Five years of paleontology at the canal expansion reveals the fauna of a 20 million-year-old tropical forest and reopens debate on the closure of the bridge between North and South America
Carlos Jaramillo knew he had to act quickly when Panama voted to expand its canal in 2006. The 100 million tons of rock that would be blasted to widen the waterway were a dream come true for the staff paleontologist at the Smithsonian Tropical Research Institute. But heavy rain and fast-growing tropical foliage would quickly close the window into the world-changing formation of the Isthmus of Panama.
"Carlos recognized right away that a multidisciplinary approach would be the way to get the most out of this once-in-a-century opportunity," said Doug Jones, the director of the Florida Museum of Natural History and one of five co-principal investigators on the major paleontology project that resulted from the expansion. "He got us all revved up and there was no looking back after that."
By the time engineers set off the first dynamite blasts, Jaramillo had a long-time Smithsonian donor and the Panama Canal Authority already on board. That support helped four research institutions from the United States and three from Panama to secure a U.S. National Science Foundation Partnership for International Research and Education (PIRE) for the project.
As the expansion nears completion, researchers have logged more than 6,000 days in the field. They located fossils, mapped geological formations, collected samples and described the geological setting. In an effort to salvage as much information as possible, they filled a warehouse in Corozal with samples. "There are entire mountains that aren't there anymore," said Jaramillo.
Before the expansion only four species of fossil mammals had been discovered along the southern stretch of the canal. Today, at least 24 mammals from eight different orders have been unearthed in sediments flanking the Centenario Bridge. These include squirrels, dogs, deer, small camels and ferocious "bear dogs."
Almost all are of North American ancestry and are similar to the fauna found throughout the continent 20 million years ago. This suggests that mammal faunal exchange from southern Canada to Panama was fairly continuous at the time, and that a formidable barrier separated the American continents. But the barrier wasn't impenetrable. Some mammals of southern origin, including bats, crossed the gap.
The researchers discovered that much of the tropical flora in Panama was also of South American origin. The findings renewed fresh debate about the timing of the final closure of Isthmus of Panama. Earlier work by STRI emeritus scientists Anthony Coates and Jeremy Jackson pegged closure at approximately 3.5 million years ago. Researchers including Jaramillo and Camilo Montes of the Universidad de los Andes in Colombia suggest an intermittent land bridge formed much earlier.
"It's a new model for the formation of the Isthmus of Panama," said Jaramillo. "We believe that the majority of the isthmus had risen ten million years ago and that the CAS (the Central American Seaway, a deep oceanic pathway along the tectonic boundary between Panama microplate and South American plate) closed by 10 to 12 million years ago. Only shallow water exchange between Caribbean and Pacific continued until a complete closure 4.2 million years ago."
ALL NEW TO SCIENCE
MacFadden says that even the six-fold increase in the number of large mammal species from the canal formations offers only a glimpse of Panama's early Miocene fauna. One expert estimate is that there should have been some 200 species of non-flying mammals in the ecosystem. A plethora of smaller creatures like lizards, frogs, snakes, birds and bats would have completed the fauna.
"We never found a locality where the fossils are super-abundant so it's been a lot of work," said co-PI Gary Morgan, a micro-vertebrate paleontologist at the New Mexico Museum of Natural History whose team has washed some ten tons of expansion material.
The majority of the canal's tiny fossils are small crocodile teeth. Fish bones were also found. "There should have been some birds but for whatever reason we haven’t found them," said Morgan, who is analyzing some 100 fossilized bat and rodent teeth. "Just about all these tropical animals have a poor fossil record, so really, anything we get is new to science."
By mid-2015 the last interns will have packed up their field tools. Yet the project's final mark on Central American paleontology won't be fully appreciated for many years.
Excavating and identifying thousands of samples became a learning opportunity for some 100 project participants, including U.S. and Panamanian students, many of whom will toil on laboratory samples and prepare future scientific manuscripts from the findings. So far the work has led to some 25 scientific publications.
Still more samples are in storage awaiting new technologies that may tease even more information from the rocks. "We have material for at least another decade," said Jaramillo.