27 Facts About Mammals: The Largest, Smallest & Smelliest In The World

27 Facts About Mammals

Look around you sometime…

Chances are – if you see an animal – it’s a mammal. Mammals are the dominant life form on this planet at the moment, at least from a human perspective.

There are about 6,399 species of mammals known on this planet at the moment. Though taxonomists are still arguing and species are still being found.

Mammals are in fact not the most speciose animal group on the planet.

Three other groups of vertebrates out-number them right now:

  • Reptiles have 11,050 species,
  • Birds have 10,988 species and
  • Fishes approximately 34,300 species.

Invertebrates – of course – have groups with huge numbers of species that outnumber all the vertebrates put together: Arachnids, with a 100,000 species and insects with 1,000,000. While even Molluscs with a mere 85,000, still outnumber any 3 groups of vertebrates put together.

Mammals however are big. You can see them easily – and perhaps most importantly you are one.

Mammals are there, everywhere you look. Large, warm-blooded, four-limbed vertebrates whose females produce milk (see What is a Mammal).

elephant image
Elephant showing its big ears on Masai Mara savannah Kenya

Elephants and Whales, Pigs, Horses, Cattle, Sheep, Dogs, Cats, Hamsters, Rats and of course Human beings (that’s you and me) are all mammals.

Mammals are friendly or fierce, cuddly, cute and/or awesome – depending on which ones you look at.

They fascinate and horrify us at the same time!

We eat them, ride them, keep them as pets, makes clothes out of them, hunt other mammals with them and use them as substitutes for ourselves in scientific (particularly medical) research.

We use them to carry our burdens, support our foolish habits (gambling) and expect them to entertain us. To most people animals are mammals.

Many people are totally dependent on non-human mammals to keep their lives functioning (vegetarians and vegans excepted) and many of us need them as emotional supports as well.

We are mammals (genetically a man and his dog are 97% the same) and we love them because they are like us.

We use them to describe people. Someone is a dog, bitch, stallion, pig, cow, kitten, bunny… we run like a rabbit, weasel out of a deal, are as sly as a fox, as strong as an Ox and can have a whale of a time!

Our mammalian cousins are very important to us.

But how much do you really know about what it takes to be a mammal?

Mammals may have only become successful as a group relatively recently, but they have been around a long time.

The first mammals appeared about 265 million years ago, a mere 10 million years after the first dinosaurs. But they remained relatively obscure for the first 160 million years while the dinosaurs ruled (see The Evolution of Mammals).

Anyhow, let’s continue our journey of learning, starting with some of the most interesting facts about mammals:

The Largest Mammal In The World

The Blue Whale, Balaenoptera musculus, is the largest mammal living today.

It is also the largest mammal to have ever lived. In fact the Blue whale is the largest animal ever to have lived on the planet, as far as we know. Bigger by far than even the largest Dinosaur.

The longest Blue Whale ever measured was a female, 33.58m or 110ft long. The heaviest weighed over 190 tonnes.

blue whale facts
The largest animal in the world, a blue whale showing its back

Well, we haven’t actually got a set of weighing scales big enough – so weights are estimated from the cut up remains.

The largest living land animal on this planet is a mammal – the bull African Elephant. The largest specimen recorded stood around 3.96m or 13ft at the shoulder and weighed over 12 tonnes.

The tallest animal on the planet is also a mammal – Giraffes, Giraffa camelopardalis, can be 6.1m or 20ft tall.

The Smallest Mammal In The World

The smallest mammal in the world is a bat from Thailand, Kitli’s Hog-nosed Bat, Craseonycteris thonglongyai.

Being only 2.9-3.3cm or 1.14-1.3 inches long and weighing a mere 1.7 – 2 g or 0.06 – 0.07oz, this bat is much smaller than many insects and snails.

smallest mammal shrew
Pygmy shrew (Suncus etruscus)

In a close 2nd place, the Pygmy or Savi’s White-toothed Shrew Suncus etruscus weighs in at 1.5 – 2.5 grams or 0.05 – 0.09oz and is definitely the smallest land mammal on record.

The Fastest Mammal

The Cheetah, Acinonyx jubatus, is the fastest animal on land – reaching sprinting speeds of over 98 kmh or 61 mph. In 2012 National Geographic radar recorded an eleven year old Cheetah named Sarah running at 98 kmh.  Sarah was a zoo kept animal who didn’t have to run flat out every day to catch her dinner and eleven years is getting old for a Cheetah, therefore scientists believe younger animals living wild can probably run quite a bit faster than this, perhaps up to 110 kilometers per hour.

fastest mammal cheetah running
Cheetah (Acinonyx jubatus) running through savannah at fast speed

The fastest mammal in the water is the Killer Whale, Orcinus orca, which has been recorded swimming at speeds of 55.5 kmh or 34 mph!

The fasted mammal in the air is the Big Brown Bat, Eptesicus fuscus, with a recorded flight speed of 25 kmh or 15.5 mph.

Which Lives Longest?

The longest lived mammals are not human beings – as many people think – but the whales.

Fin Whale Balaenoptera physalis is believed to have a maximum life-span of 90 – 114 years, a little less that the human maximum.

But Bowhead Whales (Balaena mysticetus), also known as Greenland Right Whale has been known to live to at least 170 and possibly more than 200 years since the mid 1990s.

A Few More Mammal Facts

  • Rhinoceroses have the thickest skin of any terrestrial mammal… and the thickest skin in relation to their size, of any animal. The skin on their backs and flanks can be 2.5 cm or 1 inch thick!
rhino thickest skin
Closeup on rhinoceros skin from the side
  • Nearly a quarter of all mammals can fly.
  • Yes, it’s true. With a huge 985 species, bats make up 23.1% of all known mammals by species.
  • The meek shall inherit the earth, or at least Australia (which is a reasonable portion of it). With about 67 million head of sheep, there are about 3 sheep for every person in Australia!
  • A prehistoric mammal, the extinct Irish Elk, Megaloceros giganteus, had the largest antlers ever. A specimen found in an Irish peat bog had antlers 4.3 m or 14 ft across, which weighed 45kg or 100 lbs.
  • The Giant Anteater, Myrmecophaga tridactyla, eats over 10,000,000 ants or termites a year.
giant anteater fact
Closeup of Giant Anteater (Myrmecophaga tridactyla) walking on grass
  • No two Giraffes have the same pattern of spots and no two Zebras have the same pattern of stripes.
  • Whales and dolphins sleep one side of their brains at a time. While one side is asleep the other keeps watch for danger!
  • Sperm Whales can stay submerged for up to two hours, descending over a mile below the surface.
  • The Andes Fishing Mouse was first recorded for science when scientists from the British Mammal Society watching a television programme on the ‘Wildlife of the Andes’ saw a specimen in the programme and realized that no records of it existed.
  • House mice, Mus musculus, have on several occasions been so numerous that they had a population density of over 200,000 per hectare. That’s 2 mice for every square meter of land, if they were all spaced out evenly.
house mouse population density fact
Eastern House Mouse – Mus musculus
  • Rodents, at least the few species that are pests, cost us about £43 million tonnes of damaged and destroyed food every year.
  • There is a vine in Madagascar that is pollinated exclusively by lemurs.
  • Chimpanzees can go bald as they age.
  • A female kangaroo can produce 2 different kinds of milk at the same time, when she is suckling youngsters of different ages.
fun fact about kangeroo
Female kangaroo with joey
  • Anteaters are the only placental mammals to have no teeth.
  • Hippopotamuses produce a special reddish oil from modified sweat glands that acts like a sun-cream to stop them getting sunburned.
  • Shrews evolved 54 million years ago. Today some species have such fast metabolisms that they need to eat up to 1.3 times their own weight in food everyday.
  • A contender for the smelliest mammal is most definitely the Striped Polecat or Ictonyx striatus. It releases a spray from its anal stink glands that not only blinds any attacker, but leaves its skin in searing pain.

Want To Learn More?

Well, I hope you have enjoyed all these wonderful mammal facts. But there is of course, much more to learn!

Perhaps now you’d like to know more about mammal families.

Gordon Ramel

Gordon is an ecologist with two degrees from Exeter University. He's also a teacher, a poet and the owner of 1,152 books. Oh - and he wrote this website.

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