Elder evils has the leviathan.

1 version is 50-ft space, with 20ft reach.

The 2nd advanced version is 60-ft space, but still 20ft reach.

Natural weapon damage and physical stats seem to have been improved arbitrarily (eg: its slam damage improves from 4d6 to 5d6, but tail slap remains unchanged).

Str and con increased by +4, NA by +10. Again, no apparent link.