Dinosaurs are once again facing an extinction threat. Not a giant meteor this time but changing water levels threatening a Victorian Jurassic park that has fascinated and thrilled generations of visitors for 166 years.

Historic England is announcing on Friday that it is adding the Crystal Palace dinosaurs to its heritage at risk register, worried by large cracks appearing in some of the 30 lifesize statues that were part of a pioneering project to educate and entertain people about natural science.

“This is huge for us,” said Ellinor Michel, the chair of Friends of Crystal Palace Dinosaurs. “Thank you, Historic England … the future suddenly looks brighter for the birthplace of dinomania.”

The dinosaur and extinct animal sculptures were created by Benjamin Waterhouse Hawkins, one of the finest natural history artists of the Victorian era. Given that the term dinosaur had only been coined 10 years previously, it is not difficult to imagine the excitement and wonder they caused.

“They were hugely popular,” said Michel, an American palaeontologist who lives locally. “People had never seen anything like it. All that had been available before that were museums of fossils, so piles of bones and probably fairly turgid descriptions … a request to the viewer to imagine it for themselves – and how do you do that?”

Facebook Twitter Pinterest The statues were the creation of Victorian artist Benjamin Waterhouse Hawkins. Photograph: David Levene/The Guardian

The statues were placed on artificial islands offering visitors the chance to walk through time from the Dicynodon and Labyrinthodon to the Megaloceros giganteus, or Irish elk, which died out only 10,000 years ago.

The sculptures are perhaps the world’s first example of outdoor “edu-tainment” and represented the cutting edge of scientific knowledge at the time.

Of course that means they got things wrong. The Crystal Palace iguanodons, for example, walk on all fours when the real things would have walked on their hind legs. They have nose horns, when in reality the creatures had horns on their hands. In south London they are being stalked by a ferocious megalosaurus, which could never have happened as they existed in different eras. The megalosaurus is also wrongly depicted as quadrupedal rather than bipedal.

But it doesn’t matter, said Michel. “Waterhouse Hawkins got the science as right as he could but also there was an absolute beauty and real theatricality to the way he put things together.

“The intensity of the megalosaurus is incredible, the gaze is ferocious … he has created a moment. That moment never existed for these particular animals but, hey, why not? I’ve been here hundreds of times and I still love looking at this scene.”

Michel said we should be bowled over by how much the Victorians got right at Crystal Palace. “They wanted to tell a really rich story. That’s why I get a little bit tetchy when people say the site is known for its inaccuracies because actually … the more you look at it, the better it gets.”

The dinosaur project stemmed from the Great Exhibition of 1851, which was so jaw-droppingly successful that the spectacular crystal palace building erected in Hyde Park was privately bought and moved to south London.

A park was constructed to accompany the new Crystal Palace and it was at the Penge end that the dinosaurs were located. They survive but the palace was destroyed by fire in 1936.

The creatures underwent significant conservation work in 2003 and 2016-17 but they are deteriorating, with large cracks appearing in some bodies and limbs. They are also in danger of losing toes, teeth and tails.

Facebook Twitter Pinterest Many of the statues are cracked and in need of conservation work. Photograph: David Levene/The Guardian

Historic England said the causes of the deterioration were not fully understood but ground movement and changing water levels are suspected.

Duncan Wilson, the chief executive of Historic England, said adding the dinosaurs to the register would help ensure there is a lasting programme of repairs and ongoing maintenance.

“These wonderful creatures are in a state of disrepair and require significant conservation works. We don’t want them to become extinct again,” he said.

The project to repair and conserve the statues will be led by Bromley council. Councillor Peter Morgan said a “radical new approach” was required “to ensure they survive the next hundred years for everyone to enjoy”.