Brute Tigrex Ecology

Disclaimer: This is merely a plausible explanation for the monster(s) in this article, and should not be considered canon.

Taxonomy
The Black Tigrex has few differences with it's cousin Tigrex other than coloration (obviously) and lifestyle in Volcanoes rather than Deserts.

Habitat Range
This dark colored T. rex like wyvern is found exclusively in volcanic areas.

Ecological Niche
Black Tigrex's role as top predator is no different than that of Tigrex. It's only known competitors include Agnaktor and Rathalos. Unlike the Tigrex, Black Tigrex doesn't seem to travel to temperate areas to prey on Popo every now and then so it definately needs to make the most of all prey at the volcano. It will hunt Rhenoplos, Rangurotora, Zuwaroposu, Uroktor, and immature Uragaan.

Biological Adaptations
Just as Tigrex has coloration suited to both Tropical sandy deserts and freezing snowy landscape, the Black Tigrex has just the right coloration to blend in with the Volcano's cliffs and crevices. The possible reason of its black coloration may be due to the huge amount of ash scattered in the Volcano.

Behavior
Black Tigrex is much more aggressive, and has been known to enter "prowler stance" or something akin to it. The Blk T rex can cover more of a distance in the field much faster as well with this new set of moves.