The Pakal Votan Tomb Lid: The Celestial Bird

leading from 

Established Mythology behind the tomb lid.

and

The "Pakal Votan" tomb lid  

(source: A Forest of Kings:
The Untold Story of the Ancient Maya)

Possibly a celestial bird,  from photo K8342,

1. The Celestial Bird, also known as the Serpent Bird and the Principal Bird Deity, has a long tail, personified wings, and the head of a zoomorphic monster. Often it appears with a round object and a woven ribbon held in its mouth, with a trefoil pectoral around its neck, and a cut-shell ornament attached to a jade headband. In its most common representation it sits atop the World Tree or astride the body of the Cosmic Monster. In its earlier manifestations, it appeared prominently in  the Late Preclassic art of the southern highlands. There it represented the idea of nature out of control but brought into order by the Hero Twins and their avatar on earth, the king. This concept of the king as the guardian of ordered nature first came into the iconography of lowland Maya wit the image of this bird, especially in the context of the world tree. (source: A Forest of Kings: The Untold Story of the Ancient Maya)