Diversity of Bodies & Sizes (but mostly crabs): Crash Course Zoology #3 - Free Educational videos for Students in K-12

Diversity of Bodies & Sizes (but mostly crabs): Crash Course Zoology #3 - By CrashCourse

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00:0-1	Thank you to kiko for supporting PBS as a wildlife
00:03	Ecologist . I've spent hours following bear tracks around Nevada
00:07	and new york , hoping for a glimpse of these
00:09	furry four legged foragers . Though if we look across
00:13	the whole animal kingdom , we find all kinds of
00:16	bears . Bears with four legs , eight legs ,
00:19	six legs or no legs , Some weighing over £1,000
00:24	and others that are microscopic with very few or even
00:27	know organs at all . Even bears that can walk
00:30	on pause or suction disks fly or sway in the
00:34	ocean currents . I'm talking about grizzly bears , but
00:38	also water bears , bear moths and poor bearers .
00:42	It's not always clear why such a diverse array of
00:45	animals became associated with an old english or proto german
00:48	word for a brown creature or why we thought that
00:51	poor bear upon was a good idea like water bears
00:55	look kind of like eight legged Grizzlies , but bear
00:58	moth spend most of their lives as fuzzy caterpillars and
01:01	poor bearers is a translation for the phylum peripheral to
01:05	that just contains sponges . None of those look like
01:08	bears , turns out bears come in all sorts of
01:12	sizes and body plans and very a ton in how
01:15	they move and we'll see that even though animals can
01:18	look very very different on the surface , there are
01:21	surprising similarities and how they've evolved to solve major problems
01:26	like how to support and move their bodies . I'm
01:29	Ray Wynne Grant and this is crash course psychology ,
01:41	An animal's size and body plan , shape their entire
01:44	lives , what they eat and how much how they
01:47	move , where they live and their place in their
01:50	environment . Like the Grizzlies and black bears I study
01:53	carry their £1,000 of muscle and for around on four
01:57	paws they spend most of the fall fattening up for
02:00	the winter and unlike most four legged mammals , they
02:03	can stand up and sit like us . But animals
02:06	come in a huge range of sizes and most animals
02:10	are actually very small compared to us . A human
02:13	like me weighs about 59 kg , which is about
02:16	59,000 times more than a house spider , And a
02:20	blue whale can weigh 100 million times more than that
02:24	spider . Even the animals that get big as adults
02:26	and by big , I mean more than a couple
02:29	inches long , spend a good part of their life
02:31	being very small , undergoing drastic changes in body shape
02:36	and lifestyle as they grow . For instance , some
02:38	fish amphibians , reptiles , sponges , corals and molluscs
02:43	gain both weight and length for their entire lives .
02:46	This is called indeterminate growth . Some animals have periodic
02:50	growth , alternating between growing fast and slow or not
02:54	at all . Like animals with exoskeletons are hard outer
02:57	skeletons during molting . When an animal sheds its old
03:01	skin or shell , these animals actually grow their new
03:04	exoskeletons under the old one and then inflate it with
03:07	fluid before it eventually hardens into their new larger size
03:11	. Other animals experience predetermined growth and stop growing when
03:15	they hit a more or less maximum size , but
03:17	once any animal reaches a certain size , they hit
03:20	some physical limitations . Animals thicker than about one millimeter
03:25	need extra plumbing like a cardiovascular system to move oxygen
03:29	and waste around their bodies . Bigger animals also need
03:33	to eat a lot more to feed their thousands or
03:36	millions or even trillions of cells . And big animals
03:39	need more structure like bones and muscles to support them
03:43	as gravity polls on all their weight . That's why
03:46	the biggest animals the whales live in the ocean .
03:49	The water supports their bodies instead of legs growing also
03:54	means making new tissue and animals have evolved a few
03:57	different solutions . Many clade or groups of animals with
04:01	a common ancestor , add more cells . Other animals
04:05	grow by making each cell bigger , but keeping the
04:08	same number of cells . A trait called usually other
04:11	animals like Akina terms use a weird process called maximal
04:16	indirect development and they grow their adult form out of
04:20	a special ball of cells that have been set aside
04:23	. The larval or immature form is mostly made up
04:26	of cells that already have all their development planned out
04:29	for them and a set amount of growing they're going
04:31	to do . But in the larvae there's also a
04:34	small amount of set aside cells that take over once
04:38	the other cells get old and die off . Then
04:41	the ball is set aside . Cells develop into the
04:43	many cell types needed to create the adult form ,
04:46	but the growth that probably seems the wildest to us
04:49	humans is colonial growth when animals get bigger by adding
04:53	more complete individual clones . These colonial animals like siphon
04:59	offers and brazo ones are made up of tons of
05:02	little clones that work together , sort of like how
05:05	a school of fish can coordinate and swim together .
05:07	But even though animals can grow and completely different ways
05:11	, a lot of them can look quite similar .
05:14	Basically some body designs show up again and again ,
05:18	distantly related animals , evolving similar traits independently is called
05:22	convergent evolution and it usually happens because different lineages face
05:27	similar problems in their environment or take on similar ecological
05:31	niches . One of the most stunning examples of convergent
05:34	evolution is Carson ization , a process that zoologist Lancelot
05:38	, a bora dale , famously defined as the many
05:41	attempts of nature to evolve . A crab . Let's
05:45	go to the thought bubble . It all started with
05:47	the psych Lloyd's , a group of arthropods that lived
05:49	from the carboniferous to the cretaceous era . They have
05:53	that flat crabby shape , a small abdomen and a
05:56	bunch of walking legs , just like today's crabs .
05:58	It wasn't until the early Jurassic period , tens of
06:02	millions of years after the first cyclades were around that
06:05	, the first of what we think of as real
06:07	crabs , members of infra order brock europe showed up
06:10	a little after that is when the fake crab started
06:13	showing up with things like this early squat lobster all
06:17	looking very crabby and the crab fed kept happening over
06:21	the Mesozoic era . Now we have hermit crabs ,
06:24	harry stone crabs , horseshoe crabs , crab lice ,
06:27	and king crabs , none of which are descendants of
06:30	break your ins and so none of which are actual
06:32	crabs . One way you can tell is that most
06:35	fake crabs have six walking legs instead of eight ,
06:39	But why ? Probably because crab is a great body
06:43	plan , it's tough and adaptable to life on land
06:46	or in water and they're flat and round bodies fit
06:49	into more places than a long lobster tail might .
06:52	So crab shaped animals have more evolutionary fitness , which
06:56	means they tend to survive and pass on their genes
06:58	more than non crab shapes . The real kicker is
07:02	that the psych Lloyd's , the ones who first came
07:05	up with the crab body plan , died out in
07:07	the cretaceous era at a time when there were real
07:10	crabs and fake crabs all over the place . One
07:13	hypothesis is that the psych Lloyd's got out competed out
07:17	Carson ized out crabbed by both the crabs and the
07:21	crabs we know today . Thanks thou bubble , convergent
07:25	evolution pops up when a similar solution works in different
07:28	environments for different lineages , animals bodies evolved to better
07:32	suit of function , even if it means turning into
07:35	a crab . Now , it's important to remember that
07:38	evolution has no set goals . Besides passing on genes
07:42	, there's nobody plan plan . Often a simpler form
07:46	can perform a function much better than a complex one
07:49	, civilization evolving ahead and in some cases decentralization or
07:55	evolving to not have a head are good examples of
07:58	how sometimes simpler is better , but like what is
08:02	ahead really . Heads collect the sense organs needed to
08:06	perceive the world , the mouth and the nerve cells
08:09	that coordinate them in front of the animal , where
08:11	they can react quickly to danger . Or pray .
08:14	We know that the ancestor of all the animals that
08:17	can be divided into symmetrical halves , which are called
08:19	by literary ins further bilateral symmetry had ahead . And
08:23	most animals are billet terrians , but some animal groups
08:27	have lost their heads literally because they became less useful
08:31	like bivalve molluscs like clams , Arbilla terrians that stay
08:36	rooted in one place and just filter water through their
08:38	mouths to catch bits of food , which you don't
08:41	really need a dedicated head for . So the head
08:44	pieces , like the central nervous system and sensory organs
08:47	are distributed around the clams body . Other animals with
08:51	radial cemetery have bodies at a symmetric around a central
08:54	point . Most of these are kind of terms ,
08:57	and with the exception of sea cucumbers , they don't
09:00	have anything resembling a head , butt heads or no
09:03	head bilaterally or radio lee symmetrical . For all these
09:07	forms to be possible , they need some kind of
09:10	structural support . Otherwise everything turns into a blob of
09:13	cells file um Core data solves this with a note
09:17	accord , a flexible rod that supports their body as
09:20	embryos and sometimes as adults . The no decor develops
09:23	in the vertebral column or spinal column invertebrates , which
09:27	is where they get their name . All other animals
09:30	are invertebrates and they have several different types of support
09:33	, which is part of the reason they don't form
09:35	just one file . Um In general , skeletons are
09:38	frameworks that support shape and protect soft tissues . When
09:42	you think of a skeleton , you probably picture an
09:44	endo skeleton , an internal support structure made of mineralized
09:49	tissues , vertebrates have rigid endo skeletons made of bone
09:53	which gets its hardness from large amounts of calcium phosphate
09:56	. Invertebrates have endo skeletons made of other materials ,
10:00	like a kind of terms such as sea urchins have
10:03	endo skeletons made from fused plates called obstacles , which
10:06	are made of calcite . Even sponges have an endo
10:09	skeleton made of the flexible protein sponge in and spiritual
10:13	crystals . But some sponges also secrete an outer skeleton
10:16	from cells on their skin . Which leads us to
10:19	exoskeletons , skeletons that sit outside the rest of the
10:22	body mineralized . Exoskeletons show up in at least 18
10:26	plaids including some sponges , kind of germs , corals
10:30	and molluscs . Other animals based their exoskeletons on long
10:34	chains of sugar molecules called poly sacha rides arthropods like
10:38	insects , crustaceans and Iraq needs use chitin to make
10:41	their skeletons . The third type of exoskeleton is actually
10:44	made of water , which sounds rather flimsy . But
10:48	hydro skeletons work because water is in compressible . You
10:52	can't realistically squeeze it into a smaller volume , like
10:55	you could a marshmallow . So as long as animals
10:58	can contain water in a tube or sack , they've
11:00	got the makings of a stable structure . Invertebrates like
11:03	worms and jellyfish use hydro skeletons to support their very
11:07	flexible bodies . It's an especially great adaptation for living
11:11	deep in the ocean . Endo . Exo and hydro
11:14	skeletons plus heads when animals have them are what gives
11:18	animals their shape . But animals aren't statues like you'd
11:22	see in a museum they move . And how animals
11:25	move also influences how they look . Some animals move
11:29	with the help of their environment , spiders cartwheel down
11:32	sand dunes and velella velella . A jellyfish like colony
11:36	of animals use a sale to catch the breeze .
11:39	These animals needed to evolve the right instincts and structures
11:42	to take advantage of their surroundings . Other animals move
11:46	under their own power with the help of cilia and
11:48	muscles , cilia and flow gela , our hair or
11:51	tail shaped parts of cells that beat in coordinated waves
11:55	to paddle microscopic animals forward . And how these tissues
11:59	connect with the skeleton influences how an animal moves .
12:02	Moving an entire skeleton at once is harder because they're
12:06	usually rigid and heavy . Most animals solve this by
12:09	turning their skeletons into a bunch of levers that pivot
12:12	around joints as pairs of muscles contract and relax .
12:16	Even animals with hydro skeletons use muscles to control fluid
12:20	pressure and bend their body . Animals move their bodies
12:23	in all sorts of ways , balancing where they want
12:26	to go , how quickly and how much energy it
12:29	will take . In fact , there's a whole field
12:32	of zoology called biomechanics that's interested in how mechanical principles
12:36	guide how animals are shaped and move . But all
12:39	this moving and growing takes a tremendous amount of energy
12:42	and we'll talk more about where animals find that energy
12:46	in our next episode . Evolution is a wild journey
12:49	that brings us so many different animals with a huge
12:52	array of bodies and sizes that is until everything turns
12:56	into a crab . Thank you to kiwi co for
12:59	supporting PVS kiwi coz mission is to inspire kids to
13:03	see themselves as makers by providing them with the tools
13:07	and a foundation to become creative problem solvers and critical
13:10	thinkers . The crate includes everything you'll need in the
13:13	box and covers a wide variety of topics from month
13:17	to month , like art , science , Engineering and
13:19	geography inside . You'll find the project materials of course
13:23	, a blueprint , which are the instructions written for
13:26	kids and a magazine containing lots of additional content and
13:30	experiments . Go to kiwi co dot com slash crash
13:33	course or click the link in the description for more
13:36	information . Thanks for watching this episode of Crash course
13:39	ideology , which was produced by complexity in partnership with
13:42	PBS and Nature . It is shot on the team
13:44	Sandoval Pierre stage at porchlight studios in santa barbara California
13:48	and made with the help of all these nice people
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