Tuesday, November 20, 2012

Who Ate the Dinosaurs? Part IV: Helminthic 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. Today, we’ll be talking about some of the worms that burdened our giant lizard buddies. One of the earliest records of fossilized helmithic parasites in terrestrial vertebrates was reported by Poinar and Boucot in 2006. This report described a trematodes and two species of nematodes found in a dinosaur coprolite that dated back to the Early Cretaceous.

Digenites proterus egg with arrow indicating the operculum.
            The aforementioned paper did not report an adult trematode (a.k.a. a “fluke”) but rather reported a trematode egg. The egg was described as a new species and dubbed Digenites proterus. It seems that there are many types of digenetic trematodes that parasitize modern reptiles. There are over 400 species that parasitize turtles, 75 that parasitize lizards, and 250 that parasitize snakes. These little guys find their way into many different organs…the pancreas, the gall bladder, the kidneys…and their eggs are passed out in the feces, urine, or even in oral mucus. Despite their diversity, these parasites tend to be asymptomatic (causing no clinical symptoms) in our modern day reptile friends, and were probably asymptomatic for our prehistoric buddies as well. The study mentioned only had one coprolite to work with, but the coprolite only yielded one such egg, so at the very least the dinosaur who left behind those remains was not heavily infected and probably wasn’t too bothered by the trematode(s) within him or her.

A. priscus (right) and A. gerus (left) eggs
with arrows showing developing nematode larvae.
            Much like the trematodes that Poinar and Boucot described, there were three nematode eggs that represented two new species of prehistoric nematodes,  Ascarites priscus (two eggs found) and Ascarites gerus (one egg found). Unlike the trematodes egg, these eggs had visible juveniles that had been frozen in time within the egg casings!  There are close to 100 species of ascarids in modern day reptiles. These worms typically lay lots of eggs that get passed out in the feces of their hosts. Just as before, the low parasite load from this sample indicates that this particular dinosaur probably had no clinical symptoms of being parasitized by these worms.
Everyday They’re Burrowin’ Burrowin’
            I ran across an article about another interesting find relating to helminthic parasites of dinosaurs. In this article, researchers led by the University of Colorado, Boulder’s Karen Chin analyzed the gut from a duck-billed dinosaur that they affectionately called “Leonardo”. “Leonardo” was excavated from a river formation in Montana in 2000 and 2001 before its intestinal materials were given to Chin’s team in 2006. The team found over 200 burrows from parasitic worms that were similar to either modern day annelids or nematodes. As far as I know, they couldn’t tell which specific parasites caused the tunnels, but they could tell that it was a parasite and not something that invaded the dinosaur’s body after it died. The question on my mind, and probably yours too: How exactly does one land the job looking at the intestinal materials from a dinosaur anyway?

An artist's depiction of how "Leonardo" might have appeared.

Waiter! There’s a Snail in My Dinosaur’s Dung!
            So this part isn’t COMPLETELY relevant…but it is somewhat, so I’m going to bring it up anyway. I ran across a nifty little paper describing the recovery over snail fossils in dinosaur dung. The fossilized snails were incredibly well-preserved with some 46% of the snails being whole fossils! Due to the extent of preservation, it is believed that the snails found their way into the dung after it was deposited rather than the snails being something that the dinosaurs ingested and then passed themselves. 

Lioplacodes (a fossilized snail) embedded in a
coprolite from an herbivorous dinosaur.
For those who aren’t parasitologists, allow me to enlighten you as to the significance this has for this blog. There are many different snails that play integral roles in the life cycles of helminthic parasites. Various species of snails serve as intermediate hosts for many different types of trematodes and also for some nematodes. There have been seven different genera of fossilized snails recovered from dino-dung pats, some of them terrestrial and some of them aquatic types of snails.  In my humble, personal opinion (understand that I have absolutely no literature to back this up), I believe that there very easily could have been parasites that were passed in the dung by dinosaurs and picked up by some of these snails as part of those parasite life cycles. It would be interesting to find fecal remains from animals that may have been dinosaur prey and examine them for the presence of these snails and, if possible, whatever parasites they may or may not be carrying. Hopefully someone will have the answer to that question in the future, if they don’t already. Escargot for thought?!

Moral of the Story
            When a conversation turns to dinosaurs, we don’t often think about how these majestic creatures may have hosted intestinal worms in the same way that so many creatures, including ourselves, do today. It is all too easy for us to think of dinosaurs as animals that ruled the earth as giants rather than as animals that existed as part of a vibrant and evolving ecosystem. It’s all too easy to forget that parasitism is an important part of any ecosystem, with the world on and inside of ancient reptiles being no different. If there exists some cosmic thread that connects today’s world to the world of the past, parasitism certainly makes up many of the fibers. So, the next time you are at a party, you should throw around the idea that we aren’t so different from dinosaurs because we all have played host to parasites. When you lock eyes (Personal Communication, Grant Shulman, 2012) with another person who finishes your sentence and lovingly whispers, “Psuedopulex jurrassicus” and then the two of you exchange numbers, go out for coffee, start dating, get married, and start making your own little parasites, you can come back here and comment on my blog! :p Ahh young love…sprung from parasitophilia…I’m not gonna cry…I’m not gonna cry…

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