In a recent biography of paleontologist John Bell Hatcher, I found reference to an interesting method of paleontological fieldwork. This post explores the story behind this collecting technique which features Hatcher, harvester ants, and mammal fossils.
John Bell Hatcher (1861-1904)
John Bell Hatcher, a member of my pantheon of paleontological heroes, is widely acclaimed to be one of the greatest fossil collectors who ever lived. (Hatcher is the subject of a previous post on this blog.) Paleontologist Lowell Dingus titled his book King of the Dinosaur Hunters: The Life of John Bell Hatcher and the Discoveries That Shaped Paleontology (2018). Paleontologist Charles Schuchert, who at one time worked with Hatcher, described him as the “king of the collectors” (O.C. Marsh: Pioneer in Paleontology, 1940). These titles of royalty are well deserved, though, in truth, Hatcher was a much more accomplished and well-rounded paleontologist than he is often given credit for. (This image is taken from Charles Schuchert’s memorial for John Bell Hatcher appearing in The American Geologist, Volume XXXV, Number 3, March, 1905.)
Hatcher spent much of two decades collecting for paleontologist Othniel Charles Marsh (1831-1899) of the Yale Peabody Museum of Natural History. Later, he joined Princeton University and then the Carnegie Museum of Natural History.
Admittedly, Hatcher was a prickly character, known to snap at employers and colleagues. The root causes of his often abrasive personality probably included a chronic illness that, at times, caused serious joint pain (certainly a challenge for hunting fossils). Further, the hierarchical structure of paleontology in this period grated on the man. Wealthy men dominated the museums that were amassing fossils, while they also controlled a mostly uneducated corps of men out in the field collecting. The wealthy Marsh was an exacting boss and loath to share credit for the work his collectors did. So, working for Marsh was certainly not ideal for the Yale educated Hatcher. (Ronald Rainger, Collectors and Entrepreneurs: Hatcher, Wortman, and the Structure of American Vertebrate Paleontology Circa 1900, Earth Sciences History, Volume 9, Number 1, 1990.)
Ants
Western harvester ants (Pogonomyrmex occidentalis) have a starring role in this story though it’s possible they should share the spotlight with other ant taxa. Here is a picture of P. occidentalis at Alamosa, Colorado. (This photograph is in the public domain under Creative Commons Attribution-Share Alike 4.0 International license. It was taken by Robert Webster and is available at Wikimedia Commons.)
Harvester ants are collectors of seeds and tiny rocks, the former to eat, the latter to insulate their nests. They create massive nest mounds of these collected rocks, mounds that may extend up to four feet in diameter and between two and ten inches tall. (University of Colorado Museum of Natural History, Bio Lounge, Tiny Collectors: Harvester Ants.
Pictured below is a P. occidentalis mound at Hallelujah Junction, California. (This image is in the public domain under Creative Commons CC0 1.0 Universal Public Domain Dedication. It was taken by Alex Wild and can be found at Wikimedia Commons.)
Mammal Fossils
Now, the fossils in this tale are those of mammals living in the Mesozoic Era, and, to be more specific, those at the end of the reign of dinosaurs in the Late Cretaceous Period (some 100 to 66 million years ago). Mammals surviving in the dinosaur-dominated landscape were, by necessity, slight creatures (think on the order of rats), probably nocturnal for the most part. Paleontologist Donald Prothero has noted, “They remained as tiny, nocturnal animals under the feet of the dinosaurs, or in the trees above them, through about two-thirds of their history (the entire Jurassic and Cretaceous, spanning over 120 million years).” Significantly (for this post), he added, “Consequently, Mesozoic mammal fossils are also tiny, and tend to be fragmentary and hard to find.” (Bringing Fossils to Life: An Introduction to Paleobiology, 1998, p. 384.)
Though Marsh was fixated on large fossils and is known for his rivalry with fellow paleontologist Edward Drinker Cope (1840-1897) in a frantic quest for dinosaur fossils (the so-called Bone Wars), he had an abiding interest in mammals living during the age of dinosaurs. Hatcher was pressed by Marsh for more and more mammal fossils. They were not easily collected, particularly not for a man who suffered from what he called “rheumatism.” Tiny teeth that could be gathered only by crawling across the ground on hands and knees for hours on end under a hot western sun were probably not high on Hatcher’s list of desirable objects.
And so Hatcher seized the opportunity for help when it presented itself.
Hatcher Enlisted Invertebrate Collaborators
In a letter to Marsh written on July 6, 1889, from Hat Creek, Wyoming, Hatcher wrote to announce some impressive success in the pursuit of mammal fossils.
I send you today by registered mail three packages containing over 500 mammal teeth besides many bones. You will have when all get there at least 800 teeth of Laramie mammals, abundant material for two more papers. I broke the record yesterday by finding 87 mammal teeth in one day.
Then Hatcher added the kicker:
We sifted all the anthills in the two best localities & were rewarded a hundred fold.
(The Yale Peabody Museum of Natural History has digitized the O.C. Marsh correspondence. There are multiple PDFs of Hatcher’s letters to Marsh. Hatcher wrote in a very legible hand and the letters make for fascinating reading. Dingus’ biography offers many excerpts from them.)
Sifted the anthills! Why am I not surprised that this paleontologist who pioneered grid-based mapping of collecting sites and the jacketing of fossils in the field would have solved his problem so creatively?
This fieldwork technique capitalized on the harvester ants’ intrinsic behavior. Though Hatcher doesn’t identify the kind of ant with whom he collaborated, it is accepted they were harvester ants. From a widespread area around their nests, these insects gather small rocks (as noted earlier) to create their distinctive mounds, but it turns out they are not picky about what constitutes “small rocks.” Indeed, the mix of “things” in the dirt of the mounds often turns out to be rich, ranging from seeds to beads to fossils. And the fossils “include tiny mammal, dinosaur, and fish teeth, small bone fragments, chucks of amber, and small snails.” (University Colorado Museum of Natural History, Bio Lounge, Tiny Collectors, see link above.)
Several years later, in an article about collecting mammal and ceratopsian fossils in Wyoming, Hatcher wrote a bit more about this collecting approach. (He was not consistent as to whether he thought it was “anthill” (the 1889 letter) or “ant hill” (in this article).)
In such places the ant hills, which in this region are quite numerous, should be carefully inspected as they will almost always yield a goodly number of mammal teeth. It is well to be provided with a small flour sifter with which to sift the sand contained in these ant hills, thus freeing it of the finer materials and subjecting the coarser material remaining in the sieve to a thorough inspection for mammals. By this method the writer has frequently secured from 200 to 300 teeth and jaws from one ant hill.
But it wasn’t inevitable that immediate sites likely to contain mammal fossils also supported these ants. So Hatcher gave nature a hand.
In localities where these ants have not yet established themselves, but where mammals are found to be fairly abundant it is well to bring a few shovels full of sand with ants from other ant hills which are sure to be found in the vicinity, and plant them on the mammal locality. They will at once establish new colonies and, if visited in succeeding years, will be found to have done efficient service in collecting mammal teeth and other small fossils, together with small gravels, all used in the construction of their future homes. (Some Localities for Laramie Mammals and Horned Dinosaurs, The American Naturalist, February 1896, p. 119.)
I suspect the technique has been improved and made less destructive by successive generations of paleontologists and archaeologists. The Bio Lounge piece on harvester ants as fossil collectors (cited earlier) notes that scientists looking for fossils or artifacts in the ant’s mounds try to limit the damage to the mound and “usually take only the outer layer, preferably while the ants are hibernating underground in winter. Harvester ants rebuild their nests every spring, so this doesn’t damage their nests unduly.”
I hasten to stress that harvester ants aren't friendly colleagues; they pack a nasty bite, which is a good reason to raid the mounds while they are hibernating. If that’s not possible, there are other approaches. Paleontologist Natasha Vitek, whose research includes analyzing the variation in the dentition of small mammals across the Paleocene-Eocene Thermal Maximum (some 56 million years ago), has said,
Sometimes, if a paleontologist wants to be able to spend more time at an ant hill, they try to put part of their lunch out, hoping the ant will spend more time collecting the food than attacking the paleontologist. . . . It sometimes works and sometimes not. It’s not always a guarantee.” (As quoted by Jerald Pinson, Harvester Ants: The First Solar Engineers, Fossil Hunters, The Austin-American Statesman, July 2, 2019.)
The anthill method still remains part of the paleontologist’s arsenal of tools for collecting small fossils.
In closing, I present a couple of the mammal teeth that Hatcher found in Wyoming in 1889. I assume that both were actually collected first by harvester ants. The two are from multituberculates, an extinct line of “squirrel-like” mammals (Prothero), so named because their molars have multiple cusps or tubercules. They went extinct in the Eocene, unable to compete with rodents, but they had a long run of 180 million years beginning in the Late Jurassic.
Both of these images are from the collection of the Smithsonian’s National Museum of Natural History. Much of what Hatcher collected for Marsh ended up at the National Museum. The first image is of an upper molar from an Allacodon rarus (it can be found on the National Museum’s website here).
The second fossil is from a Meniscoessus sp. which was found by Hatcher in August of 1889 (on the museum website here).
No scale bar in either photograph, I'm afraid, but, rest assured, each of these is miniscule.
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