Land mammal skeletons

On route to Ael Nurnan/Stone City of Bardh, the party came across a huge, twisted skeleton of an animal, washed up in a river. Alarë Awarthiel identified it as a land animal, while Oksana Bosko realised that the bones were twisted and enlarged from effects of Corruption. 
In a vision from Aboleth/Father, Sigrid Arnulf saw more of these skeletons at the bottom of the lake, covered in black ichor and leaking corruption into the waters, which travelled through land and rain to spread across the world. According to Father, these skeletons are the source of The Plug.
It is unknown if these creatures still exist somewhere, whether they are in Ancient Elvish texts, or how they came to be corrupted and at the bottom of the lake.
These skeletons could be previous conduits lured to the bottom of the lake to be farmed for devotion, or the final resting place of physical elven corpses that sailed on ships from Ael Nurnan.