Lol. The best reason.

I do appreciate the suggestions for a quick solution, though.

Thanks.

To do it the "hard" way:

The general rules for carrying capacity assume a medium-sized bipedal creature (such as an elf).

Quadrupal creatures can carry half again as much. This bonus is doubled each size category (x3 for large, x6 for huge)

Larger creatures can carry twice as much. This bonus is doubled each size category (x2 for large, x4 for huge)

Both multipliers count, so a Gargantuan quadruped would be able to carry 96 times as much as its Strength indicates.

*Importing from the d20 SRD*
So a medium-sized bipedal mount like a Deinonychus can carry 225 pounds.

A Wolf, a medium-sized quadruped (x1 1/2) can carry 216 pounds.

The Hadrosaurus is large (x2), but still not quadrupal, and can carry 450 pounds.

A Giant Lizard is both large (x2) and quadrupal (x3) and can carry 1350 pounds.

An Ankylosaurus is a huge (x4) quadruped (x6) and can carry 8664 pounds.

A Tyrannosaurus Rex is also huge (x4), but decidedly not a quadruped, and so can carry 2500 pounds (not that it wants to, unless stomach content counts

).

All assuming default ability scores. Realistically, these would vary slightly between different members of a given species.

For flying mounts, I would not reduce the carrying capacity other than not applying the quadruped bonus (even if it has four legs) - instead I'd reduce the flying speed by 1/3 if the creature is carrying more than half its regular capacity.

That is, a Quetzalcoatlus would have a carrying capacity of 15x15 (for Strength) x4 (for Huge) x5 (quadruped) = 5400 punds on the ground (if you have the patience for its miserable land speed). In the air that would be 15x15x4=900 pounds, and that only at a reduced fly speed of 55 ft. If it carries 450 pounds or less, however, it can fly at its regular speed of 80 ft.

Hope you want to be helped this time