The Tiniest Fossil Hunters

Ants are amazing.  They have enormous strength for their size and are immensely social creatures that build complex structures.  But did you know that harvest ants (Pogonomyrmex spp.) are the world's tiniest fossil hunters?  Harvest ants actually collect micro fossils to add to their nest mounds.  This unique characteristic is so well known that paleontologists recognize their mounds as good places to search for small fossils that might be overlooked. The mounds can last for decades, so the amount of fossils collected by the industrious insects is considerable.  Most people consider them pests since they have ravenous appetites for vegetation. Land surround their nests are picked clean for thirty feet away. [photo credit: Nat Geo]

They use small pebbles and gravel about the size of beads to fortify the entrance to their underground homes.  For some unknown reasons they have a predilection for small fossils and artifacts. When researchers at the Gullota Ranch in Nebraska studied nineteen harvester ant mounds, they found an astonishing  6,000 micro-fossils of ancient mammals.  These include small teeth and bone fragments from rodents, bats, primates and rabbit precursors that were living at the end of the Eocene Epoch, some 34 million years ago   These minute remnants allow scientists to piece together the decent and development of species through time. Over 80 mammalian taxa were recognized in the ants' extensive collection, including ten new species and four new genera.  Without the ants' peculiar collecting behavior these records of ancient life might have been missed altogether.

The bonanza of tiny fossil collections by these insects has been known since at least 1896 when paleontologist John Bell Hatcher advised collectors to frequent anthills, as "they will almost always yield a goodly number of mammal teeth".  Their behavior has become folk-lore, but not extensively studied.  In one 2007 study, the ants were found to collect small chips from stones, possible the debris from tool making by humans.  Ants will go to great lengths to find suitable material for their mounds--up to 157 feet away, or the human equivalent of seven miles.  [unidentified bat jaw fragment, credit C. Boyd]

The land was much different at the beginning of the Oligocene.  Instead of dry plains, the landscape was wetter and more forested, and the weather much more humid.  The fossils probably represent small mammals eaten by predictors and left behind in their scat to be fossilized and collected by harvester ants.  They only collect specimens of a certain size, so they cannot be considered fossil curators.  But when walking the landscape looking for fossils, it pays to keep an eye out for ant mounds. Mr. Gulotta, himself an avid fossil hunter, donated the micro-fossils to science.