He is a third of the size of an average guinea pig, and weighs in at just a few ounces - but this tiny puppy could be a big deal when it comes to world records.
The miniscule chihuahua-Jack Russell cross - appropriately named Tom Thumb by its owners - is a serious contender for the title of being the smallest dog on the planet.
Little Tom was born just three weeks ago as part of a surprise litter to mum Spice, a chihuahua.
Owners Susan and Archie Thomson were delighted when he and his brothers and sister were born at the family's West Dunbartonshire home.
His siblings are three times the size of the tiny dog, who can fit inside a teacup and cannot reach his mum to feed when she is standing up.
And he is unlikely to get much bigger - with some previous experience of rearing puppies through their early weeks, the couple are convinced that Tom is almost fully grown now.
Care development officer Mr Thomson, 54, said: 'In the past 10 years we've had six chihuahua litters and I've been involved with other breeds for most of my life - but I've never seen a dog this small.
'He's perfectly proportioned but absolutely miniscule.
'Judging by the size of his paws and head I'd be surprised if he grew much bigger than an inch or two more.
'He's a great wee dog and Susan's convinced he's a record breaker.'
With his tan-and-black markings, Tom Thumb measures less than four inches from the tip of his nose to the end of his tail and only weighs about three ounces.
He was born last month as part of a five-dog litter - although, sadly, one of Tom's brothers has died since then.
And the Thomsons thought it might also be touch-and-go for Tom Thumb, because he was so small - but he has proved them wrong.
For although Tom's siblings tower above him, he has plenty of fighting spirit to make sure he gets his fair share at feeding time.
Care worker Mrs Thomson, 51, added: 'He’s the first in there at feeding time and doesn’t let the bigger ones bully him.
'In fact, when Spice stands up, Tom Thumb goes with her because his suck is so strong.'
No-one was available for comment at Guinness World Records yesterday, but their website records the smallest living dog in the world as Heaven Sent Brandy, a four-year-old chihuahua from Florida in the USA, who is six inches long.
That means Tom Thumb is seriously in the running to challenge for the title - juts as long as he doesn't get too much bigger.
The adventures of Tom Thumb: The tiny puppy set to be the world's smallest dog | Mail Online