First I would like to say that these beasts are very cool. The teeth encased in the armored skull is a cool concept as well. With that said, let's get into the critique.
The creatures seem to fit their forest environment (more on this later). Their armored hides would work as protection as well as camouflage which makes them believable in the environment you have placed them but for the extreme look of the beasts, the environment looks a bit too peaceful, even with the mist creeping around the trees. The sharp angles give them a hunter feeling but further enforces that the environment shouldn't be so peaceful.
Consider making the environment more suited to the aggression of the beasts. The trees are a bit too smooth. Consider what these beasts would do. Animals often rub up against trees for a few reasons, they leave their scent, scrap their anglers, rub off old fur, etc. Perhaps if these beasts travel in packs, they rub the armor on the trees damaging them a bit. In addition, trees have flaws throughout the bark, it breaks, dries, etc. so they aren't so perfectly straight. By giving them imperfections, the beasts will now seem to fit better.
With the forest covered, the beasts are a cool concept but they have a lot of human anatomy mixed with animal anatomy. It's a tricky thing to cover but you've already started to get close. If you look at human anatomy, consider where the pecs tie into the delts, and the delts tie into the bi's and tri's. How do the muscles hold the heads, thick traps. Consider all this. Look at quadrupeds and see how their muscles tie in together and the neck muscles are usually large and thick. By adding these features the creatures become even more believable. I think the design is great, just a few 'familiar' things will make it stronger.
Last, composition. Study how animals travel in packs, each animal will go a slightly different direction, even when traveling in the same direction. What I mean is one looks up, one looks to the side, one looks another direction, and so on. In addition, some are further ahead than others, some behind, etc. Right now you have them all lined up in a row, all looking the same direction. Give each one it's own personality because they seem a bit 'copy and paste' right now. All of them looking up, all of them have their left arm forward, all them have the tail claw in the same place, etc.
Overall, I think the piece is strong, has a lot of potential and the color is traveling in the right direction as well, by giving these creatures their own personalities and placing them in a more menacing environment I think the piece will be stronger as well.
Hope you find this critique helpful.