devtrackers.gg
This image is from a video Jagex did in November last year, given the recent reveals through Archaeology and Jagex saying that they're 'hinting' at the new boss - this is likely it. Looks exactly like how Raksha is described in-game, and the dragon chains around it are similar to the one we see in Xolo City.
The writing to the top left of it says 'SOLO BOSS'.
Also, this is probably the 15 phase dinosaur boss which leaked last year before the release of Anachronia.
Around 48 seconds on this video for anyone interested: https://www.youtube.com/watch?v=cESwfOUFVFQ
Can tell you for a fact without Jagex clamping down on me that it absolutely won’t have 15 phases I chased down that leak personally and it was a load of BS which the person admitted they did to stir up the users.