Mammals are a large group of animals. Other large groups include Birds, Reptiles, Amphibians & Fish.
Classification: What are Mammals?
- Mammals are warm-blooded
- Mammals have hair
- Mammals breathe through lungs
- Mammals give birth to live young. They do not lay eggs.
- Mammals produce milk to feed their young
- Mammals have a backbone
- Most mammals live on land, not in the water or air
Mammals can be sub-divided into smaller groups, including Rodents, Insectivores, Carnivores, Deer and Rabbits.
The skulls, teeth and skeletons of animals in these groups are similar because they feed and live in a similar way. You will see this, if we explore the skulls, group by group.
We will look at the skulls, in this order:
- Rodents: Squirrels, Rats, Mice and Voles
- Insectivores: Hedgehogs and Moles
- Carnivores: Foxes, Badgers and Stoats
These are all British animals.
Skulls. What to look for!
Skulls are all different shapes and sizes. The different animal species have evolved over millions of years. The skull and skeleton of each animal has adapted to suit the animal's diet, habitat and way of life.
Rodents are small, furry animals with short legs and a long, thin tail. They are often prey animals but some are predators, too. They can use their front legs to collect and handle food. Squirrels, rats, mice and voles are all rodents.
The photo shows a Field vole.
The word 'rodent' comes from the Latin word 'rodere', which means to gnaw, or chew again and again.
See how similar the rodent skulls are.
Field mouse skull
It is very light and tiny, just 2.4cm long x 0.8cm high.
Brown rat skull
It is very small, just 4.5cm long x 1.3cm high.
Grey squirrel skull
This is bigger and more solid, at 6cm long x 2cm high.
These animals are all rodents.
Rodents have solid skulls. The proportions on all these three skulls are 3:1. The skulls are three times as long, as they are high.
Rodents have proportionally large eyes. Many are prey animals, as well as predators and they need to keep watch for danger.
They have large, upright ears, with a very good sense of hearing. The ear holes are therefore relatively big.
Rodents have long snouts, or noses, which are useful to sniff out prey or sense a predator nearby. They use long whiskers to feel their way around in the dark and in the undergrowth. They help them to sense where prey and predators are. The jaw bone is solid.
Rodents: Teeth & Diet
Rodents eat mainly plants such as seeds, nuts, berries, fungi, roots and bark. Rats have a wider diet, eating almost anything including smaller mammals and birds.
Rodents have a huge pair of incisors at the top and bottom, at the front of their mouth. They use these to gnaw and nibble at tough food such as tree bark and nuts.
The front of the incisors is coated in orange enamel, which is very hard. The back of the incisors is softer. As they gnaw, the back of these teeth wears down more quickly than the front. This makes a sharp, curved cutting edge.
The incisors keep growing throughout the animal's life.
Rodents have no canine teeth.
Further back in the mouth, rodents have 3-5 pairs of small, ridged premolars/molars, which they use to chew and grind up their food.
Between the front and back teeth, rodents have a large gap. This is called the 'diastema'. They can 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 is ready to be swallowed.
Scientists study animal teeth and describe the number and type of teeth which a species has, in a standard format. They state the number of teeth of each type on one side of the mouth, first giving the number in the top jaw, followed by the number in the lower jaw. You start at the front of the mouth and work backwards, so listing incisors, canines, premolars and finally, molars. This is called the 'dentition formula'.
Squirrels have 1 incisor, 0 canines, 3 premolars and 2 molars in their top jaw. They have just 2 premolars in the lower jaw. So their dentition formula is: I 1/1, C 0/0, P 3/2 and M 3/3. You multiply the numbers by two, for the two sides of the jaw and see that in total, squirrels have 22 teeth. Humans, as adults, have 32 teeth.
Rats, mice and voles have 1 incisor and 3 molars on each side of the mouth, top and bottom. They have no canines or premolars. Their dentition formula is I 1/1, C 0/0, P 0/0 and M 3/3. So they have just 16 teeth.
Insectivores are animals which eat insects. It is not only mammals which are insectivores. Many species of bird, fish, reptile and amphibian are insectivores, too. Large numbers of insects, such as ladybirds and dragonflies, also eat insects.
Hedgehogs, moles and shrews are mammal insectivores. Bats are also mammals, which eat insects. (They are classified in a group of their own.)
These animals are insectivores.
Insectivores: Teeth and Diet
The main photo shows molars in a hedgehog skull.
Insectivores eat mainly insects. Hedgehogs and shrews also eat worms, slugs and snails. Moles eat mainly earthworms.
Insectivores need to eat a lot of insects to survive each day. Insects are small and often hard to catch, so it takes a large amount of energy for these mammals to collect their food.
Insects are difficult to eat because they have a hard exoskeleton on the outside of the body. This needs to be crunched and broken up, to reach the nutritious soft body inside.
Insectivores have a large number of small, pointed teeth which have evolved to suit the task of catching and chewing up their insect prey.
Moles have 3 small pairs of incisors at the front, which they use to catch slippery worms! Then 1 pair of canines and 7 pairs of sharp, jagged premolars/molars. Their dentition formula is I 3/3, C 1/1, P 4/4, M 3/3. They have 44 teeth in all.
Hedgehogs have similar teeth, with 36 teeth in all. They have fewer teeth in the lower jaw. Their dentition formula is I 3/2, C 1/1, P 3/2, M 3/3.
Shrews have 32 teeth in all, with fewer teeth in the lower jaw.
Shrews have a red layer on the tips of their teeth. This shows there is iron in the enamel, which strengthens the points. Their skulls and jaws are so small and fragile, they need reinforcements to break up the insect cases. Plus, the iron helps prevent the teeth wearing down. Shrews' teeth do not keep growing throughout their life.
Carnivores are predators which eat mostly meat, or the flesh of other animals. Foxes, badgers, stoats, weasels, polecats, pine martins, mink and otters are all carnivores which live in the UK.
Carnivores are usually strong, fast hunters. They have sharp claws and teeth for killing their prey.
Carnivores: Teeth and Diet
Carnivores eat mainly the flesh of other animals which they hunt. They eat smaller mammals, especially rodents, small birds, birds' eggs, frogs and lizards. Badgers even eat hedgehogs!
Most carnivores also eat insects, earthworms and berries.
Carnivores have 3 pairs of small incisors at the front of the mouth. These are used to tear off the flesh and skin.
The long, pointed canine teeth are next to the incisors. There is a pair on each side. These are used to kill prey, and for display and defence.
The premolars and molars have sharp, jagged points. These are good for killing prey, slicing through the meat and crunching the bones.
Foxes have 42 teeth: on each side in the top jaw, they have 3 incisors, 1 canine, 4 premolars and 2 molars. They have 3 molars in the bottom jaw. The dentition formula is I 3/3, C 1/1, P 4/4, M2/3.
Badgers have 36 teeth: on each side in the top jaw, there are 3 incisors, 1 canine and 4 premolars and 1 molar. They have 3 premolars and 2 molars, at the bottom. The formula is I 3/3, C 1/1, P 4/3, M 1/2.
Deer are large animals with two hooves on each foot. They are herbivores and feed on grass and plants. Male deer usually have antlers.
Deer are 'ruminants'. This describes the way they digest their food. When deer first pull up clumps of grass or plants, they chew it very little and send it down to the stomach. When they have filled their stomach with large amounts of grass, they lie down in a quiet place and bring the grass back up into their mouths, to chew again. This is called 'chewing the cud'. Cows and sheep do it, too. You will see deer have very different teeth, to the other groups of animals.
There are six species of deer living in the UK. These are Red deer, Fallow deer, Muntjac deer, Roe deer, Chines water deer and Sika deer. Wild boar are also classified in their group.
Deer Teeth & Diet
Deer are 'herbivores'. They eat grass, plant shoots, acorns, nuts, heather, leaves and tree bark.
It looks as if deer have 4 pairs of incisors on the lower jaw, at the front of the mouth. In fact, these are 3 pairs of incisors and 1 pair of canines. The canines have moved and evolved to act like extra incisors.
The incisors are for collecting food: pulling up grass and tearing off leaves or berries.
Deer have a rough pad on the top of the mouth instead of teeth. They use this to grasp the grass and leaves. If they had incisor teeth on the top, they would cut through the vegetation and not be able to pull up clumps.
There is a gap between the incisors and premolars. Rodents have this 'diastema', too. For deer, they can suck in their cheeks while they are grazing to close off the back of their mouth. This prevents them choking on the plants before they have been swallowed.
The premolars/molars at the back, are for chewing and grinding up the food. The surface of the molars consists of hard enamel and soft dentine, which wear down at different rates. This makes sharp, cutting ridges across the surface of the teeth. These make the molars more effective at breaking down the tough plant matter.
Remember that rodents have a layer of tough enamel on the front of their incisors, which creates a sharp cutting edge for gnawing bark. Different adaptations for different methods of feeding.
Deer have just 6 premolars/molars on each side in the top jaw and 3 incisors, 1 canine and 6 premolars/molars in the bottom jaw. So, they have 32 teeth, in all. The dentition formula is I 0/3, C 0/1, P 3/3, M 3/3.
The photo shows the lower jaw of a Fallow deer
Rabbits are classified in the same group as hares. They are medium-sized mammals, with long ears and long back legs. They are prey animals and can both move quickly, especially hares!
Rabbits live in underground tunnels and hares live above the ground.
In Britain, there is just 1 species of rabbit and 3 species of hare.
Rabbit Teeth & Diet
Rabbits are herbivores. They eat grass, crops, vegetables, berries, leaves and buds. In autumn and winter, they also eat twigs and tree bark.
Rabbits have a pair of large incisors at the front of the mouth. They also have second pair, called 'peg teeth', growing behind these. Their teeth do not have roots and keep growing throughout their life.
Rabbits have a 'diastema' or gap in between their incisors and premolars, like deer and rodents. This is they can shut off the back of the mouth while they are gnawing and nibbling away at hard plant matter, before it is ready to swallow.
At the back of their mouth, Rabbits have 3 premolars and 3 molars in their top jaw. These are to chew and grind up the fresh food and soft droppings, which they eat for a second time around.
Rabbits have 2 incisors on each side of the mouth at the top, 3 premolars and 3 molars. (No canines.) At the bottom, they have only 1 incisor, 2 premolars and 3 molars. The dentition formula is I 2/1, C 0/0, P 3/2, M 3/3. In total, they have 28 teeth.
The photo shows a Rabbit's premolars/molars in the upper jaw.
The Collector, Photographer and 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.
BRITISH WILDLIFE PRODUCTS
Explore the whole range of British Wildlife products created by the leading schools' catalogue, TTS and 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.