PANAMA CITY (AFP) - Panama Canal expansion work has uncovered an unexpected trove of archeological and paleontological treasures, scientists said, as the massive construction project winds down.

Workers who have blasted through mountains and dug up thick vegetation, have also uncovered the fossils of some 3,000 invertebrates and 500 vertebrates, as well as of more than 250 plants -- including the remains of a forest consumed by fire after a volcanic eruption.

Experts hired by the Panama Canal Authority have identified remains of camels, crocodiles, the teeth of a giant shark, as well as bones of other animals millions of years old.

But the most surprising discovery, researchers said, was about the age of the very land beneath Panama, the southern end of the narrow isthmus that connects North and South America.

Evidence uncovered during the canal excavation showed that the land started forming 20 million years ago and finished around 10 million years later.

"What we learned at school was that it formed three million years ago," said paleontology specialist Hortensia Broce of the Panama Canal Authority.

"But we have found organisms from other epochs, which show that the isthmus emerged little by little as the waters receded, and the formation occurred much earlier than we thought," she said.

Research will continue to study climate changes and the origins of the animals that migrated across the land bridge from one America to the other, said Smithsonian Tropical Research Institute's Carlos Jaramillo, who called the new discoveries "a revolution."

Dredging work in Lake Gatun and the excavation of tons of earth also uncovered fragments from hundreds of years of human habitations -- from pre-Colombian through colonial and provincial times, through independence, which began in 1903.

Artifacts include pottery shards, arrowheads and items buried during a pre-Colombian funeral. Also found was a dagger from the 16th century, a chimney from 1908, and a collection of bottles, wagons and buckets used to mix cement during the canal's first wave of construction.

The canal, an engineering masterwork that transformed global commerce, opened on August 15, 1914, connecting the Atlantic and Pacific Oceans and saving ships the long, dangerous trip around South America.

For the past seven years, Panama has been working to add a third set of locks to the canal, to nearly triple its capacity.

The expansion was initially scheduled to finish this year, in time for the anniversary, but has now been pushed back to January 2016.