How did life emerge on Earth? How have life and Earth co-evolved through geological time? Is life elsewhere in the universe? Take a look through the 4-billion-year history of life on Earth through the lens of the modern Tree of Life! This course will evaluate the entire history of life on Earth within the context of our cutting-edge understanding of the Tree of Life. This includes the pioneering work of Professor Carl Woese on the University of Illinois Urbana-Champaign campus which revolutionized our understanding with a new "Tree of Life." Other themes include: -Reconnaissance of ancient primordial life before the first cell evolved -The entire ~4-billion-year development of single- and multi-celled life through the lens of the Tree of Life -The influence of Earth system processes (meteor impacts, volcanoes, ice sheets) on shaping and structuring the Tree of Life This synthesis emphasizes the universality of the emergence of life as a prelude for the search for extraterrestrial life.
4.10. Fish Evolution: Hook, Line, and Sinker
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来自 University of Illinois at Urbana-Champaign 的课程
Emergence of Life
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从本节课中
Week 4 - Paleozoic Life After the Advent of Skeletons
This week, you'll learn more about the Cambrian Explosion, which led to the development of external hard skeleton components at 542 million years before present. The initial successes of the invertebrates were shortly followed by the appearance of vertebrates with internal skeletons. Life then utilized these newfound evolutionary capabilities, beginning distinct cycles of radiation, diversification, and extinction, which define the three great Eukarya faunas of the Phanerozoic.
与讲师见面
Bruce W. Fouke, Ph.D.Director of the Roy J. Carver Biotechnology Center
Department of Geology, Department of Microbiology, and Institute for Genomic Biology
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So we're moving on to the next super class and so
these are the fish that actually do have the presence of the jaw.
They've developed a jaw to kind
of facilitate their feeding capabilities basically.
So the first class is the Placodermi, these guys are exciting [LAUGH].
They could have been major predators, some of these Placoderms and
the arose in the Silurian.
And they went extinct in the Devonian, maybe fortunately for us,
you'll find out why in just a moment [LAUGH].
But how you can identify a Placoderm is they're covered with these bony plates.
They have these really structural plates on the outside actually of their bodies
that kind of serves as an armor.
And their whole body may not be covered in this bony armor but parts of them were.
And so what we have here is the primitive jaw bone.
So these are the first ones with kind of the development of the jaw, and
they have sort of just a really sort of crude jaw structure there and
these guys were detrital feeders or carnivorous.
And so if you take a look at some of the really amazing specimens of placoderms you
can tell just from the head structure.
And the plate structure and that scary looking jaw that kind of comes up into
a point that these were major predators in the Silurian to the Devonian.
So we may have lucked out with that extinction.
[LAUGH] The next class is the class Chondricthyes.
This group is basically a cartilaginous fish.
Their skeleton is made primary of cartilage as opposed to a hardened bony
structure there.
These arose in the Devonian and they still persist today.
And you know these as sharks and rays, skates and chimera actually.
So these are all part of the group Chondrichthyes and again,
their lacking that bony skeleton.
But they have a cartilaginous support system there.
These are carnivorous as you probably know [LAUGH],
they're definitely carnivorous here.
And how you can identify a class Chondrichthyes or
Chondricthan from another class is that they have open gill slits.
So what that means then,
if you're observing the fish from, k ind of a lateral view.
You actually see stripes along that lateral side of their body, and that,
those are the open gill slits that you're looking for there.
And you'll see in just a minute that other fish actually have a little
covering called an operculum that cover up the gills slits in other fish.
So Chondrites, you're looking for
those stripes on the side that are those open gill slits.
So the next class is the class Acanthodii and
what these are are basically spiny fish.
So a lot of their fins,
they could have numerous fins along the sides of their body.
And they're supported by a long spine basically, kind of like sail or something.
They have this long spine that supports their fins,
and that's who you can identify as an Acanthodian.
They arose in the Selurian, and they persisted until the Permian, so
the PT boundary there, we had that great extinction event,
and these were one of the fish that met their demise at that time.
Acanthodians are also streamlined in their body shape, and
again they have the numerous fins that are supposed by a spine.
So these are kind of called the spiny fish [LAUGH], right.
The next class that we're going to get in detail
with here are the class Osteichthyes.
And so these were first to your bony fish.
Oste is kind of a term for bone really, our osteo and ichthyes is fish,
so osteichthyes, we have our bony fish here.
So they have a bony skeleton and they're the dominant fish that you see today.
So your river, your lakes,
your oceans these are most of the fish that you're going to see.
They rose in the Silurian and they persist today.
And they have the presence of an air bladder that helps them with their
buoyancy control.
So they can go up in the water column,
down in the water column with great ease because of this air bladder.
And we mentioned this earlier with the Operculum.
But this is kind of a distinguishing morphological feature
of the class Osteichthyes.
So they have this kind of bony structure that covers their gillS slits and
kind of protects the gills from any detritus or something.
And so they have this bony covering over the gill slits, and
that's called the Operculum.
So that's something to look for
if you're a little confused if you're trying to identify an Osteichthean.
You can identify that bony covering around the gills.
So within the class Osteichthyes, we have a subclass Actinopterygian.
Okay, so I know we're getting into a lot of taxonomy here, which is necessary to
try and group these organisms in kind of their like groups, if you will.
So within in the class Osteichthyes with a sub class Actinopterygii and
these are your dominant fish that you would see today.
These are called ray-finned fish.
What that means is coming off of the body they have delicate spines that
they're supporting the fins.
So these are ray-finned fish, examples would be a flounder or a trout or
a salmon, yum.
[LAUGH] And these are your ray-finned fish, your Actinopterygians.
So the second sub class in the class Osteichthyes,
again these are your bony fish, are the Sarcopterygii.
And these are your lobe-finned fish, so there aren't too many persisting today,
but the examples of those are the lungfish or coelacanth.
Which actually scientists thought until very recently that coelacanth were
extinct, and then they found one [LAUGH] and found it.
And so that's great because we can study these lobe-finned fish a little bit more
closely, if we have more examples persisting today.
And what defines them as a lobe-finned fish is that they have kind
of more robust support structures or supporting bones in their fins.
So we don't have these fine delicate rays like the ray-finned fish, but
the lobe-finned fish kind of have a fleshy [LAUGH] extension
that starts the beginning or the base of their fins.
So that's what you'll be looking out for, a fleshy pelvic or pectoral fin there.
And the reason why these are important and why we were so excited about having
the persist today is that it's thought that these are the ancestor to tetrapods.
So kind of those more robust beginning of their fins.
You can think that if you need a support structure
to grow those limbs that would ever support any weight on land and so
they think that this is kind of the predecessor of tetrapods.
So when considering these Sarcopterygians, these lobe-finned fish.
Again, these are thought to have been the ancestors to tetrapods.
And so what we want to look at a little bit more closely is what that
process would have had to have been to translate, kind of,
from the aquatic environment to the land environment.
So the transition to land, so what did fish need or what did organisms need?
Or what was the process that allowed that transition from being mostly confined
to a marine environment or an aquatic environment to the land situation here.
And so what organisms would have needed is the development of a support system,
a better support system.
So we talked about the fish vertebrae with our spool shape here.
And how it was almost like a bunch of spools stacked on top of each other that
again, allowed for great flexibility, but
maybe not as much support as a land organism would need.
So if we can contrast the fish vertebrate to those that were needed for
that transition to land the ones that tetrapods probably developed
were interlocking vertebrate.
So they have these spines basically that project across one another and
kind of interlock those vertebrate.
So it's providing more support, less flexibility.
So if you have more things kind of interlocking you're going to have less
flexibility in your vertebral column but definitely more support.
Additionally, there were fewer vertebrate in that transition to land period.
Secondly in the process to that transition to land dwelling.
Reproduction was still initially dependent on water, so
we still had that dependency on kind of the aquatic system for reproduction there.
A huge [LAUGH] evolutionary, I don't know, hurdle was the development of lungs.
So we went from being able to filter water or
capture oxygen out of the water column to actually being able to breathe air.
So that was a huge jump that occurred and allowed that transition to land.
Lastly, we have the different structure of limbs or
even the growth of limbs actually.
So we go from having fins to actual limbs that can support weight.
So that seems pretty obvious that you needed something to walk around on.
But that's one of the major features that had to occur before we had that
transition to land.
So with this transition to land,
we can now address a new superclass, the tetrapods.
So tetrapods these are four limbed animals.
So again if we could break down that term a little bit, tetra is four pod is limb or
foot perhaps but we have tetrapods here.
So these are four limbed animals and they're specialized for
walking as opposed to swimming.
So the major groups of tetrapods are your amphibians and your amniotes.
amniotes include your class avey's, you have reptilia and mammalia.
So your amniotes include your birds, your reptiles and
your mammals, and your amphibians were the first terrestrial animals.
And they were still dependent on water for reproduction and
arose out the Paleozoic, so we've thrown a lot of terms at you today.
[LAUGH] A lot of taxonomical groups and some key features there
to help you identify a fish if you run across a fossil or if you're snorkeling or
fishing, you could actually identify that fish a little bit more closely.
And we can kind of walk through geological time, kind of tracing how
these organisms evolved and changed in the marine environment.
And then they sorted, how that process started with that transition to land.
