Credit: Albert Michael/ editors Pamela Satran and Linda Rosenkrantz -- who penned the books Baby Name Bible and Beyond Ava & Aiden-- are blogging for about why celebs choose the names they do, and what they mean.

Anyone who watches Keeping Up With the Kardashians probably expected the first baby born to one of the sisters to have a name starting with the letter K, with some 'kreative' spelling. But Kourtney, 30, fooled us all when she chose a traditional name with a conventional spelling for her first son, Mason Dash Disick, born Dec. 14.

Aren't they cute? See what Kim, Khloe and Kourtney looked like as kids!

Mason is one of the most popular of the last-names-used-as-first-names trend. Its origin dates back to medieval trades and occupations, though few Hollywood parents are probably aware of the connection! (A few examples are Ryan Phillippe and Reese Witherspoon's son, Deacon, and Elisabeth and Tim Hasselbeck's son, Taylor.)

Melissa Joan Hart
and Cuba Gooding Jr. also named their sons Mason, which ranks No. 35 -- the highest it's ever been -- on the Social Security list of top baby names.

Britney Spears' son), Madison to Addison and Hailey to Bailey.

Kourtney used the nickname of her late father, the high-profile attorney Robert KarDASHian, as inspiration for her son's middle name. Dash is also the name of the boutiques she and her sisters Kim and Khloe run in California and Florida.