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These tiny baby monkey twins are only around 3cm tall and are the most recent additions to a wildlife park in Telford.

Keepers at Exotic Zoo say they were "jumping for joy" when they spotted the tiny babies clinging to their mum's back.

Pygmy Marmosets are the world's smallest species of monkey and only reach a height of 10-15cm when they're fully grown.

The species is found in the Amazon basin and are vulnerable to extinction in the wild due to habitat loss, so births like this in captivity are very exciting.

Now we know monkeys like the Pygmy Marmosets are mammals, but what's the smallest mammal overall?

The title goes to the Etruscan shrew, which is found from north Africa, to Europe, all the way to Malaysia.

They can grow to between 3.5cm and 4.8cm in length so a little bigger than the baby Pygmy Marmosets.

They needs so much energy to live, they eat up to two times their own bodyweight in a day.

The Bee Hummingbird is the world's smallest bird.

Males grow to only around 5.5cm in length - that's only a little bit bigger than a AA battery.

Females can grow a bit bigger to around 6cm and they weigh less than 2g.

These birds are only found in Cuba, the biggest island country in the Caribbean, and they're often mistaken for a bee which is how they got their name.

You'd be forgiven for thinking this is a worm, but it's actually the world's smallest snake species called the Barbados threadsnake.

It was first identified as a separate species in 2008 and are found in the tropical forests of Barbados in the Caribbean.

An adult snake will only grow to around 10cm in length. That's around the same size as four small paperclips and about as thick as spaghetti.

They feed on the eggs and larvae of ants and termites and burrow into the ground.

There's a bit of a competition for the title of world's smallest frog.

Discovered in Papua New Guinea in 2012, the Paedophryne amauensis measures in at 7.7mm long.

But the Brachycephalus pulex (otherwise known as the Brazilian flea toad), a frog species from Brazil first described in 2011 and revisited this year, puts Paedophryne amauensis' title in jeopardy.

Researchers say it should be classed as the smallest species, measuring in at 7mm long.