Old colonies: ancient formations are termites' legacy.

New analyses of mysterious pillars at two sites in southern Africa suggest that the sandstone features are petrified remains of large, elaborate termite nests--the oldest such fossils yet discovered, scientists say.

The pillars have eroded from softer sandstone outcrops of the Clarens formation, which is located along the South Africa-Zimbabwe border. At one South African site, more than 150 columns--some as tall as a regulation-height basketball hoop--stand within an area of about 200 square meters. The pillars there are spaced between 0.5 m and 10 m apart, says Emese M. Bordy, a geologist at the University of the Witwatersrand in Johannesburg. At another spot, about 45 kilometers to the northeast, a similar tableau contains more than 50 pillars.

Most of the columns have an elliptical cross section. The long axis of the ellipse, which can measure as much as 1 m at ground level, typically runs north and south, says Bordy. Other pillars sport an irregular cross section. In all cases, however, the formations are riddled with tubular structures that average about 5 millimeters in diameter. Some columns, especially the irregularly shaped ones, contain vertical shafts and internal chambers.

These characteristics closely match the architecture of modern-day termite mounds found in many arid regions, says Bordy. An elliptical cross section with a north-south orientation would have reduced heat buildup within the nest. Internal chambers could have served as nurseries, food-storage compartments, or dumping sites for dead termites or waste. Bordy and her colleagues describe the find in the February Palaios, a journal that chronicles paleontological research.

Fossilized evidence of habitats, such as termite nests, can often provide clues to a creature's behavior even in the absence of any remains of the animal itself (SN: 6/9/01, p. 362).

Volcanic rocks that in some places directly overlie southern Africa's Clarens formation have been dated to between 181 million and 195 million years old. Therefore, says Bordy, the Clarens sandstone and the pillars it entombed must be even older.

These pillars--fossilized nests that may have held up to 1 million individuals--undoubtedly were home to a species that had a highly organized social structure and could manipulate the environment to its advantage, says Stephen T. Hasiotis, a paleontologist at the University of Kansas in Lawrence. The new find pushes back the advent of elaborate nest construction at least 40 million years, he notes.

Some ancient termite nests in north-eastern Arizona date back about 220 million years, says Hasiotis. However, those nests were more simply constructed than the new finds are, mostly below ground, and small--no larger than a football and home to only several thousand insects that probably didn't have a complex social structure.