Just finished my 999 for the pet. I soloed it and it took about 7 hours give or take. I started with the Direhorn group nearest the flight masters (brown group) then worked right (green group) camoflauged along the hill behind the two larger ones to get the 3 small ones behind them. I alternated between those two groups for the first 200 or so bones. Then, I tried something else that worked better.
I'd head left up the hill to the blue group and got the three easily reached without pulling the Dinomancers or the large ones. Then, up the next hill to the white group and then on to the cave area to get the 3 small raptors (a little tougher fight -- had to keep heals up on the pet) but 50% more bones per kill too. After that it was reverse path and then back uphill again. I was able to match the re-spawn rate going back and forth between those three groups - blue, white and raptors.
That also helped when others were farming. I'd stick to the hills and leave the brown and green groups and Dinomancers for the others farming. If I'd been in a group, it would only have meant more downtime. And, even if you can kill more per hour in a group, given the re-spawn rate, it's no faster, especially if you're both looking for the pet.
I got 1,011on last raptor kill, entered the cave and cashed them in. Stick with it. It's like a rep grind - worth it to those who care.
Two tips for ranged: The Dinohorns do not charge if you're in melee range. Just park yourself alongside their hind quarters. There is no tail swipe to worry about. But, if your pet is low on health, back up cast a heal on your pet and feign, vanish, whatever just as the charge starts. The Dinohorn will walk slowly over to where you are before turning again to battle your pet. That few extra ticks of heal on your pet without taking damage may be all you need to win the fight.