Symbolism, Imagery, Allegory
If you've read Beowulf, you know there's a connection between the dragon and Grendel. Both are monsters. Both like to terrorize humans. Both obey the laws of their own natures: dragons sit on gold mounds; Grendel is exiled by primordial sin and goes around eating people.
But when Grendel describes how he actually gets to the dragon in this text, we know this monster stands for something more... metaphysical. Listen: "I made my mind blank and fell, sank away like a stone through earth and sea, toward the dragon" (56).
It's not like he went on a road trip to the Valley of Dragons or something; the dragon is like a state of mind. Of course, he's a "real" dragon, too: Grendel's so scared of him that he pees himself when he sees him. But the dragon also represents the darker (darkest?) side of Grendel's mind.
That part of him says that all created things are accidental blips in the cosmos, and that nothing really matters. It says that the Shaper's songs are lies, and that they can't really make anyone or anything better. It says that nothing Grendel does and nothing that humanity does amounts to anything—good or bad—because everyone and everything be annihilated one day.
The dragon's a real downer, and he's meant to be. He's the embodiment of cynicism, materialism, and greed.
This suits Grendel's personality kind of well, though. Grendel half suspects that things are the way the dragon says, so it's just a hop, skip, and a jump for him to go over to the dark side, where the dragon rules. In that sense, the dragon isn't just some monster who lives in a cave—he's a part of all creatures who despair.
Devonian Fish and Chaos
The dragon uses the image of the Paleozoic Devonian fish—a creature that existed as a blip in evolution, not related to anything that preceded it—to teach Grendel about the randomness of existence. Maybe all we are is dust in the wind, according to the dragon, but occasionally, nature produces a unique creature for a single purpose, like the ancestors of the shark.
What is that purpose? These creatures bring chaos. They stir things up a bit and give a new order to the world around them, even if there doesn't seem to be any logical reason for them to be there.
This example suits the dragon's philosophy. Think about what he says to Grendel: Hey, you can go against your nature and be good, but humans really need you to be bad. It gives them an identity, something to strive against. The "brute existent", as the dragon calls it, just happens to be everywhere. Props to humans for figuring out a purpose for them?
In the end, you've got to wonder: who's the Devonian fish in this scenario? The dragon implies that Grendel may be just such a unique creature, created by nature one time only for the unique purpose of terrorizing these humans. It's another way in which we're asked to consider the possibility that everything Grendel does is fated, and he has no way out of his predicament.
Now, as we know, one bit of chaos usually invites another. Grendel's mother sends out vibes to warn her son: "Beware the fish" (149). Was she listening in on the dragon's conversation? Or do all monsters follow the same philosophy?
Well, maybe the do, but it isn't coincidence that connects the "fishes" in this novel directly to Beowulf—you know, the evolutionary freak who can do battle for days at the bottom of the ocean. Gardner drops the Devonian fish into the dragon's philosophy to signal the next random twist: the coming of the hero-monster.