''Pseudopulex'' is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of extinct primitive
fleas
Flea, the common name for the order Siphonaptera, includes 2,500 species of small flightless insects that live as external parasites of mammals and birds. Fleas live by ingesting the blood of their hosts. Adult fleas grow to about long, are ...
that lived between the
Middle Jurassic and
Early Cretaceous periods in what is now modern-day
China. The Latin root for the name ''Pseudopulex'' roughly translates to "false fleas".
Taxonomy
![Pseudopolex_tanlan_line_drawing_and_fossil_images](https://upload.wikimedia.org/wikipedia/commons/5/51/Pseudopolex_tanlan_line_drawing_and_fossil_images.webp)
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
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
of China, more specifically the middle Jurassic-aged
Jiulongshan Formation
The Haifanggou Formation (), also known as the Jiulongshan Formation (), is a fossil-bearing rock deposit located near Daohugou () village of Ningcheng County, in Inner Mongolia, northeastern China.
The formation consists of coarse conglomerates ...
, making them around 165 million years old, while ''P. magnus'' were discovered to be from the Early Cretaceous
Yixian Formation
The Yixian Formation (; formerly transcribed as Yihsien Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the late Barremian and early Aptian stages of the Early Cretaceous. It is known for its exq ...
, around 125 million years ago.
Potential hosts for ''P. jurassicus'' include ''
Pedopenna daohugouensis'' and/or ''
Epidexipteryx hui'', while ''P. magnus'' may have parasitised ''
Sinosauropteryx prima'' or ''
Microraptor gui
''Microraptor'' (Greek, μικρός, ''mīkros'': "small"; Latin, ''raptor'': "one who seizes") is a genus of small, four-winged dromaeosaurid dinosaurs. Numerous well-preserved fossil specimens have been recovered from Liaoning, China. They dat ...
.''
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, enabling them to through flesh.
They also exhibit features that distinguish them from similar parasites, such as
lice, including their thinner and more elongate clawed appendages and extended mouthparts.
They exhibit some traits that are completely different from modern fleas, which may be an indication of this genus possibly having an early evolution that resulted in a dead-end lineage. Further research is needed into the evolution of fleas, but this genus is most similar to crown fleas.
''P. tanlan'' is considered to be somewhat of a transitional 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 extant fleas.
A critical difference from extant fleas, such as crown fleas, is the lack of enlarged 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.
Description
![Pseudopulex tanlan 2 (cropped)](https://upload.wikimedia.org/wikipedia/commons/9/9a/Pseudopulex_tanlan_2_%28cropped%29.jpg)
''Pseudopulex'' species have flattened bodies, similar to common ectoparasites like
ticks
Ticks (order Ixodida) are parasitic arachnids that are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external parasites, living by ...
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'' has been found to be smaller than other ''Pseudopulex'' species at about 10 mm long, with a relatively small head and thoracic cavity.
The body of ''P. tanlan'' exhibits very short and stiff
setae
In biology, setae (singular seta ; from the Latin word for " bristle") are any of a number of different bristle- or hair-like structures on living organisms.
Animal setae
Protostomes
Annelid setae are stiff bristles present on the body. ...
.
Compared to ''P. magnus'' and ''P. jurrasicus'', ''P. tanlan'' has relatively 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 exhibited antennae, dense setae, and claws on the ends of their legs, but had a very uniquely large abdomen.
Line drawings were created using fossils as reference to provide a clearer understanding of morphology.
''P. wangi'' females were about 14.8mm long with a small head with relatively short mouthparts and short antennae.
This species also exhibited larger eyes and body setae.
Males, however, were much smaller and had longer bodies, with genitalia being quite large, indicating ''P. wangi'' was more
sexually dimorphic
Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
than other species in its genus.
Paleobiology
![Pseudopulex](https://upload.wikimedia.org/wikipedia/commons/e/e6/Pseudopulex.jpg)
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
{{Taxonbar, from=Q140746
Fossil taxa described in 2012
Insect enigmatic taxa
Middle Jurassic insects
Late Jurassic insects
Cretaceous insects
Parasitic insects
Parasites of reptiles
Insects described in 2012
Prehistoric insects of Asia
Prehistoric insect genera
Fleas