(ORDO NEWS) — Dinosaurs lived a very long time ago, not a single person has ever seen living dinosaurs (not counting birds, of course). Nevertheless, we know a lot about them: both how they looked and how they behaved. And not so long ago we learned that dinosaurs, like all normal animals, had parasites. Choose an animal from the Mesozoic era, and we will tell you who is sitting in it (or on it).
On the skulls of predatory dinosaurs, bite marks are often found – this is how the lizards found out the relationship with each other. However, on the jaws of some tyrannosaurids, paleontologists also find mysterious rounded holes that do not look like bites. Some scientists have suggested that these growths were caused by actinomycosis, a bacterial infection that is still common today.
In 2009, a team of American paleontologists presented an analysis of the skulls of 61 tyrannosaurids. Mysterious holes in the lower jaw were found in almost 15 percent of them. The researchers thought that actinobacteria were unlikely to be involved, since they do not cause such lesions in modern archosaurs – birds and crocodiles.
But on the other hand, scientists have found the similarity of these marks with ulcerations of the jaws and digestive tract in birds, which are caused by the protist Trichomonas gallinae, a relative of Trichomonas vaginalis, a human parasite. And on this basis, paleontologists diagnosed tyrannosaurus trichomoniasis.
Modern birds become infected with Trichomonas through contaminated water or food. In severe cases, extensive lesions of the pharynx and esophagus make it difficult to eat, and sometimes lead to suffocation.
In populations of tyrannosaurids, the pathogen spread, most likely due to the aforementioned habit of theropods biting each other’s snouts. Another route of infection could be cannibalism. And two tyrannosaurs – one of which is the famous Sue – have jaws so seriously affected that, apparently, it was this disease that killed the animals.
In the bones of dinosaurs and other extinct animals, some pathologies are often found. For example, osteomyelitis is an inflammation of the bone, bone marrow, and surrounding soft tissues. One such case was studied by Brazilian paleontologists – their “patient” was an elderly titanosaurus (Titanosauria).
Scientists made sections of his fibula, studied the histological structure and, to their surprise, saw fossilized unicellular parasites in the vascular channels. So in 2020, the scientific world first encountered parasites in the bones of non-avian dinosaurs.
Paleontologists tentatively identified the found organisms as trypanosomatids. The same family includes, for example, the modern causative agent of sleeping sickness (Trypanosoma brucei), which kills people every year in tropical Africa.
In the bones of this dinosaur, paleontologists also found hints of a bacterial infection. It is possible that the trypanosomatids caused inflammation, and then bacteria joined them. However, it may have been the other way around.
The infective stage of intestinal parasites must be stable, since from the cozy organism of the host it (along with feces) enters the hostile external environment. In protists (for example, amoebas), this stage is the cyst, and in helminths, the egg. And since they are all dressed in a very high-quality protective shell, they have a fairly high chance of getting into the fossil record.
Parasites from the fossilized feces of Mesozoic times were not known until 2006, when American paleontologists George Poinar and Arthur Bouko presented an analysis of carnivorous dinosaur coprolites. The studied fossils came from a Lower Cretaceous locality near the Belgian commune of Bernissart.
Previously, European researchers attributed these coprolites to the theropod Megalosaurus dunkeri, but this species is now considered doubtful, so their taxonomic affiliation is unknown.
It turned out that these dinosaurs suffered from intestinal diseases. In coprolites, scientists found cysts similar to the invasive form of modern dysenteric amoeba (Entamoeba histolytica). The researchers assigned the parasite to the same family Entamoebidae, but at the same time they identified it as a separate genus and species – Entamoebites antiquus.
In addition, the coprolites also contained helminth eggs: trematodes and roundworms. They were also assigned to new genera and species: the trematode to Digenites proterus, the roundworm to Ascarites priscus and A. gerus.
Cynodonts are one of the few synapsids to survive the great extinction 251.9 million years ago. It was they who at the end of the Triassic gave rise to mammals – and passed on their parasites. This was revealed in 2014, when in coprolites 240 million years old (Middle Triassic), scientists discovered roundworm and oxyurid eggs.
The researchers placed the roundworm found in the genus described by Poinar and Buko in 2006, while studying parasite eggs in the coprolites of carnivorous dinosaurs. But the “passenger” of cynodonts paleontologists attributed to a new species – Ascarites rufferi.
And scientists identified the oxyurid nematode in a separate genus (and, accordingly, species) – Paleoxyuris cockburni. Oxyurids include, in particular, the pinworm (Enterobius vermicularis), one of the most common human helminths.
Oxyurid nematodes parasitize animals whose diet contains a large amount of plant foods. Therefore, the researchers suggested that the fossilized feces belong to herbivorous cynodonts from the Traversodontidae family.
Modern fleas are small: the length of a hungry insect, as a rule, does not exceed five millimeters. However, in the Mesozoic they were much larger: Australian Tarsiidae reached 7 millimeters in length, Saurophthiridae from Siberia and China – 12, and Chinese Pseudo Pulicidae – almost 23.
Their fossils first appear in the fossil record in the Middle Jurassic (165 million years ago). Unlike the current ones, these fleas had a large body, and their legs were not jumping. However, they also engaged in biting through the skin of the owner and drinking his blood, filling the swollen abdomen.
Today, fleas annoy mammals and birds, but the Mesozoic giants, according to a number of paleontologists, parasitized pterosaurs. Although it is possible that they did not disdain mammals or feathered dinosaurs. For a long time it was also believed that, in addition to fleas, flying lizards were also parasitized by scarecrows (Strashilidae). But later it turned out that they were not parasites at all, but only unusual aquatic Diptera.
Of the three groups of Mesozoic fleas, the role of parasites of pterosaurs is most suitable for saurophthyrs, since with their long legs they resemble modern parasites of bats – flies from the families Nycteribiidae and Streblidae.
However, Russian paleontologists Alexander Rasnitsyn and Olesya Strelnikova found out that the respiratory system of saurophthyros is arranged in the same way as in some aquatic insects. The researchers suggested that females attacked semiaquatic pterosaurs, drank their blood, and then hid under water to calmly digest food and lay eggs. Then the cycle was repeated.
But another Russian paleontologist, Dmitry Shcherbakov, disagrees with this hypothesis, since, in his opinion, the reservoir was not a safe place for females of these insects. The scientist believes that saurophtyrs were constant ectoparasites of diving pterosaurs, therefore they adapted to breathing underwater.
Rasnitsyn and Strelnikova, in their work on the digestive system of saurofters, answered that permanent ectoparasites rarely enter the fossil record, even if their hosts are aquatic, and there are quite a lot of fossils of saurofters found. In addition, permanent ectoparasites feed frequently, and the researchers did not find traces of iron in the digestive tracts of saurofters, which would indicate the presence of vertebrate blood in them.
Some scientists, however, doubt that these Mesozoic parasites are fleas. For example, American paleontologists have shown that fleas of the modern type appeared in the Cretaceous period on the territory of Gondwana and were originally associated with mammals.
Epidemiologists refer to mosquitoes (long-tailed Diptera) and other blood-sucking arthropods as vectors, as they carry pathogens between vertebrates. However, if you look closely at the life cycle of these pathogens, it becomes clear that they multiply inside bloodsuckers – that is, it is the latter that should be considered the final hosts of parasites. For example, it is the mosquito, and not the man at all, that is the final host of the malarial Plasmodium.
The mosquito itself, according to many parasitologists, should not be considered an ectoparasite, since parasitism implies close interaction, and the bloodsucker uses vertebrates only as a food source. Such animals are called predators with a pasture type of food – they differ from true predators in that they do not kill their prey. But fleas are already more like ectoparasites, as they constantly live in the host’s nest. At the same time, among them there are real ectoparasites that live on the host itself (and some even take root in his skin).
In 2004, paleo entomologist George Poinar and his wife Roberta told the scientific world that they had found single-celled parasites in a mosquito (Phlebotominae) from about 100 million years old Burmese amber. Scientists attributed them to protists from the trypanosomatid group.
At the end of the same year, the researchers published a second article on the same mosquito. In it, scientists described the blood cells preserved in the insect, which most likely belonged to a reptile. And a year later, Poinar, together with a colleague, described other blood parasites from Burmese amber.
This time, scientists have found plasmodium in a female biting biting (Ceratopogonidae). Apparently, this midge fed on the blood of large vertebrates. Thus, already in the Mesozoic, some unicellular parasites began to multiply in blood-sucking insects, using vertebrates as intermediate hosts.
By the way, George Poinar is known not only for descriptions of ancient parasites: in the 80-90s of the last century, he showed that cell organelles can be preserved in amber, and even claimed that he was able to isolate the DNA of insects. It was his work that inspired the writer Michael Crichton, the author of Jurassic Park. However, subsequent studies have shown that DNA is not preserved in amber.
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