Gnoll Ferocity( Races of the Wild, p. 151)
You embody the savage ferocity of your people. When you fl y into a berserk rage, you can bite opponents with your powerful jaws.
Gnoll, rage or frenzy ability,
When you use your rage ability, you gain a bite attack. This attack deals 1d6 points of damage, scaling normally with size (see Table 5-1, page 296 of the Monster Manual), plus your Strength bonus. Alternatively, you can make the bite attack as part of a full attack as a secondary weapon with a -5 penalty on the attack roll (your other attacks take no penalty), but in this case you only add half your Strength bonus on damage.
The DM may make this feat available to other animal-headed races if they are available in your campaign