Sunday, November 11, 2012

Who Ate the Dinosaurs? Part III-Protozoan Parasites

           At the recommendation of a well-known parasitologist, I began reading about the parasites that plagued everyone’s favorite prehistoric animals: the dinosaurs. I found lots of information on various forms of dino-parasites…everything from protists, to helminths, to insects. I’ve decided to break up this topic into a series of posts over the next few weeks.

           Today, let’s talk about some insidious little creatures that may have infected dinosaurs…protozoan parasites! These parasites are single-celled and not something that preserves well in fossils or in amber as our ectoparasites did. However, they can still be detected in coprolites (fossilized feces) and by the pathological problems they left evidence of in the bones of ancient beasts.

Confirmation from Coprolites
Entamoebites antiquus
            In 2006, Dr. Poinar and his college Dr. Boucot reported the earliest evidence of protozoans from a Belgian coprolite. This coprolite dated back to the Early Cretaceous, making this paper the first paper to report intestinal protozoan parasites from a dinosaur. This protozoan was identified as the cyst from of Entamoebites antiquus, and is more similar to our modern day genus Entamoeba than to our modern day genus Endolimax.

Always Check the Amber
            As we talked about last week, there is also a lot of evidence regarding parasitism that can be found encased in amber. Specifically, we talked about the face that insects that are known vectors for modern diseases have been found in these little time capsules. This leads us to believe that they may have been transmitting diseases back in the days of the dinosaurs as well. Some scientists, such as Dr. Poinar (co-author or What Bugged the Dinosaurs?) have claimed to find evidence of protozoans that are similar to modern-day Leishmania and Haemoproteus parasitic protists.
An adorable stuffed-protist
version of Leishmania
            However, some people, such as Dr. David Grimaldi, (with the Division of Invertebrate Zoology at the American Museum of Natural History) is skeptical of such claims. In his review of Dr. Poinar’s book he states, “Unfortunately, the vague, dark forms in their light micrographs fail to convince. Since cells within amber-fossilized insects are well known to have preserved organelles, identification of the putative pathogens should have been made with electron microscopy.
            Either way, finding protozoans in insects that have been preserved in amber can’t be an easy task. I suppose we will have to wait and see what science and technology can do in the coming years to either support or debunk claims about the presence of the tiny, unicellular menaces.

Detection of Protists Via Paleopathology
Depicting the lesions found on "Sue"
a T. rex who suffered from parasitic
protozoan infections.
            In 2009, another article came out about ancient protozoan parasites that plagued dinosaurs. By examining lesions in the jaw bones of Tyrannosaurus rex skulls, these researchers determined that the lesions were a pathological result of a transmissible parasitic disease that bears striking resemblance to a disease that plagues modern-day birds. Because they found the effects of such disease, and not the actual causative agent, scientist can’t pinpoint the species to blame. However, there is strong evidence that the parasite to blame was similar to Trichomonas gallinae. Paleopathological evidence of this disease has only been found in the bones of tyrannosaurs, so far. It seems to have been fairly common among species in some populations and was probably spread through either consuming infected prey (or cannibalism) or through nasty bloody battles over T. rex turf. Some of the specimens in this study were so heavily infested, that paleopathologists determined that those specimens most likely died as a direct result of having that infection. The idea is that these mighty beasts starved to death because it was too painful too eat when you’ve got your jaws packed full of protists.

Moral of the Story
            When a conversation turns to dinosaurs, we don’t often think about how these massive creatures may have played host to unicellular demons. It still astonishes me that something so small and seemingly insignificant can cause such pathology in animals as massive and seemingly invincible as a Tyrannosaurus rex. And those poor guys couldn’t even scratch a jaw being systematically riddled with holes. Anyway, the next time you are at a party, you should definitely throw around the name ­­­­­­­­­­­­­­ Entamoebites antiquus. If a dude introduces himself after hearing you utter such a phrase, you should let him take you out for coffee. I urge you to accept this offer because he’s either really awesome for knowing something about ancient parasites, or he reads my blog…which makes him even more awesome. ;)

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