Two jaguar cubs burned to death, their small bodies carbonized. Tapirs with raw, bloodied paws had been scalded by smoldering cinders. Nests of unhatched eggs from rare parrots were consumed by flames as tall as trees.

Wildfires are laying waste to Brazil’s Pantanal, the world’s largest tropical wetland and one of the most important biodiversity sanctuaries on the planet.

And the blazes, the worst on record since Brazil started tracking fires in 1998, are taking a deadly toll on wild animals, including at-risk species that scientists have been working for decades to protect.

“We’re watching the biodiversity of the Pantanal disappear into ash,” said Gustavo Figueirôa, a biologist working for SOS Pantanal, a conservation nonprofit. “It’s being burned to a crisp.”

The Pantanal is a maze of rivers, forests and marshlands that sprawl over 68,000 square miles, an area 20 times the size of the Everglades. About 80 percent lies within Brazil, with the rest in Bolivia and Paraguay.

Usually flooded for much of the year, the Pantanal in recent years has been parched by a string of severe droughts that scientists have linked to deforestation and climate change

Since the start of the year, wildfires have burned over 7,000 square miles, an area the size of New Jersey, in Brazil’s share of the Pantanal.

The wetlands, parts of which are on UNESCO’s list of heritage sites because of their rich biodiversity, are home to the world’s biggest parrot, the highest concentration of caimans and threatened wildlife like the giant otter.

They also harbor animals that have evolved in ways distinctive from others in their species, like larger jaguars that dive into flooded plains to fish for food.

Researchers have counted at least 4,700 plant and animal species in the Pantanal, though they say many more have yet to be discovered by scientists.

“There’s so much we still don’t know,” said Luciana Leite, a biologist and a climate campaigner for the Environmental Justice Foundation. “It’s such a special region.”

But the wildfires, fanned by strong winds and searing temperatures, are threatening this natural laboratory, killing or injuring giant anteaters, lowland tapirs, marsh deer, hyacinth macaws and caimans.

The flames have caught even jaguars, normally agile enough to escape most dangers. Three have been found dead since the fires erupted, while four others were rescued and treated for burns, according to conservationists in the region.

“If the jaguar — an animal that runs, climbs, swims — is being affected on this scale, what chance do slower animals have?” said Enderson Barreto, a veterinarian and a director of the Response Group for Animals in Disasters, a volunteer organization working in the Pantanal.

Jaguars are listed as vulnerable in Brazil, which is home to about half of the world’s population of the animal. Now, the fires are approaching a reserve that is home to the world’s highest density of jaguars (four to eight animals for each 40 square miles), and experts fear that the death toll of jaguars, and many other animals, may climb.

“We’re really nervous watching this unfold,” said Mr. Barreto, who is working on the front lines of the rescue efforts inside the Pantanal. “The outlook is not good.”

Scientists say it is too early to say precisely how many animals are dying in the blazes, since many are perishing in remote regions that rescue workers cannot reach. But they fear the toll could exceed that of fires that ravaged the region in 2020, killing some 17 million animals and burning nearly one-third of the Pantanal in Brazil.

“We’re not only witnessing a repeat of a tragedy,” Dr. Leite said. “It’s actually a situation that’s much worse.”

One animal that became a victim was named Gaia and had played a key role in the Pantanal’s fledgling ecotourism industry for a decade. Spunky and social, Gaia, a 130-pound spotted jaguar, did not shy away from the pickup trucks carrying tourists from a nearby ecolodge. She became a local celebrity among wildlife enthusiasts.

Then, this month, the flames arrived at breakneck speed. Gaia didn’t have time to flee.

The news jolted Mr. Figueiroa, who had monitored the jaguar and her siblings when they were still cubs. “That was one of the best sightings of my life,” he said, lifting a pant leg to reveal a tattoo of Gaia’s sister on his calf.

“When I saw Gaia burned, turned into coal, I could just imagine the pain she must have felt,” Mr. Figueiroa added. “It was a feeling of frustration and despair and helplessness.”

The fires have also killed at least three giant anteaters, mammals known for their distinctive long snout and two-foot-long tongue, which they use to scoop up insects.

Believed to have evolved over millions of years, the species is threatened with extinction in Brazil, and its population there has shrunk by 40 percent over the last two decades, said Flávia Miranda, president of the Tamanduá Institute, a nonprofit working to protect anteaters.

“With the loss of these animals,” Dr. Miranda said, “we lose an evolutionary story that has not yet been fully told.”

The flames from the fires have reached tree crowns and scorched 80 percent of a crucial nesting area for hyacinth macaws, large, bright blue parrots that conservationists consider vulnerable and whose population is declining.

The blazes have also disrupted food chains, leaving behind a barren landscape devoid of water and essential food sources, like plants, insects and smaller animals.

Experts think the wildfires will continue at least until October, when the expected rainy season may bring some relief. The flames are intensifying pressure on an ecosystem already stressed by unusually frequent fires in recent years, casting doubt on whether it can fully recover.

If it doesn’t, countless species may lose their last sanctuaries in South America, including the lowland tapir, according to Patricia Medici, a biologist and conservationist who studies the species. “In the Pantanal,” she explained, “the tapir is in paradise.”

For scientists like Dr. Leite, who have devoted much of their lives to safeguarding vulnerable wildlife in this region, the future looks bleak. She wonders, she said, whether the Pantanal, a rare bastion of nature where humans can still witness wildlife in abundance, will remain intact for the next generation.

“I don’t know whether my son will have the privilege to look a jaguar in the eye, like I have so many times,” Dr. Leite said, wiping away tears. “We’re losing this really magical place.”

Lis Moriconi contributed reporting.