Science Wednesday: Prehistoric Parasites

by Katie Bowell, Curator of Cultural Interpretation

A few months ago, a coworker asked me if there were prehistoric parasites. Since parasitism is a common form of life that’s evolved independently multiple times – almost every free-living species is host to at least one parasite, and some estimates say that approximately half of all the animals on earth have a parasitic stage of their life cycle – I was sure that there had been ancient parasites, but I didn’t know of any. Since most parasites are small – invertebrates, microscopic, and even single-celled – finding evidence of them in the fossil record is difficult.

It turns out, most of the evidence we find for prehistoric parasites isn’t the organisms themselves, but the damage they did to their hosts.

Zombie Ants

Fossilized leaf with evidence of an ant's "death grip" bite

Ophiocordyceps unilateralis is a fungus that can turn an ant into a zombie. Once inside an ant, the fungus consumes the ant’s non-vital tissues and, when it’s ready to spore, sends thread-like branches called mycelia into the ants brain. The mycelia take over the ant’s brain and causes it to climb to the top of a tall stem of grass, bite down onto the main vein of the grass in what’s known as the “death grip,” and stay there until the ant dies. The fungus then keeps growing, spores and infects other ants.

The “death grip” bite leaves very distinctive scars on a plant, and those scars have just been found on a leaf specimen fossilized 48 million years ago. You can read the published report here.

Pigeon Parasites

"Sue" the T. rex. Note the holes in her lower jaw

For years scientists thought that the holes in the jawbone of the famous T. rex “Sue,” and other dinosaurs, were bite marks caused by predation. A new hypothesis is that the holes are too smooth to be caused by teeth and were caused by a relative of Trichomonas, a single-celled parasitic microbe that infects the throats and beaks of modern birds. Since parasites are known to evolve with their hosts, it wouldn’t be surprising if ancient parasites that once infected dinosaurs are now common in modern birds. Pigeons carry trichomonosis with no complications, but when raptors become infected the result is lesions that can wear through bone and inflammation that can block the animal’s ability to eat and breathe. Read more about the findings here.

Gut Worms

In 2006, paleontologists at the University of Colorado found evidence of parasitic worms in duck-billed dinosaur poop. Tiny white burrows inside the gut of a brachylophosaur named “Leonard” are evidence of soft-bodied organisms moving through the gut of a prehistoric animal.

For more information on prehistoric parasites, George Poinar’s What Bugged the Dinosaurs? Insects, Disease and Death in the Cretaceous and Conrad C. Labandeira’s Paleobiology of Predators, Parasitoids and Parasites: Death and Accomodation in the Fossil Record of Continental Invertebrates are two good resources.

P.S. While not a known parasite of dinosaurs, the tropical leech T. rex, Tyrannobdella rex, shares a name with the famous reptile king. And if I had to pick which T. rex I’d rather have try to fit up my nose, I’m going with the leech.