[Warning: This episode contains material that may not be suitable for all audiences. Viewer discretion is advised. Seriously.]
[The Brain Scoop Grossometer: EXTREME - some blood, skin removal, visible organs]
This series of episodes is brought to you by the Field Museum,
the Harvard Museum of Comparative Zoology and the National Science Foundation.
- Hey! We're here at Harvard's Museum of Comparative Zoology with Dr. Kenneth Angielczyk.
- I am the Associate Curator of Fossil Mammals at the Field Museum of Natural History.
- And we're here today to do some experimentin'
on some dead animals. To learn more about those fossil mammals.
It's gonna be great.
Let's go!
[Wait!]
[Before we start the dissection]
[we have to explain synapsids.]
- In the episodes that we've been doing so far
we've talked a lot about synapsids but you might not know what they are.
So a synapsid is a member of a group of animals that includes living mammals
as their sort of living relatives
but also a number of fossil forms
that in some cases look very different.
And all of our different kinds of synapsids are characterized by one feature,
this opening back here, in the back of the skull,
just behind the eye socket.
That's an area where jaw muscles attach to the skull
and all synapsids have those.
So if you compare an animal like this,
this is Eothyris, one of the most primitive synapsids that we know about,
to a living mammal,
you can see the skull looks very different.
But we have that same synapsid temporal opening back here in this skull the way we did in Eothyris.
So this is an animal called Massetognathus,
which is a more derived, or a more advanced kind of synapsid.
You can see that it has a skull that is much more similar to our living mammal.
Synapsids have undergone a massive amount of evolutionary change over the course of their history,
and so there is actually very few features other than that,
that you can point to in all synapsid specimens.
- And that's kind of why we're here today, right,
so we're going to be looking at some of the changes
in the other parts of the skeletons of these animals.
And primarily what is it that we're going to be looking at?
- We're interested in the evolution of the backbone of synapsids.
So, living mammals have very distinct vertebral columns or backbones today
that have lots of different regions
and they have very specific functions in each of those regions.
And if we look at more primitive synapsids,
they have a much more uniform backbone or vertebral column.
We can only get so much information out of the fossils.
We need to look at some living animals
that have their soft tissues, like muscles, attached to the backbone or vertebral column.
And what we can do is learn about how the backbone functions in those animals
and then go back to our fossils and essentially model
how those vertebral columns would have been working
when they had all of their soft tissues attached.
- So, we're going to the Prep Lab.
[43 minutes and half of a sandwich later]
We are here in the Preparation Lab at Harvard's Museum of Comparative Zoology
with Dr. Katrina Jones. Katrina, what is it that you do?
- Hi Emily. I'm a researcher here at the Museum
and I study the anatomy and evolution of mammals.
- And that is what we have here in this bag in front of us.
- Exactly, yeah.
So this is a fisher cat.
And today we're going to be dissecting out its vertebral column
so that we can do experiments on it.
- But it's not-- it's not a fish, kind of,
it's a derived fish, and it's not a cat,
it's like a big ferret.
- Yeah, kinda like a giant ferret, otter.
So the skin was taken off and has gone
to be used in our collections and all the organs have been taken out
but now we need to remove the head,
the limbs, and get down to the vertebral column
which is what we're interested in.
- Let's do it!
- Should I grab this end... - Yeah, you can grab and pull it out!
- Oh, oooh! Oh, boy!
You can kind of already-- you-- if I'm gonna hold this guy up--
you can already sort of see--
Whoops, now it's bleeding on the table.
[laughter]
um, that the-- the ribs, the thoracic vertebrae and all the muscles that attach to them are kind of
contained in that area and then there's nothing here at a lumbar region.
- Yeah, so mammals actually have a region that's free of ribs called the lumbar region
and that's different than some of the ancient mammal ancestors
that you were looking at earlier, the synapsids which had ribs
pretty much all the way along their--
their, um, trunk.
- Yeah, then you can kind of see where like that would've-- that would've
perhaps inhibited a bit of movement,
a range of motion down there. - Yeah, definitely that's one of the factors,
but also the individual shape of the vertebrae
and how they fit together is really important for determining how much
mobility can happen at each joint
and that's what we want to get a handle on today.
Okay, so you want to take-- we'll start with a forelimb.
- He pooed on me.
Yeah, sure. - Yeah, he probably did poo on you. Sorry about that.
- That's okay. - It happens.
First thing we're gonna do is we're going to remove a forelimb.
So what we're going to do is cut down the midline along these –
this is the pectoral muscles. So...
loosen this up...
release that connection...
- Well, that's, wow, that's cool. So I can actually see the different muscle that you just cut off.
- So, yeah, so that was the pec major that we just, we just...
we call it "retracted," just retracted it,
and so now I'm gonna cut through this connective tissue of the neck
so that we can remove the connection with the forelimb there.
- So what is it you're kind of cutting the fascia between the muscles?
- Mhm, so some muscle attaches into bones to move bones
but some muscles actually attach to other muscles
and they do that by attaching to these like thick sheets of connective tissue
that we call fascia.
And that sort of helps them to move.
And it's kind of cool when you think about all the different things
that mammals do with their arms, like bats flying
or like, you know... Wales swimming... - Wales swimming...
- Yeah, exactly. Like a brachiating primate swinging through the treetops...
There's a lot of different functions. - A lot of googling, a lot of facebooking...
- Mhm. Exactly.
Yeah, so, this muscle serratus ventralis actually has muscle fibers
that insert in each rib, so it kind of looks jagged
and that's where the name comes from.
- So it goes all the way from the back to individual ribs.
- Mhm. Then this is quite cool here. This is what's called the brachial plexus.
So this is a really dense web of nerves,
so this is how you get nerve impulses in
to move the muscles and sensation out. - Wow.
- So I'm actually going to cut through the brachial plexus.
Sorry brachial plexus!
- Oh nooo! - Off you go.
- Now he can't use his arm. - Yeah.
Very sad. - 'Cause he's dead. Also that.
- Notice how I'm dissecting a lot with my scissors.
- Yeah.
- Even though it's called dissect, ideally you just want to split tissues
along their natural planes more than actually cutting through tissues.
- So you're just, you're just separating things.
- Separating things, yeah.
- Whoa, this looks nothing like an arm anymore.
- Yeah. It's easy to get disoriented
once you have it detached from the trunk.
- Yeah, it's also missing his little hand.
- Okay, so we're gonna work on this other limb now.
Maybe if you wanted to have a go at doing something, you...
- I'd love to!
- This is the pec muscle, which is here, which sort of flexes the arm like this.
So what you're going to do is detach it from-- from the trunk.
Start with the scalpel and then when it starts coming loose
you can actually just get in there with the scissors.
- So like that? - Mhm.
- And then use the scissors... - So then you can... I'll take that...
And you use the scissors and you kind of pull it towards me
to get some tension and then you sort of...
- Did you do... I'm trying to mimic your technique.
- Yeah, you sort of spread apart --
to feel how the tissues just spread along the natural plane
and then where there's a connection, you just snip.
- Like right there?
- Yeah. So-- Yeah.
So that's where the muscle is actually inserting onto ribs.
So we have to cut that.
- This guy has an obscenely thick neck.
- Yeah. I feel like this is an aggressive, really muscly male that we're...
- Like he was probably getting some stuff done.
- Mhm. Probably didn't want to mess with him.
- No.
- Okay, so we're definitely making progress now.
- What's holding it on down here still is the...
the serratus muscle. Exactly. - Serratus muscles. Yeah.
- And what we have over here... We saw earlier...
- The connective.. - The brachial plexus!
- Yeeah, that one!
- That's amazing. They are-- I mean you call them cables.
They are like cables.
- Mhm. It's like data cables. - Data cables.
Communicating information from the brain to the--
-If i spend too much time thinking about that,
I just have an existential crisis.
Like, oh gosh, there are so many things happening
in my body right now that I don't think about!
And then I'm cutting them! Oh noo! Okay. - Ooh, there we go.
There's actually like a web of muscle that runs all the way of the neck called platysma
and it's what sort of allows you to op--
one of the muscles that helps open the jaw.
It's kind of cool because whales have really giant ones.
- Whales?
- Mhm. Helps them to push the water when they gulp feed.
- Like baleen whales?
- Mhm. People think dinosaurs are cool lbut really mammals are so much cooler.
- Hear that, guy?
You're gonna start some stuff in the comments of this video.
- Okay, so there's only the serratuses left
so what I'm gonna have you do
is we're gonna put it like that,
you're gonna hold it and then you're just going to run your scalpel...
- Sure.
- And just cut that... And then that's gonna bring the limb off.
- Just like that. - There you go. You can have a look.
- Another limb. Two of 'em.
Wow.
- Okay, should we do a head next? - Yeah.
Lots of important things connecting the head and the body going on here.
- Yeah. I mean, I would hope there were important things connecting the head to the body.
Otherwise I'd be a lot more likely that it could... fall off.
- Yeah, that would be... that would be bad news.
So we're working our way through these layers of muscles,
hoping to get to the joint that connects the head and the neck.
It's called the atlanto-occipital joint.
- There's just one joint?
- Mhm.
- That attaches the head to the neck?
- That attaches the head to the neck. Exactly.
- What happens if you cut it?
- Then your head falls off. - No way.
- You'll see it's quite hard to get to. - Okay.
We're still working our way through muscle layers trying to get to it.
So... it's not something that's gonna happen overnight.
So you don't have to... - Okay.
- Don't have to lose sleep over it, Emily.
The top two vertebrae mammals--
The two that are closest to the head are really really really weirdly shaped.
So that the one that connects the head and the neck, the atlas,
only allows movement like this [nods]
and the one beneath it, the axis, only allows movement like this [shakes head].
So it's like the yes-joint and the no-joint.
And they work together to produce all the other movements.
- Like a bobblehead.
So you've got a lot of these neck muscles kind of dissected off.
- Yep. And we can actually start to feel the joint between the head and the neck
so if you just pinch with your thumb and your forefinger right there
and I'm gonna do a yes-action with the head
and that's where you're feeling is the atlanto-occipital joint moving
and that's what we're gonna try and cut through to separate the head off.
- I mean it's probably for the best that it's difficult for your head to be removed.
- Almost through.
Okay, I see. Ready?
- Yes! Get it!
There you go!
Ooooh! - That's fine.
- And it lost its head.
There we go. - So the head and all of the neck muscles.
- It's somehow more disturbing with just like the neck muscles as a part of it.
"How's it going, Katrina?" - Very cool.
- I'm good, thank you, dead fisher head.
[untintelligible] - Yeah, there we go.
We'll just leave this here.
- Okay, I think it's time for you to do the honors.
Remove the baculum.
- Alright. - Since you're wearing the baculum earrings.
- I'm-- Yeah. - So you're just gonna cut along this connective tissue here
so... Mhm. - Here?
I've never so surgically clipped a penis bone off.
- Great. And one on that side too.
- Wow.
I feel a bit... - We can keep that, we can keep this as well.
You know, someone might be interested in studying it one day.
You wanna cut through the urethra?
- Here we go.
- There we go. - Keep going?
- Yeah, just... just take it all off.
- Take it all off.
- There we go. Perfect.
- Alright. Well...
Just lay that out there.
- All done. - It's the bits.
This just saline solution, we gotta keep those muscles hydrated.
Hydration's important even post-mortem.
- So this is like the equivalent of hamstrings in humans
- It's kind of the groin area. - Mhm.
So I'm just running the scalpel along the pelvis
and cutting all the connections.
Okay, and then we'll cut the quads. - That's huge.
- Okay, so now all that's left connecting is the head of the femur
into the acetabulum, which is the...
- So that ball and socket joint... - Ball and socket joint.
I've just cut into the opening of the joint there.
- I can see it, yeah.
- So now we're just cutting the ligaments. Okay.
So we've opened up...
the capsule of the joint, the-- So-- - Ooh.
- This is the head of the femur.
And that fits in here into the acetabulum, and see...
I put my probe under here, there's like a connection.
- Yeah. - That's called the ligament of the head of the femur
and that actually keeps the femur in its socket.
So if you want to do the honors, this is gonna sort of allow the whole thing to just pop open.
You take the scalpel and cut through the ligament right by where my thing is
and it pops out. Once that's cut.
- That's it. And then the femur's so tiny compared to all the muscle that's around it.
I mean the bone is just not even as wide as my pinky finger.
And then all these other muscles are just coming in and...
- Yeah. - This is a powerful animal.
- Okay, you wanna have a try with the other limb?
- Sure!
- Yep.
- I can feel the bone. - And then if you wiggle...
You can feel... Okay. So you already got to the...
to the joint there. - Okay!
- And now we're gonna open up the joint capsule.
So can you-- want to put your finger and feel where it is?
- The joint-- Oh, it's right there!
- Yeah. Feel it? - Yep.
- Great. So then... Cut where you felt the joint moving.
- And you just keep cutting around? - Yeah, so you just cut into the ligament, the...
- There it is!
I just don't want to cut your finger.
Right there. - Right, right, right.
- That's good. - Whaa, I did it!
- There we go! - Aaand the leg is off.
- The leg is off. Right.
- We'll just put that over there, make sure we're hydrating those legs.
- And so now what we have left is the vertebral column,
the pelvis and the ribs.
And so before we do our experiment, we'll also remove the pelvis
and we'll remove the ribs.
That takes kind of a long time so... - Yeah.
- We might skip to the... to the next specimen. - Yeah.
- 'Cause we already have it, like a cooking show.
Already done. - Mhm.
- So this is the one that we just dissected.
- So the next step would be
to actually remove the rib cage and to start cleaning off some of these muscles.
These are called epaxial muscles,
which means muscles that run on top of the spine.
So I've started to do that in this smaller fisher
that we have from earlier
and one thing that we can see here which is super cool,
notice how there are really really long strips of muscle
running all the way down the back.
And this is kind of a neat mammal feature.
So if you were to look at the epaxial muscles of, say, reptiles,
those-- the muscles would be much shorter.
But we have these really long-- they call them tracts of muscles.
So that when the spine wants to flex like this,
they can contract and they can form the flexion and extension action
that we know is really important when mammals are using their asymmetric gaits
like galloping and bounding.
So this is sort of before and then after we remove the ribs
and all of the muscles, we end up with something like this.
And then notice how flexion, extension is happening a lot here
but if we do twisting, there's no twisting happening down here
and that's because the vertebral joints down here lock together
and prevent twisting
whereas those up here can move by each other.
- They-- Yeah, they help enable the twisting. - So you can sort of see them twisting.
- So do you... Do you hypothesize that those early synapsids like dimetrodon or edaphosaurus,
that their spine was more like the lumbar here
or more like the thoracic?
Like, was it more or less flexible?
- It was less flexible, but when you look at the vertebrae,
they don't look quite like either thoracic or lumbar.
From the shape of the joints, we suspect
that they might have been able to do more lateral flexion
but we don't think that they were able to do any of this...
- So they kind of moved back and forth - ... bending.
- like a lizard. - Mhm. Exactly.
And we hypothesize... - And they weren't galloping.
- ... that evolution of specialized joints which allow bending,
flexion, extension like this,
might be related to the evolution of asymmetric gaits of mammals.
So the division of the vertebral column interior regions
is controlled by a set of genes called the hox genes.
- So it's like, it was the evolution of the genes that enabled the...
the evolution of the morphology of the spine. - Mhm.
Well, yeah. I mean it's the genes which evolve and it's nice here
because we have such a direct link
so we can clearly see that where a particular gene is expressed,
that's where a particular region forms in the adults.
So if we can measure the presence of different regions
based off of vertebrae in the fossil record,
we can infer the expression of genes in animals that lived millions of years ago.
- So you're doing genetic research on animals that are like 200 million years old.
- Indirectly, indirectly, by mapping out how regionalization has changed through time.
- That's pretty exciting.
That's pretty cool stuff.
- Very exciting.
- Welcome to the 21st century. Awesome.
[It still has brains on it.]