A 56-year-old chimpanzee has stunned staff at an American zoo by giving birth to a healthy baby girl.
Keepers at Sunset Zoo in Manhattan, Kansas, had been aware that Susie had been pregnant after undergoing and ultrasound in July.
But the arrival of a baby female chimp last week still came as a welcome surprise.
Unlike human females, chimps spend most of their adult lives menstruating and some have been recorded as not having had a menopause late in their 50s.
Susie with newborn baby Nia pictured at Sunset Zoo in Manhattan, Kansas.
However it is extremely rare for a chimp as old as Susie to actually give birth.
'We took Susie off birth control due to health issues a few years ago and we didn't think she would get pregnant because of her age,' said Mark Ryan, the Zoo's curator, who at 47 is nine years younger than the new mum.
'Interestingly we haven't observed Susie go through any type of menopause and she was menstruating so irregularly that we didn't think pregnancy would be on the cards.
'However around June we noticed a swelling in her stomach area and observed changes in her behaviour that we recognised to be those of a pregnant chimp, so we took her for an ultrasound.
'So that confirmed it and we waited patiently for the birth this month which was natural and unaided.'
Even so, scientists are keen to come to the zoo to observe this unusual phenomenon because it is so rare as chimpanzees usually reach menopause in their early 40s at the latest.
Keepers were shocked when Susie gave birth to a healthy baby at the age of 56
Susie - believed to be the third oldest chimp alive in America and has a cataract in one eye - is otherwise in good health and is currently breast-feeding her infant girl chimpanzee.
This is Susie's third child and a gap of 22 years separates this birth and her last in 1988.
She is one of three female chimps at Sunset Zoo and has become the latest partner of 31-year-old chimpanzee, Julian.
'Julian was nine years old when Susie had her last child, so that is an impressive statistic in itself,' said Mark.
'We are keeping close tabs on her daily to check that her and her baby are doing well.'
'This might be something that we explore in the future once mother and child are at full health,' said Mark.
'It is unique to my knowledge considering that chimps usually live to around 60 at most in captivity and 40-45 in the wild.'
Read more: Chimp, 56, stuns Zoo staff by giving birth to healthy baby girl | Mail Online