Tyrion had a morbid fascination with dragons. When he had first come to King’s Landing for his sister’s wedding to Robert Baratheon, he had made it a point to seek out the dragon skulls that had hung on the walls of Targaryen’s throne room. King Robert had replaced them with banners and tapestries, but Tyrion had persisted until he found the skulls in the dank cellar where they had been stored. 

He had expected to find them impressive, perhaps even frightening. He had not thought to find them beautiful. Yet they were. As black as onyx, polished smooth, so the bone seemed to shimmer in the light of his torch. They liked the fire, he sensed. He’d thrust the torch into the mouth of one of the larger skulls and made the shadows leap and dance on the wall behind him. The teeth were long, curving knives of black diamond. The flame of the torch was nothing to them; they had bathed in the heat of far greater fires. When he had moved away, Tyrion could have sworn that the beast’s empty eye sockets had watched him go. 

There were nineteen skulls. The oldest was more than three thousand years old; the youngest a mere century and a half. The most recent were also the smallest; a matched pair no bigger than mastiff’s skulls, and oddly misshapen, all that remained of the last two hatchlings born on Dragonstone. They were the last of the Targaryen dragons, perhaps the last dragons anywhere, and they had not lived very long. 

From there the skulls ranged upward in size to the three great monsters of song and story, the dragons that Aegon Targaryen and his sisters had unleashed on the Seven Kingdoms of old...

Tyrion stood in that dank cellar for a long time, staring at Balerion’s huge, empty-eyed skull until his torch burned low, trying to grasp the size of the living animal, to imagine how it must have looked when it spread its great black wings and swept across the skies, breathing fire.

- Book 1: A Game of Thrones

 By the time she had reached eighty-seven, the room had begun to lighten as her eyes adjusted to the blackness. Slowly the shapes around her took on form. Huge empty eyes stared at her hungrily through the gloom, and dimly she saw the jagged shadows of long teeth. She had lost the count. She closed her eyes and bit her lip and sent the fear away. When she looked again, the monsters would be gone. Would never have been. She pretended that Syrio was beside her in the dark, whispering in her ear. Calm as still water, she told herself. Strong as a bear. Fierce as a wolverine. She opened her eyes again. 

The monsters were still there, but the fear was gone. 

Arya got to her feet, moving warily. The heads were all around her. She touched one, curious, wondering if it was real. Her fingertips brushed a massive jaw. It felt real enough. The bone was smooth beneath her hand, cold and hard to the touch. She ran her fingers down a tooth, black and sharp, a dagger made of darkness. It made her shiver. 

“It’s dead,” she said aloud. “It’s just a skull, it can’t hurt me.” Yet somehow the monster seemed to know she was there. She could feel its empty eyes watching her through the gloom, and there was something in that dim, cavernous room that did not love her. She edged away from the skull and backed into a second, larger than the first. For an instant she could feel its teeth digging into her shoulder, as if it wanted a bite of her flesh. Arya whirled, felt leather catch and tear as a huge fang nipped at her jerkin, and then she was running. Another skull loomed ahead, the biggest monster of all, but Arya did not even slow. She leapt over a ridge of black teeth as tall as swords, dashed through hungry jaws, and threw herself against the door. 

- Book 1: A Game of Thrones

Rakharo was the first to return. Due south the red waste stretched on and on, he reported, until it ended on a bleak shore beside the poison water. Between here and there lay only swirling sand, wind-scoured rocks, and plants bristly with sharp thorns. He had passed the bones of a dragon, he swore, so immense that he had ridden his horse through its great black jaws. Other than that, he had seen nothing. 

- Book 2: A Clash of Kings

 Ser Jorah snorted his disdain. “How profound.” The exile knight had no love for the old man, he’d made that plain from the first. “What do you know of dragons, anyway?” 

“Little enough, that’s true. Yet I served for a time in King’s Landing in the days when King Aerys sat the Iron Throne, and walked beneath the dragonskulls that looked down from the walls of his throne room.” 

“Viserys talked of those skulls,” said Dany. “The Usurper took them down and hid them away. He could not bear them looking down on him upon his stolen throne.” 

- Book 3: A Storm of Swords

“Robert took the skulls down when he donned the crown, but he could not bear to have them destroyed. Dragon wings over Westeros . . . there would be such a . . .” 

- Book 3: A Storm of Swords

Screenshot Timeline of Dragon Skulls in Game of Thrones Season 8

Screenshot Timeline of Balerion's Skull in Game of Thrones Season 8

Screenshot Timeline of Meraxes' Skull in House of the Dragon Season 2