The extinction of the dinosaurs, resulting from the asteroid impact that formed the Gulf of Mexico, (also known as either the K-T boundary or the K-Pg boundary event), is a subject much studied, normally focusing on the success of mammals.
Early terrrestrial ecosystems are shown, by paleo-botanical studies, to have been initially dominated by aquatic plants, and now, new evidence shows worms to have been one of the first creatures to make an appearance after the global catastrophe.
The evidence of worm burrows have been found in a southwestern North Dakota K-Pg boundary event site, in a study led by CU-Boulder.
The university’s Associate Professor of geological sciences, Karen Chin, said in a press release, “Fossil burrows provide direct evidence of animal activity that occurred right at that spot, and these burrows are quite extensive. 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.”
The three-dimensional burrows were found by Dean Pearson, who is from the Pioneer Trails Regional Museum in Bowman, N.D. Pearson and A.A. Ekdale of the University of Utah are co-authors for the study.
The burrows were discovered where a layer of coal and a layer of siltstone meet. The worms food source would have consisted of decomposing organic matter at the site and more burrows may be contained within underlying coal.
Chin also stated that “the fact that the burrows are so close to the K-T boundary is one reason they are so exciting.”
Buried by sediment, the worm burrows were dug in a peat-producing, bog terrain and are horizontal, indicating feeding patterns.
Though the worms are of a prehistoric nature, they are believed to be the size of today’s average earthworms. Their survival means they were capable of adapting to, or enduring, harsh conditions such as flooded regions, prolonged inundation, low oxygen levels and acidic soil conditions.
Reconstructing the past of worms is more difficult since they are not vertebrates and leave no body fossils. Their burrows, however, are an example of “trace fossils”, which are in the same group as tracks, fossilized feces or corprolites.
Chief Curator of the Denver Museum of Nature and Science, Kirk Johnson, and his colleagues, assisted Chin in understanding what the worms environment would have been like.
K-Pg denotes the division of the Cretaceous period and the Paleogene period, and the time when the Manhattan-sized asteroid struck the Earth, triggering an era of cold “nuclear winter”.
K-Pg is how it is referred to now by geologists, though it is often still referred to as the K-T (Cretaceous and Tertiary) boundary event.
Chin’s findings were given in a presentation during the 2011 annual meeting of the Geological Society of America this week in Minneapolis.
Future studies are planned to bring a more precise time-line to the worms emergence.
attributions: CU press release