While building mounds of sand and gravel, harvester ants often find and collect fossils that are just a few millimeters wide, which is a good thing for paleontologists. PHOTOGRAPHY BY MICHAEL FORSBERG, NAT GEO IMAGE COLLECTION
Recently, paleontologists have discovered 10 new species of ancient mammals with the help of harvester ants, tiny mound-building insects.
Written by MICHAEL GRESHKO
In the western United States, harvest ants, hard-working insects, are often considered pests. These ants collect seeds and live in large sediment mounds, using their nasty stingers to deal with creatures perceived as threats. An anthill can persist for decades, and to the chagrin of some property owners, the land 9 meters away is protected and cleared of vegetation.
But while building their anthills, these ants also do something remarkable: they are the world's smallest fossil collectors.
The ant colony will use small rocks about the size of beads to cover the ant hill with a 15 cm thick layer of rock. This may be to protect the ant hill from being eroded by wind and rain. In order to find the covering material, harvester ants will venture more than 30 meters away from the anthill. In addition to gravel, they also collect small fossils and archaeological artifacts that they find by chance.
The scientific value accumulated by these ants is amazing. Recently, researchers examining 19 harvest ant mounds in a field in Nebraska found more than 6,000 microscopic fossils of ancient mammals, each just a few millimeters across. Among the specimens were small teeth and jaw fragments from nine new rodent species and a new insect-eating shrew-like animal.
These tiny teeth, each only about 1 millimeter wide, come from Oligoryctes tenutalonidus. This is a new fossil species, a shrew-like mammal that fed on insects. Photo courtesy: CLINT A. BOYD
The findings were published in a recent issue of the scientific journal "Paludicola". Other fossils include the teeth of a primate, an ancient cousin of the rabbit, and an as-yet-unidentified bat. Although these teeth are small, their shape holds a wealth of information, such as their place in the mammalian lineage.
"It gives us a concentrated source of fossils that we otherwise would have to spend a lot of energy digging into rocks...or crawling around on our hands and knees year after year hoping to find scattered fossils," said study co-author, Bismarck City North Clint Boyd, a paleontologist with the Dakota Geological Survey, said.
Thanks to these ants, researchers can now use these fossils to better understand what happened in North America around 34 million years ago; a period that is very important from an evolutionary perspective, marking the end of the Eocene and Beginning of the Oligocene Epoch. During this period, the earth entered a long cooling period, leading to the extinction of some species and the reshuffling of the ecosystem of the ancient earth.
"Harvester ant mounds are like the best friend of archaeologists and paleontologists," says National Geographic Explorer Benjamin Schoville, an archaeologist at the University of Queensland in Australia. He was not involved in this study.
Little Fossil Hunters
For more than a century, scientists have discovered that ants have unknowingly mastered the art of finding fossils. In an 1896 article on fossil sites in the American West, paleontologist John Bell Hatcher advised collectors to pay attention to local anthills "because there are always a large number of mammal teeth there." Hatcher's method of obtaining the teeth (sifting the sediment through a flour sieve) worked. He claimed that he often found two to three hundred teeth and jaw fragments on an anthill.
Although there is sufficient evidence for this behavior of ants, it has a sense of folk knowledge, which means that although many people understand it, it has not been systematically studied. However, the few studies so far have confirmed that harvester ants collect some pretty cool specimens.
In 2009, a research team led by Schoville published their observations of 812 ant hills in Nebraska.Nearly one-fifth of the anthills had small flakes peeled off the stone, possibly fragments left behind when American Indians used the stone to make tools or threw sharp objects. "Fragments of human habitation are represented in these little things," he said.
There are also partial jaw fragments and teeth from bats in anthills in Nebraska, but the fossils are too fragmented to be assigned to a specific species. Credit: CLINT A. BOYD
The study also shows how far the ants will travel. In one experiment, Schoville's team placed beads in concentric circles around multiple anthills. Of these circles, the farthest from the top of the anthill is 48 meters. To Schoville's surprise, ants in one of the anthills brought beads back from a great distance, equivalent to a human being foraging 11 kilometers from home.
Combing the Plains
A new study, also conducted in Nebraska, concerns the perseverant Gulotta family. The pasture where the anthills studied by the scientists belong to this family.
Marco Gulotta Sr., an avid amateur fossil collector, knew that harvest ant mounds contained tiny teeth and bones. Together with his two sons, Mel Gulotta and Marco Gulotta Jr., he collected several liters of gravel from the outermost layer of the anthill, separated it with a sieve, and picked out ancient relics from the gravel. Gulotta then posted their photos to the Fossil Forum, an online community for paleontology enthusiasts.
Boyd and colleague Deborah Anderson, a paleontologist at St. Norbert College in De Beer, Wisconsin, saw the photos and contacted Gulotta to convince him to send some of the microfossils to Anderson. Since then, the project has snowballed, with Anderson, Boyd and Bill Korth of the Institute of Vertebrate Paleontology in Rochester, New York, collaborating to analyze thousands of tiny remains.
The researchers worked closely with Gulotta during this process. In the fall of 2020, Boyd visited the ranch and used GPS to record the location of the anthills. The Gulotta family donated thousands of microfossils analyzed in the study to the South Dakota Institute of Mines and Technology for future researchers to study.
“You know, sometimes there’s a little bit of an antagonism between academic paleontologists and landowners when it comes to fossils,” Boyd said. “But this is a great example of how we can work together to accomplish important things. Research work.
The prehistoric American Midwest
Korth, lead author of the new study, told us that when these fossils first formed, 37 million to 32 million years ago, the Great Plains of what is today the central United States was warmer, It's humid and the forest is denser. The fossils thus preserve a small group of mammals in a sweltering environment.
Many of the remains may come from predator droppings, after the small animals were eaten and digested. Once buried, the teeth and bone fragments became fossils and were remarkably well preserved.
Just a few millimeters across, the fossils not only include 10 new species of small mammals, they also fill in the biology of the known creatures, bringing in several never-before-seen tooth types from extinct rodents. "Some species were discovered from two or three specimens, and now we have thirty or forty specimens," Korth said.
Harvester ants collect gravel of a specific size, so their anthills only have fossils of that size. "They're not trying to build a perfect museum," Schoville said.
Even so, using GPS coordinates and knowledge of the terrain, Korth and Boyd's team could determine the specific rock formations sampled from each ant hill. By tracking the types of fossils found in each anthill, researchers can estimate when different species appeared and disappeared from the rock formations. The team can use this information to deduce which rock formations in this area of Nebraska record the end of the Eocene epoch and the beginning of the Oligocene epoch, about 34 million years ago.
To the researchers' delight, their ant-based estimates matched those reached 13 years ago by another method, meaning that anthills may be an independent method for refining geologic time boundaries.We have even more reason to regard harvester ants as human beings' archaeological partners.
"We're always looking for fossils as we walk," says Schoville. "We should also look for anthills along the way."
(Translator: sky4)
