"According to Ian Mortimer, who has researched the Scottish Mortimer family extensively, roger came from the Scottish Mortimers, who descend from Alan Mortimer of Aberdour (first mentioned in 1126). which would make Roger probably the 8th generation in Scotland. Roger had 2 daughters who were his coheir. they were described in contemporary documents as "heiress of Aberdour", which ties the Mortimers of Foulis to Alan of Aberdour.
See the website "Mortimer as a Surname in Scotland" at http://users.globalnet.co.uk/~mortimer/DATUMVI.html.