October 11, 2011
Worms Among First Animals To Appear After Asteroid Impact
University of Colorado researchers have found that worms were among the first animals to surface after an asteroid plowed into the Gulf of Mexico 65.5 million years ago.
Geological sciences Associate Professor Karen Chin of the university said this "K-T extinction" is often focused on the survival and proliferation of mammals, and studies show some of the earliest terrestrial ecosystems to emerge were aquatic plants.
However, new evidence from North Dakota shows networks of crisscrossing burrows less than three inches above the K-T boundary layer.
"Fossil burrows provide direct evidence of animal activity that occurred right at that spot, and these burrows are quite extensive," Chin said in a press release. "To my knowledge, such burrows haven't been documented in terrestrial environments this close to the K-T boundary. This is a glimpse of a world we don't know very much about yet."
Chin said she believes the burrows were likely made within a few thousands of years after the extinction event.
Three-dimensional burrows were found at the interface of a layer of coal and a layer of siltstone in southwestern North Dakota by Dean Pearson of the Pioneer Trails Regional Museum in Bowman, N.D.
The decomposing organic matter in the environment would have helped provide a food source for the worms.
Chin said a few of the burrows were topped by a thin layer of coal, which suggests the underlying coal may contain additional, earlier worm burrows that are not apparent.
The researchers said the fossil worm burrows indicate the creatures were about the diameter of an average earthworm. Chin said the burrows indicate horizontal movement through the substrate, which reflects feeding activity.
She said the worms must have been able to withstand the challenging environmental stress of flooded habitats, low oxygen and acidic conditions.
Chin gave a presentation on the new findings at the 2011 annual meeting of the Geological Society of America in Minneapolis.
Image 2: CU-Boulder Associate Professor Karen Chin uses a stereomicroscope to analyze fossil burrows, likely made by worms, which have been discovered just inches above the K-T boundary sediment that has been linked to mass extinctions on Earth some 65.5 million years ago, including the demise of the large dinosaurs. Credit: University of Colorado
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