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The discovery of ancient tapeworm eggs in 270-million-year-old fossilized shark poop suggests that these intestinal parasites may have existed in animals for much longer than previously known, scientists claim.

Tapeworms are parasitic flatworms that stick to the inner walls of the intestines of vertebrates, animals with backbones like fish, cows, pigs and humans.  When a larva develops into an adult tapeworm, it releases its eggs through the feces of its host to infect other animals.

Scientists say that studying the early history of intestinal tapeworms in vertebrates is difficult because fossils of these kinds of parasites that date back to the age of dinosaurs or before are extremely rare. However, investigators can study these ancient parasitic creatures by examining coprolites or fossilized feces. To illustrate how rare traces of ancient intestinal tapeworms, researchers said that tapeworm eggs were found in only one out of 500 coprolite samples.

Scientists from the Federal University of Rio Grande, Brazil, found the cluster of 93 tapeworm eggs in a spiral-shaped shark coprolite. Researcher Paula Dentzien-Dias and her colleagues discovered that one of the eggs even contains a probably developing larva, which also held a collection of fiber-like object that may have been the beginnings of hooklets adults tapeworms use to stick to a host's intestines.

The latest findings published in the journal PLOS ONE reveals that the fossils were dug up in southern Brazil and date back to the Paleozic era, 251 million to 542 million years ago, before dinosaurs even existed.  Researchers say that the latest discovery is older than other known examples of intestinal parasites in vertebrates by a staggering 140 million years.

Scientists said that they found the eggs by cutting coprolites into thin slices.  According to the study, the eggs are all about the same size, with each only about 150 microns long, which is equivalent to about 1.5 times the average width of a human hair.

Dentzien-Dias and her team say that the site where the tapeworms were found may have once been a freshwater pond where many fish got trapped together in during a dry spell, according to Live Science.

Researchers also found the mineral pyrite, commonly known as fool's gold, in the fossilized shark feces, suggesting the animals probably lived in an environment that didn't have enough oxygen, a condition that probably helped preserve the fossils for hundreds of millions of years. Researchers said that the fossil found in the study is from the Middle-Late Permian times, a historical period followed by the largest mass extinction ever known, when nearly 90 percent of marine species and 70 percent of terrestrial species died out.

Scientists say that there is no way of knowing what species of shark left behind this sample of fossilized feces because all sharks have similar intestines that produce similar feces.  However, researchers say that unless the infestation was huge, it's very unlikely tapeworm infection killed the shark that left this coprolite sample.

Researchers say that the latest discovery helps establish a timeline for the evolution of modern parasitic tapeworms that occur in foods like fish, pork and beef.  Researchers said that the fossilized eggs were found in a cluster very similar to those laid by present-day tapeworms.

"This discovery shows that the fossil record of vertebrate intestinal parasites is much older than was previously known and occurred at least 270-300 million years ago," researchers wrote in the study.