Between 122 and 108 million years ago, the Australian landmass was much farther south than today. Victoria was positioned within the Antarctic Circle, separated from Tasmania by a vast rift valley rather than open sea.

This was the Early Cretaceous, and lush forests filled with dinosaurs dominated the landscape. We still find traces of these animals in Victoria’s fossil record.

Most of the dinosaur fossils found in Victoria belong to small plant-eaters called ornithopods. But there are also a few theropod fossils — a diverse group that includes all known carnivorous dinosaurs, as well as modern birds.

More than 250 theropod bones have been found in the Victorian Cretaceous. In the palaeontology collections of Museums Victoria, we have now identified five theropod fossils of particular importance. Our work on these bones has been published today in the Journal of Vertebrate Paleontology.

Shinbones and tail bones

Research over the past decade has revealed striking similarities between Australian and South American dinosaurs. These include megaraptorids with claws shaped like scythes, and small, fleet-footed elasmarian ornithopods. There were also armoured parankylosaurians and colossal sauropods with long necks and small heads.

These parallels may seem surprising at first, but both continents retained a connection to Antarctica throughout much of the Cretaceous Period.

Our newly described fossils show that a bunch of different carnivorous dinosaurs seen in South America also thrived in the Cretaceous of southeastern Australia.

Two shinbones provide the first evidence of carcharodontosaurs (“shark-toothed lizards”) in Australia. A third shinbone provides strong evidence for the presence of unenlagiines, a southern group of dromaeosaurs (“running lizards”).

A fourth shinbone and two tail vertebrae with their chevrons, which are from a megaraptorid, represent one of Australia’s largest-known carnivorous dinosaurs.

A first for Australia

Carcharodontosaurs were apex predators in South America and Africa for much of the mid-Cretaceous. This group of theropods had large skulls, massive teeth and small arms. They were some of the largest predators to ever walk the Earth.

Despite their success in South America and Africa, carcharodontosaur fossils had never been found in Australia – until now. With the two shinbones, we now have the first evidence of the group on this continent.

Curiously, these Australian carcharodontosaurs are much smaller than their African and South American cousins, and the bones we have most closely resemble a carcharodontosaur from Thailand.

One of the Victorian carcharodontosaur shinbones was found on the Otway Coast. The other was found on the Bass Coast, in rocks nearly 10 million years older. This demonstrates these predators were successful in this area for at least 10 million years. It’s a notable find.

The large-bodied carcharodontosaurs of Africa and South America were seemingly specialised for hunting long-necked sauropods. However, this food source was likely not available to the Victorian polar carcharodontosaurs: sauropod fossils have never been found in Victoria.

The Australian ‘raptors’

Unenlagiines were lightly built (and likely feathered) predatory dinosaurs, related to Velociraptor of Jurassic Park fame.

Most unenlagiine fossil remains have been found in South America. Historically, Australia had limited evidence for their presence, as well.

Our description of a new unenlagiine shinbone from Victoria provides robust evidence for their success in polar Australia during the Early Cretaceous.

The snouts of unenlagiines were relatively longer, and their arms relatively shorter than those of their dromaeosaur cousins from the Northern Hemisphere. This implies they had a rather different diet. The Victorian unenlagiine presumably ate fish or small land-dwelling animals. One possibility is the small mammals for which the Victorian Cretaceous is perhaps most famous – more than 50 mammal jaws have been found to date, and some are from ancient relatives of platypus and echidna.

The apex predators of Victoria

Large predatory dinosaurs – on the scale of Tyrannosaurus – are notably absent from the Australian fossil record. Instead, Australian dinosaur populations seem to have been dominated by medium-sized carnivores called megaraptorids.

Megaraptorid fossils are only known from South America and Australia. The most complete skeletons are from South America, including a relatively large one – roughly nine metres long. Australia’s only reasonably complete megaraptorid is Australovenator wintonensis from Winton, central Queensland.

The shinbone and tail vertebrae we describe provide evidence for a large megaraptorid in southeast Australia. Despite being almost 30 million years older than the roughly five- to six-metre-long Australovenator, the Bass Coast megaraptorid was at least 5% larger: approaching the size of its South American relatives.

The large, muscular arms and fingers tipped with fearsome scythe-like claws were presumably the primary weapons of megaraptorids. In contrast to almost every other group of medium-sized carnivorous dinosaurs, megaraptorids had elongated snouts with small teeth.

The abundance of ornithopods in Victoria presumably made this region more suited to smaller prey specialists like megaraptorids, rather than sauropod-stalking carcharodontosaurs.

More discoveries yet to come

We have much to learn about Australia’s Cretaceous dinosaurs. Our study shows how even five isolated and incomplete bones can improve our understanding of our continent’s fossil heritage.

Carcharodontosaurs might have been the apex predators in South America, but megaraptorids ruled the roost in the land down under.

The fantastic dinosaur fossil record of Victoria has grown over nearly 40 years thanks to the efforts of Dinosaur Dreaming, an ongoing volunteer palaeontology project, and citizen scientists like Melissa Lowery. Thanks to their efforts, our window into Victoria’s ancient past continues to become ever clearer.

Jake Kotevski, PhD Candidate, School of Biological Sciences, Monash University and PhD Candidate, Museums Victoria Research Institute and 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 of all ages. If you have a question you’d like an expert to answer, send it to curiouskidsus@theconversation.com.

Why is water different colours in different places? – Gina T., age 12, Portland, Maine

What do you picture when you think of water? An icy, refreshing drink? A crystal-blue ocean stretching to the horizon? A lake reflecting majestic mountains? Or a small pond that looks dark and murky?

You would probably be more excited to swim in some of these waters than in others. And the ones that seem cleanest would probably be the most appealing. Whether or not you realize it, you are applying concepts in physics, biology and chemistry to decide whether you should leap in.

The color of water offers information about what’s in it. As an engineer who studies water resources, I think about how I can use the color of water to help people understand how polluted lakes and beaches are, and whether they are safe for swimming and fishing.

Light and the color of water

Drinking water normally looks clear, but ponds, rivers and oceans are filled with floating particles. They may be tiny fragments of dirt, rock, plant material or other substances.

These particles are often carried into the water during storms. Any rainfall that hits the ground and doesn’t go into the soil becomes runoff, flowing downhill until it reaches an open body of water and picking up loose materials along the way.

Particles in water interact with radiation from the Sun shining on the water’s surface. The particles can either absorb this radiation or reflect it in a different direction – a process known as scattering. What we see with our eyes is the fraction of radiation that is scattered back out of the water’s surface. It strongly affects how water looks to us, including its color.

Depending on the properties of the particles in our water sample, they will absorb and scatter radiation at different wavelengths. The light’s wavelength determines the color we see with our eyes.

Waters that contain lots of sediment – such as the Missouri River, nicknamed the “Big Muddy” – backscatter light across the yellow to red range. This makes the water appear orange and muddy.

Cleaner, more pure water backscatters light in the blue range, which makes it look blue. One famous example is Crater Lake in Oregon, which lies in a volcanic crater and is fed by rain and snow, without any streams to carry sediment into it.

Deep waters like Crater Lake look dark blue, but shallow waters that are very clear, such as those around many Caribbean islands, can appear light blue or turquoise. This happens because light reflects off the white, sandy bottom.

When water contains a lot of plant material, chlorophyll – a pigment plants make in their leaves – will absorb blue light and backscatter green light. This often happens in water bodies that receive a lot of runoff from highly developed areas, such as Lake Okeechobee in Florida. The runoff contains fertilizer from farms and lawns, which is made of nutrients that cause plant growth in the water.

Finally, some water contains a lot of material called color-dissolved organic matter – often from decomposing organisms and plants, and also human or animal waste. This can happen in forested areas with lots of animal life, or in heavily populated areas that release wastewater into streams and rivers. This material mostly absorbs radiation and backscatters very little light across the spectrum, so it makes the water look very dark.

Bad blooms

Scientists expect water in nature to contains sediments, chlorophyll and organic matter. These substances help to sustain all living organisms in the water, from tiny microbes to fish that we eat. But too much of a good thing can become a problem.

For example, when water contains a lot of nutrients and heats up on bright sunny days, plant growth in the water can get out of control. Sometimes it causes harmful algal blooms – plumes of toxic algae that can make people very sick if they swim in the water or eat fish that came from it.

When water bodies become so polluted that they threaten fish and plants, or humans who drink the water, state and federal laws require governments to clean them up. The color of water can help guide these efforts.

My students and I collect water samples at High Rock Lake, a popular spot for swimming, boating and fishing in central North Carolina. Because of high chlorophyll levels, algal blooms are occurring there more often. Residents and visitors are worried that these blooms will become harmful.

Using satellite photos of the lake and our sampling data, we can produce water quality maps. State officials use the maps to track chlorophyll levels and see how they change in space and time. This information can help them warn the public when there are algal blooms and develop new rules to make the water cleaner.

Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to CuriousKidsUS@theconversation.com. Please tell us your name, age and the city where you live.

And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.

Courtney Di Vittorio, Assistant Professor of Engineering, Wake Forest 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.

Is water blue or is it just reflecting off the sky? – The students of Ms Brown’s class, Neerim South Public School, Victoria.

This is a wonderful question as it involves many of the puzzles that motivated research into the physics of light in the early 20th century.

The short answer is that the sea is blue because of the way water absorbs light, the way particles in the water scatter light, and also because some of the blue light from the sky is reflected.

But to explain what I mean by that, I have to tell you a bit about light and physics.

How light works

First, we need to know some fun facts about the nature of light.

The light we see, which we call white light, is made up of incredibly tiny particles called photons. A photon is even smaller than an atom. You can’t see them, but they’re there.

These particles are very strange because when we measure them, sometimes they move like a tiny ball and sometime like a wave – weird, right?

White light is made from photons that have many different wavelengths, some shorter and some longer, and together make up all the colours of the rainbow. The photons with the shortest wavelength we can see look blue, while those with the longest wavelength look red.

So let’s think about sunlight. The photons stream from the sun and interact with all matter on Earth. Depending on what the light touches, some of the photons will get absorbed or soaked up. And some will bounce back. When they bounce back, we call this “scattering”.

The photons that get scattered are what gives things their colour. For instance leaves are green, because the green photons bounce back towards our eyes and that is what colour our eyes perceive. Other coloured photons are absorbed by the leaves.

What colour is a glass of water?

Now that we know a bit more about light, we can begin to answer your question.

Experiments have shown that pure water (water with nothing else dissolved in it) absorbs more of the red light than the blue light.

But how much of the red light will get absorbed? Well, that depends on how much water the light has to pass through.

You might be wondering why the water in a glass looks clear. It is because the glass of water is too small to absorb more red light waves. To see the effect with your eye, you would have to look through a glass of water as big as a swimming pool. That amount of water could absorb quite a lot of red light, so the water would look quite blue.

Now imagine a glass that held an entire ocean’s worth of water. It would be enormous! With that much water, you could absorb a LOT of red light. So it would look very blue.

But when it comes to how light interacts with the ocean, there’s more to the story.

For starters, sea water is not pure. Sea water has lots of things dissolved in it, like salt and small pieces of dead sea creatures. These particles in the water reflect some of the light before it has time to develop the full blue colour. The light coming back out from the sea is usually more greenish-blue in colour.

You asked about the sky. We know the sky is blue and the sea does reflect some of this light. So, yes, it does play a role.

To sum it all up: the sea is blue because of the way water absorbs light, the way particles in the water scatter light, and also because some of the blue light from the sky is reflected.

Finally, we need to think about the time of day and the position of the Sun in the sky. When the Sun is shining bright, the sea appears bluer than it does late at night, when the sea looks very dark and almost black.

Like many questions in science, the answer is not as easy as a simple yes or no. There are often lots of correct, but incomplete, answers to many questions. To me, that’s what makes science so interesting.

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

Justin Peter, Climate Scientist, Australian Bureau of Meteorology

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.

How do babies learn to talk? – Ella, age 9, Melbourne.

What a great question, Ella!

Babies are born ready to learn and although they don’t “talk” in the first weeks of life, they know how to communicate what they are feeling. They do this by crying. And it is something they do a lot before they produce words.

Babies begin to learn the rules of language as soon as the little bones inside their ears and connections to their brain have grown. They can hear the rhythm and melody of their mother’s voice for three months before they are born and this changes the way their brain develops.

The experience that babies get from eavesdropping on their mother’s conversations in utero helps their brain tune into the language that they will learn to speak once they are born.

Infant-directed speech

Have you ever heard someone talking to a baby with a funny voice that sounds almost like they are singing? People often use a higher pitch, speak slower and repeat what they say when they talk to babies.

Research from baby labs all over the world shows that adults help babies work out the sounds of language by using this special style of speech. Researchers call it infant-directed speech.

Scientists have developed different methods to test what babies like to listen to. We know that in the first year of life, babies turn their heads towards a speaker using infant-directed speech. Or they may suck on a dummy that will play recordings of someone who is using infant-directed speech instead of the flatter style of speech adults use to talk to each other.

This shows that babies prefer infant-directed speech to adult-directed speech.

Using a sing song voice helps babies tell the difference between words like “mummy” or “daddy” because:

1) the higher pitch draws the baby’s attention to speech

2) speech sounds like “ma” and “da” are exaggerated, simplified or repeated. That gives babies a better chance at hearing the difference between them.

3) the affectionate tone of voice encourages infants to play with caregivers who draw attention to different words by speaking more loudly or slowing down their speech.

Learning a language

When babies listen to lots of speech, the connections in their brains are more sensitive to speech that is spoken in the environment around them.

So a baby who hears lots of Cantonese or Mandarin, for example, will learn that the difference in the tone of the speaker’s voice is important and can change the meaning of a word.

A baby learning English, on the other hand, will learn that the tone of a speaker’s voice does not necessarily have the same effect on meaning.

Did you know?

Parents who respond to their baby’s happy babbling sounds by imitating them or talking about the sounds they were making might be onto a good idea. Researchers found that this was linked to the baby making more complex sounds and developing language skills sooner.

Infants can understand many words before they can say them. By nine months of age, babies can usually understand words like “bye-bye” and wave when somebody says it.

As infants get older, they babble more and their babble begins to sounds more like words than non-speech sounds.

By the time babies reach their first birthday, most infants have started to produce their first words. At one year of age, babies can usually understand as many as 50 words, and can say one or two words like “mama” or “dada”.

The story of how babies learn to talk is a fascinating one, Ella. It is amazing to think that you and I, and even your own parents were once little babies learning how to use language to communicate.

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.

Christa Lam-Cassettari, Interim Leader MARCS Institute BabyLab, Western Sydney 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.