The Five Key Rules of Animal Anatomy

Stuart Sumida

One of the highlights of today's Annecy film festival was the talk by palaeontologist Stuart Sumida. Stuart is a world expert on animal anatomy and creature locomotion, widely consulted for his technical expertise on animated feature films like “Spirit”- Stallion of the Cimarron”, "Beauty and the Beast" “Lion King”, "Zootopia" and and “How to Train Your Dragon”.

In a packed room on the third floor of the Imperial Hotel, with lines snaking out into the halls (and no doubt a few fire regs being bent in the process), Stuart gave a talk titled "The Five Most Important Anatomical Rules for Animators".  

Stuart Sumida

Stuart describes himself as “a paleontologist who gets to work with animators” and, while his day job is to teach anatomy to medical students, he also consults on movies for Disney, Pixar and DreamWorks.

I was personally lucky enough to work with him both on "Lion King" and also on "Spirit". On both pictures he helped the animators to achieve much greater levels of believability in our work.

Sumida describes palaeontology as a dry subject, brought to life by artists, because the bones of a long dead animal tend not to make sense until an artist makes sense of it all.

As Stuart puts it: "Science and art go together". Did you know (for example) that the famous T Rex has only one complete surviving skeleton in the whole world? - the rest is left to artists.  Jurassic Park was "hugely important", because it brought dinosaurs to life as never before.  Animators and scientists "should work together". But, we're "not making documentaries"; it's entertainment.




Dinosaur movies take big liberties. But, after all, Jurassic Park is not paleontology. It’s not a documentary.  Big dinosaurs almost certainly could not rear up on their hind legs as they did in the movie. Their bodies would likely have collapsed under their own weight if they had tried to do this.  So the clip above - says Stuart - couldn't happen.

The Five Most Important Anatomical Rules for Animators

Rule 1 You are what you eat
You can ride a horse, "because it eats plants". Plants are surrounded by cellulose, which makes them hard to eat and digest. Plant eaters need to eat constantly just to survive, with barrel-shaped bodies. Carnivores, by contrast, have short digestive tracts, so they are much more bendy; cats are bendy "because they can be".  The guts of a horse are four times longer than a carnivore, so they need a rigid backbone to hold up all that gut.  So, what you eat determines your body shape. You can ride a horse because of its straight back.

Gaits are different too; gallop is different depending on whether you are a carnivore or a herbivore.  Herbivores do a "transverse gallop", while carnivores do a "rotary gallop". In a cheetah's run, the cat locks its head in place so it can fix its attention on the target.



Herbivores run differently. In The Lion King, the Wildebeest did a "transverse gallop"; the wildebeest bob their heads as they run "because they can".

What you eat even affects where your eyes are. In carnivores, their eyes are in front. Herbivores have their eyes on the side, to make way for their huge jaws, needed for endless chewing.

Hyenas are "bone crackers" with huge jaws. They have "very high shoulders" and "very low hips", which we can caricature.

In Lion King, they wanted "a fat guy and a skinny guy", which means "a herbivore and a carnivore". The warthog and the meerkat eat different things, so their body types contrast one another.

Bears are omnivorous, but have jaws built like carnivores.

Stuart pointed out a great online resource, paid for by the US taxpayer: www.digimorph.org is a great resource for skulls online. They have thousands of skulls and skeletons online, all of them free.


Rule 2 Size matters
The bigger you are, “the more you are affected by gravity”.  Big animals “have to keep their limbs straight just in order to stay upright”. And galloping is difficult if you are big. A giraffe is “about as big as you can get and still gallop”.

Bigger animals like elephants “cannot gallop – they are just too big”. So when elephants want to run, they instead “do a really fast walk”.



The elephant in George of the Jungle had to be animated to behave like a dog, even though it was an elephant. The CG team first rigged it like an elephant, but it didn’t work, so they had to “rig it like a dog”, because in the movie, “he thinks he’s a dog”. The animation was funny, but in reality “an elephant cannot do this.” But then, "we're not making documentaries".

In the first scene with Remy the Rat in Ratatouille, he moves just like a rat. Later, he stands on his hind legs like a person but at the start he is "just a rat".

When it comes to animal locomotion, “size matters”. Small animals are “much more bendy”. For example, “they can bound”. The bound “is is a three beat gait – hind, front - front.” Mice do this often.  Stuart worked on this for Pixar on Ratatouille. Rats are small, and animals have very big thigh muscles - all the power comes from the back legs.

Rule 3 Age matters
We are hard wired to think babies are cute - this is evolution at work; it's why we don't kill our children (even if we might want to sometimes!). Babies have big heads and small bodies; it's why we like puppies and kittens.  Winnie the Pooh is basically a toddler, and piglet is wearing a onesie - he's a baby.  Look at Mickey Mouse over the years; he has evolved from a mouse into a baby in terms of his proportions.

Rafiki represents age and wisdom; he has wrinkles and a long face; he is the wise sage, contrasting with the cuteness of baby Simba.

Rule 4 Sex matters
Women have broad hips, because "they need to pass a head through the gap" during childbirth. Men have narrow hips because they only need to "fit a few tubes through the space". Women tend to have long legs and short torsos; men have longer bodies.  So, because women have long legs and wide hips, their "hips tend to swish" when they walk.

We select for these characteristics when we create extreme characters.  You can play with these rules and mess with them.

Rule 5 Skeletons matter
When you build animals and creatures, you need to leave room for muscle and fat on top of the skeleton.

Rule 6  - Creatures and mythical creatures are built out of parts we already know
What's the anatomy of a dragon? The Gronkle was a crocodile and a bumble bee. You need to go and find the original parts that make up the mythical composite, not just copy what other animators have done.

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