New York, Jan 11 (IANS): Scientists have discovered oldest-known fossilized digestive tract -- 550 million-year-old -- in the Nevada desert in the US that could be a key find in understanding the early history of animals on Earth.

An analysis of tubular fossils by scientists led by Jim Schiffbauer at the University of Missouri (MU) reveals what scientists believe is a possible answer to the question of how ancient animals are connected.

Over a half-billion years ago, life on Earth was comprised of simple ocean organisms unlike anything living in today's oceans.

Then, beginning about 540 million years ago, animal structures changed dramatically.

During this time, ancestors of many animal groups we know today appeared, such as primitive crustaceans and worms, yet for years scientists did not know how these two seemingly unrelated communities of animals were connected, until now.

"Not only are these structures the oldest guts yet discovered, but they also help to resolve the long-debated evolutionary positioning of this important fossil group," said Schiffbauer, associate professor of geological sciences.

These fossils fit within a very recognizable group of organisms -- the cloudinids -- that scientists use to identify the last 10 to 15 million years of the Ediacaran Period, or the period of time just before the Cambrian Explosion.

"We can now say that their anatomical structure appears much more worm-like than coral-like," Schiffbauer added in a paper published in Nature Communications, a journal of Nature.

In the study, the scientists used MU's X-ray facility to take a unique analytical approach for geological science -- micro-CT imaging -- that created a digital 3D image of the fossil. This technique allowed the scientists to view what was inside the fossil structure.

"With CT imaging, we can quickly assess key internal features and then analyze the entire fossil without potentially damaging it," said study co-author Tara Selly.