These things can be aggroed on by:

Allosauruses,

Spinos,

Rexes,

Alpha Rexes,

Yutyrannuses,

Carcharos,

Gigas,

Rhynios,

And finally megatheriums that somehow got the insect buff

If it is able to aggro onto a bronto without it aggroing the animal first that means it is aggressive to and will attack any and all other tames.

This also applies to the paracer as in terms of prey the paracer can be aggroed on by the same creatures listed above.