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…

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. ;)

Sunday, November 4, 2012

Who Ate the Dinosaurs? Part II: More on Arthropods

       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, let’s continue talking about things living on the outside of our beloved reptiles and make a transition into their upper respiratory tracts for a look at some nifty little arthropods. Then we will discuss some of the possible parasite vectors and their roles in the extinction of dinosaur populations.

A piece of Canadian Cretaceous amber with a
preserved feather and associated mite.
            It appears that mites were some of the first animals to walk on land some 400 million years ago. They would later give rise to the group of animals we now call ticks, but that wouldn’t come along until much later. In 1998, eggs from a type of feather mite were found on feathers belonging to a Cretaceous (120 million years ago) dinosaur from modern-day northeast Brazil. Later researchers claimed these eggs to be more similar to mites in the family Cheyletoidea (these guys cause a form of dermatitis known as “walking dandruff” in modern mammals and birds).

T-Rex Ticks?
            Ticks were once thought to have originated about 42 million years ago on the modern continent of South America. However, a recent discovery of a tick stuck in amber from New Jersey pushes tick origins back to about 90 million years ago. This fossilized larval tick was named Carios jerseyi and was a type of soft tick. Unlike most soft ticks, this species had dozens of tiny hairs aligned in two rows along its back. Because this is the only known specimen from this time period so far, its gut contents can not be examined for the blood of dinosaurs. However, because it lived at the same time, and because we know that ticks today feed on everything from birds, to mammals, to lizards and snakes, we can assume that this species probably did feed on dinosaurs. 

Carios jerseyi
Tongue Worms in Dino-Lungs?
           Pentastomids are a group of crustaceans that date back to 500 million years ago! These little guys live in the respiratory tracts of terrestrial vertebrates. Close to 85% of modern pentastomids are found in the lungs of reptiles. Being present so early in the fossil record indicates that these animals have had associations with vertebrates for a very long time. Given what we know about these arthropods, it wouldn’t be too much of a stretch to assume that they may have been present in dinosaurs. From what little bit I’ve read, it seems that many scientists are convinced that dinosaurs played host to tongue worms….however, I have not found any studies confirming this. The problem is that soft-bodied invertebrates, as well as dinosaur lung-tissue, does not preserve well over millions of years. Will we ever know if these guys parasitized dinosaurs for sure? Maybe…we are learning more and more as technology progresses…but for now, suffice it to say that they were probably a common dino-parasite.

A modern-day pentastomid
(Armillifer agkistrodontis)
from a snake.
            Insect populations exploded during the time of the dinosaurs. We are talking, like dragonflies with two-foot wing spans exploded. This was because the environment was right for them, the world being covered in warm-temperate, subtropical, and tropical biomes. Naturally, many of those species were blood-feeders, such as everyone’s least favorite little blood-sucker, the mosquito.  In addition, there existed many other species of biting flies, and the lice and fleas I mentioned in a previous post. With the arrival of blood-feeding insects, it was only natural that these animals would become choice candidates as vectors for disease transmission.

            Many forms of diseases we know about today are blood-borne. For the sake of brevity, which is as we all know the soul of wit, I will say that the insects that lived with, and probably feed upon, the dinosaurs were probably carrying various infectious agents. These could have been viral, bacterial, or parasitological (as in protists or intestinal worms, perhaps). There have been instances of finding sand flies preserved in amber, which we know to be the vectors of Leishmania today. Dr. Poinar, author of “What Bugged the Dinosaurs?”, has spent much of his time looking at specimens from amber such as the one mentioned above. He was quoted as saying this in an interview I found online: 

“Our research with amber shows that there were evolving, disease-carrying vectors in the Cretaceous, and that at least some of the pathogens they carried infected reptiles.”

            He went on to discuss how big of a role insects played in the gradual downfall and eventual extinction of our archosaurian predecessors as best I could understand from reviews about the book. Needless to say, this one is definitely makings my “must-read-someday” list. Apparently he also co-authored another book called "The Quest for Life in Amber", which may have also made said list.

 Moral of the Story
            When a conversation turns to dinosaurs, we don’t often think about how arthropods may have annoyed them as much as they sometimes annoy us. It is pretty amazing to think of all that we have learned about dino-parasites, but even more amazing is that which we have yet to learn or what information has been lost to evolutionary history. So at the next party you attend, you should casually mention how far back into the fossil record you have to reach to find the presumed origins of arthropods like mites and pentastomes.  Maybe you will start up a vibrant conversation with someone worth talking to. If so, you should most certainly ask them to join you for a cup of coffee sometime and the two of you can contemplate the role of parasitism in the extinction of the dinosaurs. You could make a new friend just because you read my blog. You are welcome. ;)