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Mammal Skeletons By The Nature Collection for British Wildlife

Why do animals have a skeleton?

  • Support: it provides a framework for the body.
  • Movement: the bones are linked by joints, which enable animals to move, using their muscles.
  • Protect vital organs: the skull protects the brain and the rib cage protects the heart and lungs.

Vertebrate Skeletons

Vertebrates are animals with backbone, like mammals, birds, fish, amphibians and reptiles. Invertebrates are animals like insects, spiders, worms, crabs and woodlice, which do not have a spine; most have a tough exoskeleton, instead.

Almost all vertebrates have a similar structure to their skeleton.

  • A long, flexible spine supporting the skull
  • Ribs forming a cage around the heart and lungs
  • Four limbs which come off the spine, connected by the shoulder blade and pelvis.

The photo is looking down into a Rat's spine.

The mammal skeleton can be divided into two sections: the 'axial skeleton' and the 'appendicular skeleton'. The axial skeleton is the skull and spine and ribcage; all the bones in the body's long axis. The appendicular skeleton is the bones which 'append' to the axial skeleton: the front and back legs, the shoulder blade and pelvic girdle.

This study of mammal skeletons is divided into two parts: Part One: The Axial Skeleton and Part Two: The Appendicular Skeleton.

Mammal Skeletons

The skeleton will be examined, in the following order.

Click below, to go directly to a section.

For Bird Skeletons, click here

In this presentation, I will focus on different parts of the skeleton. Search on Google for images of the whole skeletons of a fox, badger, rabbit, mouse, hedgehog and squirrel. Try here, to see the skeleton of a squirrel, a rodent. Try here, to see a chimpanzee skeleton, another mammal more like a human.

The main photo is looking into a Brown rat's rib cage. Each vertebra is 0.5cm tall x 0.7cm wide. The ribs are 1.5-2.5cm long.

Many of the photos of smaller mammals' bones, from the shrew, vole, mouse and mole, were taken through a microscope. They are often just a few millimetres wide and are too small to photograph through a normal lens.

Skull

Mammal skulls are all very different shapes. Over millions of years, the shape has adapted to reflect the lifestyle and diet of each animal species. Some animals have large eye sockets and others have very small ones. Some have huge jaws for killing their prey and others have jaws which are ideal just for chewing grass.

The main photo is of a Rabbit skull.The incisors extend about 0.7cm beyond the skull.

The skull is formed of several pieces of bone which fuse together as the animal grows up. In babies and very young animals, the sections are not yet sealed. This makes it easier for the mother to give birth.

Rabbit skull. See the network of holes and the wavy lines, which mark the different sections. This skull is 8.5cm long and 3.5cm high.

Some animals' skulls are solid and heavy whereas others are light and full of holes. Animals which have evolved to move quickly, often prey animals which need to escape danger, have light skulls. The Rabbit's skull is covered in weight-saving holes, particularly at the back.

Hedgehog, a much more solid skull! it is about 4.3cm long x 2cm high

Eye Sockets

Projecting eye socket, 4cm diameter, on a Fallow deer skull.

The position of the eye sockets, indicates whether the animal is a predator or prey.

Prey animals like deer and rabbits, need to keep watch in all directions, even when their heads are down to feed. Their eye sockets face out to the side, so the animal can see what is happening on either side and behind them. The eyes are high up on the head and can scan a wide area.

Fallow deer, skull, 26cm long x 13cm tall. See how high up, the eye sockets are.

Predators such as foxes, stoats and badgers, have forward-facing eyes, so they can hunt for food in front of them. They do not need to worry about being attacked, from behind.

Fox. See the sharp teeth and long snout.

Foxes have a much shorter skull. Their eyes are level with their nose and do not project beyond the skull. This is good for sniffing out prey and hunting. They have smaller eyes than deer. Foxes' eye sockets face forwards.

Fox, skull, 15cm long x 6cm high

Moles spend most of their life underground. They are nocturnal. They have tiny eyes, close in to the skull. The skull is long and narrow, suited for a life of tunnelling.

Mole, skull, 3.5cm long x 0.8cm high

Spinal Cord

The brain is enclosed at the back of the skull.

There is a large, oval hole at the base of the skull, where the spinal cord enters and connects to the brain. The hole is called the 'foramen magnum'.

Grey squirrel, skull. Hole 1cm wide, at the base for the spinal cord. The skull is 6cm long x 2cm high.

Nose

Hedgehogs have a long, pointed nose, for sniffing out food.
Hedgehog, skull. See the delicate folds of bone inside the nose, which are covered in organs, for the sense of smell. The nasal cavity is 6mm wide.

The skull does not extend over the whole length of the nose. There is just cartilage, at the end.

Animals with a very good sense of smell, for hunting and communicating with each other, have a long snout. Mice and foxes are like this.

Rabbit, nasal cavity, 8mm wide. See the multiple folds of thin bone inside the nose, which contain the organs for smell.
Mole, skull, 3.5cm long. The long snout shows they have a good sense of smell.

Ear Holes

Animals which rely on a strong sense of hearing, usually prey animals like rabbits and deer, have large, upright ears.

Rabbits have wide tubes at the base of the skull, leading into their inner ear.

Rabbit, skull. See the wide, tube-like bone, 5mm diameter, halfway up at the back of the skull.
Rabbits have long, upright ears which they can twist, to catch the smallest sounds.
Brown rat skull, 4.5cm long x 1.3cm high

See the round hole, low down at the back of the Rat's skull, in the photo above. This leads to the inner ear bones. Rats have a very sense of good hearing.

Jaw Bones

Mammals have a pair of jaw bones, which attach near the ears, at the back of the skull. They contain the lower teeth.

Fallow deer, jaw bones, showing incisors at the front and molars, further back. The jaw bones are 22.5cm long x 10cm high.
Rabbit, jaw bones, 6.2cm long x 3.5cm high
Grey squirrel, jaw bones, 4cm long x 1.6cm high. Note the huge incisors.
Squirrel, jaw bones from the inside. Four pairs of grinding molars, further back in the mouth.

Teeth

Animals have different types of teeth, depending on their diet.

Predators, or carnivores, illustrated here with a fox's skull, have sharp, pointed canine teeth to kill their prey and jagged, carnassial teeth further back in the mouth, to crunch, break and slice through the bones. The small incisors at the front, are for tearing flesh off the bones.

Fox skull, 15cm long x 6cm high

Stoats are fearsome predators. They have a blunter snout with six pairs of small incisors at the front and two long, piercing canines, on either side.

Stoat skull

Herbivores, like rabbits, have grinding molars at the back of their mouth and large incisors at the front, to pull up tufts of grass and plants. Rabbits have a second pair of short incisors growing behind the first; these are called the 'peg' teeth. Can you see these in the photo below?

Rabbit's upper teeth. The surface of each cheek tooth is 0.5cm x 0.2cm. The gap between the incisors and molars is 2.5cm.

Rodents like rats, mice and squirrels, have huge incisors at the front, for gnawing away at roots and nuts. Squirrels have a tough orange layer of enamel on the front of their incisors and a softer layer behind. This gives the teeth a sharp, cutting edge. The incisors get worn down by use, so keep growing throughout the animal's life. Rodents have small molars further back in the mouth, for chewing and grinding up their food.

Rabbit, incisors, each 0.7cm x 0.25cm

Rodents such as rabbits, squirrels, rats and mice have a large gap in between the front and back teeth. This is called the 'diastema'. They suck in their cheeks while they are gnawing to close off the back of their mouth. This prevents them choking on nut shells or chunks of tree bark, before it has been chewed.

Grey squirrel, skull, 6cm long x 2cm high
Black rat at The British Wildlife Centre
Roe deer skull, showing the same gap between the incisors and molars

Deer have no teeth in the top of their mouth, at the front. They have a rough pad instead. They pull up tufts of grass and bracken between this pad and their incisors.

Red deer, female. Deer are herbivores.
Deer have incisors in the lower jaw but none in the upper jaw. These teeth are 1.6cm high.

Spine

Animals with a backbone, or 'spine', are called vertebrates. All mammals, birds, fish, amphibians and reptiles have a spine.

The spine is a series of small bones, called 'vertebrae', which link up to form a flexible column in the centre of the animal's skeleton. The spine connects at the top, to the skull and extends to the tip of the tail. It forms quite a rigid column, with most of the flexibility at the waist and, for some mammals, the tail.

The number of vertebrae in the spine, varies in different animals, especially in the tail. Foxes have about fifty vertebrae.

Muscles attach along the length of the spine, which help the animal to move different parts of their body. The shoulder blades and pelvic girdle attach to the spine, connecting the central column of the body to the limbs.

Brown rat, spine and ribs. The rib cage is 3.5cm wide.

The spinal cord runs along a tunnel, called the 'neural canal', formed inside the small vertebrae. Nerves branch out from the spinal cord, through gaps between the bones.

Field mouse, vertebra, 0.4cm wide and ribs.

The first type of vertebrae in the spine are the neck, or 'cervical' vertebrae. The first two bones are called the 'atlas' and 'axis'. They have special features which enable the animal to nod and twist its head.

Grey squirrel, atlas. The top vertebra, which connects with the skull.

The first vertebra below the skull is called the 'atlas'. See the above photo. This is a ring-shaped bone, which allows the head to nod.

The second vertebra is called the 'axis'. This is the topmost bone in the main photo. It has a ball shape on which the skull can swivel. The atlas, which lies above the axis, has a socket which this ball slots into. In small mammals there are usually five more cervical vertebrae below the atlas and axis.

Field vole. From right to left: the atlas and axis, five more cervical vertebrae, then the thoracic vertebrae connecting with the ribs.

In mammals, the shape of the vertebrae varies, depending on whether they are in the neck, chest, back, hips or tail. The different vertebrae are neck (cervical), chest (thoracic), lower back (lumbar), hip (pelvic) and tail (caudal).

Hedgehog, barrel-shaped chest, or 'thoracic', vertebrae, seen from inside the rib cage, which is 5cm across, at the widest part.
Hedgehog, cervical and thoracic vertebrae and ribs, from behind the rib cage.

The thoracic vertebrae each connect to a pair of ribs. In some mammals, like foxes and rats, the thoracic vertebrae have a projection on the back, which forms a ridge along the animal's back. This is called the 'neural spine'.

Brown rat, from right to left, neck and chest vertebrae. The section shown is 5cm long.
Hedgehog, thoracic vertebrae, are flat across the back, enabling the hedgehog to curl up easily. The section shown is 4cm long. Each vertebra is 0.7cm wide
Stoat, thoracic vertebrae. See the tall projections running along the back, for the muscles to attach onto. Stoats are very strong and often carry rabbits as prey, much bigger than themselves.

Below the thoracic vertebrae, are the lower back , or 'lumbar' vertebrae. These support the lower back and connect the ribcage to the pelvis. There is often more flexibility in this region, which allows the animal to bend at the waist.

Grey squirrel, lumbar vertebrae, leading to the pelvic girdle. The four vertebrae measure 3.5cm long. The widest one is 2cm across.
Rabbit, from left to right, lumbar vertebrae and thoracic vertebrae. This section is 15cm long.

The hip or 'sacral' vertebrae form part of the pelvic girdle and may even be fused with the bones of the pelvis, for extra stability.

Mole, sacral vertebrae fuse with the pelvic bones. It is 2.5cm long x 0.8cm
Field vole, sacral vertebrae and pelvis, 1.5cm long x 0.4cm wide

The spine continues for the whole length of the body, up to the tip of the tail. The tail or 'caudal' vertebrae can vary in number. Grey squirrels have about twenty five tail vertebrae whereas the hedgehog has less than ten. Click here to jump to the Tail section.

Grey squirrel, tail vertebrae

In snakes, which are not mammals but reptiles, the vertebrae are all the same shape. This is because a snake has no shoulder blades, pelvis or legs. The vertebrae all connect to each other with a ball and socket joint. This enables the snake to twist its body in all directions, up and down and side to side. Mammals have a much more rigid spine.

Grass snake, vertebrae, each 0.4cm wide. They connect to each other with a ball and socket joint.

Grey squirrel, neck and chest vertebrae, in the main photo. This section is 3.5cm long.

Rib Cage

Inside a Mole's rib cage in the main photo. The whole rib cage is just 1.5cm long.

All mammals have a rib cage, which surrounds and protects their heart and lungs.

The rib cage needs to be flexible. Ligaments and muscles, woven in between the ribs, make the walls of the rib cage solid. As an animal breathes in, their rib cage rises and the lungs can expand, to take in more air. On the outward breath, the rib cage compresses back down.

In humans, seven pairs of ribs attach to the spine at the back of the body and to the breastbone, or 'sternum', at the front. Small mammals like moles and mice, also have seven pairs of ribs attached to the breastbone. Lower down, the ribs attach not to the breastbone, but to the ribs above. There are also floating ribs, which do not attach at the front.

Field mouse. A tiny, delicate rib cage, 1cm long x 1.5cm wide.

Mice have a lightweight skeleton. They need to be able to collapse their body down, to fit through small gaps and cracks in rocks and walls.

House mice at The British Wildlife Centre

Hedgehogs can roll their whole body up into a ball, if they are in danger. Their spine is very flexible. The vertebrae and ribs are closer together and sturdy.

Hedgehog, spine and ribs
Safe from predators!
Brown rat, breastbone, with sections of some of the lower, sternal ribs, still attached. 3cm x 3cm

Tail

Tiny bones from a Common shrew: tail bones, hind legs and feet. The feet are 1.4cm long.

The row of small bones in the tail are an extension of the spine. The number of tail bones, or 'caudal vertebrae', varies for different mammal species.

Foxes use their long, bushy tails to help them balance when they leap or pounce onto prey.

Many small mammals like squirrels, mice and rats have long tails which help them balance in the trees, climbing fences or standing up on two back legs.

Brown rat, tail bones, each about 0.8cm long.
Black rat using its very long tail for extra stability, on two legs.
A tiny Weasel, using its tail for better balance.

Other mammals such as the Mole or Hedgehog, which spend most of their time on solid ground, do not need long tails.

Mole, caudal vertebrae, each 0.3-4cm long. The whole tail is just 3cm long.
Hedgehog, tail vertebrae, each about 0.2cm long. A short tail, just 3cm in total.
Common shrew, the tiny tail vertebrae are connected with a bow-shaped bone. Like pasta!!
Common shrew, tail bones from the side, just 0.2cm long x 0.05cm wide.
Field mouse, tail vertebrae with proportionally smaller connections
Field mouse, tail vertebrae, 0.4cm long x 0.2cm wide

Click here for Part Two, to explore the rest of the Mammal Skeleton, Part Two: the Appendicular Skeleton; the shoulder blades, pelvis, legs and feet.

The Collector, Photographer & Author

I am Susanna Ramsey and I have a unique collection of natural history objects relating to British Wildlife. Over the last ten years, I have assembled an extensive range of skulls, skeletons, bones, skins, feathers, wings, antlers, insect specimens and taxidermy, all from animals in the UK.

During 2010-2018, I took my Nature Collection into local primary schools to display and run workshops for the children, linking the exhibition to science topics in the National Curriculum such as Adaptations, Bones, Classification, Food Webs, Habitats, Life Cycles and Local Wildlife.

In 2018-2020, I worked with the leading schools' catalogue, TTS ,to create a range of Educational Resources for primary schools, nurseries, after school clubs and families. To find out more about these products, click here or see below.

In the school workshops, children and teachers were always completely fascinated to see what is inside the animals we see everyday, in the garden or local parks. On these web pages, I want to continue to share my enthusiasm for the skeletons of our local wildlife. I hope you find these intricate structures as beautiful and amazing as I do!

Conclusion

The more I examine the bones in my Collection, the more amazed I am at the miracle of every living creature. Each bone is so intricately-shaped and different to the rest; each fits perfectly in just one place on the skeleton like the overlapping tiers of feathers on a bird's wing. The skeleton provides the framework for the entire body from the tip of the nose to the tip of the tail and out along the limbs, to the tips of the claws. The joints allow the parts of the body to move in different directions so that each animal can do everything it needs to.

When you interweave through this complex skeleton, the network of muscles, tendons, veins, arteries, nerves and sense organs, plus the heart, brain, digestive and respiratory systems, waste and reproductive organs, all fully functioning, you can't help but be in awe.

The miracle too, is that every different species is a variation on a theme, with the same basic skeletal structure and individual bones, each evolved into a slightly different shape and size.

Among my favourite items in the Collection are the fragile rib cages of birds and small mammals. They are so delicate, yet despite death and cleaning by flesh-eating beetles, they still form a rigid, basket-like structure, sufficient to protect a beating heart and lungs. The rib cages of a Field mouse and a Robin are so similar, yet the animals live and move so differently! It is fascinating to compare the skeletons of birds and mammals and to discover how each species has adapted to its own habitat and way of life.

Robin, rib cage, 2.2cm long
Field mouse, rib cage, 1cm long x 1.5cm wide

If you enjoyed this web page and would like to find out about bird skeletons or look in detail at skeletons of individual animals, follow the links below.

Other Natural History Topics

Especially for Children

So much still to discover!

The above photo shows some of the 40 photo cards in the Classification: Natural History pack. (See below.)

Exhibits and Thanks

Almost all of the animals in my collection were either found by myself, Susanna Ramsey, or donated by friends and family to The Nature Collection, as an educational resource. Huge thanks for all the tiny, carefully-wrapped bundles of feathers and bones, to Steve and Sam Read, John Lock, Chris Matcham, Franko Maroevic, Tim Howard, Jan Wilczur, Simon Richards, Peter Veniard, Paula Redmond, Phil Davis, Bob & Sally Black, Jo & Frank Sheppard and Katie Ramsey. Many of these people are naturalists and experts in their field; I am indebted to them too, for all that they have taught me about our local wildlife.

Over the years, I have been lucky enough to be a regular visitor to the Angela Marmont Centre for UK Biodiversity at the Natural History Museum, London. The unimaginably-vast collection of British insect specimens, stored in row upon row, of metal, floor-to-ceiling cabinets has been a massive inspiration to me. There is something infinitely satisfying about the way every species has its own box, within a drawer, within a cabinet and that each can be found within minutes, by the care and expertise of the staff. To witness the incredible number of UK species of moth, beetle, butterfly, fly, grasshopper etc, is simply mind blowing and I feel so privileged to be able to visit and photograph some of the specimens!

I have used the photo stacking equipment at the Angela Marmont Centre to take highly-detailed photos of some of the specimens to put into slideshows for my primary school workshops. When I was young, I always wanted to be an archaeologist and it was my ambition to work in a museum; to sit in the Centre, using the equipment and handling the specimens, listening to the chatter of the experts at work, has been a dream come true. I am so grateful to the staff at the Centre for their encouragement and for always making me feel so welcome.

Thanks also to Tonja Grung, of Made from the Dead Taxidermy, for sharing her incredible knowledge, patience and skill. I will never forget our amazing sessions on animal taxidermy.

The delicate skeletons were cleaned to perfection by a colony of flesh-eating, dermestid beetles, skilfully managed by Edward de Geer.

Sources of Information/ Further Reading:

BRITISH WILDLIFE PRODUCTS

If you know children who are interested in nature, are a teacher, or would like to learn more about British Wildlife yourself, explore the range of British Wildlife products recently created by The Nature Collection and the leading schools' catalogue, TTS.

The Classification: Natural History pack features 40 small photos of animal skeletons, skulls, feathers, insect specimens and much more, all from The Nature Collection!

The products are perfect for use in primary schools, nurseries, after school clubs, forest schools or at home with friends and family. Click on the links below to find out about each product.

Look & Learn Cards: British Birds, Mammals, Minibeasts

Food Webs Activity Pack

Classification: British Wildlife & Natural History

Identification Wheels: British Birds, Mammals & Minibeasts

Discovery Bags: British Birds, Mammals, Minibeasts

Playground Signboards: Birds, Mammals, Minibeasts

Mouse in Mammal Discovery Bags, ID Wheel & Mammal Look & Learn Cards
Created By
Susanna Ramsey
Appreciate

Credits:

Susanna Ramsey