January Jones has left the father's name off her son's birth certificate.

The 'Mad Men' actress - who welcomed Xander Dane Jones into the world on September 13 - has always refused to say who the dad is and when she went to register the tot with the Los Angeles County Department of Public Health on Friday (23.09.11) she left the space blank.

Following the news of Xander's arrival, January's 'Mad men' co-stars were quick to praise her mothering skills.

Elisabeth Moss says the 33-year-old actress will be a great mother because she has all the right credentials for parenthood.

She: "I think she's going to be a great mom. She's a very caring and protective person, and I think she's going to fit in very well with motherhood."

Before the birth, January - who intends to bring her son up alone - said she was enjoying a period of "nesting" at home preparing for the arrival.

She revealed: "I've been enjoying a nice break.

"I've been in a nesting phase just preparing my house and stuff. I've had the luxury of a couple months off."