Stygian Quacks

When the world was gaseous and green, and the mountains rumbled, and the rivers bubbled, and the vines were thick and writhing, the fanged ducks roamed the lands.

Amorphous balls of muscle, purely predatory, wrathful beasts with calls and screeches that reverberated deep within the valleys of shadow.

"QUACK!" "QUACK!"

They were seated firmly at the top of the food chain and no environment was safe from their insatiable hunger. They ruled the mountaintops. The ruled the lowly ponds of scum. They ruled the clouds and the hills, and the tall grasses, and even the prehistoric public restrooms.

Their feet could easily disembowel a male Bull-Sloth in under thirty seconds. They could outrun a full-grown Jagopotamus. But what truly made them the most feared beast of the Lost Ages was the imperious stare from the milk-white saucers of their eyes. Any chance of escape was lost when the portentous glare ensnared its prey.They did not lose focus. They did not blink. No compromise. They could only target and pursue. In an instant, the prey knew that the ducks wanted to hunt them down more than they themselves wanted to escape.
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But, you can stare as much as you want at an asteroid that's about to collide into your planet and wipe out the entirety of your species--asteroid's not gonna mind one bit.

"QUACK!"