Evolution Gone Wild: Meet The Living Giants of New Zealand

New Zealand. An island nation isolated from the rest of the world by thousands of kilometers of open ocean. Landscapes forged by titanic forces. Peaks carved by fire and ice. Rugged coastlines and primeval forests. Over millions of years these islands and neighbouring Australia became extraordinary evolutionary laboratories. Bizarre species found nowhere else on earth emerged and thrived. Many of New Zealand's native species share an unusual characteristic. Gigantism. To discover why some species grow to such large sizes scientists are exploring their remote habitats. Birds, fish and insects grow to giant proportions. Why did some species evolve to be so large? Just 80 kilometers from New Zealand's largest city Auckland lies the most significant wildlife sanctuary in the country. This is Little Barrier Island known to the indigenous Māori people as Hoturu o Toi. The remains of a volcano that erupted from the ocean three million years ago. Just six kilometers across this little island is the only home of an ancient giant of the insect world. The wetapunga. Little Barrier is so special that for more than a hundred years the government has tightly controlled access. But a research team has been granted permission to investigate one of its most unique residents. Leigh Joyce is a Department of Conservation ranger. It's an arc really. It's like New Zealand used to be and I always say it's like it could be in the future as well and hopefully should be. It's like stepping back in time you know you go into the forest and it feels ancient. Leigh is accompanied by Nicola Torkey the official government ambassador for New Zealand's endangered species. I'm particularly interested in discovering some of our really special invertebrates and in particular I really want to see a wetapunga which are thought to be the heaviest insect in the entire world. Weta are an ancient relative of grasshoppers and crickets. Their ancestors evolved 190 million years ago. Over 70 different species are known and live everywhere from the coast to the mountains. But weighing more than a hamster the little barrier wetapunga is the biggest of them all and the rarest. It's the mystery of their size that brings Nicola and Leigh to this island. Their goal is for the giant wetapunga to be reintroduced onto the mainland but that will only happen if they're successfully protected here. The subtropical climate of Little Barrier allows lush forests to thrive. These are Nikau the southernmost palm in the world. They're also a good place to look for giant insects. Wetapunga are nocturnal and hide under dead palm fronds during the day. She's making an escape. There we are. A male. Oh you can kill one? Yeah. Oh wicked. He's a beauty. He is lovely. Look at the colour on him. Yeah he's quite dark eh? He's amazing. He's quite feisty. Well they like your hair Nick. It is only since humans arrived in New Zealand 800 years ago that wetapunga have become endangered. Their existence today is remarkable. They have survived for 180 million years outliving the dinosaurs. I know that early Maori called them wetapunga which basically meant the god of ugly things that they were a bit frightening but in fact you know he's fairly docile he's not biting he doesn't want to hurt us. They look heavily armoured and dangerous but wetapunga are in fact harmless. This has led to their numbers being driven to the edge of extinction by introduced predators like rats. Since the early 20th century they cease to exist in the wild outside of this island. Their only defence is to raise their spiked legs in the hope it will scare predators away or make a desperate jump for freedom. Other giants of the invertebrate world can be found throughout the country. This 20 centimetre long stick insect has evolved to perfectly mimic a twig and hide from the eyes of predators. Giant centipedes prowl the forest floor. They can grow 25 centimetres long and kill their prey with poison-tipped claws. Other unusually large predators take their time to kill. Giant palifanta snails also live on the forest floor. These creatures first evolved about 200 million years ago and belong to the oldest family of coniferous land snails on earth. They can grow 90 millimetres across, the size of a man's fist. Their favourite prey are giant native earthworms which they devour like living spaghetti. It's a slow and gruesome way to go. The worm isn't being swallowed whole, the snail has a tongue covered in tiny teeth which it uses like a belt sander to scrape chunks of flesh off. The giant worm is ground down while still alive. New Zealand's extraordinary giant invertebrates are found nowhere else in the world. It's a phenomenon known as island gigantism. The research team carefully release their male wetapuna. To fully appreciate the scale of these insects, Nick and Lee continue onwards in search of a female which can grow even bigger. You going to mug me? I might get a mug here. It's that gorgeous one, eh? And I believe I can run a decent marathon. Thank you very much. What caused New Zealand's animals to evolve to be so much larger than their relatives across the oceans? In its nearest neighbour, Australia, the same evolutionary forces are at play, but with very different results. To understand the giants that evolved in New Zealand, we need to travel to its nearest neighbour, 2,000 kilometres away across the Tasman Sea. A very different land, dry, flat and vast. Australia. Just like New Zealand, it was isolated for tens of millions of years. In both countries, this resulted in the evolution of iconic wildlife. Although similar forces are at work in both nations, Australia's animals took a very different direction. Narrow Court in South Australia is famous for two things. Wine and caves. When the owners of a local vineyard were excavating, they got a surprise. Their bulldozer fell through the ground. Underneath the vineyard, a graveyard sealed for hundreds of thousands of years. This is a very special cave. It was found about 12 years ago, but at the time we just didn't have the capacity to do it justice. Paleontologist Dr Liz Reid and her partner Steve took a quick look in the cave and realised it held something very special. The vineyard owner sealed up the entrance to protect it, and no one has been inside it since, until today. And we're now at the point where we can go in and excavate. So this is incredibly exciting because we have no idea what we'll find. Dr Reid is a paleontologist from the University of Adelaide. Her team hopes to find the remains of a group of giant animals unique to Australia, extinct giant marsupials known as megafauna. Australia is a land ruled by marsupials, a group of mammals whose biology is so primitive they use pouches instead of placentas to develop their young. In Australia, there are more species than the rest of the world combined. Some are fierce predators, like the infamous Tasmanian devil. Others are leaf eaters, like Australia's national symbol, the kangaroo. The red kangaroo is the largest marsupial alive on earth. But not long ago, Australia was ruled by gigantic versions of today's marsupials. The team believes the remains of these mega marsupials could be inside the cave and might shed light on these extinct species. 30 million years ago, Narrow Court was at the bottom of a tropical ocean. Sediments turned into limestone, which was then lifted up above the surface again. Over millions of years, rainwater eroded the rock and created a maze of caves. Sinkholes formed in their roofs. These holes became deadly traps for animals living on the surface. Once they fell in, there was no way out. When Liz and Steve saw the main fossil chamber for the very first time, they knew it was a treasure trove of fossil remains. There are bones everywhere. Now they will excavate them and identify the giant marsupials that died in this lonely underground tomb. Okay, so when we first came in, Jess, some of the things we noticed. This extinct kangaroo skull over here, see the tooth row just sticking up? Yeah, yeah. And then panning around, big limb bones on the surface. It's going to take a little while before we get there, but it's a really nice one. Desperate animals who had fallen into the cave would have tried to get out, but there was no escape. Claw scratches line the cave walls, still perfectly preserved after half a million years. Every square inch will be painstakingly studied. It will take years to cover the whole cave. Some people might think it looks quite tedious and boring sitting there in a cave for hours on end, digging one little square of sediment, but that area I was just digging, I found so many bones of multiple species. So I often think of it like a jigsaw puzzle, except I don't start with the box with the picture. I have to try and piece it together myself. But what I'm digging up are pieces of history, pieces of time. So for me, that is so intriguing to be rebuilding part of Australia's history that's now lost. Yeah, I think I'm ready to lift it, Liz. Steve has found the skull of an extinct kangaroo, perfectly preserved hundreds of thousands of years after it fell into the cave. Excellent work, Steve. Nice skull. Really stunning. Very young juvenile of an extinct short-faced kangaroo. This would have still been in its mother's pouch when it entered the cave, probably. One of the main differences between marsupials and other mammals is how they bring up their young. Marsupial babies are born much earlier and crawl into their mother's pouch to finish their development. Nearby lie the remains of an adult kangaroo, possibly the baby's mother. It's a nice specimen too, isn't it? It's an excellent specimen. The team has barely scratched the surface, but they've already made some striking finds. Even better, the other half is in there. They take the results of their day's work back to the lab at the Museum of South Australia. This new cave will add to the remarkable finds in other narrow-caught caves excavated over the last hundred years. Already dozens of bizarre giant animals have been discovered. Among them, the largest marsupial carnivore ever to live, the marsupial lion. Weighing as much as 160 kilograms, marsupial lions would have easily rivaled modern tigers in size. And lots of things about its skeleton tell us what it did. The most striking would be those teeth, the very sharp blade-like premolar tooth that acts like scissors, just slices flesh off its prey. Very powerful animal and certainly a formidable predator. The marsupial lion preyed upon giant kangaroos and the largest marsupial to ever live, a massive wombat called Diprotodon that weighed almost three tons. And as Australia became drier, gigantism was a good survival strategy. Getting big is a really good way to deal with being able to eat lots of relatively poor nutrition food. If you're big, you can deal with times when the resources are low and you've got relatively poor food to eat. But why were these giant animals only found in Australia? Paleontologists like Dr Reid are only just beginning to understand Australia's extinct marsupials. This new cave discovery will provide vital new pieces of the puzzle. It would be impossible to overstate how important this cave is and it's been a surprise for us. It exceeded our expectations. There's so much more bone, more species than we thought. This is an incredible find, one of the most significant in decades and it really can tell us a lot of things about the megafauna and build on this amazing story that we know from the Narrow Court region. That makes that one complete. That is, that's beautiful. There are hundreds more caves in the Narrow Court area that have never been studied. Who knows what secrets they might hold? South Pacific neighbours New Zealand and Australia are home to some of the most dramatic animal examples of island gigantism, a phenomenon where wildlife evolved to massive proportions on island environments. But why did Australia end up with giant marsupials while New Zealand has giant birds and insects? To solve this mystery we must travel back to an ancient age when the two lands were joined together. In the wildest reaches of New Zealand, dense rainforests are dominated by ancient plant species whose lineage goes back 150 million years to the Jurassic period. The kings of the canopy are a group of primitive trees called podocarps, towering over 60 metres tall, the height of an 18-storey building and capable of living for a thousand years. Before humans arrived, forests of ancient podocarps once covered New Zealand. Now only a few precious fragments are left. In Puriora, the main forest canopy is 30 metres high but it is regularly pierced by giants that tower above the rest. There are 15 native species in New Zealand and the tallest and most ancient is the kahikatea. Andrew Harrison is a professional arborist. He studies and looks after trees for a Today he has brought some of his students with him to Puriora to help him climb an ancient giant. It makes me feel when I come into these places that I'm going back in time, that this is what New Zealand would have once been like before humans were here. In fact some of these individual trees would be older than human history in New Zealand. It's uplifting for me to come and be in the forest and even more exciting if I get to climb them. Every rope must be double-checked. Andrew is going to be 50 metres off the ground in an 800-year-old tree. Okay, as far as climbing disciplines go, it is unique climbing a living organism. There is a different feel to it and especially when the wind blows, you're moving around with the tree. You've got to put your faith in the tree that that's not going to let you go. My name is Catherine Kirby and I am an ecologist that studies epiphytes which are plants that live on other plants, so primarily plants that grow up trees. These forest giants don't just feed birds. Their limbs support unique forest ecosystems 50 metres above the ground. Catherine has come to Puriora Forest because of the size of these podocarp trees. Because Puriora is so dense with podocarp, it's awesome for a canopy explorer like myself because the species in the world up in the treetops is like no other. Look at this. These aerial gardens start slowly and may take hundreds of years to form. Mosses and small ferns are the first to settle on a bare branch and as they build up they provide a base for larger plants. Once the canopy community is established, the canopy soil starts to build and the ecosystem really thrives and you can get lots of insects and birds and reptiles living in amongst those plants, so it is quite a unique ecosystem up in the canopy. Climbing these trees that are older than human history in New Zealand, it's a special feeling that it's probably unlikely that people have climbed that tree that we climbed this afternoon. We're going to a place where no one's ever been before. The story of Puriora's podocarps speaks to the dramatic differences between the giants of New Zealand and neighbouring Australia. Fossil pollen has revealed some species have remained unchanged for 180 million years. Back then, New Zealand was joined to Australia as part of the supercontinent of Gondwana and ruled by a group of giant reptiles, the dinosaurs. Gigantic four-legged browsers called titanosaurs were the largest animal to ever walk the earth, reaching high into the canopy with their extraordinary necks. Titanosaurs grew 40 metres long, 20 metres tall and weighed as much as 77 tonnes. Dinosaurs dominated all of Gondwana, including ancient New Zealand and Australia, but since then the two landmasses have taken very different evolutionary paths. 80 million years ago, New Zealand split from Gondwana and drifted away on its own into the Pacific Ocean. Australia remained attached to the supercontinent and a few million years later was colonised by small ancient marsupials. Then one of the most destructive events in history occurred. 65 million years ago, a large asteroid struck the earth, causing a chain of events that drove almost every large species to extinction. Being huge didn't help the dinosaurs. Debris from the extraterrestrial collision blocked out the sun, smothering the forests and wiping out most of the planet's food supply. The only survivors were small animals which needed less food. Small marsupials survived the mass extinction and 45 million years ago, Australia broke away taking them with it. Modern mammals hadn't reached Australia yet, so the marsupials had it to themselves. With the dinosaurs gone, they had no competition and evolved to become giants. New Zealand had separated before the arrival of mammals. Unlike Australia, there were no marsupials. There were birds. Conditions in their new home led many to become huge. The giant moa was the tallest bird ever known, up to three and a half metres at full stretch. These giant browsers were hunted by the largest bird of prey in earth's history, Haast's eagle. Both moa and giant eagles became extinct when the first humans to reach New Zealand hunted them into oblivion. Other giant birds are still alive. The kākāpō is a primitive parrot, the heaviest in the world, that evolved to climb in the forest canopy and feed on the fruit of potocarp trees. There's another sturdy bird that is also the giant of its family, water birds known as rails. And until humans arrived 800 years ago, there were no rodents scavenging on the forest floor. So wētā took their place. Since it had broken away from the rest of the world before mammals reached it, New Zealand became a land of giant birds and insects and also fish. An extraordinary freshwater fish also joined the list of island giants. The same forces that tore Gondwana apart also uplifted dramatic mountain ranges in the South Island, which became covered in ice and snow during the Ice Age. Glaciers carved out huge gouges in the land, which filled with water, forming narrow lakes. The northernmost of these glacial lakes is Lake Rotuiti, home to New Zealand's very own lake monster. The largest of its kind in the world. Dr Don Jellyman is an expert in these giants and is on a quest to figure out why they grow so large. Deep below him lurk the objects of his search, an ancient and unusual group of fish called freshwater eels, or as the Māori call them, tuna. We have two main species of eel in New Zealand, the shortfin and the longfin. It's the longfin which we mainly find here because it's the species that goes well inland and it also goes to a much larger size than the shortfin. Anything up to two metres long and it's quite probably the largest of any of the freshwater species worldwide. But this eel, the longfin, is endemic. It's found only in New Zealand. Don has been studying the unique eels to find out more about their population and habits and help conserve and protect them. The fish are threatened, just like the country's other giants. The giant eels lurk deep in the lake during the day, but as the shadows lengthen they begin to emerge from their hiding places and hunt. Early the next morning it's time to check the net. It's bulging with slimy longfin eels. To calm the eels down while he measures them, Don uses a natural anaesthetic, clove oil. It gently tranquilises the giant eels. Oh, she's a beaut. She's just over a metre long, 101 centimetres, and we know they only grow at about a centimetre a year, so she'll be pushing 100 years old. Quite amazing, isn't it? Slow growth rates in these cold glacial formed lakes. You don't have much of a feeding zone around the edge because they're so deep, so there's not a huge amount of food, so they grow slowly. And there are much larger eels than this lurking in Lake Rotuiti. They've been reported as growing up to two metres and weighing up to 25 kilograms. Mysteriously, males never grow longer than a metre. The giants are all females. Eels can absorb oxygen through their skin. This one will happily breathe out of water as long as Don keeps her skin wet. Longfin eels are the top predators in New Zealand's many lakes and rivers. They've evolved incredible senses to help them find their prey. You can see the nostrils there, ones that people call the horns, where the water is taken in and it comes out this other little nostril just in front of the eye, because eels have a phenomenal capacity to smell. It's a very, very highly developed sense. They kind of call them the equivalent of freshwater bloodhounds because they just need one molecule of some substance in the nasal cavity and they can detect it. Once they've sensed their prey, they wait patiently until it's close and then make a surprise attack at blinding speed. Yes, she's starting to get a bit wriggly. I was going to show you her teeth but I'm not sure I want to put my fingers down her throat at the moment. There we go. Now those teeth are very small and facing backwards, so you can put something down there but you try and pull it out and it's almost impossible. So they're small grasping teeth which means they're great for coming up to a piece of prey and they'll latch onto it and if it's too big, they'll grab it and start twisting and they can do 10 or 12 revolutions a second. So they spin quite rapidly and those little teeth there just really get a good grip and certainly you wouldn't want a big eel like this grabbing hold of you. But there are stories of them coming up and nudging people, especially in dirty water and turbid water. They'll just come up trying to see what's lurking around. I've only ever been bitten a couple of times since it's been my own fault on both occasions. There are 19 species of freshwater eel in the world found on all the major continents, yet New Zealand's female longfins are almost twice the size of their continental cousins. Why have they been the subject of island gigantism and not the males? It turns out living quietly in Lake Rotoiti is only part of this remarkable animal's life cycle. While they live here, they are preparing for an epic journey across the Pacific Ocean. New Zealand's longfin eels are the largest freshwater eels in the world. Females grow much larger than males. Why? Freshwater ecologist Dr John Jellyman is convinced the secret is their incredible life history. Eels first evolved in the western Pacific Ocean near present-day Indonesia and soon spread around the world. When they first reached New Zealand around 20 million years ago, it had already broken away from Gondwana and was isolated deep in the South Pacific. The only other fish in the rivers were small and harmless. These are banded quokkapu, a member of an ancient group called galaxids that first evolved on Gondwana and drifted off with New Zealand when it broke away. They're so primitive they don't even have scales, just smooth mucus-covered skin. There are dozens of species in New Zealand and they form a major part of the longfin eels diet. With no predators or competition and plenty of small fish to eat, the eels thrived. And in New Zealand they've done particularly well because the other species of native fish are really quite small and often quite uncommon. So it was kind of a wonderful opportunity for eels to arrive and to kind of take over the environment. And so they're found throughout New Zealand, right from lowland swamps and estuaries right through to our high country lakes. But there's a catch to living in eel paradise. These eels must make a mysterious and epic voyage back into the tropical ocean to reproduce. They don't let anything get in their way and they will even travel over land for short distances if they have to. All freshwater eels are basically a marine species that have invaded freshwater. The significance of that is that they all still spawn in the tropics, so they're marine spawners and because they originated in the tropics they go back to the tropics. It means a very long journey, maybe three and a half, four thousand kilometres depending where you start from in New Zealand. The exact location of the long thin eels spawning ground is one of the great mysteries of New Zealand natural history. No one has ever seen it but Don and his colleagues are getting closer and closer to tracking it down by attaching satellite tags to migrating females. They leave the coast of New Zealand and all head in the same direction, northwest towards the tropical ocean surrounding the pacific islands. It turns out that our most successful tags, the ones that stayed on the longest, were over towards New Caledonia between New Caledonia and Fiji. We think that's probably where they spawn. When they reach their secret spawning ground males and females mass together and release their eggs and sperm into the water. Then after possibly spending a hundred years building up to this one moment, they die. Their offspring start life as leaf-shaped larvae called leptocephalus. No one has ever seen this stage in New Zealand's long fin eel. The larvae then somehow find their way back to New Zealand over 3,000 kilometres of ocean carried by wind and currents. Nobody knows how they navigate to their home islands. Another mystery of the long fin. The leptocephali spends nine or ten months at sea and it comes back towards New Zealand and then it metamorphoses into the baby eel that we call a glass eel. So a little eel about six, seven centimetres long like a miniature adult. They come into freshwater and then the freshwater life history starts from there. The young eels can climb 40 metre obstacles. Even waterfalls don't stop them. Sometimes it takes several years for the eels to reach a location suited to them. But once she's safe in a deep glacial lake like this, an eel may spend the next hundred years preparing for the ultimate journey. Don is convinced this is why New Zealand's female long fin eels grow larger and older than any others. As a strategy to increase their success of reproducing. It's because they're the biggest species around and they're not really subject to much predation pressure. There's not much that's going to eat you when you get that big. The females can hang around and get very big and when they do that they have a very large number of eggs. So a female eel of this size might have two or three million eggs but if it delays its migration to the sea to maybe a metre, metre and a half, it might have 20 or 30 million eggs. So big, big benefits and hanging around, getting old, getting big, lots and lots of eggs. Okay old girl, we'll put you back. Any year now this giant female will decide to begin her one-way 3,000 kilometre journey to New Caledonia. For now she is safe in Lake Rotuiti and can afford to take her time. She may wait for decades, slowly growing larger and increasing her fat reserves and eggs. An island giant ready for a mysterious and epic journey. A thousand kilometres north on Little Barrier Island, the search continues for New Zealand's textbook example of island gigantism. Rangers Lee Joyce and Nicola Toki have already found an enormous male wetapunga. But just like with long thin eels, the females are much bigger. I just found it underneath that thing. There she goes. Down under there. She is enormous. She's beautiful isn't she? There we go. Look at that. Oh wow. That is something very special. It's amazing. Despite their fearsome appearance, wetapunga are gentle giants. She's not that frightening though is she? No. She's not aggressive at all. The little antennae are just waving around. She's trying to figure out what's going on. You can see the little, oh you probably can't see, you're probably a little bit too close, but she's got these amazing little quilts on her end of her feet which actually hang onto your teeth. Like eels, it's an evolutionary advantage for female wetapunga to grow larger than males so they can produce more eggs and increase their chances of reproducing. They don't live very long, they only live maybe two or three years, but in that time she can lay like 300 to 500 eggs. So she looks really kind of ferocious really just because of her exoskeleton and the spike that sits out of the back. The ovipositor it's called. So it looks as though she's like this incredible kind of scary monster, but she's not. She's very docile, she's very gentle and she very rarely bites. She might raise your legs up if she's an alarm, but her ovipositor, the spine out the back, is actually for laying her eggs and she'll push that down into the ground when the soil's nice and moist and it splits her eggs actually come down the middle. So it's like a little channel I guess, a little tube that helps you put the eggs underneath the soil deep enough that they won't be disturbed. Yeah, so they're amazing, they're incredible critters. Okay, shall we pop her in and see how much she weighs? The 11 species of giant weta are all forest browsers. The wetapunga of Little Barrier Island is the biggest of them all, as heavy as a small mammal or bird. I would say definitely heavier than a sparrow. Yeah, and she's better on your head. Yeah. The heaviest wetapunga ever recorded weighed over twice the weight of this female, 71 grams, three times the weight of a mouse. This is a true island giant. When people think of New Zealand wildlife, people tend to go straight to kākāpō or kiwi, some of the big charismatic megafauna, but it tends to all be birds and yet our invertebrate fauna is something very, very special. I mean, island gigantism has occurred here because we don't have any native four-legged mammals and these beautiful things have evolved to fill the niches that in other places things like rodents would take up. With few threats from predators and no competition from mammals, New Zealand's animals evolved with an eye towards getting big and increasing their chances at reproducing. Throughout its 100 million year history, New Zealand and its unique wildlife have adapted and evolved. While it's impossible to say what new adaptations the next 100 million hold, for now, New Zealand remains a land of giants.