Pseudopulex

Pseudopulex Temporal range: Middle Jurassic to Early Cretaceous,
Pseudopulex wangi fossils
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Siphonaptera
Family:	†Pseudopulicidae
Genus:	†Pseudopulex Gao, Shih, and Ren, 2012
Species
P. jurassicus Gao, Shih, and Ren, 2012 P. magnus Gao, Shih, and Ren, 2012 P. tanlan Gao, Shih, Rasnitsyn, and Ren, 2014 P. wangi Huang, Engel, Cai, and Nel, 2013

Pseudopulex is a genus of extinct, primitive fleas that lived between the Middle Jurassic and Early Cretaceous periods, found in modern-day China. The Latin root for the name Pseudopulex roughly translates to "false fleas".

Taxonomy

P. tanlan fossils and line drawing

There are currently four identified species in this genus discovered through fossil remains: Pseudopulex jurassicus, Pseudopulex magnus, Pseudopulex wangi and Pseudopulex tanlan, with most current research focused on P. jurassicus and P. magnus.

Fossils of P. jurassicus date back to the mid-Mesozoic of China, more specifically the middle Jurassic-aged Jiulongshan Formation, making them around 165 million years old, while P. magnus were discovered to be from the Early Cretaceous Yixian Formation, around 125 million years ago. Some possible hosts of P. jurassicus were Pedopenna daohugouensis and/or Epidexipteryx hui (feathered dinosaurs) and Sinosauropteryx prima or Microraptor gui for P. magnus. These organisms have similar features to other studied ectoparasites, and they share traits with present-day fleas, most notably in their wingless bodies and stylets that are very long and sharp (used for piercing through flesh). They also contain features that distinguish them from similar parasites, such as lice, because of their longer and more thin, clawed appendages as well as their extended mouthparts specific for bloodsucking. There are traits that are completely different from modern fleas as well, which is said to be representative of this species possibly having an early evolution that resulted in a dead-end lineage. There currently isn't much information regarding the evolution of fleas, but this genus is most similar to crown fleas. P. tanlan is considered to be somewhat of a transition organism between P. jurassicus or P. magnus and existing fleas as it has a smaller body plan, more compact antennae, and other features associated with today's fleas. Maybe their most critical difference from extant fleas, such as crown fleas, is the lack of hind legs, prohibiting them from jumping or running, which is a common mode of transportation for most extant fleas. Presently, there has been a total of six other flea-like fossils that have been discovered along with this genus, which contributes to a better and more full understanding of the evolution of fleas.

Description

Pseudopulex tanlan

The most common trait of these prehistoric fleas are their flat bodies, similar to common ectoparasites like ticks or bedbugs. Even between the species of Pseudopulex, however, there are distinct differences in morphology, with P. jurassicus being slightly longer and containing a shorter stylet while P. magnus are thicker and have very long mouthparts. P. tanlan was discovered to have an average sized body but smaller than other Pseudopulex species at about 10 mm long, with a relatively small head and thoracic cavity. The body was also seen to contain setae that are very short and stiff. Comparing to P. magnus and P. jurrasicus, this species has relative small male genitalia and short tibia on females. P. jurassicus was much larger, with a length of 17 mm and mouthpart length of 3.4 mm, twice the size of its head. This species had very small eyes, antennae, and a short torso covered in long thin bristles. Their legs were also quite long and contained a pair of large claws on the ends of each leg. P. magnus was even larger, being 22.8mm long with 5.2mm long mouthparts. Their heads were relatively small and bodies compressed and stout (compared to P. jurassicus). This species also contained antennae, dense setae, and claws on the ends of legs, but they also had a very uniquely large abdomen. Line drawings were able to be created using fossils to provide a clearer understanding of morphology. P. wangi females were about 14.8mm long with a small head with relatively short mouthparts, comparatively, and short antennae. This species also contained larger eyes and body setae. Males, however, were much smaller and had longer bodies, with genitalia being quite large, indicating P. wangi showed much sexual dimorphism .

Paleobiology

Restoration of P. jurassicus

While these parasites show similar characteristics to modern fleas, they also show major differences in body morphology and size due to the large difference in host, such as more flattened bodies and longer claws. They also possessed serrated stylets, likely for feeding on blood through thick layers of skin. Moreover, these organisms are likely to be about fifty times larger than the dog flea. It is reported that the puncture of this parasite is compared to a hypodermic needle injection for these large dinosaurs.

Better understanding of these prehistoric fleas can contribute to research into events such as the breakdown of Mesozoic biodiversity and ancient food chain. Furthermore, the method by which ectoparasites switched from solely infecting mammals to being hosted by birds can provide insights into parasitic evolution. The Pseudopulex phylum displays the tremendous diversity present even millions of years ago, along with host-interactions that further aid in the study of ectoparasite evolution in today's world, giving novel insight into evolution, ecology, and host-parasite interactions that can be applied to modern-day ectoparasites.

References

Data related to Pseudopulex at Wikispecies