Spinal Flexibility and its Influence on how Creatures Squash and Stretch.

Animal Movement Breakdowns

Here are a few wonderfully informative extracts from Richard Williams Animator Survival Kit simplifying animating animal locomotion.  If you don't have the book yet go get it, it is a must have for every animator.

        

What the Spine has to Offer?

While touched on a little in the horses gallop I feel Richard Williams doesn't really highlight just how much of an effect the spine has in an animals locomotion.

Unlike people on the move animals spines can undergo some significant compression and stretching, this varies widely depending on the species in question and has real influence in how believable your animation is.

Below are two animals on different ends of the flexible spectrum, despite both having similar timings and footfall patterns (Albeit a longer period of suspension in the lighter hound) the horse and dog have significant differences in the squash and stretch of their bodies from the differing spinal flexibility.

Eadward Muybridges Slides once again to the rescue

For the sake of a bit of fun, here is a rather extreme example of how much influence the spine has on an animals movement can appear:- Quadruped Stiff vs Flexible Spine

Thinking Fictional Spine Time

Bringing the spine into initial planning can be especially important in fantasy creatures where no comparable reference footage can be found. As the most flexible region of the spine is the lumbar its length in relation to the spine as a whole is a great clue as to how much a creatures spine can bend. 

While both the cat and horse have quite close numbers of lumbar vertebrate (7 and 6 respectively) the size of the spines region given is significantly different. When looking at just about the least flexible creature I can think of, the elephant, Its rib cage effectively terminates at the pelvis.

No lumbar =  No Bending.

Example

Here's an example of this theory applied to a fantasy creature that will heavily affect how the animation is handled..

Creature created by Kabiralib

Initially this bulky big cat creature would have an animator perhaps looking to more feline reference footage for inspiration. Although many of its mannerisms may still have roots in a tiger or lion, after investigating its skeletal anatomy I doubt when its on the move it will be anything close to catlike.

From the telling landmarks of where the rib cage ends and the pelvis appears to begin this creature is left with a very limited space for lumbar vertebrate. The result will be a very stiff spine which would leave me now looking into perhaps warthog for my references.
This departure from the obvious inspired by speculative spinal springiness will lead to a much more thought out and interesting creature animation.



I hope this post gives you another element of your creatures to consider and perhaps helps to speed up the animating process.

In another post I will look into another wonderful area of animal study, Types of Predation, as a way to quickly determine how an animal will act when confronted with different external stimulus.