Two Recent Fossil Discoveries Show Insects' Recycling Traits

October 27, 1996

Recent discoveries of beetle-ravaged dinosaur bones and the oldest fossil evidence of ants on Earth have opened a new window on the powerful recycling role played by insects in Jurassic ecosystems, according to a University of Colorado at Boulder researcher.

Stephen Hasiotis, a doctoral researcher in geological sciences, said the two finds are further evidence that "ancient insects were the engines driving and maintaining ecosystem health." They also help to fill in the complex ecological picture of the Jurassic Period some 200 million to 144 million years ago, he said.

Hasiotis and his colleagues, who examined an allosaur skeleton discovered in Wyoming by researchers from Montana's Museum of the Rockies, found evidence the animal was scavenged by carrion-eating dermistid beetles following its death about 150 million years ago. The finding is the first confirmation of dinosaur decomposition by a beetle species and pushes back the known origin of dermistid beetles on Earth by about 115 million years, he said.

A second find of 150 million-year-old fossilized ant nests in Utah, Arizona and New Mexico by Hasiotis and Tim Demko of Colorado State University predates the known origin of ants on Earth by some 70 million years. Similar to nests made by harvester ants and honey-pot ants in the Southwest today, the fossil networks are evidence ants consumed and recycled plant material and other nutrients as they churned their way through the soil building colonies and reproducing.

"Without microbes and insects, the ecological system would have stalled," Hasiotis said. "These types of trace fossils give us new insights into ecological succession."

Two papers on the findings by Hasiotis and colleagues from the Museum of the Rockies, the Dallas Museum of Natural History, Dinosaur National Monument, the University of Wyoming and CSU were presented at the annual meeting of the Geological Society of America in Denver Oct. 27 to Oct. 31.

Scanning electron microscope images of the allosaur bones, which show distict marks from beetle mandibles, indicate dermistid beetles carved out circular or elliptical BB-sized pits on about 12 percent of the skeleton. Similar pitting has since been documented on dinosaur bones from Dinosaur National Monument in Utah.

The presence of the beetle borings indicate the dead, 4-ton allosaur must have had partially dried flesh still attached and was lying above the water table, Hasiotis said. The lack of beetle boring on the remainder of the bones led the researchers to conclude that scavenging occurred near the end of the dry season.

After calculating the length of the beetles' larval and pupal stages and the drying time for a carcass of that size and weight, the researchers calculated that the time between the dinosaur's death and eventual burial by sediments was between 19 to 25 weeks, he said.

The roughly 700 to 1,500 species of dermistid beetles on Earth today live in semi-arid regions and generally consume the muscle tissue, fur and skin of dead animals ranging from mice to elephants. The beetles, which pupate from larvae to adult by boring into hard substrate like bone or wood to form cocoons, have even been known to bore into lead pipes, masonry and concrete.

"Studies have shown that in the absence of these beetles, dead animals can lay bloated on the landscape for months on end," said Hasiotis. "But a group of dermistid beetles can completely break down a dead horse in just a few weeks."

Found in 1995 and 1996, the fossil ant nests consist of interconnected galleries and chambers, an indication the ants were behaving socially, he said. "They had to be social in order to construct and maintain these networks, brood their eggs and larvae, and collect food for the colony," he said. "This type of complexity points to much earlier origins of ants, perhaps as early as the Triassic."

The largest of the roughly 50 nests discovered in the sandstone formations are up to five meters on a side and up to three meters deep, indicating they had been expanded upon for decades or centuries. The nests are similar to fossil ant nests from Utah, Wyoming and Colorado dating from 65 million years ago to the present.

The fossil ant nests were found near Arches and Canyonlands National Parks and on the Navajo Reservation. The oldest previous ant evidence were ant body fossils from New Jersey, Siberia and Canada that date to about 80 million years ago.

Hasiotis, who discovered 220 million year-old fossil termite nests in Arizona's Petrified Forest National Park in 1991, said the ancient ant nests lack the dried saliva and feces linings characteristic of fossil termite nests.

The Jurassic ants also may have consumed insects and perhaps even dried dung from sauropod dinosaurs, much like some desert ant species today eat dried cow dung, he said.

Trace fossils like tracks, trails, burrows and nests help researchers understand the biodiversity of ancient ecosystems. "They help reconstruct the food chain by showing an animal's involvement with the ecosystem, "Hasiotis said. "And they are powerful tools for interpreting ancient rainfall and temperature conditions." - 30 -

University of Colorado at Boulder

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