It seems like people are predisposed to seeing things in the sky. Be it giant birds, angels, UFO's, or just about anything you can think of. So it should be no surprise when people claim to have seen flying dinosaurs, or Pterosaurs. In parts of Papua New Guinea, they see a strange light in the sky at night, which has become one of these creatures of legend.
Size: While sizes are hard to come by, considering most sightings are at a distance and are mostly the light the creature emits, estimates are of a wingspan of up to six feet. Which would make this one of the smaller cryptids.
Appearance: Many sightings only see the light it emits from it's underbelly, but other close-up sightings describe a small body, leathery wings, short fur, and a long, pointed tail.
Threat: Low. The small size of the creature, plus most reported behavior, would lead one to believe this creature doesn't pose a threat to people. Claims are that it uses the light on it's belly to attract fish to the surface of the water at night, which it then swoops down and scoops up in it's mouth. The only thing which may suggest any threat to people, are claims that it occasionally breaks into or digs up fresh graves and eats the bodies of the dead. So it is possible that a particularly bold specimen could become accustomed to the taste of human flesh and move up from eating dead people, to eating live people.
The possibility of this creature isn't as far-fetched as some might think. Very large areas of Papua New Guinea remain unexplored to this day and it is commonly said that there are likely groups of indigenous tribes living in the jungles who still haven't made contact with the outside world. Even though the Ropen is relatively large for a flying animal, it would be easy for it to remain hidden. Sleeping in caves or among the trees during the day and only coming out at night to feed.
The possibility that the creature could exist doesn't stop people from trying to suggest it is an already known animal. Many people think the Ropen is just a frigate bird. Their silhouettes in flight are remarkably similar, and the behavior of fishing matches up as well. However, that doesn't explain the light the Ropen seems to emit, and most frigate birds aren't nocturnal. The other suggestion is the flying fox, a large, fruit-eating bat. That covers the close-up descriptions, and the nocturnal behavior, but not the light or the fish-catching.
The truth is likely both. Sightings of both animals on separate occasions leading to the creation of a creature which is a combination of the two by superstitious people who aren't used to the animals they're seeing. Or, the truth could be that the Ropen itself is a real animal as described, and is still hiding in the depths of the jungles of Papua New Guinea.
Still, who knows whether everything we see in the sky is actually what we think it is.
(for those of you curious, this is post #20 out of 31 posts of monsters. Sorry this is taking me so long to get through.)