Marc Anthony Don't Forget About MY Hot Young Rebound

4/25/2012 7:13 AM PDT

Jennifer Lopez isn't the only one running around town with a hot piece of ass who's half her age ... Marc Anthony's got a hard-bodied 24-year-old of his own ... and last night, he trotted her out in a SKIN-TIGHT sausage-casing of a dress.

43-year-old Anthony has been dating Venezuelan model Shannon De Lima for several months ... and last night, the two strolled in to a private party together in Miami Beach.

With J.Lo still playing chaperone to her ripped boy-toy Casper Smart ... we gotta ask ...