Ex-NFL Star Arthur Jones, Jon Jones' Brother, Dead at 39

3:40 PM PT -- It's still unclear how Arthur Jones passed ... but according to new police audio TMZ Sports has obtained, it appears he might have suffered an issue with his heart on Friday morning.

An official can be heard in the audio stating a 39-year-old male's "defibrillator went off" and "he received a shock and now he's not answering the phone."

Former NFL star Arthur Jones -- the brother of UFC legend Jon Jones and football player Chandler Jones -- has died, the Baltimore Ravens announced Friday.

He was 39 years old.

Details surrounding his death have not been announced.

Jones - a Super Bowl champion in 2013 -- played for Baltimore, Indianapolis and Washington during his seven-year career. He tallied 173 tackles, 10 sacks and two forced fumbles.

In Super Bowl XLVII against the San Francisco 49ers, Jones had a fumble recovery, a sack and two tackles.

He was a fifth-round pick out of Syracuse in 2010 ... earning all-conference honors in three seasons.

"Arthur's presence was a gift to everyone he encountered," the Ravens said. "His big, bright smile, infectious energy and eternal positivity created a presence that continuously uplifted others."

"He was kind, courteous and enthusiastic -- always displaying a love for family, teammates and friends."

"We send our deepest condolences to the Jones family and all who loved Arthur."

Arthur is Jon and Chandler's older brother ... with all three thriving at the professional level in their respective fields -- Chandler played 11 seasons in the league with the Patriots, Cardinals and Raiders ... and Jon is widely considered the greatest fighter in UFC history.