At first I thought we might see references to Dragonne Papré since at this time he should be locked up in the Battlespire where Imperial Battlemages train which links him to Abnur Tharn seeing as how he is one and all.. but the more I read on about Durnehviir the more it seems to line up with what we've seen so far. He is also immortal described as somewhere between life and death and is said to be unable to truly die, so killing him in this era would have no real impact on future events in ES.
"Some time ago, presumably in the early Merethic Era, Durnehviir lived amongst his kin in the skies above Tamriel.
While his brethren used more traditional forms of combat,
Durnehviir pursued an interest in necromancy that eventually led him to the Ideal Masters. His wish was to raise armies of undead for his own ends, so he made a pact with the Ideal Masters to gain access to their realm's undead. The pact specified that Durnehviir was to serve as the keeper of the Soul Cairn, and guard Valerica until her eventual death - terms to which Durnehviir, being an immortal dragon, agreed. But the Ideal Masters had deceived Durnehviir, as Valerica was a vampire, and thus also immortal. As a result, Durnehviir was doomed to guard the Soul Cairn for eternity.
Durnehviir is unique in appearance, and does not appear to be of any breed of Dragon previously encountered. His body bears a resemblance to the Frost Dragon, with massive protruding spikes from the back of his neck and extending down to his tail.
Four horns sprout from his head. As an undead Dragon, Durnehviir's flesh is greatly decayed and his wings look extremely weathered. He is grey-green in complexion, and his scales are constantly dripping and oozing. Flies can be seen around his body, and yellowish drool can be seen constantly dripping from his mouth.
When he is defeated by the Dragonborn, his body burns with a unique, purplish fire, though his Dragon Soul is not absorbed. Durnehviir is the only Dragon able to use a unique shout that lets him summon Bonemen, Mistmen, and
Wrathmen."
There is kind of a resemblance here.. maybe its just me. Anyone care to speculate?