A female lion at Oklahoma City Zoo is the subject of a mystery for the facility's veterinarians after she surprisingly grew a small mane. Lion manes typically grow on males at around 1-year-old thanks to increased testosterone, the Zoo said.

Bridget the lioness is 18-years-old, and her sister, also 18, has remained without any kind of mane. The zoo said that the growth of Bridget's new mane had occurred between March and November of 2017.

According to a blog put out by the zoo, though lionesses growing manes is rare, it's not totally unheard of. A 13-year-old lioness at the National Zoo in South Africa began growing a mane in 2011 after an issue with her ovaries led to the production of excess testosterone - the mane went away when the issue was resolved.

In 2014, five lionesses were observed in Botswana with manes, with researchers believing that because the five came from the same pride, there was likely a genetic reason they had developed the mane at a young age.

At the Oklahome City Zoo, vets are awaiting the results of a blood sample from Bridget taken last week that could hold a clue to her mane. Staff are worried that the growth could be the result of a tumour around hormone regulating glands.

Aside from the hair, staff do not think that the mane will affect Bridget's quality of life in any way and have not seen any changes in her health. They added that she was born in 1999 and gave birth to a littler of cubs in 2007, she's also over the average life expectancy for lions.

Some on social media joked that the lion was simply not conforming to gender norms. "... meet the mane growing lioness who has no time for your gender normative beauty standards," wrote Twitter user Nick Ramsey, while another called the big cat "little honey with the lace front".