Saturday, October 27, 2012

Who Ate the Dinosaurs? Part I: Ectoparasites

An artist's rendition of a Jurassic flea.
        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 things living on the outside of our beloved reptiles. In doing so, we will also mention a little about how these creatures probably feasted on the blood of ancient birds and mammals as well. You will also have the pleasure of reading a bit about ectoparasite evolution, and how studying these little guys helps us to paint a more accurate picture of life over a 100 million years ago.

            Lice are thought to have evolved over 65 million years ago according to a new study using modern lice DNA. That time frame places their ancestors in the same place as dinosaurs. One study is even showing that lice began diversifying on mammals and birds before the dinosaurs went extinct! (Which means that mammals and birds may have been diversifying at this time as well?!) How interesting is it that these little guys could be proxy indicators of bird and mammal radiations preceding what has been conventionally accepted as post-dinosaurian diversification of these types of creatures!!?!?!!  Here’s an awesome quote from Dr. Vincent Smith, a researcher who has been working on dino-lice at the Natural History Museum in London:

Fossilized lice remains from 44 million years ago (left) next to
a modern-day louse from an aquatic bird (right).

Lice are like living fossils. The record of our past is written in these parasites, and by reconstructing their evolutionary history we can use lice as markers to investigate the evolutionary history of their hosts.  It was thought that after the dinosaurs went extinct that's when these birds or mammals diversified into these different niches, but based on the evidence from lice, the radiation of birds and mammals was already under way before the dinosaurs went extinct.”


           Pretty cool huh? Some researchers believe that louse-lineages may even go back as far at 115-130 million years ago! It’s thought that these ancient lice may have fed on feathered dinosaurs such as China’s Sinornithosaurus. The most recent numbers I could find in the literature regarding lice stated that the first instances of parasitic lice occurred between 100 million and 125 million years ago. The same study suggested that these little guys didn’t become parasites until animals began to develop fur or feathers. It seems that modern birds may have gotten their modern louse-burdens from feathered versions of their dino-brethren. 

Fossilized flea from the Jurassic period.
            Okay, so maybe some dinosaurs had lice…but what about another exciting group of ectoparasites…fleas? There are fossils of fleas that date back to the Jurassic, some 100 million years ago. They were anywhere from twice to ten times the size of modern fleas and lack the jumping potential that our familiar forms possess. They also donned elongated sucking mouthparts that were serrated…presumably for piercing hides that were much thicker than the hosts’ hides that contemporary fleas must penetrate. They were dorso-ventrally flattened rather than laterally compressed. (For those who aren’t biologists, this means that the bodies are flattened from front to back rather than from the sides. Fish, for example, are laterally compressed.) They also had spiny bodies and claws that helped them to cling to prehistoric feathers and fur. It is most likely that these guys fed on pterosaurs and early rodent-like mammals. 

Jurassic flea fossils from China.
(Note size compared to the human hand.)
A recent examination for fossilized fleas from China found that some fleas existed 165 million years ago! Two species have been named from these Chinese fossils. They were given the names Pseudopulex jurassicus and Pseudopulex magnus based on compression fossils, which provide much more detail of the fossil’s anatomy as opposed to impression fossils. P. jurassicus is smaller in size than P. magnus. It is believed that these fleas fed on feathered dinosaurs, such as Epidexipteryx hui and Pedopenna daohugouenis, during the mid-Jurassic period. I read a few articles that mentioned other types of dinosaur fleas, but I have yet to uncover the scientific names of those fleas.

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 ectoparasites in the same way that animals like corgis do today. We think of the astounding size of these animals and about how they ruled the planet so long ago. As interesting as they are, I think it’s even more fascinating to know that they were not exempt from the most efficient form of symbiosis found in any ecosystem. In my head, I can’t help but picture a pissed off velociraptor rubbing up against a tree to sooth the itch of a group of 2cm long fleas feasting on his back. (For the record, that’s purely a figment of my imagination, there’s no evidence to support that fleas actually fed on velociraptors.) Anyway, the next time you are at a party, you should throw around the name Pseudopulex jurrassicus. If this attracts a woman, she’s a keeper. If it doesn’t, then no woman at that party is worth your time anyway! :p

1 comment:

  1. P - This post is a really nice one. But don't forget mites and ticks, both of which occur on modern "reptiles" and have a very long history (although ticks supposedly blossomed during the Cretaceous and later). And, to my knowledge, nobody is strongly contesting the fossil pentastome material from the Cambrian.