Byrne joined Dunfermline from Shamrock Rovers

Former Shamrock Rovers left back Byrne, 23, has agreed a three-and-a-half year deal at Pittodrie.

"Obviously I know Richie well from my time at Dunfermline and he'll be a useful addition to the squad," said Aberdeen manager Jimmy Calderwood.

The Dons have also signed up Finnish brothers Mikko and Markus Paatelainen until the end of the season.

The players, who are the younger siblings of former Pittodrie striker Mixu, were both with AC Allianssi in their homeland.

"Mikko and Markus have looked good in training and having them here for the rest of the season will give us a good opportunity to have a close look at what they're capable of," added Calderwood.

Markus plays in midfield, while Mikko is a centre forward.

The Byrne move was delayed when the Dons demanded a new scan on a troublesome pelvic bone injury that has prevented the defender playing for the Pars since November.

Meanwhile, defender Andrew Considine has joined fellow youngsters Darren Mackie and Richard Foster in agreeing new contracts at Pittodrie.