Millions of years ago, this desert in Peru was a gathering place for fantastical sea creatures: whales that walked, dolphins with walrus faces, sharks with teeth as large as a human face, red-feathered penguins, aquatic sloths.

They reproduced in the gentle waters of a shallow lagoon buffered by hills that still wrap across the landscape today. Eventually, tectonic shifts lifted the land from the sea. More than 10,000 years ago, people arrived. With them came art, religion and monumental architecture.

Researchers have pieced together these snapshots of the distant past from the bones and tombs found scattered in the Pisco Basin, a thick layer of fossil-rich sediment that stretches across 200 square miles of badlands and riparian corridors between the Andes Mountains and the Pacific coast of southern Peru.

Discoveries from the region have come at a brisk pace in recent decades, with at least 55 new species of marine vertebrates found so far. In August, paleontologists unveiled what may be the region’s most remarkable find yet: Perucetus colossus, a manatee-like whale now considered the heaviest animal known to have existed.

“There seems to be always something new coming from Peru,” said Nicholas Pyenson, a paleontologist and curator of marine mammal fossils at the Smithsonian Institution. It’s not just the abundance of fossils that makes the region special, he said: “In many cases they reflect species we see nowhere else, and we don’t really know why.”

But paleontologists in Peru warn that this unique bounty of bones is under threat from one of the more insidious ways the country loses its natural and cultural heritage: unplanned development.

In the farm town of Ocucaje, the gateway to the Pisco Basin, the desert is quickly being carved into plots of land for real estate projects, squatter settlements and chicken farms. New roads cut into windswept swaths of desert and sand dunes. Along them, mud barriers and posts strung with barbed wire have gone up.

“We’re being dissected,” said Laura Peña, Ocucaje’s mayor, as she inspected rectangular demarcations in the sand on the outskirts of town. “This used to be an open pampa. There were no roads before. There was just the land. In the last few years, it’s all been fenced off.”

It has happened so rapidly, Ms. Peña said, that she is still trying to sort out who owns what and how much of it is legal. Like many small-town mayors, Ms. Peña has no land-tenure map of her district and struggles to track decisions made by the provincial and regional governments.

Many of the subdivisions contain fossils or pre-Columbian sites that should have been declared off-limits years ago, she said.

Unruly growth has long been a challenge to preserving Peru’s countless ancient ruins, especially along the arid coast, where pre-Columbian civilizations once flourished in the river valleys occupied by Peruvians today.

In Ocucaje, Manuel Uchuya, 73, lives in a squatter community atop a ceremonial center of the pre-Columbian Paracas culture. More than a century ago, the German archaeologist Max Uhle unearthed several mummies at the site that were at least 1,000 years old and were wrapped in elaborate funeral bundles, including one with a serpent motif and a headpiece of macaw feathers.

“We had nowhere else to go,” Mr. Uchuya said.

The site had already been picked over by looters when he and his wife built a shack on a small plot of land to retire on about 20 years ago, he said. Around the corner from their small shack, the remains of a pre-Columbian adobe wall still stood, and shards of ceramics, cobs of corn and shreds of reddish textiles littered the ground.

Because of Peru’s huge housing deficit, neighborhoods tend to be built first and legalized later. In the past 15 years, 90 percent of urban development has happened informally or outside of regulations, said Andres Devoto, a lawyer.

As available land has dwindled in the arid region between the Andes and the Pacific Ocean — where most of Peru’s population and economic activity is concentrated — speculation has spurred settlement claims in increasingly unlikely areas.

Ocucaje, a remote outpost in the booming agricultural export region of Ica in southern Peru, has a population of fewer than 5,000 people, no sanitation system and an annual budget for public work projects of about $30,000. Older residents once toiled without pay at the hacienda there, until land reform came in 1969. Today, most people grow crops, harvest seaweed at nearby beaches or work as laborers in cities.

In Ocucaje’s main square, children play with a sculpture of Megalodon, a shark three times the size of the great white, and a paleontological museum displays fossils to the odd tourists.

Mario Urbina Schmitt, a paleontologist based in the capital, Lima, who has emerged as Peru’s most prolific fossil hunter, said he was shocked when he returned to work in the region in 2021, after the Covid-19 pandemic lockdowns. While many Peruvians spent the year under strict lockdowns, land claims and squatter settlements exploded. “It’s like going to the Grand Canyon,” Mr. Urbina Schmitt said, “and suddenly there are signs everywhere that say, ‘This is mine!’”

Archaeologists know Ocucaje as a crossroads of ancient civilizations — a place where the Paracas and Nazca peoples created figures of animals and warriors on hillsides and the Incas laid a path to connect the region to their empire.

Paleontologists consider the region one of the best places in the world for investigating the evolution of marine animals. The virtual absence of rainfall — Ocucaje receives one millimeter a year on average — has preserved even the red color in the feathers of the five-foot-tall Inkayacu penguin and the hairlike filters in the mouths of whales.

“It is beyond a UNESCO World Heritage site in terms of the scope of its abundance,” said Dr. Pyenson, comparing the area to Wadi al-Hitan, a celebrated marine fossil site in Egypt. “It’s like you have a Wadi al-Hitan of many different time periods.”

Mr. Urbina Schmitt said that even after four decades of exploring the desert of Ocucaje, he still finds so many fossils that he can afford to be picky. “Anyone can find a normal whale,” he said. “They’re everywhere. I don’t count those. I want the new ones. The strange ones.”

A decade ago, he spotted a massive Perucetus vertebra embedded in the side of a cliff. The revelation of the new species, published last month in a paper in Nature on which he was a co-author, has been widely celebrated in Peru.

At the Natural History Museum in Lima, where vertebrae and part of the pelvis of Perucetus are on display, visitors line up to take selfies with Mr. Urbina Schmitt. “It’s like we won the World Cup,” he said.

Peruvian paleontologists hope the excitement will translate into more support for their underfunded field and their efforts to protect Ocucaje.

Government officials in Peru have talked for at least a decade about creating some sort of park in Ocucaje. The idea has barely advanced, in part because of a dispute over which state institution should lead the effort.

The Geological, Mining and Metallurgical Institute, an agency within the Ministry of Energy and Mines, wrested authority for overseeing fossil protection from the Culture Ministry in 2021. But it is still reviewing which areas to declare off-limits and plans to rewrite Peru’s proposal to add the region to the UNESCO World Heritage list, said César Chacaltana, its director of paleontology.

In the meantime, at least four real estate projects are advertising plots of land to build suburban-style homes in the desert of Ocucaje. In videos on social media, one cites the discovery of Perucetus as a reason to invest in the region. Another promotes quad motorbiking in the desert.

None have requested a permit to certify, before breaking ground, that there are no fossil remains on their sites, as required by law since 2021, Mr. Chacaltana said.

Heavy machinery appears to have already leveled the ground in some demarcated areas, taking any potential fossils with them. “Any evidence on the surface would have been destroyed,” Ali Altamirano, a paleontologist with the institute, said during a visit.

Ms. Peña, who took office in January, suspects that at least some of the newly demarcated areas in Ocucaje are the work of land traffickers — mafias that organize squatter occupations to appropriate public lands. “We don’t know what they want in Ocucaje,” she said. “There’s no water here. We only get water once a week for a few hours.”

Under Peruvian laws that aim to protect the landless poor, squatters cannot easily be evicted from vacant public lands and can eventually petition authorities for property titles and public services.

But increasingly, criminal groups are exploiting those safeguards. They might pay people to put shacks on vacant lots to demand land titles that they can later sell or repurpose, or they might use violence or bribes to win approvals from local officials. “Land trafficking is one of the most lucrative businesses for mafias in Peru,” Mr. Devoto said.

Some fenced-off areas in Ocucaje show only the faintest signs of occupation. Near Cerro Blanco, where faded signs flag groups of whale fossils for visitors, a one-room brick house sits in the sun, without access to water or any indication that someone lives there. “We never see anyone in it,” said Elvis Ormeño, a local tour guide. “This wasn’t made by a family in need.”

The winds that whip across the desert’s dunes still conceal and reveal clues about the ancient past; it takes trained eyes to see them. Paleontologists and archaeologists fear that uncontrolled development in Ocucaje could destroy potentially valuable finds before they are known.

“You can be standing there, you know, day after day, doing your work, and not see a geoglyph because of the way the sun hits the landscape,” said Lisa DeLeonardis, an art historian with Johns Hopkins University. “And then when you do, the rocks all line up and you realize, oh, there’s a geoglyph there.”

Geoglyphs — large-scale designs made by scraping the soil or lining up rocks — were once thought to have been made only by the Nazca civilization, whose famous figures stretch across the desert some 50 miles north. But earlier geoglyphs by the Paracas are increasingly found on hillsides in Ocucaje and nearby valleys, Dr. DeLeonardis said.

One resident, Mirtha Mendocilla, 28, remembered taking her son and his friends to see a geoglyph that locals spotted not far from town — only to be met with fences and a sign that read “Private Property.”

“What private property?” Ms. Mendocilla said. “This is our heritage. We have to take it back before it’s ruined.”