Dinosaur Fleas Were Ten Times Bigger Than Fleas Today

The discovery of large flea-like fossils, about ten times bigger than the fleas we see today, is enough to make your skin crawl. Imagine the poor dinosaur that had to endure a painful bite from such a paleo-pest crawling onto its soft under-belly. The only consolation is that these blood-sucking organisms could not jump like their modern counterparts, but previous research indicates that they were not spared the additional torment of lice.

Dinosaur Fleas Fossils Were Located in Inner Mongolia

The flea-like pests had large mouthparts, making a bite similar to being injected by a hypodermic needle. George Poinar Jr., Zoology Professor Emeritus at Oregon State University, likens it to a ‘flea shot, if not a flu shot’ in his comment that accompanies the recent article from the journal ‘Current Biology’. The authors, Chungkun Shih and Dong Ren, conducted research at the Capital Normal University in Beijing and described two new species of flea-like insect from fossils found in Inner Mongolia.

Pseudopulex jurassicus and P. magnus were described from ‘compression fossils’ that differ from impressions, since they are the actual insects that were preserved through the fossilization process over time. This type of fossil offers a great level of detail and preservation of the body structure, akin to taking high-resolution photos of these ancient insect species that lived 165 million years ago.

What Did Dinosaur Fleas Look Like?

These paleo-pests appear to have had dorso-ventrally flattened bodies, similar to that of ticks and bedbugs, which is quite the opposite to the laterally flattened bodies of modern fleas. The paleo-pests would have had long claws for reaching over dinosaur scales in order to hold on while feeding, by sucking blood. The body shape and shorter antennae of modern fleas, on the other hand, are properties that adapt them to quick movement through the feathers or fur of their modern-day hosts.

Pseudopulex jurassicus (loosely translated as the ‘pseudo-flea from the Jurassic’) is the smaller of the two newly discovered ecto-parasitic taxa, with a body length of 0.7 inches (17 mm), excluding the antennae. Its mouthparts are 0.13 inches (3.4 mm) long, reaching over double its head length. The larger of the two species, P. magnus, has a body 0.9 inches (22.8 mm) long, with mouthparts reaching a length of about 0.2 inches (5.2 mm). The overall large-sized body and serrated, long mouthparts of these paleo-pests allowed them to pierce through the thick, tough hides and skin of their hosts. These were probably quite large pterosaurs or feathered dinosaurs, or they may have been mammals of medium size from the Early Cretaceous (but according to Shih the latter would not be from the Middle Jurassic).

Which Dinosaurs Hosted these Dinosaur Fleas?

To ascertain which dinosaurs would have acted as hosts, the researchers studied evidence showing what other animals may have coexisted with these insects at similar locality over the same time. The Middle Jurassic yielded possible feathered dinosaurs as hosts, e.g. Epidexipteryx hui and Pedopenna daohugouenis. Pseudopulex magnus, however, lived during the Early Cretaceous and may have used Microraptor gui and Sinosauropteryx prima as hosts for blood meals.

Three Dinosaur Fleas Have Previously Been Discovered

This discovery is not the first of its kind. Recently the journal ‘Nature’ carried an article by Diying Huang et al., from the Chinese Academy of Sciences, that describes similar ‘dinosaur fleas’. Shih comments that their two new species bear some resemblance to the three previously known taxa, but also mentions that there are some noticeable differences. Despite studying the ‘Nature’ paper with its figures and online supplemental information, Shih can only speculate on whether all of these fossils are the same species. He would need high-resolution microscopy and images, as well as access to the actual fossil material, to determine this.

One similarity is clear – neither the flea-like taxa from the ‘Nature’ article, nor the two new taxa, had hind legs modified for jumping. The ability to jump distances of 50 to 100 times that of their body length would have evolved some time between the existence of these early flea-like taxa, and the species we see today.  Modern fleas appear to avoid the bigger beasts; of a possible 2 300 species, about 94 percent feed on mammals and the rest feed on birds. It is truly amazing to see how fleas have evolved from dinosaur fleas to the fleas of today!