Imagine the Amazon rainforest without the jaguar. Imagine Perú without the llama. Imagine the Caribbean without coral reefs.
As Panama’s government works to expand the country’s canal, tearing down hillsides and digging trenches, researchers at the Smithsonian Tropical Research Institute have a unique opportunity to recover fossils, which tell the story of the 20-million-year-old connection that shaped wildlife in North and South America.
Smithsonian research fellow Jorge Moreno has worked with the project since May 2014. He outlined the historical significance of Panama, which brought the Americas together.
“The jaguar, the llama, the tapir, these are actually immigrants from North America,” Moreno told Latin Correspondent. “During tens of millions of years there were no cats in South America. And cats evolved in the Old World [Europe, Asia and Africa] and they dispersed in North America and when the isthmus of Panama rose these types of animals reached South America.”
South American native species took advantage of the connection as well, according to Moreno.
“For several tens of millions of years South America behaved as an island continent much like Australia today,” Moreno said. “South America’s flora and fauna were almost completely isolated, so there were a lot of endemic animals that evolved there and nowhere else.”
Just as Australia today hosts unique wildlife such as the kangaroo and koala, Moreno listed sloths, anteaters and armadillos as the legacy of South America’s isolated development. However, there was another side to this land bridge: the separation of marine life.
“Once you close the isthmus, the Caribbean gets isolated, gets hotter and more saline and more depleted in nutrients,” Moreno said. “So many forms of life went extinct in the Caribbean, but others thrived, for example corals.”
Most of the fossils that Moreno and his team are recovering come from what geologists call the Miocene epoch, a period spanning from approximately 23 million years ago until 5 million years ago. Geologists consider it the last warm period in Earth’s history, with no glaciation at the poles. At its height, geologists estimated that the Earth was on average five degrees Celsius (nine degrees Fahrenheit) hotter than today.
“Bear dogs” and camels that looked like pigs
At the beginning of the Miocene, Panama was a seaway between the Caribbean and the Pacific. Land began to rise approximately 21 million years ago due to volcanic activity. In the canal dig sites, researchers have identified and dated volcanic ash to that period. Geologists had previously thought that Panama rose and cut off the seaway 3 million years ago, but a new paper in the journal Science backdated that event to at least 13 to 15 million years ago.
Moreno said that researchers have recovered thousands of fossil specimens since excavation began in 2007. Animals range from sea crustaceans such as crabs and shrimp to animals marking Panama’s terrestrial rise. The land animals identified include some peculiar relatives of those living today, such as a small deer-like horse; short, long-snouted camels that resembled pigs; and early relatives of dogs that would have looked similar to a mongoose, according to Moreno.
In addition, Moreno said that some extinct mammal groups have been found in the excavation. The team recovered four-legged deer-like protoceratids, whose males had horns protruding from their ears and noses. Amphicyonid specimens have been found as well — a group dubbed “bear dogs” due to their appearance. Moreno said that these mammal groups are also well represented in fossils recovered in North America, in the Great Plains and Texas.
The Smithsonian is working alongside the University of Florida in recovering and identifying the fossils. The university provides the project with interns that have helped extract and examine the thousands of specimens. Some fossils are kept in Moreno’s laboratory in Panama City, but many are shipped to Gainesville, Florida.
Looking for clues in bones
Moreno’s laboratory sits in Ancón Hill, which looks out over the canal on the western edge of Panama City. Numerous chunks of rock are scattered across the laboratory’s tables, awaiting exploration. Some are the size of a person’s torso with clearly exposed dark lines of bones, while others appear to be nothing more than fingernail-sized pebbles at first glance.
Sophie Westacott, a recent geology graduate like many of the interns, works at Moreno’s laboratory. She described the field work as a slow, careful process. Interns generally bring a rock hammer, screwdriver, chisel and brush while laboriously working a tiny area. Sometimes a day’s labor only returns a pebble-sized fossil.
“A lot of what we find is unidentified bone,” Westacott said, holding a small grey rock the size of an aspirin tablet, which contained an even smaller black spot that shone like a daub of paint in the laboratory light. “That glinting black is a real good clue.”
Westacott said the black dot was a piece of snake vertebrae.
Moreno said that field teams leave at six in the morning and work only until noon, due to the tropical heat. The most common survivors in the rock are teeth, often found through tedious combing of rocks, but significant finds emerge as well, such as whole jawbones.
Ironically, Panama’s climate and rich wildlife limit the ability to recover the fossils from the field.
“Every time they [the canal diggers] cut open and expose a stretch of rock, the vegetation starts growing and the climate starts weathering the rock very, very fast,” Moreno said. “So we have a very narrow window of time to work in.”
Fossil plants and climate change
Some canal fossils tell tales about the future. Another Smithsonian researcher, Carlos Jaramillo, who co-authored the paper in Science backdating the rise of Panama by 10 million years, is also studying well-preserved plant fossils in order to reconstruct the past climate of the Earth. He believes a close study of fossilized leaves will help in evaluating a climate model that can predict future changes as greenhouse gases rise.
“We are able to predict the climate of the past by looking at the leaf morphology,” Jaramillo told Latin Correspondent. “Today you find a very good relationship between the area of the leaf and how warm the place is.”
In a process called leaf margin analysis, Jaramillo explained that the edges of plant leaves would have “teeth” or a jagged shape in a cold area, while leaves in tropical climates have a smooth edge. Jaramillo said that jagged leaves have an evolutionary advantage when they form by having a larger surface area for photosynthesis as they bud in the early spring. Making this margin costs the plant energy, which is why the jagged leaf margin did not evolve in tropical plants.
“Over a geological time period, if you spend energy on something you don’t need, you will be out of the game,” Jaramillo said.
The size of leaves can indicate rainfall, and an even closer look at their stomata – microscopic pores – can estimate the level of carbon dioxide of past climates.
“During the morning the stomata of the leaves open and allows CO2 to get inside, for the plant to do photosynthesis,” Jaramillo said. “But always there is a catch. A trade-off, like everything in life. When you open the stomata, water from the leaf will go out, because of evaporation and oxygen will go out.”
Jaramillo said that due to this water loss, a hot tropical forest, plants have to shut down photosynthesis during midday, despite the peak levels of radiation. However, in a high carbon dioxide climate, plants can capture more carbon per amount of water loss. The microscopic geometry of these leaf pores, stomata, can reveal these ancient conditions. Jaramillo explained that the only way to know what Earth’s climate looked like with the high carbon dioxide levels of today is in the fossil record, as today’s emerging climate last existed five million years ago.