Science & Environment

The bony secrets behind marvels of animal world

Labrador Image copyright Science Photo Library

The mammalian skeleton is a marvel of nature. Here, Ben Garrod, who presents the series Secrets of Bones on BBC Four, explains how a basic template has been adapted in different ways to some enable extraordinary animal behaviour.

It's late and I'm sat at my desk, pen to paper; I'm a bit 'old school' and therefore write everything down before typing it all up.

And it's here that the wonder of the skeleton strikes me once again. Whilst doodling away in the edge of the page, I look at my hand . . . and think about the 27 individual bones that make up my hand and wrist, all delicately working together to allow the precision grip on my old fountain pen.

Each bone is uniquely shaped and perfectly adapted to fit snugly with its neighbouring counterpart.

Delicate enough to hold a pen, yet strong enough to climb a mountain (if I really wanted to); these little bones are a perfect example of the wonder of the skeleton.

Most of us know that newborns have a delicate area of skin on the top of the head (the "fontanelle"), where the delicate skull bones are yet to fully fuse. But less well known is that a tiny baby has a bundle of between 275 - 300 bones, which will eventually fall to the 206 found in adults.

Where do they go? Well, they fuse, often incorporating several tiny bony pieces into one bone. Even our femur (the thigh bone); the strongest bone in the human body, doesn't start off as a single bone.

Bones are amazing, bones are undoubtedly cool, and bones are undeniably essential for the way we live - if you're in any doubt, imagine being a big pink blob sliding across the ground.

They provide us with an effective internal support system; provide key protection for delicate organs, such as the brain, and act as "cellular factories", producing for example, over 2,000,000 red blood cells every few seconds.

Image copyright Science Photo Library
Image caption Bone's strength comes down to its composite nature

They owe their incredible strength to the fact that they're based on composite of two very different materials; the inorganic, calcium-rich hydroxylapatite, and the flexible, organic collagen.

When testing this recently, I discovered, along with Prof Richie Gill, at the University of Bath, that the femur of the rather diminutive roe deer can sustain 1.7 tonnes of force before snapping: a phenomenal thought when you consider that this British species isn't much bigger than a Labrador after transferring these results to larger animals. We predicted that rhino femur could tolerate a staggering 109 tonnes.

It may be rather obvious by now that I'm rather besotted with all things osseous. It's not just that my academic research focuses on them, or because I just finished filming a whole series dedicated to the skeleton, or even because I have a sheep skeleton (Gloria) sat in a chair in my flat (after all, why keep skeletons just in the closet), it's more than that.

I've long been fascinated by bones and one thing which has intrigued me the most is how very often they look so similar to one another.

I grew up in coastal Norfolk and loved nothing more than endless beach walks. My brother once brought back a "big bird skull" and was amazed to find that it was actually a porpoise.

This is because skeletons have a shared ancestry and in many ways, often work from a very similar skeletal blueprint - their body plan.

Image copyright AP
Image caption Despite their length, giraffe necks have the same number of vertebrae as human ones

Skeletons (as we understand them today) first started appearing on the scene about 420 million years ago. First seen in small fish, such as the recently-discovered Entelognathus, from China, the skeleton was a definite win, in terms of offering a whole host of evolutionary advantages. And as is often the case in life, once something works, everyone wants a piece of it.

As a result, skeletons blossomed and within a few million years, early tetrapods were hauling themselves out of the seas (skeletons enclosed, ready to take over the lands and the skies). This inexorable skeletal invasion ensured that there were certain elements that are ubiquitous across the vertebrates.

Skulls and vertebral columns are, by definition, inevitable. And structures such as the pentadactyl limb still follow an ancient body plan that ensures that no living vertebrate has more than five digits.

And for those who are thinking of a white and black bamboo-muncher, pandas don't count - it's not a "real" thumb. Let's say no more. Even horses with their single toes and birds with their three-digit wings share the basic five digit plan, all linked through shared evolutionary ancestry.

One of my favourite "fun bone facts" is that we have seven vertebrae in our neck and that we share this number with giraffes.

We both have seven cervical vertebrae, but the giraffe is evolved to tweak this basic mammalian body plan, to lengthen each vertebrae, creating the wonderfully long-necked browsers that they are.

The skeleton of the blue whale (Balaenoptera musculus), up to 190 tonnes and 80ft in length, is not only the world's largest vertebrate, but also the largest animal to have ever lived.

The skeleton of Paedophryne amaensis, a tiny 7.7mm-long frog from Papua New Guinea (holding the title as the smallest vertebrate on the planet) might seem as different an animal as it's possible to get from the whale. But even a cursory look at the two skeletons is enough to see lots of similarities between these two creatures.

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Image caption The ball and socket joint in the wrist of a gibbon gives them unrivalled flexibility in the trees

To really understand the important roles that skeletons play in ecology, behaviour, and evolutionary studies, looking at the similarities is nothing compared with looking at the often subtle differences that separate them.

Looking at the hand again, a whole range of seemingly similar primate hands can (with a few minor tweaks) perform a whole range of tasks.

The aptly-named colobus (meaning "docked thumb") refers to a group of large-bodied monkeys, which are at home in the canopies. They have just the tiny remains of a thumb, which allows for a much better swinging grasp. But it is spider monkeys that have taken this to the extreme, and have lost their thumbs altogether.

Gibbons have a joint in the wrist unlike any other animal. They have a ball and socket-like joint (more akin to our hip joints), allowing for a massive range of rotation, permitting them to exhibit unrivalled canopy acrobatics.

Finally, there is one hand amongst our primate kin that really stands out and appears more Swiss Army knife than hand. It's the aye aye's. The largest of the nocturnal primates, the aye aye is adept at finding even the tastiest of grubs hidden deep inside the trunk of a tree.

Using highly specialised fingers, it performs "percussive foraging", tapping the wood and, after gnawing a hole in it, using another, specialised, elongated finger, to hook and ensnare its tasty prize.

These slight adaptations in the same body part enable closely related species to display drastically different behaviours, allowing them all to exploit very different ecological niches. This phenomenon can be seen in skeletons again and again.

Secrets of Bones is on BBC Four at 8:30pm on Tuesday 18 February

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