Form and function

One of the key things that we are going to look at this module are how can we explain the diversity of vertebra.

the diversity of vertebra. What is it that's so special about vertebrates that they are almost everywhere?

almost everywhere? They are very diverse in form and in size and in habitat. So how can we explain this explosion of the vertebrates? And we're going to do it by looking at how they develop, how they evolve, how they grow. So I'm going to start off with this basic concept that very often you'll find that the morphological features that you see in vertebrates and this also applies to a lot of invertebrate taxa as well.

They have common origins and one of the best examples of this is your hand and your arm, the pentadactyl limb, five digits. Generically you can break down your limb into a stylopod which is the upper limb, the zuga part which are the two bones in the lower part of the limb and then the outer part which is the hand or the ankle, the foot.

So this applies, this generic description applies to both your forelimbs and your hind limbs. What do we mean by common homologous origin? They are evolutionarily descended from a common ancestor and we can look at this during development and during evolution by looking at the fossil record. So on here you can see the limb buds of the developing chequembryo and the blue stain you can see at the end is a key structure in that limb bud called the apical ectodermal ridge. Don't have to worry about that for a moment, we will come back to it later. If you look at this, this is the skeletal structure of a bird wing. This is the skeletal structure of a bat wing and here's a human hand. Although this has only got three digits, the evidence tells us that it is descended from a five digit origin. So we have a common homologous genetically evolutionarily descendant relationship. So many structures that you look in vertebrates are common to the vertebrates and they are derived from a common homologous ancestry.

So we talked about the hand but we could also say the seven cervical vertebrae of a vertebra is really a very very common feature. So although the giraffe has an enormous neck, it's got seven vertebrae just like you in the cervical or the neck region. So what we're seeing are variations of the feet or modifications of design and engineering. We can account for a lot of the morphological difference. What we're not seeing is de novo or brand new evolution of features, not very often.

evolution of features, not very often. So when we've got these related but very different morphologically speaking structures, how can we quantify that?

How can we describe them accurately? How can we measure those differences?

How can we measure those differences? In other words, how can we quantify what has been going on? So ask the name the most significant book about biology ever written in English and I think most people would put their hands up and say Darwin's origin of the species. Yeah it's pretty much taken for granted.

Yeah it's pretty much taken for granted. But what would you say is the second most significant book? Anyone like to suggest some ideas? You have read books on biology, haven't you?

Any standout ones?

standout ones? Do read. Okay read some of these books because they will open your mind, literally.

The answer to this question in 1917 or the years after 1917 would be a book I am very much doubt you've ever heard of and it's Darcy Thompson's On Growth and Form and there's Darcy Thompson I think it was at St Andrews and there's a really interesting review about this guy. Just read it.

it. It's an interesting read. So Darcy Thompson's Growth and Form. Well what was so special about that?

that? What he did was develop a method to describe these differences that I've been talking about in mathematical and geometrical terms.

in mathematical and geometrical terms. He was able to quantify this and present it as scientific evidence. Whereas before he'd say oh yeah seven vertebrae that size, seven vertebrae that size, he was able to put that within a scientific framework. Biological structures have to conform to laws of physics as well as genetics and natural selection. So if you're going to have a neck that is 10 foot long five but can you get a neck that is 300 foot long?

long? No probably not because then you're you're going way beyond the laws of physics. There are constraints upon what can happen.

So you have to conform to the laws of physics as well as genetics and natural selection and he enabled people to get this holistic picture. So variations of it on a theme.

Modifications of design and engineering. This is a small fish fry. You can just about see the remnants of the yolk sack here underneath them and pretty much fish when they first hatch all look much the same. Okay and yet from a common basic starting point looking like this you can get fish with these strange morphologies.

So this one okay with the very long snout is well how about this one with just one long one with one long lower jaw. Okay so you can see there's a lot of similarity here but how do we explain this animal having such a short upper jaw and this one having such a long one and how can we describe the processes that are going on behind them. They have common homologous embryological origins and morphologies.

That's the starting point and then they go a little bit bananas and how do we describe these processes. So one of the key things to one of the key terms you need to get hold of to understand this is the idea of isometric.

Isometric is the same. Metric is measure.

Same measure. So if you compare the body morphology of an animal this is of some newts and these are different species of newts but you can see if you just scale these up they are pretty much like a graded series they seem to merge into one another seamlessly. They are isometric in regard to one another. What does that mean in strict terms? Well it means that maybe the ratio that size the head to the size of the limb or to the size of the thorax or to the size of the whole body is constant for each animal. They're a series. Equally you can say this is a growth series that this is a juvenile and this is the adult. Both instances are known.

So this is a demonstration of isometric.

Same relative proportions. So when you look at these two dinosaurs we've got Banderacta and Sinornithosaurus underneath it. We can say at first glance they look relatively isometric yet one is twice the size of the other. If you look in close detail yes there are things that are different but broadly speaking you'd look at that and you would say they're pretty similar. So when we're looking at growth or evaluationally changes in morphology we can be thinking about size and scaling.

we can be thinking about size and scaling. What if they're not isometric to one another? What's the term we use then?

the term we use then? The term is allometric so different measurements. So in comparison of body morphology if relative proportions of body parts are different they are allometric with regard to one another.

So in this case this is very clear this is an allometric relationship in comparison to that.

The upper parts of the mouth here is allometric in regards to the upper part of the mouth.

And to give you an artificial idea of what I'm talking about what I've done is lock off the head of here and paste it onto this body here.

So now this head is allometric in relationship to this series here.

relationship to this series here. Can you nod if you understand what I'm talking about? Yeah good. How do we measure this?

How do we measure this? And this is one of the things that Darcy Thompson is famous for. He came up with the idea of using Cartesian analysis and this enables you to map the process of the change. You can do this between the juvenile and the adult or you can do it as the animal grows and so you can measure the way that the different parts of the animal grow. So this is the starting point and you can see there's a grid here and you pick out key morphological features and then you do another map on an adult specimen and you mark out where they are with the sizes of the adult.

And you can see you get this kind of spread and this shows you where the most growth or change has occurred.

So this gives you a handle on what is starting to happen here. It doesn't give you the whole picture but in 1917 this was breathtaking. Where is the predominant region of allometric growth in the human head? Top is a fetal skull, below is yours.

So where is the predominant region of allometric growth? And I expect people to answer.

And I expect people to answer. Okay this is an rhetorical guess. Teeth?

Teeth? Yeah an actual fact I don't know whether you see teeth at this stage but they would normally be well embedded in the jaw.

be well embedded in the jaw. Yeah it is the jaw which includes the teeth. So that's much smaller than that. Yes there's a difference in other areas as well but that is the predominant region. Why?

Why? Haven't got any explanations? Yeah from soft milk to hard food.

Soft milk to hard liquid diet.

Okay uh yeah it's interesting to do with being able to give birth easier.

Yeah that's the generally accepted reason. You're not necessarily wrong okay but you've got to think of the broad picture here. It's a lot easier to give birth to an animal that is smaller. So give birth to an allometric infant. Now from the known start and end points you can predict intermediate stages. Hopefully that is clear.

Okay so this is a fish. The operculum is the flap which goes over the gills. You're going to find out a lot more about bioregorical classes and the main structural bone of that flap is the bone here. So the whole thing together is the operculum.

Common homologous origin. This is just some pictures and some diagrams of the diversity of the shape of this bone. It's huge okay.

You can do transformation analysis on the operculum. So these are sticklebacks.

Sticklebacks have an oceanic origin and when they get stranded in lagoons those lagoons eventually come fresh water you get isolated populations which then speciate. So there's a huge diversity of stickleback populations. Fish evolve really really rapidly as we will see.

So this is an oceanic. This is a transformation analysis. You can see that change described.

What use is that? Well maybe you've got two different subspecies of this critter then maybe by doing a transformation analysis it will help you to understand their relationships or whether they're actually separate species.

So this is a tool that zoologists can use.

So you find key landmark points. You find the relative position of those with the mouth and then you can compare them to other specimens.

So here's another preparation of a couple of sticklebacks. Different species and you can see there are some major differences here. So the spines here are very different for example. This one has very trivial spines but if you look at them you would recognize them as sticklebacks.

Darwin stentures. Okay everyone's heard of Darwin stentures. Then in Darwin stentures what has been the focus of evolutionary research? Yeah go for it. They're beaks.

What this should tell you is that evolution can focus profound change in distinct parts of the body with having minimal effect on the rest of the body. So evolution can focus on one particular region of a species of a morphology.

on one particular region of a species of a morphology. So what does that suggest about the ontogenetic processes going on?

the ontogenetic processes going on? So ontogeny, developmental and genetic processes.

So remember they all come from a common origin like a fry and yet you can have distinct changes arise in parts of those bodies without affecting the rest of the bodies. So what does that tell you in terms of the ontogenetic processes? And then hopefully you're getting the germ of an idea in your head. You may not be able to express it yet but you're starting to get a picture of what I'm talking about. So let me give you some real meat for the bones here. The answer is that animals can evolve in a modular fashion.

Bits bolted onto one another. So you might think of Frankenstein but that's not a very good example to use. But if you think that we are made up of different components that make up a whole and those components can evolve separately.

You can dissociate the processes that create an adult. The evolution can focus on how the limb is going to develop, how the forelimb or the hindlimb is going to develop.

going to develop. Those areas can be selected for and that selection yes it takes place at the adult stage but how does that adult stage come to pass through the developmental processes that create it?

Do you get where I'm going to?

going to? Yeah cool. How do we define these processes? You'll see that there's various terms in the literature for this.

Mosaic evolution is one which you may well have heard about. I think that's quite commonly taught on the modular, ontogenetic development.

This idea of developmental modules.

My background is developmental biology or one of my backgrounds anyway hence that's why I'm talking about it. How can we explain these processes at the cell and tissue level? So how can we explain the production of an animal like this with a very truncated upper bill? At the cell and tissue level.

So I'm moving on from the broad picture now. I'm trying to get you to focus in on what's going on in the in the developing animal itself. I don't have time to go into the real genetics of this but we can have an idea. I can get across you so the ideas of the cell and tissue level changes going on.

So if you think that a bird beak for example starts off with what's known as an amlagon or an initial part which is going to develop into that beak is going to have to grow. Those cells are going to have to multiply and they're also going to have to grow out in a in an axis. They're going to have to go down a particular kind of growth. It's not a big blob it's a directed structure that you're making.

big blob it's a directed structure that you're making. So how can we explain that? What we need to explain is this is where it starts and yet by this stage the beak has grown much more than the head and very much more than the head in this case. So what could explain that differential growth?

differential growth? Well one possible cause is to accelerate cell division in the cells at this part of the beak.

Make sense? Or perhaps what's going on is you're decelerating the cell division of the cells making up the skull.

So there's a differential beak cause.

You could also argue that it might be because there's a prolonged or a shortened development time for these different regions. So this bits after developing for a while but this just keeps on developing for longer.

So it's the same rate of cell division but the process goes on for longer in one part.

It's all logical isn't it? So you can use that to explain the differences in the lengths of the wings of some of these animals. Obviously the comparison of a hummingbird and mouth cross is a little bit of a strange one to make but if you scale these out relative to one another you can see that one of the big differences is actually in these two bones the forearm.

So I said if you know beginning stage then you can have an idea of the intermediate stages but if you've also got animals which are very similar to one another and you don't have the full evidence then you can make predictions. And one of the things that Darcy told to predicted was the shape of a missing pelvic region of a Papantasaurus.

So he based it on this one up here he said well if I compare that one with this one I think this is what we're going to have. So he did it by a partisian analysis. Does that make sense? Any questions on that part before I go on to the next part? Yes.

I think it is but it is also so old it will be out of copyright and so you should be able to download a free copy of that. It should be able to. So apologies for the lawnmower.

So apologies for the lawnmower. You'll be able to get something else droning on apart from me. So why?

So why? Why developmental alimentary? Why do it? What are the forces that are causing this? What is natural selection that are acting on? You can ask all kinds of sub-questions to this thing of why. Here's an example that I want you to think about. So this is C.

devices. This is from one of my favorite books by Rudy Ralph called The Shape of Life and here we have a developmental series of this dinosaur.

This is an animal at hatch. This is a juvenile animal with lower jaws for these ones and this is the adult.

and this is the adult. So why? Why not hatch with this kind of proportion of the skull? So why?

So why? Alometric development. Part of it is that they're hatching out of an air space as limited and so is nutrition. So it would make sense to say to make some nutrients while being a different species. I'm going to try and sum up what you said so that everyone here. So one is the amount of nutrients that are available in the egg and the other is the available space in the egg.

It's a really good answer. Any other reasons? Okay so let me try and sum up what you're saying. I think what you're saying is that you need to have the proportion of body mass and musculature to be able to support a head like this which wouldn't be present in a new hatch.

Yeah? Any others to explain why? Could it be also different lifestyles as a juvenile encounter to the adult? Sorry I've got three brilliant answers.

Sorry I've got three brilliant answers. So the question to ask here is what is this eating and what is that eating?

and what is that eating? They have different lifestyles. This thing is probably going to need a jaw that large. Whereas this one well it's taking down large animals. It's got to dismember them.

Okay it needs this kind of jaw whereas this one doesn't get any idea. So here we have a pelican. Brown pelican.

So this is a brand new hatch. You can see it's very altricial. So there are no feathers. It's blind and just on the tip of its beak here you can see a little nub. That is known as the egg tooth. The egg tooth is what the animal needs to break out on the shell. And you can see that there's a massive allometric difference between the beak size of this animal and this size. So what's the explanation for that? We've already had it.

It's because of the size of the egg.

So let me explain how a bird gets out of a shell. You ever wonder that? All right so it's stuck in that shell.

The head is at the top of the egg. That's the blunt end where there's an egg space over the top. It doesn't breathe through that primarily but it does start to exercise its lungs using that airspace. But to get out of it it's got to score a mark all the way around the shell.

It doesn't just punch a hole in the side. It needs to create pretty much a lid.

So when you take off the top of your oil bag you don't just mash it. You actually try and cut through it and take a slice off.

How does it do that? Well it's poked downwards and it rotates its body and its skulls align on the inside of the shell when we can see it and that enables it to come through. And in fact this this part here on some eggs which shown are hatching up you can see this poking through as the bird rotates around. I'm not seeing the pelican but I see any chickens.

So that's a reason why. If the beak was all the way down this size in comparison to that it would be down by its feet.

So there's a functional requirement for this beak to remain short.

Does that also explain why this has to be as short as well? Maybe it's not just the space. Maybe it's the physical constraints on getting out of an egg. Of course we can't see that in a dinosaur to check which is sadly.

which is sadly. So now the question is how does the beak know how big to grow?

Because trust me if you took a thousand pelican chicks and you took the measurements and you did the ratio of the size of the beak to the head or to the weight or something like that it would be pretty constant. The evolution is selective for this feature. I would put it another way. How does it know when to stop growing? Because it has been growing and at some point it said whoa rain it back that's big enough. How does it know?

How does it know? And this is pretty much a mystery. We don't know the molecular basis of how this has worked out. We've got some ideas for some features in vertebrate development but not many.

But one of the things that Darcy Thompson was able to show was to demonstrate is that you have an allometric scaling relationship. That whatever the mechanism is that's interpreting this is interpreted from an allometric scaling relationship. So this would be the arithmetic growth for the size of a lobster claw. It would be listening but we've got an allometric relationship here.

It would be listening but we've got an allometric relationship here. That claw is always bigger. How does it know how to know how big to grow?

How does it know how to know how big to grow? On this one we've got an arithmetic growth of the head of the bird but we've got an allometric geometric progression to produce this not big. So what Darcy Thompson showed was that it's derived from a locked or a controlled disproportional growth.

So the claw size is always larger than the thorax by a defined measure. Similarly there's a defined measurement, a defined difference or ratio of the size of a head compared to the size of a bee.

So it's not a random thing. It is controlled and it is proportionate but in a non-arithmetic way.

Why is that? Well it's easy to understand with the lobster. If this animal here had a claw that big it would not be able to function. By making sure that this remains in a defined relationship to the size of the thorax the animal is always able to use that claw.

It's always able to move. Makes sense? Cool.

So the scaling relationship leads to beaks development of one feature is correlated with other features in a precise quantifiable reproducible relationship.

That's why Darcy was left on as being so informative and it doesn't just apply to a bird for animals it applies to other life forms as well.

Okay so allometric development in humans.

Well you can see that that relationship has swapped here with the size of the head.

Tenrometry positive to torso pre and post basal negative towards the juvenile animal.

Why? We've already talked about that. Part of it is giving birth.

it is giving birth. But why have an infant with such a large head?

with such a large head? Brain size. So intelligence of humans has driven us to this situation. So many of you ladies I presume in your later years will have children. You can blame the pain on the intelligence of your forefathers.

on the intelligence of your forefathers. So what is going on here?

is going on here? We have a scaling relationship that you need to understand here.

So size, area, mass and volume. So if you double the size of something the surface area increases by a factor of four but the volume increases by a factor of eight.

eight. Remember if volume increases increases so does the weight. If you're thinking in terms of a anatomical feature the demands of that feature have gone up by a factor of eight. So let's think you've got to supply it with blood or you've got to supply eight times more blood generally speaking. If the cube doubles in size, height with its volume weight goes up eightfold. So that means if you just arithmetically increase the size of something you get in you get into problems with scaling. What does this mean?

What does this mean? What it basically means is illustrated by this. If you took an ordinary pussycat, six point about four kilograms.

If you just increased it up to the size of a tiger in actual fact it would not work.

About seven times the size but 75 times the weight. So if you just simply enlarge that isometrically it would be unable to support its own weight without breaking its bones.

But clearly this is a cat in a cat family. This is in a cat family. They're very similar, they're very clearly related. So how can you get a tiger as big? And the answer is allometric development of certain features of the animal which enable it to support this massive weight, to support this massive volume. So you can see that allometric can help you understand the diversity that you see within the vertebrae.

So there's a little scale here which goes through some of the other size differences and things like that. You can look at that at some other time. What you need to understand in terms of this huge bulk of an animal being supported on bones is that the strength of the bone is determined by its cross-sectional area. So if you have a heavy animal or a much heavier animal evolving it will need to have a larger cross-sectional area on some of its key bones to support it.

That can explain this difference, cross-sectional area.

If a limb doubles in size isometrically its bones will be twice as big but carry eight times the load. There will be a mismatch in loading capacity.

capacity. Is that clear to you now? So if you want to work through this, if you don't believe the suntans just go through this slide at the end here and it will help you to understand that. So a few dinosaurs here, we've got the T-rex at the bottom, porniferosaurus at the top and this is an allosaur. So the femur is this bone here and here and here. On this one you can see it's distinctly curved. So why is it curved?

So why is it curved? If increasing size increases from weight to loads, they can only do it within a certain limit. That would be my answer to that.

So there's some famous x-rays out there where if you actually look at the bone structure of a range of different people, the most famous one is between a skinny person and a very obese person. There's very very little difference in the skeleton between the two and that's also true for body builds but with a caveat.

The most interesting example of this I know is tennis players.

So tennis players usually have a favored arm and their favored arm is much stronger than their non-favored arm and the bones of their arms change in morphology in comparison to the other one to enable that to happen.

So your bones are an active living tissue which do respond to stress and when they are under stress they will increase in size.

in size. So within limits but there are limits. So why is this curved?

Balance. That's actually not a bad answer, it's not what I'm looking for. Is it with the curved being a support plane?

Is it with the curved being a support plane? Because it's a bit more flexible it's able to support the amount of weight being put on it and it's in touch with the muscle so if it was completely straight then people wouldn't be able to bend you with the weight of the animal. Okay so you're talking here about there's a functional requirement here for it to be able to move the lip okay.

At the back, the weight of the head. You're actually it's not such a strange answer okay.

I think weight has a lot to do with it let's see if you've got one. Okay does that increase the cross sectional area of the bone? Maybe I don't know we'd have to chop it through and see to check out but let me just ask you this question. This animal spina is relatively straight.

Intuitively if you just swapped that straight limb onto that limb what would you think would happen? You think hang on there's yeah you just did that it's not going to be able to support it.

In terms of engineering it works on a low weight but once you scale up the size this engineering is not going to it's not going to fit the purpose you have to change the design. So this curvature of the bone enables this animal to fulfill its requirements and part of it is yes the movement but part of it is just supporting the weight as well. If you put it another way if all of the weight is at an angle like that you know the shear forces on the bone are going to be really quite hard and it's going to snap it but if you bend it that force is distributed along the curve of the bone.

the curve of the bone. We're going to think about this a little bit later in another lecture about this roll of the curves and things like that but are you getting just an inkling of what I'm talking about?

about? It's all going to grow folks. Let's think about the vertebrate head. The vertebrate head is absolutely nuts.

I've not put a triceratops on here have I? No but I could have done. That's really really strange. I mean we've got teeth we've got things sticking out the back of the head platypus is just crazy.

platypus is just crazy. We've got the sawtooth I mean it is just so diverse. The vertebrate head is really diverse. How can we explain that?

How can we explain that? What is going on here? Our observation is to tell us that the cranio mandibular morphology that's the head cranial top part mandibular that's the jaw is a hot spot for allometric based evolution.

The picture before showed it so does this one here.

So colored in are the homologous bones within the heads of these animals.

So this is just looking at fish diversity and you can see that there's a huge variation in allometric development with the different bones that make up that head. So this blue bone here massive massive massive absolutely tiny absolutely tiny.

So you can explain some of the morphology differences between different species of fish just by doing that Cartesian analysis on the component bones and you can see where evolution has put selection pressure on.

pressure on. What about this one? So this is one whale this is an ancestor of the whales. What's going on here?

going on here? Whales are mammals so are we. We share some of those common bony plates within the skull that I got you to look at in the practical class and here they are colored in.

Parietal parietal huge difference occipital look at the size difference here but the one that everyone must look at here are the nasal and the maxilla and the premaxilla.

Well that's ours there.

So you can explain this enormous protrusion by developmental differences in growth, allometric growth of these bone regions here. Once you can identify these regions then you can start focusing in on the genetic, maybe the molecular and the cellular processes that are going on in them makes it hugely interesting. This is a diagram of a bird skull and sorry the bones that make up a bird skull and you can see they are kind of coded and apart from the black bones all of bone in this head is derived either totally or in part from the neural crest.

So neural crest is an embryological tissue I'm going to explain to you what it is in the next slides and neural crest seems to be especially malleable in regard to evolution.

evolution. So the neural crest has been key in the diversity of the head of vertebrates. So what is the neural crest?

So what is the neural crest? So it's an embryonic tissue. Have any of you any idea what I'm talking about when I'm talking about embryonic tissues? There's three basic types that you'll find in just about all the most animals at all.

the most animals at all. You're going to find the endoderm, the mesoderm and the ectoderm. Have you covered those in invertebrate zoology?

Have you covered those in invertebrate zoology? Some of you have, or some of you remember doing it here.

In neural crest you only find invertebrates. It's known as the fourth germ layer, the fourth germ tissue.

So what happens in development, this is looking at a bird, I believe a bird or a mouse they're very similar. So what happens is the developing cells of the embryo, underneath here you get the motor cord which we'll talk about later on.

These tissues on the top is ectoderm and then it folds together and comes together to create a single sheet. So what we've got happen is this lump of tissue is pitched off from the overlying tissue and that produces the spinal cord.

At this region here, just as those two parts are coming together, this turns into neural crest.

As it comes together here you get one layer of ectoderm over the top and then the neural crest cells are gathered underneath and these cells migrate.

They migrate all over the place but especially within the head.

So these migratory cells, ectones and fourth germ layer, they migrate everywhere.

They go into the head and they are a distinctive feature for vertebrates. So they are a synapomorphy of the vertebrata and they are key for the neurogenic and the skeletal tissues especially in the head.

I've spouted a lot over that slide. I'm going to give you a second to take that in whilst I have a mouthful of tea and you can think of any questions.

The fact that it's called neural crest is derived from the fact that it is key for the neurogenic tissues and neural tissues as well.

So I like to laughingly say that the neural crest is the key to the world domination of vertebrates. So the neural crest is involved in so much of the skeletal structure of vertebrates especially within the head that it has enabled us to become the most successful taxa on the planet apart from people's and things like that.

So take home messages. Body size, relative proportions of its parts, it's regulated. We don't end up the way we are looking through some kind of random process.

It is tightly controlled. Allometric growth is required where isometric growth would compromise function.

Don't forget that we've got natural selection working in on this. Allometry is a common result of evolutionary selection for morphological change. Changing a pre-existing thing is much easier than creating de novo and new one. Allometric proportionality is linked non-arithmetic to another feature of the animal. This feature might be weight loading, the volume of blood in the circulation or even the heart and respiration.

Those things it will link together. So hopefully you can see that having an understanding of isometry and telemetry really does enable you to come up with some interesting answers about vertebrate diversity.

So at the end of this course I would hope that if someone was to present you with an image, two images like this, you would have an idea of the size of them just by looking at them.

You would intuitively know that something like velociraptor which was tiny could never be as big as this root because you would just say no no that just doesn't look right. The bones wouldn't support it and if you were pushed you would come up with a scientific explanation to back up why you think that.

That is the velociraptor actually in scale to t-rex up there now. So you could just scale this up to that size because it wouldn't work. Hopefully you'll get that now. So if you want to look at this slide that's the one I was talking about you can go through that later.

This is another quick example of allometric development in whale evolution but here the important thing to notice on these diagrams is the position of the nostrils. So this is an evolutionary progression and you can see how these nostril positions have moved up to here to the top of the head and you can explain that progression by looking at the lobometry and isometry.

Now this one's just for a bit of a laugh really but you can do what you like with it. Significant books on biology, A selection, so these are some of the ones which I think have really been really significant and influential.

It's not exclusive and no I haven't read all of them but I'm betting I've read a lot more of them than you have. None of us would have ever read that one because it's in Latin and that's very old so that's the 1600s but he was the guy who discovered about circulatory systems.

The ones that are a little bit more modern you definitely should read Selfish Gene if you've never read it.

You definitely should. I've tried reading it, got bored, I'll make that. For the ones that you should read, for those of you who are just doing general biology, zoology, The Red Queen by Ridley is absolutely brilliant.