Cerrejón has provided Bloch with many such moments.
The search for the river monsters of the Paleocene Epoch began here by accident 18 years ago, when Colombian geologist Henry Garcia found an unfamiliar fossil. He put the specimen in a coal company display case, where it was labeled “Petrified Branch” and forgotten.
Nine years later, Fabiany Herrera, an undergraduate geology student at Colombia’s Industrial University of Santander, in Bucaramanga, visited Cerrejón on a field trip. Tramping around the coal fields at the mining complex, he picked up a piece of sandstone and turned it over. There was an impression of a fossil leaf on it. He picked up another rock. Same thing. And again.
Herrera showed his discoveries to Jaramillo, who was working for the state oil company at that time and suspected that Cerrejón might have a lot more to offer than interesting rocks and coal formations. He and Herrera organized a full-scale expedition to Cerrejón in 2003 and invited paleobiologist Scott Wing, curator of fossil plants at Smithsonian’s National Museum of Natural History, to join them.
Most fossils, plant or animal, are found either in temperate climates or in isolated niches in the tropics, such as deserts or high altitudes, where wind blows away sand and stone to expose ancient remains. Other fossils near the Equator lie buried and inaccessible beneath millions of tons of soil and vegetation. At Cerrejón, the quest for coal had stripped away this shroud.
Herrera, with help from other researchers, spent four months at Cerrejón, collecting more than 2,000 plant specimens from several different pit mines. He did not know what to expect, because no one had ever explored a site of Cerrejón’s age and location. Instead of an ancient forest filled with unfamiliar species, “the plants were all relatives of stuff we find today,” Herrera said. “We’ve got chocolate, coconuts and bananas and legumes—not as diverse as today, but the origins of the modern South American rainforest are suddenly there.”
When Wing arrived at the mine, he looked in the coal company display case and decided that the “Petrified Branch” was not what it seemed—and that plants were not the only attraction in Cerrejón. “I had a point-and-shoot camera,” Wing recalled. “Early in the visit I asked if the company could open the cabinet, but nobody could find the key.” Wing took some pictures through the glass, returned to the United States and e-mailed them to Bloch at the University of Florida in Gainesville, a collaborator on an unrelated project.
“I flipped out,” Bloch said. He was looking at part of the fossil jawbone of a land animal. Terrestrial vertebrates of that age had never been seen in the tropical latitudes of South America. The jawbone came from a dyrosaur, a very large crocodile-like creature now extinct. The fossil signaled that there were probably other vertebrate discoveries to be made.
Bloch and Wing immediately made plans for another trip and met Herrera and Jaramillo in Cerrejón. Wing showed Bloch the display case and started wiggling the lock. The glass broke. Wing reached in, plucked out the dyrosaur specimen and found a second bone hidden behind it, which “looked like a piece of pelvis,” Wing recalled. It was.
Garcia explained he had found the fossil at a mine site known as the Expanded West Pit. He took the visitors there. A layer of coal had been removed from the surface, leaving a vast expanse of naked mudstone baking in the tropical sun. “It was covered with turtle shells,” Herrera recalled. They were bleached white and shimmering in the heat.
The team collected fossils and returned to Gainesville. Over the next few months, U.S. and Colombian students explored other Cerrejón sites and e-mailed photos to Bloch. The La Puente Cut, an enormous open pit covering 6,000 acres of Cerrejón’s North Zone, appeared to be the most promising.
“I was extremely excited,” Bloch recalled. “I was sure we were going to see unbelievable stuff down there.”
La Puente is a forbidding, naked surface of soft mudstone cut by gullies leading downslope to a lake filled with runoff and groundwater. The only vegetation is an occasional scraggly bush clinging to the scree. The pit shimmers at temperatures above 90 degrees Fahrenheit, while a hot wind blows constantly, with 25-mile-per-hour gusts. Methane fires belch periodically from the naked cliff face across the lake. Immense trucks can be spotted in the distance, driving loads of coal scooped up after blasting.
The mudstone was the paleontological pay dirt. “Wherever you walked, you could find bone,” Bloch said, recalling the wonder of the first trip.