This news article is based on the open-access journal article (Nonsrirach et al., 2023) published in PLOS ONE. The article and figures are published under a Creative Commons Attribution 4.0 license.
Summary points about the Triassic parasite coprolite:
- Age: Late Triassic, more than 200 million years old
- Location: Huai Nam Aun locality, Huai Hin Lat Formation, Chaiyaphum Province, Thailand
- Specimen: A cylindrical vertebrate coprolite about 74 mm long and 21 mm in diameter
- Discovery: At least six potential parasite structures representing five different morphotypes
- Best identification: One morphotype is consistent with an egg of an Ascaridida nematode
- Possible producer: A crocodile-like reptile, possibly a phytosaur
- Big idea: Ancient coprolites can preserve direct evidence of host-parasite relationships that body fossils usually cannot
Introduction: The Triassic Had Parasites Too
As if being a crocodile-like predator in the Late Triassic was not stressful enough, one ancient reptile apparently had parasites too.
Researchers studying a vertebrate coprolite from northeastern Thailand cut the fossilized feces into thin sections and examined them under a microscope. Inside they discovered several tiny organic structures interpreted as parasite eggs or cyst-like reproductive stages.
The result is a rare snapshot of a host-parasite relationship from more than 200 million years ago - preserved inside fossil poop.
A Late Triassic Fossil from Thailand
The coprolite was collected near Nong Yakong village in Chaiyaphum Province, Thailand, from the Huai Nam Aun outcrop of the Huai Hin Lat Formation. The rocks were deposited in a quiet freshwater or brackish-water setting.
The Huai Hin Lat Formation preserves a diverse vertebrate community including fishes, lungfishes, temnospondyl amphibians, early turtles, and phytosaurs. The formation spans part of the Late Triassic and is more than 200 million years old.
The 7-Centimeter Fossil That Held a Microscopic Surprise
The studied coprolite is approximately 74 millimeters long and 21 millimeters in diameter. It is elongated, cylindrical, curved on one side, and rounded at one end.
To investigate its contents, the researchers embedded the specimen in epoxy resin, cut it with a diamond saw, mounted slices on glass slides, and ground them thin enough for transmitted-light microscopy.
That destructive-sounding preparation paid off. Hidden inside were several tiny structures measuring only tens to a little more than one hundred micrometers across.
Five Morphotypes, at Least Six Parasites
The scientists recognized five different morphotypes of potential parasite eggs, sporocysts, or cyst-like structures. At least six individual structures were documented in the single coprolite.
Most cannot yet be assigned to exact parasite groups. Some could represent nematode eggs; another might be a protist cyst. The researchers considered plant spores as an alternative for some morphotypes but found that the observed structures lacked several diagnostic features expected in fern or moss spores.
One Egg Looks Like an Ancient Ascarid Nematode
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The clearest identification comes from morphotype V, an oval structure about 60 micrometers long and 43 micrometers wide with a thick shell. Its shape and wall structure match important characteristics of eggs produced by Ascaridida, an order of parasitic nematode worms.
Ascarid parasites today infect a broad range of vertebrates. Fossil ascarid eggs are rare, but previous discoveries show that these worms were already parasitizing vertebrates deep in the Mesozoic.
Who Produced the Coprolite?
The fossil does not preserve the identity of its owner directly. Its cylindrical, curved shape and lack of obvious prey remains resemble coprolites associated with Crurotarsi, the crocodile-line branch of archosaurs.
True crocodiles are not known from the Huai Hin Lat Formation, but phytosaurs are. Phytosaurs were large, often long-snouted reptiles that looked remarkably crocodile-like even though they belonged to a different branch of the archosaur family tree.
The authors therefore suggest that the animal was probably a crocodile-like reptile, possibly a phytosaur. That identification is plausible, but it is not certain.
One Animal, Several Parasites
Finding several morphotypes in one coprolite suggests that the host carried more than one type of parasite. Multi-parasite infections are common in modern animals, but documenting them in the deep fossil record is difficult.
For a predator, the route of infection may have been straightforward. Parasites move through food webs. A crocodile-like reptile eating infected fish, amphibians, or other reptiles could acquire parasites from its prey.
That means this one coprolite may preserve evidence of several biological levels at once: the predator, the prey it ate, and parasites living inside the predator.
Why Fossil Parasites Matter
Parasites are extremely common in living ecosystems, but they have a terrible fossil record. Most live in soft tissues, and soft tissues usually decay before fossilization can occur.
Coprolites offer a workaround. Parasite eggs and cysts leave a host through its digestive tract and can become trapped inside feces. If that feces fossilizes, microscopic evidence of infection can survive long after the host's organs are gone.
This Thai coprolite is the first record of parasites in a Late Triassic terrestrial vertebrate host from Asia and provides rare evidence that complex parasite-host relationships were already established in Mesozoic ecosystems.
Not every great fossil has teeth, claws, or a beautiful skeleton. Sometimes the important discovery is a microscopic worm egg inside a 7-centimeter piece of fossilized poop.
Journal Article:
Nonsrirach, T., Morand, S., Ribas, A., Manitkoon, S., Lauprasert, K., & Claude, J. (2023). First discovery of parasite eggs in a vertebrate coprolite of the Late Triassic in Thailand. PLOS ONE, 18(8), e0287891. Published August 9, 2023. https://doi.org/10.1371/journal.pone.0287891.
Image and reuse license: The PLOS ONE article and figures are published under the Creative Commons Attribution 4.0 International License.
FAQs: Triassic Fossil Poop and Ancient Parasites
Quick answers about the parasite eggs, the possible phytosaur producer, and why paleoparasitologists study coprolites.
- How old is the parasite-filled coprolite?It comes from the Late Triassic Huai Hin Lat Formation of Thailand and is more than 200 million years old.
See: Late Triassic Thailand - What was found inside the fossil poop?Researchers identified at least six small organic structures representing five morphotypes of potential parasite eggs or cyst-like reproductive stages.
See: Five Morphotypes
- What kind of parasite could be identified?One oval, thick-shelled morphotype is consistent with eggs of Ascaridida, an order of parasitic nematode worms.
- What animal produced the coprolite?The exact producer is unknown. Its shape suggests a crocodile-line archosaur, and the authors propose a crocodile-like reptile, possibly a phytosaur.
- Was the coprolite produced by a dinosaur?Probably not. The study favors a crocodile-line reptile, possibly a phytosaur, rather than a dinosaur.
- How large is the coprolite?The specimen is approximately 74 millimeters long and 21 millimeters in diameter.
- Why are parasite fossils so rare?Most parasites live in soft tissues, which rarely fossilize. Eggs and cysts passed in feces can occasionally be preserved when the feces fossilize into coprolites.
- Did the animal have more than one parasite?Probably. The presence of at least five morphotypes suggests a multi-parasite infection, although most morphotypes cannot yet be assigned to exact parasite groups.
- How might a Triassic predator have acquired the parasites?The authors suggest that a predatory host could have acquired parasites by eating infected fish, amphibians, reptiles, or other prey.
- Why does this discovery matter?It provides rare direct evidence of host-parasite interactions in a Late Triassic Asian vertebrate and helps trace the deep history of parasitism.
Jump to Sections
Key Facts | Introduction | Triassic Thailand | The Coprolite | Parasites | Ascarid Egg | Possible Producer | Multiple Parasites | Why It Matters | Journal Article | FAQs
