Big Kills, Big Killers lecture

 
 

 

Transcript

Announcer:  Dr. Rolf Schmidt, Dr. Tim Holland, and Dr. Erich Fitzgerald presented this lecture, "Big Kills, Big Killers" on the 8th of July to celebrate the opening of Melbourne Museum's newest permanent exhibition, 600 Million Years: Victoria Evolves. [applause]

Dr. Rolf Schmidt:  Our story of the predator begins with an explosion: the Cambrian explosion. For anybody who has not heard of this, what is the Cambrian explosion? To give you a bit of an orientation briefly what we're talking about, this is what we call a geological time scale. You can see where the Cambrian explosion is continuously happening at the bottom. On the right hand side is pretty much the whole time of animals. On the left hand side is the whole history of the Earth. You can see it spans only a short time at the end, so during all of the rest of the time, we just had little microbes living, nothing big.
 
But suddenly, life just went crazy and exploded. So what happened? What happened that made this occur? Not everything exploded; there were some interesting things before the explosion. We have what we call the Ediacaran biota, named after the Ediacara Hills in South Australia, mostly squidgy stuff, mostly no skeletons, probably no eyes, no mouths, no teeth, nothing you would call a predator, really.

These things probably even just absorbed their food through their skin. They were probably so thin they just soaked it up from the microbial mat that covered everything at the time. So, not exciting. I'm sure you've come here because of the title, predators. You want to see blood and guts. This is not happening at this time.

During the Cambrian explosion, suddenly bang! Everything just goes crazy. We get all the groups of animals that we know of today. You probably barely recognize anything that's on there, but you'll note something that's distinctive: most things have shells, hard parts, and a lot of them have got eyes. There are probably a few you might recognize could be predators. There are quite vicious little things with claws and teeth and chomping bits.
 
So what changed? Why did this suddenly change? There are numerous ideas. There are probably changes in oxygen. We need oxygen. Before this time, there was just not enough oxygen for big animals. There was a huge supercontinent that broke up and produced a lot of extra shelf space for new environments for these animals to evolve into.

But these are all what we call extrinsic outside factors that just changed. There are also probably intrinsic factors, which means from the animals themselves, which is what I'd like to talk to you about in a bit more detail. Predators are an important part of the food chain. Usually, it doesn't quite work like this; this is not a real food chain. But predators at the top, they feed on other animals. A predator is defined as an animal that feeds on other animals in such a way that kills them. There are other types of feeding, like parasitism or grazing, that usually don't kill the other creature.

Also, "food chain" is probably not a good way to describe it. Really, what we're talking about are pyramids, and predators sit at the top. At the bottom, you have primary producers, so to speak. They're the farmers. They create from sunshine and whatnot, lots and lots of them.

Above that, you have the things that eat those things, still lots and lots of things. But then, right at the top, you get the predators, and there are only a few of them usually to all that other stuff. You need a lot of production to keep the predator alive, and this in itself is actually what makes predators so vulnerable to any change.

This will probably be a thread throughout this talk, how predators seem to be the ruling animals. They're the Lion Kings. They're the things that everything is afraid of, but really, when you look at it, it's the other way around. The predators are the things that are most sensitive to any kind of change, so a small change in what they feed on, a reduction in that bang! They're gone. That has happened a lot of times.

The niche of the predator has almost always been here. There's almost no environment where there is no predator, and especially top predators, which are the things that don't have to fear any other animal. They're at the top. They don't get predated on.

The niche of the predator has always existed, but who holds that position, that has changed, and it has changed mainly due to two reasons: changes in the environment, which usually cause mass extinctions where you can quite randomly wipe the slate clean. Something new that previously was insignificant suddenly arises to dominance, and the previous one becomes insignificant or completely dies out.

But there are also evolutionary changes, novelties popping up that suddenly make a previously fairly unimportant group of creatures more dominant in terms of the predation. Again, there are lots of examples of both.
Strictly speaking, food pyramids are not accurate either. The things that we look at are food webs. Everything is interlinked in quite complex ways. Just try and remember the right hand diagram.

This is a modern food web in the ocean. The aquatic food webs are usually a lot more complicated than the land ones. Land ones are fairly simple, often. In the ocean, there's just so much stuff to eat.

Back to our Cambrian explosion. On the left hand side is the Ediacaran sea floor, covered in slime made of bacteria and algae, and the things feeding on top of it, the squidgy things climbing around and just soaking it up. On the right hand side is the Cambrian sea floor, which is suddenly different: all sorts of things churning it up, eating one another. It goes quite crazy.

As I pointed out earlier, something must have changed, and not just the environment, but also the animals must have had something in them that would have allowed them to exploit that change, this massive explosion of diversity. The things are mainly eyes and skeletons is what often sets these two times apart.

I'd just like to digress a bit on the eyes. You can consider their origins... Throughout the animal kingdom, many origins but one common ancestor. How does that work? How can you have many origins but one common ancestor?

If you look at some of the most common eyes in the world, you have things like insect eyes, which are lots of little facets. You have the vertebrate eye, like us, quite a complicated lens. You've got things like the octopus, also a nice little lens eye.

Now, if you look at it superficially, you'd think our eyes and the octopus eyes, they're obviously probably related. Well, not actually. As it turns out, when you look at how they develop, the octopus eyes are more closely related to the insect eyes.

At a very early time, our branch of the evolutionary tree that includes us and birds and sea urchins branched off, and everything else that you know, worms and squid and everything else squidgy, branched off in a different way.

Some people say if you look at it in the way we develop from an embryo, us humans are just upside down, back to front, inside out worms. Basically, our mouth is where the hindquarters of a worm usually are, that kind of thing.
There's a fundamental difference there, but if you go further back, there's a common origin for all of the eyes. If you look at the genes, which we call regulatory genes, which are called Hox genes... This is now getting a little bit technical, but it's interesting, because these genes don't actually code for a character.

These genes don't say, "OK, build a leg like this." They're more involved in saying where to build the leg or where to build the eye or when to develop it, that kind of thing. It's quite important where your eyes end up, because you don't want them on the back of your head. You want them on the front of your head.

These genes are actually shared almost in a fundamental way identically across all animals, except for maybe jellyfish. But after that, everything has the same kind of genes that regulate how and when and where things develop. We've all got one common ancestor some way back, all us animals, which I find quite fascinating.

This thing probably predates the Cambrian because at the Cambrian all the eyes, the totally different looking ones, the insect faceted, crabs with faceted eyes, and the squid and the primitive vertebrates, they developed their different incarnations of the eyes, but the basic, fundamental aspect of it was set way back.

Another interesting thing, actually, is things like insects and squids, their eyes develop from the skin, sort of an inversion, the classical idea of it inverting from the skin, light sensitive... Our eyes actually come from the brain outwards. They're not developed from the skin, so again, inside out worms, that's what we are.

Going back to fossils, in the Cambrian, like I said, predation really started, but most of the predators are fairly small and probably not really ferocious. But we do find trilobites. These are the ubiquitous trilobites that just dominated the whole Cambrian time.

These trilobites have got these bite marks, quite ferocious ones as well. What could have done that? They're quite hard skeletons. They've got actually two layers of skeleton. One outer layer is made of a hard calcite, which is a mineral which is really rigid, and underneath is a cuticle, which gives it extra strength from pressure. So the outer one gives it strength in one direction, and the underlying one in another direction.

Not much can get through that, so how did something break that? Was it something really ferocious? Actually, truth is usually stranger than fiction, and what we find in these sediments are these strange appendages. You can see that's about one cm, so that's quite large. It's more than 10 cm in length, which is bigger than most of the animals at the time.

This was originally interpreted as a shrimp, but turned out it's actually just a part of a bigger animal. We also find these things, large circular structures with big, jagged things on the inside. Again, these were interpreted as jellyfish initially, but they turn out that they all belong to one ferocious predator, which is Anomalocaris, "strange shrimp."

To me, this is basically the platypus of the Cambrian. It looks like there's a lot of different animals just tacked on to one another. You've got these shrimp like appendages at the front, these bulbous eyes. They don't have legs. They don't belong to the greater arthropod group, which includes crabs and trilobites.

They have this circular mouth, almost like a lens, that can crunch together. But you couldn't eat something with that; you'd have to break it open first. So what they did - this is the thought - they grabbed it with the two big appendages at the front, like this trilobite similar to the one you saw initially, and they basically just bend it back and forth. That gradually weakens the two layers, the calcified outer layer and the soft inner layer. Gradually, that just fractures, and they break open, and they suck the pieces into their mouth with the sharp teeth to stop it coming back out.

We're pretty sure that these guys did eat them, because there is fossil poo    coprolites, technically, that contains fragments of trilobite, and the size of this fossil poo is so large that only these guys could have done it. These guys were the top predator of their time. Remember that food web at the beginning. This is an interpretation of the food web at the time, very similar. There's Anomalocaris at the top, trilobites up here, and all the other stuff at the bottom, apparently very similar to today.

Within a short amount of time of animals diversifying, you get what we have today, the whole structure of an ecosystem, which is quite interesting to have it that quickly. In terms of size, some of them got huge, not so big to us, but if you compare it to everything else that lived at the time - these are the other little critters; this is a relative of it - it is gigantic. It is literally the Godzilla of its time. If you compare it, we're this little, tiny squidgy thing at the bottom, and even King Kong can't compete. This was humongous for its time, and obviously it didn't have to fear anything else at the time.

This is a drawing of another species hunting these little critters. The funny thing is, this one possibly is interpreted as not being something that did that to the trilobites, but actually just scooped through the sediment churning up things that live in it and sucking them in through the mouth. They had different life strategies, but it was probably still predatory and fairly large compared to everything else.

Now, these things are more or less restricted to the Cambrian. There have recently been ones found from later, but they're totally insignificant, really. So how did something this successful that lasted for tens of millions of years    why did it vanish?

There's one theory that says trilobites, which were its main food source, started developing this feature in which they roll up. Some people have said they rolled up as a defense against predation, like a porcupine, basically. But other people think actually the protective thing was just a side effect.
If you roll up like this, you can't bend it. It's like if you have a flat credit card, you can bend it easily. But if it's a curved thing, you can't bend it against the curve, so they lost their leverage.

But for these trilobites, the initial reason for why they did this was probably they have to molt, which means because they have the skeleton on the outside, if they want to grow they have to get rid of their skeleton, get out of it all soft and squidgy, and then re puff themselves up to the next size and regrow the skeleton.

That was actually quite difficult for some of them, because we find fossils where it went wrong, horribly wrong. Things only partly came off, and they got stuck and basically died molting. So these probably developed this flexing thing to make that easier. Side effect was they were protected from Anomalocaris eating it, so Anomalocaris probably vanished.

Now after the Cambrian, the next thing to take over in what we call the Ordovician period were these giant squid like things, nautiloids, straight shelled. They started preying on the trilobites. They probably just lay on the floor, some of them, just waiting for a trilobite to crawl past and then eat them. They probably weren't even that fast.

Some of the trilobites started developing these spines against it, but what do you do when something like that attacks you? Here's a Legend of Zelda character for scale. These things were huge. This is like 10 metres long.
At the end of this period, we have a major mass extinction. I mentioned these as one reason why things die out. Now these nautiloids, or cephalopods in general, are notoriously affected by these mass extinctions. They almost get wiped out, and then something small survives, and they just go crazy after that.

But after this mass extinction, there are still predators, but something else took their place, something quite ferocious looking. This isn't a mouth; this is a claw. This is a claw of what we call sea scorpions. They're not scorpions; they're related to horseshoe crabs, but they are the top predator of this next period, which is the Silurian. But they're also ferocious. Again, they look quite nasty. They've got either claws or these quite vicious appendages.

Here's a timeline. They evolved early on, but they really took off here in the Silurian, and they became gigantic. This is almost three meters long, this thing. Funny enough, these guys back here, they probably evolved in the oceans, but then they moved into the lakes and streams. They moved into the freshwater realm. This one possibly terrorized the rivers at the time.
This other branch, which survived longer, is actually probably not predatory. Again, they just filtered sand, but they were huge as well. This one here, you can see. This is a track way of it. There's one set of legs. There's the other. That's this thing. That was as big as a car, probably, but probably not predatory, probably more like a hippo. It's dangerous, but not really predatory.

Again, these guys had their peak during this period, but after that, they vanished, more or less. These other groups continued. So what happened? There wasn't really a big mass extinction at the time, but something displaced them. To talk about that, I'd like to invite Dr. Tim Holland up on stage.
[applause]

 
Dr. Tim Holland:  Thank you, Rolf, for that stellar introduction to underwater invertebrate predators. I know there's probably a lot of terrestrial invertebrate parasites in my hair and underneath my clothes that would give you a round of applause if they could. But me, as a vertebrate paleontologist and as a vertebrate too, I'm interested in more of a story with a bit of a backbone, so I'm going to push on now and talk about the evolution of gigantic predatory fish.

The geological map is dotted with several key events. As paleontologists, there's a perception by the general public that we just look at dinosaurs or charismatic Pleistocene megafauna or something, but I'm more interested in delving way back in time to look at the key events when features that are common to us all first evolved.

This is the Paleozoic, the area I'm going to be talking about, and I've put in a couple of key moments that I'm going to quickly run through tonight, starting off with the evolution of chordates and the first jawless fishes, moving right along to the evolution of fishes with jaws, and then finally, the arrival of tetrapods.

Going back to the start of this series, we have the first chordates in the Cambrian, some 350 million years ago. This is Haikouichthys. It is a chordate and defined as one by a number of key features, such as a post anal tail, pharyngeal gill slits, a nerve cord, and also a notochord. A lot of these features are also present in the first jawless fishes, except that the notochord has been replaced with a more strong vertebral column. I get the impression that they would have lived lives like our creepy crawlies in our swimming pools, pretty much just staying on the bottom of the ocean sucking up gunk.

If you look at modern jawless fishes today, sadly, there's a lot less diversity, and also, sadly, there's a lot more disgusting qualities about them. Hagfish and lampreys have been described as the most disturbing animals alive on the planet.

If you ever have the misfortune of picking up a hagfish - they're called hagfish; they must be pretty bad - they emit this horrible slime, just like out of the horror movies. They also are able to contort themselves into all different types of shapes, so they'll probably get out of your hand pretty quickly anyway.

Despite these foibles, these jawless fishes, and also studies in embryology, have given scientists ideas about the evolution of jaws. If you look at a jawless fish, one of the things you'll notice as distinct from a jawed fish is it has more gill slits and more gill slit supports.

We think that early jawless fishes converted their first gill arch support as a precursor for the upper and lower jaws. The second gill arch support would later go on to become secondary supports, a sort of shocker system for the rest of the skull.

Gnathostomes, or jawed vertebrates, animals that can take a bite out of you, are survived today by two different groups. We have the chondrichthyans, the sharks, rays, things that kill prominent Queensland celebrities, and also the osteichthyans, your bony fishes, which are represented today by actinopterygians, ray finned fishes, things that are good to eat on a plate, such as tuna and salmon, and also sarcopterygians, fleshy finned fishes.
For the people listening via podcast right now, I'm going to make a point of saying that Tony Danza is in a cladogram, because he pretty much just represents a highly derived, walking, talking, and probably not very funny sarcopterygian fish.

There are also several totally extinct groups of gnathostomes, including acanthodians, commonly known as spiny sharks, but they're a distinct group in their own right, and also placoderms, which are armored fishes.
I find placoderms really groovy, and I think I'm probably the only person in the room. But they're really interesting for paleontologists because they can tell us a lot about early gnathostome reproduction, biology, and anatomy.
If you look at the top of the screen on the right, you'll see a pair of placoderms copulating. We found specimens in Victoria which have pelvic claspers, indicating internal fertilization. On the left, you'll have another type of placoderm found in the Kimberley of Western Australia which have been found to have embryos inside of them. So we have this incredible soft tissue preservation.

This is also followed by another type of placoderm down at the bottom of the screen called Eastmanosteus, which has had a paper written on it recently where they found muscle fibers, believe it or not. Placoderms are also cool because they represent a diverse group. One type of placoderm, called an arthrodire, is pretty neat because it took on the mantle as top predator in the Devonian oceans.

This is Dunkleosteus. This is a picture I took in North America of a gigantic fish. It's pretty neat, not only for being totally black, but also the lower jaw's longer than my arm. They're tipped with these rigid, sharp points, and have been calculated to have amongst the strongest bite forces of any animal known to ever exist, including T. Rex and alligators and other sharks.

To get an idea of the size of Dunkleosteus, here's a picture I've included with it next to a bus. They're thought to get over 10 meters in length. Interestingly enough, I've got some colleagues in Western Australia who have reported finding a similar sort of critter out in the field - I'm not going to tell you where it is, because I don't want you to go off and dig it up because we want to study it - and it has armor plating that's over an inch thick, so a pretty serious beastie.

On our left here, we have another picture of Dunkleosteus with a representative of a surviving group. This is Cladoselache, a primitive shark. It is four meters long, so again, you get another appreciation for how big these damn placoderms were.

That was a general pattern for sharks and bony fishes throughout the Devonian. You'll see that they remained relatively small in diversity and size, coincidentally, until the end, where they suddenly skyrocket and continue on into the Carboniferous.

Placoderms, on the other hand, which evolved in the Silurian, hit peak diversity in the mid  to late Devonian, crashed. There was an extinction event at the end of the Carboniferous, where up to 70 to 80 per cent of species died off. This is still debated by paleontologists what the cause was, but some of the more prominent theories include a dive in the levels of oxygen around the oceans associated with sea level drop.

One group that survived through are the sarcopterygians, or the lobe finned fishes. They are represented by three groups today. We have the coelacanths, the actinistians. Latimeria was discovered off the coast of South Africa in the 1930s, and more recently they found another population surviving in Indonesia.

We have the dipnoans, or lungfish. If you've got some time in Melbourne - I don't know if you're from interstate or not. Anyway, come see the new exhibition, because we've got several live lungfish on display.

Lucky last, we have the Tetrapodomorpha, which includes us tetrapods, and also some tetrapodomorph fishes, so our fishy ancestors. Some of the key characteristics that unite us with these tetrapodomorph fishes include the number of nostrils, believe it or not.

If you look at unrelated actinopterygian fishes, you notice that they have two pairs of nostrils. These are shallowly connected under the flesh and are used to pick up smell. If you look at a tetrapod, such as a mole on the screen, you'll see there's only one pair of external nostrils, but they are different in that they have another set inside the palate.

This is called a choana, and this is connected to the external nostril and allows us to breathe through our noses. If you look at Devonian tetrapodomorph fishes, like Gogonasus, which I worked on for my PhD, you will find the same pattern. They have an external nostril and an internal nostril.

Other characters that link tetrapodomorph fishes to us include those of the pectoral girdle and foramen. If you look at ray finned fishes, such as this lizard fish, you will find a series of elongate rays in the fin called lepidotrichia. This is in stark contrast to sarcopterygian fishes, which have a very fleshy lobe and a relatively short number of lepidotrichia.

If you look inside these fleshy pectoral fin lobes, what do you find? Bones. Yes indeed, a series of bones. In tetrapodomorph fishes, on the right there, you'll see there's actually a set of bones arranged in a homologous way to our forelimb. They have a humerus, a radius, and an ulna, and a bunch of more distally positioned bones.

This example is from a fish called a rhizodont, which grew to very large sizes. They were the apex predators mainly of the Carboniferous, but they evolved in the Devonian. They had a worldwide distribution, including North America, Antarctica. In Australia, we're lucky to have the most primitive forms in Gooloogongia.

I also, in my travels to the U.K., meant to take my photograph with my hand next to one of the teeth of the larger forms known, called Rhizodus, which is thought to get over 10 metres long, and it would have lived in freshwater environments in Scotland. They're thought to have lived in slow flowing rivers and lakes and used their muscular fins in an environment to be ambush predators.

We also have an Australian form related to Rhizodus called Barameda, which, believe it or not, was found in Mansfield. So next time you're on the way to the snow fields, say a prayer for our Carboniferous fishes.

Another group of large tetrapodomorph fishes that took the dominant apex predator role are tristichopterids. Some of the smaller forms have been used in your classical textbooks about the development of the sarcopterygian fin into the tetrapod forelimb. This is Eusthenopteron, and again you see the same arrangement of pectoral fin bones.

I'm going to show you a slide now of one of the larger forms from North America, called Hyneria. These tetrapods get attacked by this large predatory fish. That's Hollywood for you, but unfortunately, when you actually look at the bones of early tetrapods, the limbs are not actually adapted for walking on land. They can't support much weight.
So pretty much, scientists think they were pretty adapted for living in water. What were they doing with legs in water? Walking around on the sea floor, probably in environments where there were lots of plants that had fallen in, looking for food, or, perhaps, trying to escape a large predatory fish.
Anyway, I'm going to pass it on to my friend, Erich Fitzgerald, now. He is going to talk about everything beyond this point. Thank you.[applause]

Dr. Erich Fitzgerald:  It is a truly curious thing that in the very long history of life, which we can think of really, as a really long experiment that fish (such as Tim just spoke about) only seemed to have crawled onto land, eventually after fits and starts, only once. Yet, many, many times in the history of life, it seems that the evolutionary tape was rewound. That is to say that the descendants of these fish like animals, these tetrapordamorphs, these lobe fin fish, which as Tim has pointed out, we are but a weird example of.
They seem to have gone back into the water. Here, are two examples of the end result of tetrapod evolution. Both are mammals: both the end results of spectacular evolutionary experiments.

One, of course, is a whale: a humpback whale. The other is naked ape with some fairly sophisticated aqualung equipment et cetera. One thing about these experiments is that over the last 250 million years, different players, if you like, have taken to this stage of life in the water or returned to the life in the water.

If we want to understand the origins of the mammal in the lower half of the picture, the whale, we actually need to go a bit further back than their origins and look at one of the earlier experiments to help understand the context for that evolution.

If we go back a hundred or so million years, the seas were not full of marine mammals, such as whales, seals, and dugongs. The sea was filled with reptiles: large reptiles.

The large critter in the center there is a marine reptile, a plesiosaur called a Kronosaurus: the king lizard. It swam in the seas that covered most of central Queensland from about hundred to 90 million years ago.
To give you an idea on just how big these marine reptiles got, here's the skull of Kronosaurus, partially reconstructed, in plaster, to the point we sometimes call it Plastersaurus. Its skull was two to two and a half meters long. Compared to later experiments, if you like, that returned to the sea this was a minnow, as you will soon see.

One other thing, in the history of these, if you like, secondary aquatic tetrapods or lobe fin fish that went back to the water, is the role of contingency. That is history: the evolutionary roll of the dice and the results. The subsequent evolution of life, in particular whales and humans, is often largely due to external factors.

About 65 million years ago, if you like, at the end of the age of dinosaurs, a asteroid or some other extraterrestrial body or a comet collided with Earth. In fact, it collided in the region of the Gulf of Mexico. It played a part in a mass extinction: one of the largest of the last 600 million years.

Despite the resemblance to a baked potato that's been rejected from Master Chef, that is meant to be an asteroid. It is not quite to scale, but it gives you an idea of the cataclysmic even that overtook the world about 65 million years ago.

The effects of such mass extinctions is that you, if you like, wipe the slate clean. So, for the ensuing 10 million years or so the oceans were devoid of very large big killers or apex top big predators. There were some sharks, but the sharks didn't seem to fill the role of those marine reptiles.
Instead, we had to wait for the rise of another group, a relatively inconspicuous group, called the mammals. One group, in particular, which gave rise to whales. So, if we journey back to look at the world 53, 54 million years ago, we will see that it's quite different to today.

The continents are more or less in the positions they are, at present, but there are some important differences. Number one, Australia was much further south than it is today. In fact, it's barely breaking away from Antarctica. It's freeing itself from the very last connections with ancient Gondwana: the supercontinent.

Secondly, we have this eastward extension of the Mediterranean Sea called Tethys, which invaded the lands, where, today, you have the Himalayas, which were just being formed at this time, as the Indian subcontinent was slamming into southwestern Asia.

It is in this warm, shallow sea that the crucible, if you like, of whale evolution occurred. If we go back to that time: a time of global warming. In fact, at about 53 to 55 million years ago, it was a time known as Paleocene Eocene Thermal Maximum, where temperatures were up to 12 degrees centigrade or more warmer than today. Really stunning global warming. It is at that time, relatively small herbivorous animals (like this thing here), which is in fact an even toed hoofed mammal are related to such things as cows, sheep, and other things you might find in a butcher's shop. It is from them that whales evolved.

In a relatively short space of time, within about 10 million years, they had become semi aquatic. This is an example: Ambulocetus, which means the walking whale, which lives something like a sea lion. For up until about 45, 42 million years ago, whales were amphibious. They retained functional hind limbs, and they seemed to have given birth on land. That was the final thing that forced a connection between whales and the land.

Once whales evolved the ability to give birth in water, they were free to go about life in the water, completely devoid of any connection with the land. That's when their evolution really took off. You can see a replica of the skeleton of this particular whale in the new exhibition 600 Million Years.
Then, at about 34, 33 million years ago, the icehouse cometh, and I'm not talking about a band full of classy mullets. I'm talking about switching from greenhouse conditions of the previous 20 odd million years to much cooler conditions. It was a gradual cooling, but begins with the pulse of cooling and the refrigeration of Antarctica, as Australia finally separated away from the Gondwana supercontinent.

What that affected was the beginning of circulation of really cold water around Antarctica, which deflected away warm southward flowing currents from the Tropics. It led to a great increase in the abundance of plankton and nutrients. Therefore, there was a lot more food, and whales were poised to take advantage of this increased food resource.

They evolved into the two major modern groups that we see today. Those are the tooth echolocating whales, such as the sperm whale and the baleen whales, which filter feed, using this hair like substance, baleen, and don't have teeth as adults. When they are embryos, they do have teeth, but those are lost, before they are born.

Now, these two new groups of whales, if you like, the modern whales and dolphins, they evolved some really impressive new weapons, in their search for prey. One was the baleen. One was the ability to echolocate or use sonar, much like a fish finder that you'd use today, when going fishing. That's using the echoes of sound they produce to detect their prey and communicate underwater.

It is within these two that the largest, the biggest killers, predators of them all finally took their place on the world stage. I should say the world's oceans. Today, the sperm whale grows to about 18 meters long, and primarily feeds on squid, including the giant squid.

But, in the past, it's had some truly fearsome relatives. About 100 years ago, some extremely large teeth were discovered. These are the teeth of a very large sperm whale, and they've been found all over the world. But just recently some fossils including a skull were found in Peru.

To give you an idea of the size of these teeth, the largest ones are 36 centimeters long and for scale here you have the tooth of Tyrannosaurus rex which is piddling almost, then you got a modern sperm whale which is again much smaller and a killer whale. These are substantial animals. So what were they doing, these sperm whales? Well if you look at their skull which is massive and robust, a human could actually sit inside, lie inside the jaws. This is a head at least three meters long and it is hypothesized that these sperm whales were specialists on eating baleen whales.

Now just to give you some scale here, in the past some baleen whales were relatively small, so that is not a blue whale, that is about six meters long and this extinct sperm whale Leviathan melvillei, named of course after by the storied author of Moby Dick, Herman Melville himself, grew to about 13 meters long. And often think that if Captain Ahab was out there hunting for a Moby Dick like this in the story, he might look over the side of the boat down to this Leviathan and say, "I think we are going to need a bigger boat."
But what about the baleen whales themselves? Well, they started out relatively small, but they were predatory, they were raptorial and they fed on fish, maybe even small sharks, but from small beginnings great things grow. And by about five million years ago, we had the beginnings of perhaps the most marvelous magnificent animal that has ever lived on Earth, the blue whale.

Of course, I find it really stirring to think that over the 600 million year history of complex animal life on this Earth, humans happen to be around at this very moment in geological time to appreciate this absolutely marvelous animal. It is a real privilege in a way and this is an animal of superlatives. Up to 30 meters long, 200 tons in weight, its tongue is as heavy as a bull African elephant. If we laid out the tongue of a blue whale, we could fit 50 people standing on it. Its heart is the size of a family car. Kids, you could crawl through the aorta of its heart quite happily and make a cubby house. It would be disgusting but it could be entertaining too.

And just the scale here, here is the skeleton of a blue whale, here is a bull African elephant, here is the largest dinosaur or one of the largest dinosaurs, Brachiosaurus and this is a large pterosaur or Quetzalcoatlus, a replica skeleton of which is on display in the Dinosaur Walk. And as you can see, the largest dinosaurs were pathetic compared to a blue whale. No dinosaur that we know off matched the blue whale in size. In length and weight, the blue whale is truly immense.

It is one of those ironies though of biology that the largest animal feeds on one of the smallest, and in what fashion does it feed on? Krill, these defenseless little shrimp like animals and the blue whale in the space of 24 hours can eat up to 40 million of them and they all must die, "krillocide." It feeds on them using a great lunge and in doing so its throat expands and the blue whale can take within one gulp over 100 tons of seawater and krill. It has been described as the greatest, largest, most powerful biomechanical event in the history of life. Truly stunning!

I'd like you to go away from this talk and consider the blue whale not so much as a gentle giant, a grazer of krill, but imagine it more as a predator, a murderer of tiny little plankton, the defenseless krill taking a great lunging bite out of a big school of little shrimp like animals. And that is how it feeds.
So the blue whale and the other baleen whales have evolved through some momentous times in the climatic and oceanic history of our planet. And through all these changes, they seem to have been relatively unaffected. They almost sailed through. If we actually look at this chart, this is number of genera, so that is sort of diversity, and this is geological time starting with the person over here going backwards in millions of years down along here.
We can actually see that whales have peaked in diversity in the past and have then declined but then increasing diversity within the last two or so million years. It was a time of really great oscillation, if you like, tumultuous changes in global climate, the ice age's glaciations, interglacials and the cetaceans seemed to have sailed through this period.

So based on the fossil record, climate change doesn't seem to be such a big deal for whales. They seemed to be able to adapt, change their distribution patterns. However, recent developments have been little bit more difficult for the blue whale and its kin to deal with. And of course that's with the rise to prominence and the dominance of the greatest predator that's ever lived, us.
If we look at the blue whale in particular, it hasn't had such a good time. Before industrial whaling, that is before the 1930s, there are estimates of the population of blue whales worldwide even just in the southern ocean may have been over 200,000 individuals. Just think of that biomass, all those 200 ton whale swimming around then.

We also know that because female blue whales on average at adulthood are at least one and a half metres longer than the males, we know that the largest animal that ever lived was actually a female. So, there you are to all the females in the audience, the largest animal that ever lived was actually a girl, not a guy.

What we can see though is that from the 1930s onwards is this gradual decline in the number. So here we have thousands of whales, the number of blue whales caught, a really catastrophic decrease and that's because blue whales were targeted relentlessly by industrial whaling when it was the norm for most large industrialized economies.

What we see with the other species of whales is what happens when there is a drop off in blue whales, well what did we do, we started killing the next largest whale, the fin whale and then is there is a drop off in them and then their populations collapsed beyond sustainable yield, and then when they drop off we target the next largest, the sei whale and then they drop off.
So during this period, it is more or less consensus among cetacean whale biologists that the international whaling commission actually regulated the unmitigated slaughter and drive to extermination of these very large baleen whales, basically because there was no research done to really understand how many were out there, so disaster.

So blue whale numbers now are very low indeed. So today, we are left with a global population of blue whales that may number less than 10,000 individuals. And it seems a real tragic irony that the very immensity of the blue whale, which for so long protected it from attack, proved just too irresistible a target for Earth's greatest predator, as I have said, which is of course us. And now the blue whale’s fate truly rests in our hands.
The profound tragedy if you like of the blue whale is really the reflection of a much greater one and that is of us, of all humankind. We have to ask ourselves what is the nature of a species that knowingly and without really good reason exterminates another.

How long will we persist in the belief that we are the masters of this earth rather than one of its guests? When will we learn that we are one form of life among countless millions that live and have lived as we have seen on this small world, each one of which is in some way related to and dependent on the others.

The greatest homage we can pay to the blue whale and all the great predators that have come before it is to learn the lessons of dependence on and if you like kinship with all of life, past, present and even future. If our species does not learn these lessons, then the greatest animal that has ever lived, perhaps the greatest predator may yet be extinguished in vain, having taught nothing to its one and only mortal enemy. Thank you.

[applause]
 
And I would like to invite my co speakers or compatriots here to come back up on to the stage and to field questions from all of you. Thanks for your attention.

Man 1: Thank you very much indeed. That was an extremely interesting set of lectures. You're coming at the beginning of the 600 million years ago, to the end of the Cryogenian. How did he Ediacaran and the other biota survive that Snowball Earth, if it was a Snowball Earth?

Dr. Schmidt:  There is some controversy at the moment actually about when did multicellular life really start. There's been a paper just released in the last week or so where they think they found, I think in Africa, a 2.1 billion year old deposit of multicellular animals which is highly controversial. I've read a few things that saying it's a mineralised microbial mats. The Ediacaran, which started about 630 million years ago, just after this major set of glaciations is the first probably indisputable set of animals, of real animals. Everything before that could have been just microbes. There are some fossils that are the size of your fist but we have found single cells organisms on the sea floor today that are this big rolling around on deep sea floor.

So if your question is: how did the first animals survive this massive Snowball Earth? Well they might not have needed to. They might have coming out of the Snowball Earth and the changes that happened after that, the change in the ocean chemistry, the oxygenation, that might have actually started them evolving the first place. So they might have missed that whole "hell on earth" scenario if it really was that extreme and it only occurred a few tens of millions afterwards, after that actually happened.

Woman 1:  It seems to be that predators seem to naturally become extinct. So you reach a certain level of predation become extinct. So is it just a natural thing that's happening with the blue whale now that that will naturally become extinct? We are currently top predator, and we, ourselves, will naturally become extinct..?

Dr. Fitzgerald:  That is admittedly sort of line of argument or point that many, if you like skeptics, of environmental damage and climate change and the impact of humans on global biodiversity would make. I think a key thing in terms of humans replacing other animals as the top predator, taking in consideration the rate at which it happens and the fact that humans are different to other organisms, other predators, in that that we have an ability to wage mass war much more rapidly. And also, that if you actually look back in time, say 10,000 years, where human populations were much smaller, we weren't replacing as much of, if you like, that megafauna... There's a lot of talk of this megafauna extinction, the extinction of Ice Age giants.

What's happening in the ocean now is the delayed marine megafauna extinction. So we've taken out the mammoths and saber toothed cats and we're dealing pretty rapidly at the moment with elephants, rhinos and tigers. They don't have much longer. But the ocean was the last area to deal with.
And so you could argue that we are naturally replacing those predators, sure. But it's the rate at which it's happening and it's the vast imbalance in biomass. So humans have effectively, I think you could effectively argue, replaced all that biomass of those megafauna with our six billion and counting. So it could be true, but it's the way it's happening that I think is the problem.

Dr. Schmidt:  Can I just...? Just a minor tangent to that. We were mainly talking about top predators. But obviously there's other predators as well, which are often called mesopredators. They're sort of the smaller ones. You have the lions, say, and then you have smaller ones like the hyenas and the whatnot. There's a theory that the top predator is actually incredibly important in an ecosystem's health because it actually keeps those mesopredators in check. If you remove a top predator it has been shown those middle predators, they go crazy and they can literally wipe out their food source because they just explode in population.
So the question is now - are we just a mesopredator that's happened to get rid of all the competition and is now wiping out our food source? Rather than having a more or less dynamically stable ecosystem, we're causing a boom and bust cycle which is not a good thing as we can tell financially. So it's not good in the environment either. We might actually be, I don't know, when the cat's away we're suddenly tearing down the house. [laughs]

Stephen:  My name's Stephen. I'm just curious: as modern paleontologists in your field, what would be your dream find? So we've got Ediacara, Canowindra, Riversleigh in Australia. What would be the dream find? And how much of this is not a crapshoot anymore? How much of it is really a long time thinking about the sediments that are there, versus what you might be able to come across? Thank you.

Dr. Holland:  For me personally it would be Genoa River where they have released evidence of tetrapods on land in Gondwana. As far as predicting where you will find fossils, a lot of the time it's just persistence. I know some colleagues from North American in the Arctic, spent six years going back to the same site until they found what they were looking for in one of these tetrapodomorpha fishes in Tiktaalik.
 
I think yeah, we are getting better. You can use satellite systems to look for outcropping these days. We sort of have an advantage over our counterparts from the past.

Dr. Schmidt:  My dream find would be a Cambrian rabbit. [laughs] Naw, naw - seriously, we are very into our subject. You might not have been able to tell by the dispassionate way we tell their story. My specialty isn't actually any of this stuff. My specialty is a group of animals that people disparage all the time. They're called moss animals, bryozoans. They barely make anyone scared. But I have found unexpected things doing my research that have really been quite exciting.

And under the microscopes that sometimes, as Tom Rich who is in the audience, he can say... Some of the most exciting things are the smallest things you can find that everyone else would go what on earth are you going on about. But are the spectacular finds like, I don't know, an Australian T rex or a new Ediacaran site or something like that but I mean they're great, can be paradigm shifting, but for us often it's the small things that are quite beautiful.

Dr. Fitzgerald:  For me a really, really exciting find, because we have a more of less blank on it, is the very early echolocating dolphins and whales. So I showed a picture of a toothed baleen whale called Janjucetus, which is found near Torquay here in Victoria. We don't have the equivalent for the toothed sonar using whales and dolphins. They just appear. And as soon as they appear in the fossil record, they got all their kit - they've got all the tools of their trade. We don't have any, if you like, transitional forms between dolphins and the very archaic whales. So that's one thing. Another thing, if you like, if I can use this term, a "holy grail" of vertebrate paleontology, for example, is the origin of bats. When bats appear in the fossil record, whether it's in Australia or elsewhere, they're bats, more or less. We don't have for example something that might be something in between a shrew, a small insectivorous mouse like animal and a fully formed evolved bat. That would really exciting. And I can't really add any more to what Tim said about where we can find fossils. You can look at a geological map and if the rocks are of the right age and it's a sedimentary environment, fine.
 
One other thing, fossils and in fact there's a big blank in the record - early kangaroos, early wombats, early possums. We know nothing. Again, when they appear in the fossil record they're kangaroos, they're wombats, they're possums. What they were like a bit before then, unfortunately, Australia geology hasn't been too kind to us, yet.

Woman 2:  I hope people enjoyed this evening's three lectures. And it's been a pleasure to have you here this evening. I'd like to let you know that we appreciate your feedback. You've all been given an evaluation forms and we'd to suggest that you fill those in and hand them in on your way out. But can you now all please join me in thanking these gentlemen for their fabulous talk. [applause]
About this audio file Dr Rolf Schmidt, Dr Tim Holland and Dr Erich Fitzgerald presented this lecture, "Big Kills, Big Killers" on 8 July 2008 to celebrate the opening of Melbourne Museum's newest permanent exhibition, 600 Million Years: Victoria Evolves.
Length: 59 min

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