Fossilized poop reveals a reptile full of parasites

Ancient parasites discovered in 200-million-year-old reptile poop

Researchers have shown that although extinct reptile predators that resembled crocodiles today were fierce hunters, parasites were able to withstand their scaly armor and sharp teeth.

According to CNN, an unusual case of parasite infection in a reptile that lived between 252 million and 201 million years ago during the Triassic Period has just been discovered by paleontologists. The creature might have been a phytosaur, a short-limbed, long-snouted predator. Instead of finding the parasites in the teeth or bones of phytosaurs, researchers extracted them from a coprolite, which is a fossilized excrement nugget.

Scientists discovered microscopic organic structures that resembled eggs when they dissected the preserved excrement that was discovered at a site in Thailand that is around 200 million years old. Upon closer inspection, the 0.002 to 0.006-inch (50 to 150 micrometer)-long objects were found to represent at least five parasites.

The scientists published their findings in the journal PLOS One. This is the first indication of parasites in a Late Triassic terrestrial vertebrate from Asia. Additionally, the specimen is unique among coprolite samples from this era and location in that it contains several parasitic species, including nematodes, a class of parasitic worms that are still in existence today. Contemporary nematodes are known to infect a wide range of animals and plants, including fish, amphibians, reptiles (such as crocodiles and alligators), and mammals.

“Our results give us new ways to think about the environment and way of life of old animals,” said lead study author Thanit Nonsrirach, a vertebrate paleontologist in the Department of Biology at Mahasarakham University in Kham Riang, Thailand. “In previous studies, only one group of parasites was found in a single coprolite. However, our current study shows that a single coprolite can contain more than one type of parasite.” According to the research, the animal had many parasitic infections.

‘Hard, smooth and grey’

The coprolite was collected by scientists in 2010 from the northeastern Thai outcrop known as Huai Nam Aun. According to Nonsrirach, during the Triassic period, this would have been a brackish or freshwater lake or pond inhabited by a variety of animal species, such as shark-like fish, progenitors of turtles and other reptiles, and primitive amphibians known as temnospondyls.

“Such conditions were conducive to the transmission of parasites,” he said.

About 3 inches (7.4 centimeters) long and 0.8 inches (2.1 centimeters) in diameter, the fossilized poo had a cylindrical shape. The surface of the specimen under study was described by the study’s authors as “hard, smooth, and grey in color.” Although coprolites may not have an impressive appearance, paleontologist Martin Qvarnström, a postdoctoral researcher in the Department of Organismal Biology at Uppsala University in Sweden, claimed that hidden inside them are mysteries regarding “who ate whom” in ancient ecosystems. Qvarnström did not participate in the recent study.

“Surprisingly, coprolites often contain fossils rarely preserved elsewhere,” Qvarnström said in an email. “These include muscle cells, beautifully preserved insects, hair, and parasite remains. But despite being treasure chests in this regard, coprolites are opaque, so identifying their inclusions can be challenging. Detective work is also needed to find out who produced the now fossilized droppings, which is arguably the trickiest part of studying coprolites.”

Scientists can determine which ancient animal group may have created the poop by looking at the coprolites’ size, shape, location, and contents. For instance, according to Nonsrirach, some fish have spiraling intestines that eventually produce spiral-shaped coprolites. Furthermore, he clarified that reptiles and amphibians typically generate coprolites that are largely cylindrical.

The absence of bones in the coprolite suggests that the owner’s digestive system was strong enough to break them down. Although crocodiles are known to possess this physiological characteristic, the study notes that crocodile fossils have not been discovered at this site and that the earliest crocodilians would not appear for another 100 million years or so.

However, according to Nonsrirach, “it’s plausible that the coprolite originated from an animal similar to crocodiles or one that evolved alongside them, like phytosaurs.” Furthermore, fossilized phytosaur remains were previously discovered close to the location of the coprolite excavation.

Eggs and cysts

Upon initial observation, phytosaurs and crocodiles appear to be nearly identical. Both have large bodies covered with stiff scales at the top, long, powerful tails, and elongated, toothy jaws. According to the University of California Museum of Paleontology in Berkeley, one obvious distinction is that crocodiles have nostrils at the end of their snouts, whereas those of phytosaurs are perched on a bony ridge behind their eyes.

Despite the fact that these animals resemble each other essentially, they are not closely related. Convergent evolution, in which unrelated creatures independently evolve similar traits, is the cause of their copycat body plans.

The coprolite was cut into thin sheets, which the scientists then examined under a microscope. What they discovered was that there were five different kinds of organic structures—some ellipsoid, others spherical. An egg of a parasitic nematode in the order Ascaridida was discovered by the researchers after slicing one object in two and discovering an embryo inside.

According to the study, another object had “a well-developed shell and organized bodies within the shell”, and might be a different kind of nematode egg. The remaining ones were found to be cysts from single-celled parasites and eggs from unidentified worms.

“Studying the remains of parasites in coprolites is important since it provides us with rare insights into ancient parasite-host relationships,” Qvarnström said. “Thanks to the coprolite data, we can investigate when such parasitic relationships arose and how parasites and their hosts may have co-evolved through time.”

Nevertheless, Nonsrirach noted that it is unclear if the reptile became ill as a result of having the parasites.

“The determination of the animal’s health status cannot be determined by only the observation of the parasite contained within its coprolite,” he said. “Parasites can use their host as a way of development without causing disease to the host animal.”

According to the study, the reptile may have picked up its parasite community by consuming various kinds of infected animals.

“This event raises interesting questions about how prey animals and parasites interact with each other. It suggests that parasites may have been inside the bodies of prey before they were eaten,” Nonsrirach said. “This new point of view gives us a deeper understanding of how past ecosystems were connected and how they affected the lives of prehistoric animals.”