IN the early 1970s, an undergraduate geology student on vacation had just returned home to Nanyang in Xixia County, Henan Province. He was strolling around a quaint stone village when he noticed something strange about the walls - they were built of oval-shaped stones with a peculiar green tinge.

He took one of the peculiar stones back to his university and asked a professor for help in identifying it.

They soon discovered this was no ordinary rock, but a fossilized dinosaur egg, one of many thousands in the Funiu Mountains in southwest Henan. The range runs 400 kilometers east to west and small farming villages are scattered on the slopes.

The eggs were so numerous and handy that locals used them to build houses and barriers.

The story about an inquisitive geology student is often told, but it may not be true. Some geologists tell a different story - the eggs were discovered during a search for oil.

According to Wang Deyou, senior engineer from the Henan Research Institute of Land and Resources, it was demand for natural resources that led to the discovery of dinosaur fossils in Henan.

In the early 1970s, Wang was part of a team searching for oil in Xixia and Xichuan counties in Henan. Instead of oil, they found fossilized eggs in a shallow layer of earth in a Xichuan village. The year was 1974.

Seventy million years ago, during the Late Cretaceous Period, the Funiu Mountains teemed with dinosaurs or all kinds. Back then the reptiles enjoyed a comfortable average temperature of over 20 degrees Celsius - much warmer than the current average of 16 degrees.

Today's lower temperatures result in part from tectonic uplift, which has raised the mountains. The average elevation is now 1,800-2,200 meters, compared with 600-800 meters some 70 million years ago.

Such milder conditions made the Funiu Mountains a dinosaur haven. Paleontologists say a large number of dinosaurs lived here, and went to the rivers in groups during their mating season. Their reproductive patterns resemble those of turtles. Each dinosaur laid between five and - sometimes more than 80 - each time they went to the water.

Today visitors can see many of these eggs at the Xixia Dinosaur Relics Park in the village of Sanlimiao in Danshui town, Xixia County. Many fossilized eggs are still embedded in the walls of a 236-meter-long rock tunnel.

Circular nests

The sheer number of eggs in the area is astounding. Paleontologists estimate that 20,000 dinosaur eggs lie within an area of 1,200 square meters around Sanlimiao - that's more than 15 eggs per square meter. Yet vast deposits of fossilized eggs still remain buried under the surface.

The highlight of the exhibition is a nest of oval-shaped fossilized eggs laid in a circular pattern. Experts believe that in laying her eggs the female would first choose stable ground, use her claws to dig a hole, lay her eggs in a circle, with each one pointing outward. After covering her eggs with a thin layer of sand, she would move outside the circle and repeat the process.

Based on the position in which these eggs were found, paleontologists believe two were laid at a time. This suggests that some dinosaurs may have possessed a double-fallopian tube system, through which they could lay two eggs simultaneously. Many dinosaur eggs were discovered on the southern slopes of the Funiu Mountains, in a strata that dates back to the Cretaceous Period, around 145-65 million years ago. The end of this period also marked the end of the dinosaurs.

Some paleontologists believe the dinosaurs died out not from a sudden catastrophe, such as an asteroid impact, but from climate change. Around 70 million years ago, the Late Cretaceous climate had become increasingly hot and dry. Under these circumstances, dinosaur eggs that could hatch only at a specific temperature were unable to hatch.

At the same time, there appeared to be a decline in the fertility of the dinosaurs, causing some eggs to be laid, but not fertilized. It seems likely that this combination of environmental stress and the loss of reproductive functions led to the demise of the dinosaurs.

Soon after fossilized eggs were discovered in Xichuan in 1974, more discoveries were made elsewhere in China. Large quantities of dinosaur eggs were found in the neighboring counties of Xixia and Neixiang.

Unfortunately, these findings received little attention because of the almost exclusive focus on oil at that time. Only after a decade had passed did the Nanyang geological team turn their attention back to the dinosaur eggs. The team purchased the eggs at 5 yuan (73 US cents) each from local villagers, then sold each egg to research institutes for 30-40 yuan. This triggered a surge in interest in the Henan fossils, and people from all over China and abroad came to hunt for dinosaur eggs.

This wave reached its peak in 1993, when a dinosaur egg could be sold for thousands of dollars. The high price of dinosaur eggs also created incentive for people to steal fossils and excavate sites illegally. The theft of fossils and unauthorized excavation caused irrevocable damage to the progress of science. Researchers found themselves in a frantic race to find fossils - before thieves did.

Despite this, many significant discoveries were made.

In 1993 in Neixiang County, paleontologists unearthed a skeleton of a dinosaur with a missing skull. In 2000, this species was named Nanyangosaurus zhugeii, in honor of Zhuge Liang, a brilliant military strategist who lived during the Three Kingdoms Period (AD 220-266).

The Funiu Mountains are unique in that both fossilized eggs and bones can be found in the same area. Conversely, in Australia and China's Sichuan Province, paleontologists have found dinosaur bones, but not relatively nearby eggs.

One possible explanation is that the fossils from these places date to a much earlier period. The fossils from Sichuan date back to the Jurassic Period, around 200?145 million years ago. Dinosaur eggs laid during the Jurassic were able to hatch successfully, and thus few fossilized eggs from this period were left to be found.

The world's first discovery of dinosaur egg fossils was made in southern France in 1869. Chinese scientists first discovered dinosaur eggs in the 1920s, in present-day Erenhot in Inner Mongolia Autonomous Region and in Djadokhta in Mongolia.

The Funiu Mountains are remarkable in terms of the number and diversity of dinosaur eggs discovered there. In some areas, four or five eggs have been found in a single square meter. The eggs discovered thus far in Henan comprise 36 species, 12 genera and eight families. In fact, four out of every five fossilized eggs found in China were unearthed in Henan.

These eggs vary greatly in size. Some are as small as a chicken egg, with a diameter of 4-6 centimeters, while some elongated ones can be half a meter long. The longest egg found so far is shaped like an olive and is 61 centimeters long. This whopper, dubbed the "long cylindrical egg of Xixia," is not found anywhere else in the world.

Could these dinosaur eggs shed some light on ancient climate change? Some paleontologists think so. The thickness and porosity of the egg shells varies between the early, middle and late stages of the Late Cretaceous Period.

Germs on the slopes

Dinosaur traces are not confined to the southern slopes of the Funiu Mountains. In the last three years, paleontologists have also found a wealth of fossils on the northern slopes, in particular around Ruyang County in Henan.

The truth is that villagers in this area have long been digging up dinosaur fossils without even realizing it. For decades they have been consuming "dragon bones" that were believed to have special healing powers. Little did they know that these "dragon bones" were the fossilized remains of sauropods - massive land dinosaurs with long heads and necks. Sauropods are the largest creatures ever known to have walked the face of the Earth.

It was in Ruyang that researchers got lucky. Excavations in 2007 led to the discovery of Huanghetitan ruyangensis, widely billed as Asia's heaviest dinosaur. This sauropod was 18 meters long and weighed 60 tons, or the equivalent of 10 elephants. It was closely related to another sauropod discovered in Gansu Province in 2004, the Huanghetitan liujiaxiaensis, but the "Ruyang giant" was much larger.

In December 2008, researchers found another dinosaur that was even larger than the Ruyang giant - and is believed to be an entirely new genus.

Six other previously unknown dinosaur species have been discovered in the counties of Ruyang and Luanchuan. These include the Zhongyuansaurus luoyangensis, an ankylosaur with short limbs and bony armor - it is the only ankylosaur ever found in China.

Another new species discovered was the Luanchuan raptor (Luanchuanraptor henanensis), a carnivorous, bird-like theropod that walked on two legs. Some raptors had skin resembling feathers, while others had well-developed feathers. Many believe that these creatures represent the link between birds and dinosaurs.

Other raptors found on the northern slopes of the Funiu Mountains possessed so many bird-like features that many paleontologists at first thought they were ancient, flightless birds.

However, the name "raptor" (which means "thief" in Latin) is something of a misnomer. The raptor was discovered in Mongolia during a 1923 expedition by the American Museum of Natural History. A raptor with a crushed skull was found on top of an egg-filled nest, around which lay the fossils of several ceratopsians - herbivorous dinosaurs with a pronounced bony beak.

Meat-eaters

Researcher Henry Fairfield Osborn suggested that the unfortunate raptor could have been caught in the act while stealing ceratopsian eggs, and named it Oviraptor, or "egg robber;" the shortened name "raptor" is now commonly used to refer to similar birdlike dinosaurs. However, subsequent findings have indicated that the eggs belonged to the raptor, and that what Osborn "witnessed" was really the valiant act of a parent defending its own nest.

Researchers in Ruyang and Luanchuan have also uncovered several fossilized teeth of large carnivorous dinosaurs. And bone fragments belonging to giant theropods have been found scattered in the homes of local residents.

Researchers hope their findings may one day lead to a more complete large theropod fossil in China. So far, the most intact skeletons of such "tyrant lizards" are the Tyrannosaurus found in the United States and the Tarbosaurus found in Mongolia.

Such a rich variety and high concentration of fossils suggest that the northern slopes of the Funiu Mountains were an oasis for dinosaurs. However, many scholars are puzzled by the fossils' distribution: large numbers of eggs are found on the southern slopes, while skeletons are scattered mainly on the northern slopes.

Researchers from the Henan Geological Museum speculate that the dinosaurs may not have lived and laid their eggs in the same place. Seventy million years ago, prior to tectonic uplifting, the mountains were much lower than they are now. This would have made it easier for dinosaurs to travel long distances to lay eggs.