You're seeing what will eventually become the creature's tail on this egg.
Astos can be commonly found on farms across Ark. They're gentle donkeys that are often mistaken for llamas or extremely large bunnies due to their very large, floppy ears.
Astos do tend to have problems with their ears because sometimes they can become longer than the creature's height, leading the Asto to trip and step on their own ears (ouch!). There is a safe and effective surgical treatment to shorten Asto ears that many Astos undergo. Cosmetically modifying their ears does not affect their hearing at all. If anything, it improves their hearing because there is less flesh blocking soundwaves.