We all know the tapeworm, and have shuddered at the parasitic wasp. But how far do parasitic pests go back? What lurked in the primordial ooze? Did dinosaurs have fleas? Were they different?
Now we can scratch our itch of curiosity thanks to a review of the parasites plaguing extinct animals, published by Paula Cascardo, Elisa Pucu and Daniela Leles of Fluminense Federal University in the Journal of Parasitology in May.
Yes, dinosaurs had fleas. And lice, which brings to mind the image of a T-rex scratching madly. In babyhood at least. Actually T-rex adults were likely mostly unfeathered, experts suspect.
“Parasitism is inherent to life and observed in all species,” the authors evocatively begin their piece. Even bacteria harbor viruses (which are parasitic by definition) and these parasitic viruses may harbor other viruses, called virophages.
Think not that parasites are the degenerate, wretched dregs of life, “an insult to evolutionary progress” – if that opinion once prevailed, it doesn’t anymore. On the contrary, they are highly specialized, fully-fledged life-forms: they are ecological engineers, parasitologists say, vital to all ecosystems. Think of it as added value in your sushi, folks.
Moving beyond their social status, it seems that throughout the existence of life, nobody was exempt.
The first life
The question of parasite origin starts with life origin, possibly. Right now there are about 8.7 million eukaryotic (enucleated) species on the planet, give or take 1.3 million, according to the Census of Marine Life: 6.5 million on land and 2.2 million in the sea. That number doesn’t include the prokaryotes, i.e., bacteria, archaea or viruses. We can’t count those.
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Going back to the first primordial spasm that we could call life, the thinking is that there have been over 5 billion species, of which 99.9 percent are extinct. And what did they have in common, aside from the breath of life? Parasites. We even have some proof of paleoparasites, like the fossil worm-like critter infecting a clam over half a billion years ago. That surely wasn’t the first parasite; it’s just the earliest such fossil of a parasite found so far.
We don’t know what the earliest life was, let alone the earliest parasite. We don’t even know if viruses were always purely parasitic or whether, eons ago, they were independent, if primitive, forms of life that discovered an alternative to “metabolism.”
So we shall skip the very earliest phases and go straight to the fun stuff.
Happiness is a therapsid public toilet
The ways to investigate parasites of extinct animals include coprolites (fossil feces), lesions on ancient bones and tissues, amber (which is essentially fossil resin) and, for more recent deaths, mummies. Even analysis of ancient DNA, a fairly new science, provides clues.
Not entirely germane to the current discussion but good to know: Coprolites can shed light on behavior. In one case, paleontologists deduced that dicynodont therapsids living in the Triassic about 240 million years ago engaged in communal latrine behavior: repeatedly using specific sites for relieving themselves. Until then, communal toilets had been thought to be the fief of mammals such as elephants, raccoons and donkeys.
Back to isolated pieces of poo: They can teach what the animal ate, the environment it lived in and the parasites plaguing its existence. Paleoparasitology was greatly assisted by the discovery of rehydrating non-mineralized ancient feces. The study of mineralized specimens was aided by treating them with hydrochloric acid – let’s not ask.
As early as the year 1895, scientists were reporting on noticing, as opposed to identifying, bacteria in coprolites dating to the Permian period 285 million years ago. (Bacteria, by the way, were first discovered in 1676.) By the 20th century, science had grown confident enough to get specific: in 1946, researchers reported on identifying the bacterium Thiobacillus, and other microbes, in coprolites dating to the Triassic. Come 2006, paleoparasitologists were reporting on nematode eggs and protozoans in a coprolite found in Belgium from the Cretaceous – they think the creature responsible for that one was a Megalosaurus.
The finds would go on, proliferating and multiplying. Worm eggs were found in coprolites of early bony fish from about 270 million years ago; nematodes in an extinct shark that could be as much as 570 million years old; roundworm eggs were found in extinct Cretaceous crocs found in Brazil – there is no end.
Other research looked at coprolites of recently extinct animals that coexisted with hominids, finding nematodes and other nasties in feces associated with the extinct European hyena – with whom ancient hominins had a great deal of interaction, which could have led to shared parasitic infection. No, the hyenas weren’t tamed, they were competing with the ancients for cave space and scavenging rights.
There is even a theory based on coprolitic evidence that a cache of dead cave hyena cubs found in Pakistan from 1.2 million years ago were killed by hyper-infection with deadly Toxocara canis parasites.
Sometimes the fossil evidence of parasitism is direct, not defecated, such as the discovery of fossil parasitic copepods inside the skulls of fossil fish dating to about 115 million years ago. In this category, however, the true stunner has to be primitive fish found in Latvia from the Devonian from about 880 million years ago, which were also infested with parasites.
As for the fleas on dinosaurs: proto-birds had mites too. In 1998, researchers identified mite eggs on feathers in Brazil from 120 million years ago, the early Cretaceous. “The discovery of feathered dinosaurs and the identification of these ancient ectoparasites from the Early Cretaceous in fossils suggest that these birds may have acquired certain ectoparasites from feathered tetrapod dinosaurs,” the team suggests.
Trichonomas and the T-rex
And endoparasites. Lesions in fossil bones may also reveal ancient parasitism: Ewan Wolff and colleagues reported in 2009 finding lesions seemingly from Trichomoniasis gallinae in a tyrannosaur skull.
This parasite is a plague of modern birds too. In fact, thrichomonads today are a plague of many a vertebrate and invertebrate species – including us folks. Yes, gallinae is a cousin of Trichomonas vaginalis, which causes a sexually transmitted disease in men and women that is sometimes confused with chlamydia. Apropos, koalas also suffer massively from chlamydia, as do the great apes. Truly, we are not special.
Nor are we unique in suffering from tuberculosis: bones from extinct bison and musk-ox show these bovids had it in North America 17,000 years ago.
Which brings us to the more recently dead – since we are writing about the paleoparasitology of extinct animals, we won’t get into human mummies and the infestation-related horrors we can learn from them. Naturally mummified animals are rare but they do exist, and are sometimes discovered melting out of the permafrost in this era of climate change.
Unsurprisingly, the mummified animals were riddled with parasites – as we were, before we discovered real medicine.
Amber is also a great source for learning about ancient parasites, such as the trypanosomatids (parasitic infectious protozoans) caught for eternity in the innards of a sandfly. Latter-day trypanosomatids include the cause of sleeping sickness in people. This one and its host fly lived about 100 to 110 million years ago. The same team also recognized worms parasitizing a midge.
A different team found fungi parasitizing a mosquito in Dominican amber dating to around 40 million years ago. Also in Dominican amber, a cancerous caterpillar was found and the postulation arose that its condition was caused by viruses possibly 26 million years ago.
Other amber produced lice nymphs in dinosaur feathers from the mid-Cretaceous amber: that, the study pointed out, corroborates genetic analysis of modern lice that indicated they’ve been around since the time of the dinosaurs.
So yes, dinosaurs had fleas and the fleas had worms and the worms had parasites too. All these paleoparasitology studies bring us to the authors’ point that many parasites seem oddly unchanged over the eons. But not all.
Vive la difference
“Considering how ancient and successful parasitism is, most parasite fossils show considerable morphological similarity to their modern relatives,” write Leles and the team.
Let us be clear that morphological similarity doesn’t necessarily indicate genetic similarity. The coelacanth looks like it did hundreds of millions of years ago, but its genome has changed. Geneticists deduced that the “living fossil” fish developed 62 new genes in the last 10 million years. Sharks also look unchanged, nautiluses look unchanged – and the list could go on. Some insects caught in amber, their little feet hopelessly glued to the tree for eternity, look the same.
But some parasites did evolve. Jurassic fleas couldn’t jump: it seems they crawled to their meals, or ambushed their hapless hosts, likely feathered dinosaurs and/or pterosaurs.
And they were huge. Modern fleas max out at a centimeter in length, but the paleo-flea could reach an inch in size. Their jaws were armored structures studded with saw-like projections, unlike the smooth jaws of modern fleas with their siphon mouthparts, scientists reported in Nature in 2012. Just as well they don’t look like that now.