by Deb on June 6, 2011


So I’m tackling the big one. The one most of my readers’ children already know heaps about but want to know more. They have probably consumed books by the dozen, so what am I going to say in a blog post?

How about some whys and wherefores?


Dinosaurs are, most certainly, reptiles. But they are not giant lizards. Back during the Permian, around 300-250 million years ago, two types of advanced reptiles developed – the mammal-like reptiles and the archosaurs. The mammal-like reptiles eventually turned into mammals, like us, and the archosaurs became the crocodilians, dinosaurs/birds and possibly pterosaurs.

Both groups were ‘advanced’ in that they had developed new features over standard everyday reptiles, with things like teeth in sockets, complex teeth rather than pegs, and legs held under their body for upright gait. In some environments the animal that can chew better, isn’t going to have teeth pulled out or spends less energy walking has more energy to put in to other things like looking after babies, so it will probably have more grandchildren. However in other environments reptiles still have advantages, especially with things like retaining water and not needing as much food to look after those babies, so we still have lots of reptiles. This is what evolution is about.

The mammal-like reptiles dominated the Permian, but were almost wiped out during the mass-extinction around 250 million years ago. Yes, this is our lineage’s second shot at being the most common animal (although really it is, and always will be, the Age of Bacteria). During the triassic period the archosaurs were dominant, and that is when dinosaurs and pterosaurs developed.


An early crocodilian. Note how the legs are under the body, not sprawling to the sides.


The earliest dinosaurs were medium sized, bipedal (two-legged) carnivores. All the later four-legged giants like brachiosaurus came from bipeds, but as they got bigger four legs could support the weight better.

There are two main lineages of dinosaurs, the ornithischians and saurischians. These mean ‘bird-hipped’ and ‘lizard-hipped’ but it doesn’t mean they’re more closely related to birds and lizards, it just means their hips were similar shapes.

Dinosaur families

Click on the picture to see the full size showing how groups of dinosaurs are related.

Both lineages of dinosaur split into several groups. The three types of ornithischians are the armoured dinosaurs, the horned dinosaurs and the hadrosaurs. The saurischians split into the theropods, which remained bipedal carnivores, and the giant sauropods. The theropods also developed feathers and some of them learnt some interesting tricks.


A lot of people want to know why some dinosaurs got so big. Gigantism is quite common in the fossil record, it seems to be a common trend to get bigger when it is possible. There are a lot of advantages to being big. Bigger animals can find more food, because they can eat the leaves from trees as well as groudcover. They can store more food, and their metabolism works much slower than small animals so they can last through shortages. At an individual level, larger animals have an advantage when competing against other animals as predators or prey, or against their own species for mates. If there is an advantage in being big, a big animal is more likely to survive and mate with other big animals to have big babies, so the entire species gradually becomes bigger.

That may not sound like it would have much effect, but think about some numbers. Say mice were getting bigger at 1mm per generation, which is not unreasonable. A mouse generation is 2-3 years, so in 5000 years they would have had around 2000 generations and be 2000mm bigger. That’s 2m – they would be rhinoceros sized. And 5000 years is an eye-blink in geological time, it’s less time than humans have been writing things down. Obviously it’s a lot more complicated than that, but you can see that given the right conditions, animals can get big very quickly.

So what were conditions when the dinosaurs were around?

We might be finding out sooner than we want. The level of carbon dioxide in the air was much higher, so there was a substantial greenhouse effect. The super-continent of Pangaea was breaking up during the Jurassic, which was when the Sauropods were developing. Having all the land in one place with a vast ocean covering the rest of the world had a profound effect on climate, the interior was extremely arid but there was also a mega-monsoon. This made large regions extremely lush and tropical, providing plenty of food for enormous herbivores. Camarasaurs

And there you have a whirlwind overview of dinosaurs – where they came from, how they are related and possibly why they got so big.

The intriguing thing I haven’t talked about is those feathered dinosaurs with the interesting tricks. Unfortunately that is a whole other story that will have to wait for another time.

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{ 11 comments… read them below or add one }

Helen MacMillan via Facebook June 6, 2011 at 7:52 am

Is the giveaway open internationally? :0) My 4yo is dinosaur mad so looking forward to sharing your blog post with him.


Marita June 6, 2011 at 8:12 am

Filled in survey, what a great idea 🙂


Science@home via Facebook June 6, 2011 at 8:55 am

Yes definitely! That’s the beauty of the digital age.


Bernadette Jee via Facebook June 6, 2011 at 10:18 am

great article


Penny Whitehouse June 6, 2011 at 3:30 pm

I just took my daughter to the museum last week and we had a blast looking at dino bones! I wish I had read your post before I went.


Christine C June 6, 2011 at 10:11 pm

Timely 🙂 B has been interested in dinosaurs for a little while now after going to the muesum for special exhibition on Dinosaur Eggs (we have been back another two times), as you mentioned most children are interested! I found a new cassette tape for a $1 at an op-shop with the lyrics book titled Weesing Dinosaurs (i just googled it and it is now available on CD). It is brilliant, absolutely brilliant for kids! It has been playing for two weeks in our house and even I have learnt so much. B was in tears one day as she finally understood that the dinosaurs were kaput. Interesting though that some of my friends have made comments such as “that’s different a girl liking dinosaurs!” She has gone from wanting to be a fairy to a paleontologist…I say bring it on! 🙂

I’d be interested to know what you have in mind for that little bird!!! I look forward to it.


Christine June 6, 2011 at 10:14 pm


This is the exhibtion we saw that is touring at the moment. You may have seen it.


Bec @ Bad Mummy June 9, 2011 at 11:49 am

Erin loves dinosaurs she’ll over the top excited about going to see the dinosaurs at the museum with the Brissy bloggers so we’ll definitely be customers when you get your products up 😀
Bec @ Bad Mummy´s latest amazing offering ..I’m grateful for…My Profile


Kate Schultz via Facebook June 14, 2011 at 2:04 pm

Have you drawn the winner for this? 🙂


Science@home via Facebook June 14, 2011 at 4:38 pm

Sorry, was announced on the blog and I forgot to put it here. The winner was Catherine Butcher.


Catherine Butcher via Facebook June 15, 2011 at 12:04 am

yay thank you!! having difficulty choosing -will get back to you soon 🙂


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