Posted on behalf of Sid Perkins.
Native Americans that lived in the Mimbres Valley of southwestern New Mexico more than a millennium ago are well known for their distinctive pottery, but now they may have a new claim to fame. They collected fossils — apparently for ritual use in their homes, and probably from a site dozens of kilometres from their village.
Lauren Falvey, an archaeologist at the University of Nevada, Las Vegas, and her colleagues have excavated more than a dozen of the ‘pit houses’ found at the Harris Archaeological Site located just east of the town of Georgetown. These structures, each about the size of a bedroom in a modern-day American home, were made by digging a 2-metre-deep pit and then lining the wall with adobe bricks. The home’s roof was supported by wooden posts placed at intervals around the inner edge of the pit. Residents entered the homes via a ramp dug into one wall of the pit. Homes were occupied for several decades before residents demolished them and built new homes nearby. The abandoned pits were then used as trash dumps, says Falvey. Previous studies suggest that the pit houses excavated by Falvey and her colleagues were built between 850 and 1000 AD.
One day, while digging out one of the village’s homes, Falvey, who also has a keen interest in palaeontology, noticed fossils in the rubble that didn’t match the stones or other material used to make the adobe walls. Besides appearing in limestone hand tools found at the site, 25 individual fossils — including a wide variety of marine creatures, such as corals, and shelled creatures, such as brachiopods — have been recovered from 14 of the 19 homes excavated thus far. The fossils, which came from limestone dating to between 318 million and 385 million years ago, stood out because they didn’t come from the rocks immediately surrounding the village, says Falvey.
Several of the fossils were found within the collapsed adobe walls of a pit house, sometimes alongside other objects believed to have ritual importance, such as crystals and bits of turquoise. These objects — but no fossils as of yet, says Falvey — have sometimes been found at the bottom of postholes. The intentional placement of such objects during the home’s construction may have been somewhat like embedding a lucky coin in the foundation of a new home today.
Although outcrops of limestone that once entombed the fossils are located within 4 kilometres of the Harris Archaeological Site, several clues hint that the fossils actually came from Cookes Peak, a mountain 43 kilometres away that was apparently revered by the people of the village. For one thing, says Falvey, all of the ramps leading out of the pit houses point towards the mountain, an orientation that ensures that residents departing their homes get a clear view of the distant peak. Also, she notes, rock carvings found on Cookes Peak suggest that the Mimbres people conducted rituals or ceremonies there. Detailed geochemical analyses of the fossils could help to determine where the fossils were originally collected, she notes.
Finding fossils at archaeological sites in the American Southwest is unusual, say Falvey and Brett McLaurin, a geologist at Bloomsburg University of Pennsylvania and senior co-author of the GSA presentation. Nevertheless, Falvey notes, researchers excavating other sites — especially those without a background or interest in palaeontology — may not have not reported any such finds simply because they didn’t recognize the anomalous provenance, and therefore the ritual significance, of any fossils they had unearthed.
Correction: An earlier version of this blog post incorrectly stated that some of the fossils were found at the bottom of postholes.