A giant saltwater crocodile after it was caught in the Philippines
A giant saltwater crocodile, which is suspected of having attacked several people, after it was caught in the Philippines. Photograph: Reuters

A crowd of people have gathered in a woodland whose leaves are turned deep fresh green by the water-sodden air. They line up quietly, so the photographer can use their numbers to measure a monster. In front of them, chained flat to a low cart, is a crocodile 20 feet – 6.1 metres – long. Its tail alone appears immense, dwarfing the crowd, who from this angle look as if they could all fit inside the beast.

Imagine it in sepia instead of rich full colour and this might be a photograph of a Victorian expedition team who have made it through miles of jungle into the Lost Valley of the Dinosaurs, and bagged themselves an iguanodon. Sometimes photographs transfix us on the present, which is why they are the perfect messengers of news. But sometimes they seem unanchored in time, and surface in this week's news only to lead us into timeless realms of the imagination.

So it is with true pictures of fabulous beasts. Like the first photographs and video of a live giant squid rising from the depths that appeared around the world in 2006, or a surreal picture taken in 2009 of a great white shark resting, alive, on the deck of a boat off Guadalupe, Mexico, this picture brings the ancient myths and terrors of humanity into the light of reality.

The events that led to this crocodile's capture were all too real. It is believed to have killed at least two people, including a 12-year-old child, near the town of Bunawan in the Philippines. No wonder so many people turned out to see it caught – and 70 hunters were involved in the operation. Yet this was not an act of revenge. The immense reptile was taken alive and is now in an eco-tourism park, a wonder to be observed in its natural context, though it has been reported to be stressed and refusing food.

What is lovely about this photograph is the sense of the marvellous that everyone in the calm crowd appears to share. Along with satisfaction in a successful hunt for a local terror, there is respect for the sheer mystery and strangeness of those gigantic scales, that powerful tail, that chained legend.

This is welcome after a summer in which disastrous encounters between humans and predators were sometimes reported as if the animal involved were a malevolent terrorist making war on us. Television reports on the funeral for a man tragically killed by a shark on his honeymoon arguably gave that impression, while a nation that had become fixated by polar bears as cuddly images of the endangered Arctic seemed shocked to discover they are actually powerful and ravenous hunters. Does that mean the polar bear's fate in a warming world will no longer be a matter of concern?

We need a cultural reckoning with big beasts. Ecology is not well-served by sentimental images of nature that exclude its violence. Sharks are in danger of extinction, and need protecting far more urgently than many soft and furry favourites.

Yet the reflex response of concerned naturalists whenever a shark attack makes the news is woefully misplaced. In the face of sensationalism, to calmly insist that sharks – or in this case crocodiles – have nothing inherently scary about them, that they rarely kill humans, and so forth is a weak, unconvincing argument.

The human terror of certain animals is incredibly old, as if hardwired into our brains by evolution; and it is also a fascination. The way to protect crocodiles, sharks and polar bears is not to misrepresent what they are but to admire their marvellous ferocity: to revel in the fact that, after all we have done, there are still animals out there that can eat us.

That is why this photograph is so beguiling. It shows people who respect the enormity, the horror and awe, of an animal that looks today just as it did at the end of the Cretaceous era 65m years ago. The basic design of a crocodile is one of the oldest land-living vertebrate forms that evolved: in the Natural History Museum in London you can see the fossil skeleton of a crocodile-like amphibian. The same museum has a skull that looks just like a modern croc's, toothy grin and all, except it is the same size as the T-rex skull displayed next to it.

So it is not fantasy to see in this photograph something uncanny, an encounter between humans and the monsters of prehistory. Crocodiles are survivors of the dinosaur age (although they are not dinosaurs). They connect us directly with the giant reptiles that swam in Jurassic seas, as well as with fantasies of fire-breathing dragons that humans created as they contemplated the abundance of the natural world. Crocodiles have been worshipped as gods, their skins have been worn as armour, and finally, in the 18th century, they started to be drawn accurately by naturalists. Hunted or cherished, they have never lost the fearsome charisma that comes with guile and age.

All the animals that have caused gruesome headlines lately are throwbacks to a remote past. The reason we should do everything possible to preserve sharks is their incredible antiquity: sharks appeared early in the history of vertebrate fish and have essentially never changed, because they are perfect. They ought to be celebrated as the world's oldest and greatest hunters – not soft-soaped, but revered for their lethal mystery. Meanwhile, polar bears take us back to our own cultural origins in the ice age, when humans rivalled bears for access to caves where we painted the giant mammals that were our contemporaries.

This photograph is a document of the marvellous, a token of respect for nature – not a nature sentimentalised, but fearsome and fantastic. That side of nature needs to be defended not just for its own sake but for the sake of our imaginations and our curiosity.