Roughly 425 million years ago, in the warm seas over what is now southern China, there lived a metre-long bony fish with jaws full of clusters of spiky teeth.

Long extinct, this predatory fish (Megamastax amblyodus) was an ancient forerunner of all animals with a skeleton and a backbone alive today – including you and me – and was the world’s oldest known vertebrate apex predator that lived at the top of the food chain in its environment.

In a new paper published in Nature today, we report the discovery of a remarkable new fossil of this strange creature.

This fossil gives us an unprecedented view into the early evolution of bony fishes, and fills a key gap in our understanding of the evolution of vertebrate diversity seen on Earth today.

The dawn of bony fishes

Bony fish are known as osteichthyans. They make up around 98% of all vertebrate species on Earth.

By the end of the Silurian Period (419.2 million years ago) the osteichthyans had branched into two main lineages: the Actinopterygii (ray-finned fishes) and Sarcopterygii (lobe-finned fishes and limbed tetrapods, including humans).

Until recently, our knowledge of the very earliest bony fishes (stem-osteichthyans) that branched off before that great split was restricted to tantalising fragments from Silurian and Early Devonian rocks, giving only the briefest glimpse into their bizarre anatomy.

Megamastax: the early discoveries

We first described Megamastax in 2014 based on isolated jaw bones from the Kuanti Formation of Yunnan in southern China.

The largest jaw would have been 17 centimetres long when complete, suggesting an animal roughly one metre long that was – and still is – the largest known jawed fish from the Silurian period. While there were sharp, conventional teeth on the biting margins of the mouth, the inner surface of the lower jaw displayed a row of big semicircular “lumps” unlike anything seen before.

We identified these as an inner row of large blunt teeth, presumably for crushing armoured prey, and so named the new fossil Megamastax amblyodus – the “big mouth with blunt teeth”.

‘Big mouth’ gets a makeover

We hoped to find more fossils of this fish in subsequent field trips to Yunnan. But nothing prepared us for what turned up just few years later: a complete skull and jaws that revealed a creature far weirder than we could have ever imagined.

The skull was long and narrow, with small eyes and a huge mouth with a sharply hooked snout. The anatomy was an odd mosaic of features associated with many different vertebrate groups.

On the one hand, the cheeks and gill covers were typical for an early bony fish. But other features were strikingly similar to the strange Silurian fish [Entelognathus], which was a type of “placoderm” (a group of extinct armoured fish) that lived at the same time. One such feature was the configuration of the bones on the skull roof which are singular instead of paired.

In most bony fishes, the paired bones at the front of the mouth are simple structures that sit flat against the front of the snout. But in Megamastax and Entelognathus, these bones also had broad horizontal shelves that extended into the roof of the mouth.

High-resolution scans revealed internal features which were unusual for a bony fish. The way the braincase extended far backwards was once again similar to Entelognathus, while the major arteries branched at the back of the skull in a manner identical to early shark relatives.

A mouth full of pincushions

Inside the mouth, we learned the truth of those strange lumps on the original lower jaw.

The new skull showed complementary rows of lumps on the roof of the mouth. Also present were odd little circular structures that, in life, would have slotted onto these lumps, each topped with a cluster of sharp fangs.

So those mysterious lumps were not teeth at all, but the mounting points for bony tooth cushions.

Tiny isolated tooth cushions had previously been found with Lophosteus and Andreolepis, two fragmentary bony fish from the Silurian period in Europe. These were originally interpreted as being associated with the gills, but it was also suspected they may have instead been a kind of tooth plate. But how they fit into the mouth was a mystery.

Megamastax finally answers this and reveals these cushions were widely distributed at the base of the bony fish radiation, but were lost in the common ancestor of the ray-fins and lobe-fins.

So instead of having a few blunt teeth for cracking armour, Megamastax instead had a mouth filled with clusters of piercing fangs for snagging softer-bodied prey. However, it was a vastly larger fish than any other animal in its habitat and could likely devour most of them regardless of armour.

It was likely the earliest vertebrate apex predator in the fossil record.

A complementary find

The new skull of Megamastax is one of two new major Chinese fossil discoveries.

The other is Eosteus chongqingensis (by a different team of authors), a tiny 3cm long bony fish from the famous 435 million year old Huixingshao Formation, Chongqing.

This find complements the outstanding cranial detail of Megamastax in preserving the whole body and fins. At over 10 million years older than Megamastax, this is the earliest osteichthyan in the fossil record.

The great-uncle of all living bony vertebrates

With only jaws, it was hard to pinpoint where Megamastax sat within the osteichthyan family tree.

We previously suggested it could be a primitive lobe-finned fish. But the new skull revealed it to be something else. Our new family tree moves it closer to the great split, but above all the other stem-osteichthyans in the analysis.

If correct, then Megamastax is the closest known form to the common ancestor of the ray-finned and lobe-finned fishes.

This new skull bridges the gap between placoderms and bony fishes. In revealing the anatomical “default settings”, Megamastax provides a template for exploring when and how the osteichthyans acquired key features – a journey that would ultimately lead to their incredible modern diversity.

Brian Choo, Postdoctoral Fellow in Vertebrate Palaeontology, Flinders University and Jing Lu, PhD Candidate, Evolutionary Biology, Chinese Academy of Sciences

This article is republished from The Conversation under a Creative Commons license. Read the original article.

This is an article from Curious Kids, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky!

Bula! My name is Emelia and I am 6 years old. My little brother and I live in Fiji and we love listening to the Imagine This podcast! We love the episode about why cats don’t wear shoes. I would like to know why man lions have manes and lady lions don’t?– Emelia, age 6, Fiji.

Thank you, Emelia, for your very interesting question.

For a long time, people thought that boy lions had big shaggy manes to protect the area around their necks from being bitten or scratched during hunts and fights.

However, as time passed, scientists began to see that this idea didn’t really make sense.

The first reason it didn’t make sense was that when lions fight each other, they don’t usually attack the neck at all. Instead, when they get into fights, they tend to bite along the back and hips. That means it is unlikely their neck would be close enough to another lion’s teeth to get bitten. So it wouldn’t make much sense for the mane to protect a place that wasn’t in danger.

Another big reason that people no longer think that manes are there to protect boy lions is because of the way lions hunt. When looking for food, lions hunt in a group called a pride. But both boy lions and girl lions in the pride work together when they hunt. So if manes were supposed to be for protection, then why wouldn’t girl lions and boy lions both have manes?

So because scientists found that their old ideas couldn’t be true, they came up with new possibilities that would fit with what they were seeing. This happens all the time in science.

Instead of being for protection, people now think that the boy lion’s mane shows the girl lions how healthy and strong he is. The idea is that the stronger and healthier a boy lion looks, the better the girl lion’s babies will grow since they would have a dad with good genes. (Genes are the “recipe” that tells a baby animal or plant how to grow, so having parents who are strong and healthy makes you more likely to grow up strong and healthy.)

Some studies show that female lions even prefer darker coloured manes to bigger manes. A pale mane might mean the lion is experiencing stress – for example, they might not be getting enough of the right foods or they might be feeling sick. The dark colour seems to show that the boy lion is under less stress.

In the same way that dark clothes make us hotter than white clothes would, the dark mane shows that the lion can do well in hot weather.

This is really important in the warm climates where lions live.

Lions aren’t the only animals that choose their mates based on how they look. For instance, girl peahens tend to like boy peacocks with the biggest and showiest feather displays.

So scientists now think that a lion’s big puffy mane probably isn’t there for protection.

Instead, we think the mane, and especially its colour, helps the boy lions show the girl lions how healthy and strong they are. Then the girl lions will know who will be a good dad for her babies.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to us. They can:

* Email your question to curiouskids@theconversation.edu.au
* Tell us on Twitter

Please tell us your name, age and which city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question but we will do our best.

Nadya Sotnychuk, PhD candidate, University of New England

This article is republished from The Conversation under a Creative Commons license. Read the original article.

This is an article from Curious Kids, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky!

Why do sea otters clap? Is it fun? – Alex, age 5, Melbourne.

Hi Alex. Those are some great questions. Sea otters are one of my favourite animals.

Something we have to ask ourselves when trying to work out why an animal does something is whether or not the behaviour is natural.

If you’ve been lucky enough to observe a sea otter clapping in a zoo or aquarium, you might have been watching an animal that has been trained to clap by its human keepers.

But what about wild sea otters? Do they clap too, and if so, what might it be for?

How do wild sea otters use their hands?

Sea otters are fascinating creatures. They are air-breathing mammals and yet spend almost their entire lives at sea. They swim mostly with their back feet, which leaves their hands free to do other things while swimming about.

In the wild, sea otters sleep out on the water. To stop themselves drifting away in their sleep, they use their hands to hold onto seaweed (or each other), creating a raft of animals floating together. When resting during the day, they’ve even been seen covering their eyes with their paws to help them sleep.

Sea otters also use their paws to groom their fur. They have one of the thickest fur coats of any animal, which helps them to keep warm in the freezing waters of the North Pacific Ocean. To keep their coat healthy, they use their hands to rub down their fur, trapping air against their skin to stay warm and dry. This can look like clapping their hands against their sides.

But the most interesting thing sea otters do with their paws happens while feeding. After catching hard-shelled prey like shellfish or sea urchins, sea otters will break open the shell by hitting it against a stone resting on their belly. Otters have even been known to have a favourite stone that they carry around in their armpits. As well as looking like they are clapping when doing this, you can even hear the “clap” sound of the hard shell hitting the stone!

So, even for wild sea otters, “clapping” may play a useful role in both grooming their fur and preparing their food.

Is clapping fun though? Hopefully, one day you will meet some sea otters and you can ask them yourself.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to us. They can:

* Email your question to curiouskids@theconversation.edu.au
* Tell us on Twitter by tagging @ConversationEDU with the hashtag #curiouskids, or
* Tell us on Facebook

Please tell us your name, age, and which city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question but we will do our best.

David Hocking, Research associate, Monash University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

This is an article from Curious Kids, a series for children. The Conversation is asking kids to send in questions they’d like an expert to answer. All questions are welcome – serious, weird or wacky!

Do worms have tongues? - Ren Ashley, age 3, Melbourne.

That’s a really interesting question, Ren Ashley. The short answer is no. Worms do not have tongues.

Some people think that worms have tongues because certain worms do have something in their mouth that they can poke out, like a tongue. It is called a “stylet” and it looks like a needle.

Worms that eat plants pierce the outside of the plant with their stylet. They then use the stylet like a straw, to suck out food from inside the plant. But the worm’s stylet isn’t actually a tongue.

Since you were curious enough to ask the question, I imagine you would be interested to know a bit more about worms and about tongues.

You have probably seen worms in the soil in your garden, or maybe your family has a worm farm, where worms eat up your fruit and vegetable scraps. These worms are called earthworms.

But they are not the only kind of worm. In fact there are many thousands of different creatures that we call worms. Some worms are so tiny that you need a microscope to see them. Other worms are very big. One type of worm, called the bootlace worm, lives in the sea and can grow to be as long as an Olympic swimming pool!

So how do all these worms live without a tongue? To answer this question, we need to think about what a tongue does.

What does a tongue do?

One of the important jobs of our tongue is to crush up food when we are eating. Inside our tongue is a set of muscles. These muscles let our tongue move food around in our mouth. Our tongue crushes food by squashing it up against the hard part at the top of our mouth.

Like us, worms need to crush up their food. But instead of using a tongue, worms have muscles in their gut that do this.

Another important job of our tongue is to taste food. Our tongue is covered in tiny bumps. Inside those bumps are taste buds that can sense whether the food we are eating is sweet or salty or sour or bitter. That can help us work out if a food might be dangerous.

Without a tongue, worms don’t have taste buds. But earthworms can still taste, using special cells inside their mouth and other cells that are in their skin. As well as tasting, these cells also allow earthworms to smell. By sensing smells and tastes in the soil, worms can work out where they need to go to find food.

So even though worms don’t have tongues, they can use different parts of their body to do some of the jobs that our tongues do.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to us. You can:

* Email your question to curiouskids@theconversation.edu.au
* Tell us on Twitter by tagging @ConversationEDU with the hashtag #curiouskids, or
* Tell us on Facebook

Please tell us your name, age and which city you live in. You can send an audio recording of your question too, if you want. Send as many questions as you like! We won’t be able to answer every question but we will do our best.

Hannah Nicholas, Senior Lecturer in Molecular Biology, University of Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Curious Kids is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.

Why do we have two kidneys when we can live with only one? – Question from the students of Ms Morris’ Grade 5 class, Ringwood North Primary School, Victoria.

This is a really great question. The answer is scientists are not completely sure but we do have some theories. That is often the case with science.

Most of the animals you see above ground on Earth today, including humans, are the same on both sides. We have two eyes, two ears, and even two nostrils. Scientists gave this a fancy name called “bilateral symmetry.”

If you look in the mirror and draw an imaginary line down the middle of your reflection you will see that you have an arm and a leg on each side. If you had goggles that let you see your insides, you would see that you also have a kidney and a lung on each side too.

But it wasn’t always like this. And some animals still only have one kidney.

Around 500 million years ago, our long-lost relatives that were living in the ocean (some of whom probably only had one kidney) decided to leave the water to walk and live on land.

This was a very important moment in our history because on land, animals could change to grow a very complicated body with all of the important organs that are inside you, including two kidneys.

Two kidneys better than one?

Right now, your kidneys are getting rid of all things your body does not need. They do this by “cleaning” your blood.

All of this waste will exit your body when you go to the toilet to pee. But your kidneys do a lot more than just clean your blood. They help your bones stay healthy, tell your body when to make new blood cells, and even help you stay upright when you’re walking around all day by taking care of your blood pressure.

With all those important functions, scientist think having two kidneys must be important for our survival.

Growing up with one kidney

It is true, you can live with only one kidney. Some people are born with only one because the other one did not grow properly. Other times, the two kidneys touch each other when they are first growing and join together, making one kidney shaped like a horseshoe. People with these types of kidneys have to be very careful because they might get sick more easily than someone who has two kidneys.

Needing an extra kidney

Sometimes our kidneys stop working. When this happens our blood cannot be cleaned and we can get very sick. The only way to stay alive is to be attached to a big machine that cleans your blood for you, or have a kidney transplant.

This happened to me when my kidneys stopped working properly. My dad gave me one of his kidneys. Thanks, Dad.

There are two people involved in a kidney transplant: a donor who is going to give their kidney, and a recipient who will receive the kidney.

After the new kidney is put into the recipient, both the donor and recipient only have one kidney that works properly. Both the donor and the recipient can live long happy lives with only one kidney. They just have to take extra care that they eat healthily and exercise to stay fit. One person living in Australia has been using a transplanted kidney for 45 years!

So, while your body works best when all of your organs are inside you and working properly, scientists still don’t exactly know why we have two kidneys. However, it is good to know that we have a few spare parts that we can live without.

And if you’re an adult reading this, it’s good to make sure you are registered as an organ donor and also chat to your family so they know you want to donate. You may one day save a life.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au

Please tell us your name, age and which city you live in. We won’t be able to answer every question but we will do our best.

Brooke Huuskes, Lecturer in Human Anatomy, Physiology Anatomy & Microbiology, La Trobe University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Curious Kids is a series for children. If you have a question you’d like an expert to answer, send it to curiouskids@theconversation.edu.au You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.

Why do we have fingernails and toenails? - Jake (age 9) and Ben (age 7), Melbourne.

The reason we have fingernails and toenails is not to pick our noses or to scratch our siblings.

The short answer is we have evolved to have nails because they help us pick things up (like food), pick things off (like bugs), and hold tightly onto things.

Early humans who had these type of nails (instead of claws) tended to live long enough to have babies and pass on the fingernails gene to their kids. So over time, the number of human ancestors with nails grew and the number with claws shrunk. That’s how evolution works.

But the story goes back further than that.

Our primate ancestors and cousins

Humans are members of the primate family. The primates are the most intelligent group of mammals (mammals are animals who do not lay eggs). Primates have evolved to have nails.

That’s why you see primates like apes and monkeys also have nails on all their fingers and toes, as well as our closest primate “cousins”: gibbons, bonobos, chimpanzees, gorillas and orangutans.

While humans don’t usually use our toes these days to pick things up, our primate cousins do. So our toenails are a hangover from a time in our evolutionary past where we often used our feet to pick stuff up and pick stuff off.

All these primates – including us – evolved from a common ancestor that had claws.

Nails vs claws

So why did we evolve to have nails instead of claws? The answer is that nails let us do a lot of important things that you can’t do with claws.

Compare your nails to those of a dog or cat. Your nails are wide, flat and shield-shaped. They are also on the back of the tip of your fingers and toes.

A dog or cat has claws that are thin, curved and pointed. They wrap around the end of their “fingers” and “toes”.

By having nails, you can pick up tiny things like small LEGO bricks off the ground, pick off stickers, or pick a bug off you easily. You can make and use tools. Can a cat do that with its claws? No! In fact, having super-long, clawlike nails can make it really hard to do a lot of things humans need to do – like eating, washing and holding things.

On the other hand, claws are useful for some things that cats and dogs often need to do.

By having claws, your cat can quickly run up a tree (even if it doesn’t have many lower branches) to catch a bird. Plus your dog can dig up your backyard in one afternoon (to find food, for example).

Primates also climb trees but we mostly do it by grasping onto branches, and long claws get in the way when you’re grasping. Nails provide a rigid backing to primates’ fingertips to improve grasping. We dig too, of course, but we use tools for that. You don’t have the same needs as a dog or a cat, so you don’t have the same type of nails or claws.

Each type of animal has evolved to have the type of finger-covering (either claws or nails) that best suits its needs.

What if we didn’t have nails?

Imagine for a moment that humans didn’t have nails. First, a lot of nail salons would go out of business, and we couldn’t enjoy painting our nails lots of different colours.

But more importantly, having a lump of soft skin at the end of our fingers would make it harder to hold things and control our grip on them. The ends of our fingers and toes have changed to match our changed lives.

So next time you’re at the zoo, look at the hands of gibbons, chimpanzees, gorillas and orangutans, and you’ll see they have nails just like yours. Think about all the amazing things we primates can do with nails.

Hello, curious kids! Have you got a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au

Please tell us your name, age and which city you live in. We won’t be able to answer every question but we will do our best.

Amanda Meyer, Lecturer of Human Anatomy, The University of Western Australia

This article is republished from The Conversation under a Creative Commons license. Read the original article.