Why do dolphins jump out of the water?

Charlize, age 8, Melbourne

Have you ever seen images of dolphins jumping out of the waves and performing impressive acrobatics in the air? Or maybe you’ve seen it in real life?

When a dolphin jumps, it can launch its whole body out of the water. While it looks like fun, it must also be hard work!

So, why do dolphins jump out of the water? There are several possible reasons. Let’s jump in and explore them.

To stay in touch

Dolphins are social animals and live in groups. But it’s hard to see long distances underwater. So, they use the power of sound to stay in contact with each other.

Sound travels much farther underwater than through the air. When dolphins jump, the slap of the landing makes a loud noise, and would be heard some distance away.

Some species, such as spinner dolphins, use jumping to communicate their location to other group members, especially at night. This helps them keep track of each other.

As an aside, spinner dolphins are very skilled jumpers. As the name suggests, they spin up to seven times in the air before landing back in the water!

The need for speed

Have you ever tried to walk underwater? You will have felt how hard it is. That’s because water is more dense than air, which creates a “drag”, or resistance.

Dolphins have streamlined bodies to reduce drag, but they still feel it. So, if they want to travel quickly – for example, if they are trying to escape a predator or hunt fish – they sometimes jump.

While in the air, they travel faster than they would through water, and also save energy.

To gather food

Some dolphins weigh less than 50 kilograms, such as the Hector’s dolphin. Others weigh several tonnes, such as an orca.

Either way, when a dolphin crashes back into the water, you can be sure it makes quite a noisy splash.

Some dolphin species, such as dusky dolphins, use this noise to herd fish at the surface to make them easier to capture.

Shaking off hitchhikers

Fish called remoras can attach themselves to dolphins using a sucker on their head. This is good for the fish, because it can keep them safe and they have plenty to eat, such as small parasites and old bits of dolphin skin.

While the remoras don’t hurt the dolphin, they probably slow it down. So dolphins may try to get rid of the little hitchhikers by jumping to dislodge them.

Fighting and frolicking

Dolphins are highly intelligent animals. They have big brains and can learn tricks and solve puzzles. With intelligence also come other traits: playfulness and social behaviour.

Sometimes, that social behaviour can end in a “fight”. Dolphin experts say two dolphins jumping around together might be actually trying to hit each other!

Dolphins also love to frolic – not just with each other but with other marine mammals such as whales and sea lions, with turtles – or even just a piece of seaweed! So they might jump as some sort of “game”.

As you can see, dolphins may jump for a range of reasons – sometimes just because it’s really fun!

Katharina J. Peters, Lecturer in Biological Sciences, University of Wollongong

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

Since the late 19th century, sauropod dinosaurs (long-necks like Brontosaurus and Brachiosaurus) have been almost universally regarded as herbivores, or plant eaters.

However, until recently, no direct evidence – in the form of fossilised gut contents – had been found to support this.

I was one of the palaeontologists on a dinosaur dig in outback Queensland, Australia, that unearthed “Judy”: an exceptional sauropod specimen with the fossilised remains of its last meal in its abdomen.

In a new paper published today in Current Biology, we describe these gut contents while also revealing that Judy is the most complete sauropod, and the first with fossilised skin, ever found in Australia.

Remarkably preserved, Judy helps to shed light on the feeding habits of the largest land-living animals of all time.

Plant-eating land behemoths

Sauropod dinosaurs dominated Earth’s landscapes for the entire 130 million years of the Jurassic and Cretaceous periods. Along with many other species, they died out in the mass extinction event at the end of the Cretaceous 66 million years ago.

Ever since the first reasonably complete sauropod skeletons were found in the 1870s, the hypothesis that they were herbivores has rarely been contested. Simply put, it is hard to envisage sauropods eating anything other than plants.

Their relatively simple teeth were not adapted for tearing flesh or crushing bone. Their small brains and ponderous pace would have prevented them from outsmarting or outpacing most potential prey.

And to sustain their huge bodies, sauropods would have had to eat regularly and often, necessitating an abundant and reliable food source – plants.

Although the general body plan of sauropods seems pretty uniform – stocky, on all fours, with long necks – these behemoths did vary when we look more closely.

Some had squared-off snouts with tiny, rapidly replaced teeth confined to the front of the mouth. Others had rounded snouts, with much more robust teeth, arranged in a row that extended farther back in the mouth. Neck length varied greatly (with some necks up to 15 metres long), as did neck flexibility. In addition, a few of them had taller shoulders than hips.

Absolute size varied too – some were less enormous than others. All of these factors would have constrained how high above ground each species could feed and which plants they could reach.

Food in the belly

Sauropod discoveries are becoming more regular in outback Queensland, thanks largely to the Australian Age of Dinosaurs Museum in Winton.

In 2017, I helped the museum unearth a roughly 95-million-year-old sauropod, nicknamed Judy after the museum’s co-founder Judy Elliott.

We soon realised this find was extraordinary. Besides being the most complete sauropod skeleton and skin ever found in Australia, Judy’s belly region hosted a strange rock layer. It was about two square metres in area and ten centimetres thick on average, chock-full of fossil plants.

The fact this plant-rich layer was confined to Judy’s abdomen and located on the inside surface of the fossil skin, made us wonder – had we unearthed the remains of Judy’s last meal or meals?

If so, we knew we had something special on our hands: the first sauropod gut contents ever found.

Multi-level feeding

Analysis of Judy’s skeleton, which was prepared out of the surrounding rock by volunteers in the museum’s laboratory, enabled us to classify her as a Diamantinasaurus matildae.

We scanned portions of Judy’s gut contents with X-rays at the Australian Synchrotron in Melbourne and at CSIRO in Perth, and with neutrons at Australia’s Nuclear Science and Technology Organisation in Sydney.

This enabled us to digitally visualise the plants – which were preserved as voids within the rock – without destroying them.

We did destructively sample some small portions of the gut contents to figure out their chemical make-up, along with the skin and surrounding rock.

This revealed the gut contents were turned to stone by microbes in an acidic environment (stomach juices, perhaps), with minerals likely derived from the decomposition of Judy’s own body tissues.

Judy’s gut contents confirm that sauropods ate their greens but barely chewed them – their gut flora did most of the digestive work.

Most importantly, we can tell Judy ate bracts from conifers (relatives of modern monkey puzzle trees and redwoods), seed pods from extinct seed ferns, and leaves from angiosperms (flowering plants) just before she died.

Conifers then, as now, would have been huge, implying Judy fed well above ground level. By contrast, flowering plants were mostly low-growing in the mid-Cretaceous.

Based on other specimens (especially teeth), scientists previously thought Diamantinasaurus browsed plants relatively high off the ground. The conifer bracts in Judy’s belly support this.

However, Judy was not fully grown when she died, and the angiosperms in her belly imply lower-level feeding, as well. It seems likely, then, that the diets of some sauropods changed slightly as they grew. Nevertheless, they were life-long vegetarians.

Judy’s skin and gut contents are now on display at the Australian Age of Dinosaurs Museum in Winton. I’m not sure how I’d feel about having the remains of my last meal publicly exhibited for all to see posthumously, but if it helped the cause of science, I think I’d be OK with it.

Stephen Poropat, Research Associate, School of Earth and Planetary Sciences, Curtin 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.

Who was the first ancient mummy wrapped up? - Jake, age 5, Swansea.

The first mummy to be wrapped up comes from the Chinchorro culture of South America, in the area of southern Peru and northern Chile. The oldest of these mummies was a person who died in 5050 BC, over 7,000 years ago. These Chinchorro mummies are 2,000 years older than the mummies in ancient Egypt!

One of these Chinchorro mummies was preserved by nature, and was not wrapped up, and it is 9,000 years old (meaning it is from 7,020 BC).

Chinchorro means “gill netters”, which is their way of fishing with nets. The Chinchorro people lived by the sea, the Atacama Coast, along the Pacific Ocean. Most of what they ate was seafood (fish and shellfish), sea birds and sometimes sea lions. They also hunted animals for meat and collected some plants, too.

Pictures of these mummies may frighten some curious kids. Parents are advised to search and look at images online before showing them to children.

These mummies have remained the same until today because the place where the Chinchorro lived was very dry, even though they lived by the ocean. Much of this area is a desert and some areas have not had rain in over 400 years!

How are Chinchorro mummies made?

The Chinchorro had different ways of preserving (to keep safely so that it does not spoil) the dead bodies. They would start by removing all the organs inside the body, even the brain. The hair and skin would also be removed using stone tools, not metal knives. Some of the sharpest knives were made using a pelican’s beak.

Sometimes, the head, arms and legs would be removed and the body was put back together later. The body would be dried out using a mixture of hot coals from a fire, as well as ash. They would place sticks inside the body to keep the body stiff and fill the insides with straw and feathers. The face would be covered in clay and left out to dry for 30-40 days. Sometimes the bodies would be painted red or black.

How did the Chinchorro mummies die?

Some of these bodies had diseases and broken bones. Arthritis and bone decay are two common diseases. Some mummies have damage in their ears suggesting that some people may have been deaf. This damage likely came from diving in the ocean for shellfish. Many mummies have broken bones that have gotten better. These injuries are either from accidents at work or fighting inside the community.

All sorts of people were made into mummies - men, women and children, young and older people, too. Even some babies were mummified, which could be because they died during childbirth; these babies were some of the most decorated mummies.

After the mummy was finished, it was not buried. People would put them in their houses and other places where people lived, worked and played. Some people think the mummies brought good luck.

We are not exactly sure why the Chinchorro made these mummies but we think it is because they cared for their dead families and wanted to keep their physical body, and their memory, alive forever.

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.

Dr Serena Love, Honorary Research Fellow, The University of Queensland

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!

Hi Curious Kids, My name is James and I live in Melbourne and I’m 10 years old. Why do our ears pop when we reach a certain altitude? - James, age 10, Melbourne.

Hi James. What a great question.

There are three key sections of our ear – the outer ear, the middle ear and the inner ear. Your question relates to the middle ear and the area around the ear drum.

The middle ear space is pretty airtight, although air can pass into and out of this space by the opening and closing of the Eustachian tube (the tube that links the middle ear to the back of the throat). Most of us can do this by yawning or opening our jaws, which often results in our ears “popping”.

Your ears pop because of the pressure difference between the air outside and the air inside your middle ear space. I’ll explain how that works.

You have a small amount of air sealed in the middle ear space. And then there’s all the rest of the air outside, in the atmosphere.

Normally the air pressure inside the middle ear and in the atmosphere are very similar, or at least not different enough to cause you any trouble. As you increase in altitude (either in a car going up a hill, going up in a lift, or taking off in an aeroplane) the air pressure in the atmosphere decreases, making the air “thinner”, while the air pressure in the middle ear remains relatively unchanged.

This puts pressure on your eardrum as the air pressure in the middle ear expands relative to the air around it. This expansion causes not only the discomfort you feel before your ears “pop”, but also makes it harder to hear things, because the pressure on your eardrums makes the sound harder to transmit.

There is no specific altitude at which your ears pop, and during quick ascents, like during an aeroplane take-off, you may have to equalise or “pop” your ears a few times to keep up with the pressure changes.

Other times, like on a slow walk up a hill, your ears may equalise themselves without you even noticing.

The reverse can happen when you are descending in an aeroplane or going down a hill. The air in the atmosphere increases in density through the descent, while the air pressure in the middle ear space remains low like it was at the higher altitude.

This forces pressure on the eardrum and causes it to retract inwards (instead of bulging outwards on ascent) until your ears pop to make the pressure between the middle ear and the atmosphere more equal.

You can have some trouble if you are doing a significant ascent or descent and have a cold or an ear infection.

The mucus from a cold or ear infection can block the Eustachian tube, making it hard to equalise your ears properly. This can make your ears ache from even small changes in altitude and the eardrum is pushed inwards (on descent) or outwards (on ascent).

Babies and young children often have blocked Eustachian tubes – this may be one reason they don’t like flying.

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.

Chris Brennan-Jones, NHMRC Research Fellow, Telethon Kids Institute, The University of Western Australia

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! You might also like the podcast Imagine This, a co-production between ABC KIDS listen and The Conversation, based on Curious Kids.

Are mermaids real? – Isobel, age 12, Strathfield.

Sadly, no. There are a lot of TV shows, movies, and fairy tales about mermaids. Some of them are fun and lighthearted, others are designed to be scary.

Some people have claimed to have seen real mermaids, but these have been proven to be hoaxes.

One thing we do know is that mermaids have been a part of human storytelling around the world for a long time.

Thousands of years ago

Thousands of years ago in the ancient Neo-Sumerian Empire (located in the Middle East) the goddess Atargatis (also known as Derketo) was described as being half woman and half fish.

The ancient Roman writer, Pliny also described mermaids from Gaul (modern France, Luxembourg, Belgium and Western Germany). Pliny says that there were a lot of people who washed up on the shore, and these people were covered in scales.

In the Middle Ages, there were many depictions of mermaids, and these depictions were very common across Europe. They were depicted as human from the waist up, and a fish from the waist down. Mermaids in the Middle Ages were viewed as dangerous and said to drown sailors. Many tales warned men to stay away from beautiful women and be careful at sea.

A case of mistaken identity

When exploration became more widespread, sailors began to see animals such as the manatee and dugong more, often mistaking them for mermaids. Both animals have a long tail that resembles the traditional mermaid’s tail. The dugong and manatee are most commonly found in oceans near Africa, and Southeast Asia.

Sailors who saw their tail splashing often believed they were seeing a mermaid’s tail as she was diving under water. During this period, the mermaid was still seen by sailors as an omen of ill luck. Some folk tales about mermaids described them as beautiful women who distracted sailors when they sailed past their rocks and made the ships crash.

In 1837, Hans Christian Andersen wrote The Little Mermaid and the image of the frightening mermaid changed. While previous tales focused on mermaids luring sailors to their deaths, The Little Mermaid was notable for having the mermaid save a human life.

In 1842, P. T. Barnum, who owned a museum in America, attempted to prove mermaids existed. Barnum announced he had come into possession of a “Feejee (Fiji) Mermaid”. The mermaid was a carefully sewn together forgery: a baby monkey’s head, chest and arms were attached to the tail of a fish. This captured the imagination of Barnum’s audience, who had previously seen dugong and manatee tails displayed as genuine mermaid tails. While the Feejee Mermaid is now known as one of Barnum’s many fake animals, it drew a lot of attention, and many more fake mermaids have been created in the same manner.

While we have no proof that mermaids exist, there are many cultures with traditions of part-humans who live in oceans or lakes. Many of the mermaids in Western Europe, and the Middle East are shown as part human, and part fish, although in other cultures the fish tail may be a snake tail instead.

Very few mythical creatures can be found in so many diverse cultures across such a long period of time without changing. So even if mermaids are not real, they will likely continue to lurk in the human imagination.

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.

Adam Turner, PhD student, University of Newcastle

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