terms of vertebrates as
the age of mammals and can also be referred to in terms of invertebrates as the age of insects these
are the two main dominant types of organisms for vertebrates and invertebrates respectively and
so now let's talk about the events that occurred evolutionarily and biologically for the marine
invertebrates the terrestrial invertebrates the marine vertebrates the terrestrial vertebrates
and then the plants so starting with the marine invertebrates we had the modern forms of bivalves
such as clamps oysters and scallops evolve we had gastropods expand to inhabit practically
every single marine and terrestrial environment and gastropods also represent the second
most abundant invertebrate during the entire cenozoic second right behind arthropods and then
we had sclerotinian corals after the rudest wind extinct sclerotinian corals were able to become
the major reef builders again and ever since then have been dominating reef building and reef
communities in marine environments and then we also have calculus microplankton we talked about
coccolithophores in the mesozoic being dominant in the cretaceous and causing the cretaceous
to be named after the rock they form which is chalk and in latin that is krata however in the
semizoic cocolita wars were no longer dominant actually the dominant forms of calculus plankton
were diatoms dinoflagellants and foraminifera these are just other groups of microorganisms that
grow their skeletons or tests or shells whatever you want to call it with calcium carbonate then
we also have ethanoids such as sand dollars and sea urchins diversifying cenozoic and then we had
marine arthropods and arthropods in the ocean you might think about lobsters and shrimp but they
were much more than this the most common cenozoic forms are annelid worms which are not preserved as
body fossils but are preserved most often as trace fossils forming tracks and burrows in the sediment
so now let's move on to terrestrial invertebrates which we already mentioned at the beginning
of the cenozoic lifestyle that arthropods such as insects were dominant and remain dominant
throughout the cenozoic and i just realized that this slide says dominant vertebrates pretend
like that says invertebrates arthropods are not vertebrates so insects are the most successful
in the cenozoic but arachnids such as spiders and scorpions are also very abundant so moving
on to marine vertebrates now we have most of the fish in the cenozoic being bony fish however
some cartilaginous fish such as sharks remained abundant and continue to remain abundant today
there is one difference in today's sharks than in for example the eocene sharks during the eocene
sharks with jaws more than six feet across had evolved and these were called corchardon megalodon
and i'm sure you all have heard of megalodon fish thankfully they are now extinct my goodness that
would be terrifying now regarding marine reptiles we talk in the mesozoic about marine reptiles
that resemble today's marine mammals however after the kt extinction only a few marine reptiles
had survived and these went on to become things that we know in the modern day to be sea turtles
and sea snakes and therefore the niche that had been filled by mesozoic marine reptiles could now
be filled by marine mammals so that brings us to the next slide of marine invertebrates which
is cetacean evolution cetaceans are just marine mammals like whales dolphins and other porpoises
and during the eocene whales evolved and during the miocene dolphins evolved and it's just kind
of crazy to think that mammals had evolved from fish that had learned to walk on land and
become tetrapods and then millions of years later mammals that had become primed to walk
on land decided to go back into the ocean and become marine mammals and this diagram shows the
example of whales which started from animals such as pakistanis which is this first picture here
a land tetrapod that looked somewhat like this evolved into each one of these stages of whale
evolution before becoming what we know today as humpback whales and there's obviously a lot
more intermediate stages in between each one of these major stages but it's just crazy how much
we have in the way of whale preservation and all the stages that point to this which seems like the
most unlikely pathway but it is and it's so cool so moving on to terrestrial vertebrates like we
said earlier mammals were dominant and that's why the cenozoic is sometimes referred to as the age
of mammals however mammals were still small and rodent-like by the end of the mesozoic in the
beginning of the cenozoic however by the end of the eocene they had greatly diversified and
this is largely because of the fragmentation of continents causing more geographical isolation and
therefore more speciation so the four main mammal groups we will go over in this lecture include
marsupials primates ungulates and carnivores first marsupials and monotremes which are just mammals
that give birth to really underdeveloped young and then raise it in a pouch these were the only
two mammalian groups to migrate to the southern continents before they fragmented and this meant
that in australia marsupials and monotremes diversified and became dominant and still remain
dominant and by the pliocene north and south america had been joined by the panamanian land
bridge allowing south american marsupials such as possums to migrate north and now possums are
the most successful marsupial in north america moving on to primates primates had evolved by
the latest cretaceous in the late mesozoic and by the paleocene in the early cenozoic primates
had inhabited both north america and europe and they resembled lemurs however by the eocene
primates had evolved into old world monkeys and africa and new world monkeys in south america
which are just the terms we use to describe these two physiologically different groups of primates
the old and new has nothing to do with time but regarding great apes chimpanzees and humans
we all evolved from a common ancestor with old world monkeys moving on to ungulates ungulates are
just placental hooved herbivores these evolved by the eocene and the appearance of grasses in the
miocene allowed grazers such as deer horses and cows to evolve regarding carnivores such as dogs
cats bears etc these evolved by the paleocene so very early in the cenozoic and remained small to
medium-sized until the pleistocene so throughout most of the cenozoic these were small to
medium-sized however by the pleistocene a lot of things got mega-sized including not only
some of these carnivores but also some of the herbivores we were just talking about they evolved
into giant forms in the pleistocene due to cooler temperatures and this is because large bodies
have smaller surface area per volume and can more easily conserve heat and a couple examples
of some of these megafaunas include things like mammoths and giant ground sloths but unfortunately
many of these giant pleistocene mammals became extinct by the end of the pleistocene and it's
debated among researchers whether this is due to hunting by early man or whether this is due
to rapid climate change and vegetation change that had occurred at the end of the pleistocene
so moving on to plants we have angiosperms or flowering plants that we talked about last time
in the mesozoic video evolving in the cretaceous they then went on in the cenozoic to become
the dominant type of terrestrial plant and along with that they did a lot to contribute to
the evolution of pollinating insects and then in the myosin grasses began to expand and cover vast
plains of all continents and the rise in grasses like i mentioned earlier co-varied with a rise
in grazing animals because they have a mutually beneficial relationship so to give you the
paleontological summary of what happened in biological evolution during the cynozoic
we have the first primates evolve in the paleocene we have large flightless carnivorous
birds evolve in the paley scene then we have ungulate encitations evolving in the eocene
remember ungulates are placental hoofed mammals and cetaceans are marine mammals such as dolphins
and whales we have old world monkeys evolving in the beginning of the lego scene we have new
world monkeys evolved in the oligocene as well then we have large sharks such as megalodon
during the middle cenozoic then we have song birds evolve we have grasses and grazing ungulates
expand covariantly we have the first hominins in the pliocene and then mega mammals evolve in the
pleistocene like we talked about with the cooler temperatures and then we seem to be ending every
era video paleozoic mesozoic and the cenozoic with a mass extinction this is still under development
but it is largely confirmed that we are living in the beginning of the sixth mass extinction but
thankfully i'm not getting into that in this video this is just to mention the major events
of the cenozoic and we've done that so with that thank you so much for watching i hope this video
was helpful and you learned something about the geologic and biological history of the cenozoic
and i can't wait to see you all next time bye