Making a Mokele-Mbembe Animal Companion

[Prehysterical]

I need some help from the more mechanically inclined members of the Pathfinder community here on the Playground.

See, in this one Serpent's Skull game that I am involved in, I would like for my Beast Rider cavalier to have a Mokele-Mbembe (http://www.archivesofnethys.com/MonsterDisplay.aspx?ItemName=Mokele-Mbembe) animal companion that will eventually serve as his mount. I like the notion of a half-orc finding beauty and kinship in such a strange, strong, and dangerous creature.

However, the only stats that are available are for full-grown adults. Could someone help me tone it down to a Medium creature at the start and make an appropriate 7th level progression for it?

[duboisjf]

Do you want to go from medium to huge with 7th level progression or just from large to medium ?

You could simply remove the giant template two times from the stat block you have to get your starting creature. It compares to the elk but with a lot more natural armor.

Apply the giant template as the 7th level progression and have the whip tail attack appear at that moment too.