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4.9. Heavily Armored Fish Without Jaws

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生命起源

伊利诺伊大学香槟分校

4.4（63 個評分） | 9.1K 名學生已註冊

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.

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4.4（63 個評分）

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CG

Mar 16, 2019

Enjoyed every minute of the course and learned so much at the same time!

SZ

Apr 11, 2017

Excellent lectures. Personal transformation observed while watching.

從本節課中

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.

4.1. Cycles of Radiation and Extinction7:33

4.2. Cambrian Explosion3:43

4.3. Cambrian Fauna: Origin of Vertebrates14:40

4.4. Burgess Shale Experiment5:38

4.5. Invertebrates: Successes of Life Without a Backbone18:26

4.6. Paleozoic Fauna12:06

4.7. Vertebrates: Successes of Life With a Backbone3:28

4.8. Evolution of Jaws and Perfecting Predation13:15

4.9. Heavily Armored Fish Without Jaws6:44

4.10. Fish Evolution: Hook, Line, and Sinker10:16

教學方

Bruce W. Fouke, Ph.D.
Director of the Roy J. Carver Biotechnology Center

腳本

[SOUND].

[MUSIC].

I'm Carly Miller from the University of Illinois, and

today we're talking about fish.

Alright, so to get a little taxonomical terminology going here,

we're in the phylum Chordata and the subphylum Vertebrata.

So most people probably have an idea of what that is, but

we have a few technical definitions that I'd like to go through real quick here.

So the physical traits that define a fish as opposed to a mammal or a tetrapod or

an amphibian, something like that, is first of all, the presence of gills.

So gills are kind of openings on the lateral sides of the organism that allow

for the, kind of the diffusion of oxygen and kind of the capturing of oxygen for

the usage of that organism.

Next they have vertebrae that are spool-shaped actually so

we have a nice, huge specimen here.

[LAUGH] And so what we're looking at here is kind of this overall circular shape.

And if I could turn it to the side even

you can see that it kind of pinches in on the side a little bit.

And so that's where we're getting our spool-shape, and

I'll turn it another direction so you can see here the spool-shape of that.

And so, what I want to show you here, just point out so you're saying, well,

overall that's not spool-shaped.

Well, what this is is actually is a neural spine.

So, the opening here coming through the middle is kind of a passageway for

the spinal cord really or nerves running down the kind of the vertebral column.

That's what this is for.

And so, how that differs from land animals is that we

have this spool shape, and so if you can think of them kind of connecting together.

They're almost just bumping together as opposed to being really interlocking In

their skeletal structure there.

So that's something that's unique to fish, and

what it does is it allows the fish to be more flexible really.

And so it can use its muscles a little bit better to swim through the water column.

So we have this spool-shaped vertebrae that's specific to fish.

Additionally, all fish are aquatic, that seems logical if you've ever seen a fish,

all right, so all fish are going to be aquatic organisms.

We have no amphibians here transitioning from land to water or anything like that.

So they're all going to be aquatic organisms.

Additionally we want to introduce to you the idea of how the shape of the organism

can translate to kind of its life strategy or the function of its overall body.

So we're going to talk about the fish triangle,

sounds exciting, it's pretty exciting.

>> [LAUGH] And so what this is,

is kind of a diagram that describes how you can observe the fish.

And then sort of place it on this diagram and then identify what it does.

So we'll kind of dive in here.

We have three groups of fish.

We have accelerators, cruisers, and maneuverers.

So I'll kind of walk through each of these and let you know which features to look

for when trying to identify what these guys do.

Accelerators, if you can imagine a fish kind of

lurking in the murk in a pond or a river.

And they kind of have to dart out and maybe catch their prey or

maybe escape a predator.

These are called accelerators, and how you can identify them, is

the back of their tail is actually kind of thick compared to the rest of their body.

So they're almost like a tube or a column shape.

And so there's no real indentation where that tail is but,

it's just kind of a really thick muscular tail.

And it allows them to do a really quick, whip motion and

they can accelerate through the water really quickly.

So we're kind of looking for almost like a shapeless fish,

kind of like a column shape for that fish to identify as an accelerator.

The cruisers, these guys are kind of gorgeous I think.

These are really kind of hydrodynamically shaped fish.

So they're really sleek, they kind of have that fusiform body shape,

they can cut through the water really easy.

And what cruisers are thought to be able to do is just go for

miles underwater in our vast oceans on Earth here.

And with very little expenditure of energy.

So these are our cruisers, and you might think of a shark,

actually they're a great example of a cruiser.

They have those stiff pectoral fins that just slice through the water.

Their bodies are really sleek.

And just a little flick of the tail every now and

then just sends them right through the water.

So these are our cruisers.

The last group of fish are the maneuverers.

These guys are wildly varied in their shapes of their bodies.

But what they primarily do is use their pectoral fins to kind of just pivot.

[LAUGH] Turn on a dime if you will, just pivot in the water and

they can just kind of maneuver into tight spaces.

They're not really built for speed [LAUGH] unfortunately.

But they definitely have a great function and

that's just pivoting around in the water.

They can kind of weave their way into a protective area perhaps.

So you're looking for these really,

just kind of nice pectoral fins that they can use to maneuver around.

Alright, so within the group fish we're going to dial into this superclass

Agnatha.

So gnath, g-n-a-t-h that refers to the jaw.

And anytime you put An or A before that in your Greek and

Latin roots there, that means the lack thereof, more or less.

So we have Agnatha here, and these are your jawless fish.

So jawless fish arose in the Ordovician, and

they still persist today in the recent.

There's between four and seven classes depending on taxonomy,

that gets a little dicey with your taxonomical hierarchies there.

But there's between four and seven classes of Agnathans.

So these are filter feeders primarily or detrital feeders.

And so if you think about it, if you don't have a really great functioning jaw,

it's going to be difficult to chew, for example.

[LAUGH] So they're usually kind of scooping up some of the detritus or

the sediment on the bottom of the ocean.

And kind of filtering it out and absorbing the nutrients that way.

Or they're kind of swimming through the water column and

maybe picking up some plankton or

something like that, the nutrients from the water column as they swim.

There are some, I think I've seen on a great program where they're actually

allowed themselves to maybe a whale carcass or something.

And they can almost tie themselves in a knot and pull themselves off,

it's kind of amazing [LAUGH].

And they actually do get a chunk of meat there, which is amazing.

They don't even have a job but they're allowed to get those types of nutrients.

So, I don't think I would want to work that hard to eat my dinner, that's for

sure [LAUGH].

But they've adapted very well there.

[MUSIC]

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