Editing Flea (section)

=== Fossil history ===
[[File:Flea in amber.jpg|thumb|upright|[[Cenozoic]] flea in [[amber]], c. 20 [[mya (unit)|mya]], is morphologically modern.]]
[[File:P.wangi fossil image.png|thumb|''[[Pseudopulex|Pseudopulex wangi]]'', a primitive flea from the Early Cretaceous of China]]

Fleas likely descended from [[scorpionflies]], insects that are predators or scavengers.<ref name=":0" /> Fossils of large, wingless [[stem-group]] fleas with siphonate (sucking) mouthparts from the Middle [[Jurassic]]<ref>{{cite journal |author=Huang, D. |author2=Engel, M.S. |author3=Cai, C. |author4=Wu, H. |author5=Nel, A. |date=8 March 2012 |title=Diverse transitional giant fleas from the Mesozoic era of China |journal=Nature |volume=483 |issue=7388 |pages=201–204 |doi=10.1038/nature10839 |pmid=22388812|bibcode=2012Natur.483..201H |s2cid=4415855 }}</ref> to Early [[Cretaceous]] have been found in northeastern China and Russia, belonging to the families [[Saurophthiridae]] and [[Pseudopulicidae]], as well as ''[[Tarwinia]]'' from the Early Cretaceous of Australia. Most flea families formed after the end of the Cretaceous (in the [[Paleogene]] and onwards). Modern fleas probably arose in the southern continental area of [[Gondwana]], and migrated rapidly northwards from there. They most likely evolved with [[mammal]] hosts, only later moving to [[bird]]s.<ref>{{cite journal |last1=Zhu |first1=Qiyun |last2=Hastriter |first2=Michael |last3=Whiting |first3=Michael |last4=Dittmar |first4=Katherina |title=Fleas (Siphonaptera) are Cretaceous, and Evolved with Theria |journal=Molecular Phylogenetics and Evolution |date=September 2015 |volume=90 |pages=129–139 |biorxiv=10.1101/014308 |doi=10.1016/j.ympev.2015.04.027 |pmid=25987528|bibcode=2015MolPE..90..129Z |s2cid=13433327 }}</ref>

Siphonaptera is a relatively small order of insects: members of the order undergo complete metamorphosis and are secondarily wingless (their ancestors had wings which modern forms have lost). In 2005, Medvedev listed 2005 species in 242 genera, and despite subsequent descriptions of new species, bringing the total up to around 2500 species,<ref name=Whiting2008/> this is the most complete database available. The order is divided into four infraorders and eighteen families. Some families are exclusive to a single host group; these include the Malacopsyllidae ([[armadillo]]s), Ischnopsyllidae ([[bat]]s) and Chimaeropsyllidae ([[elephant shrew]]s).<ref name=Krasnov3>{{cite book|author=Krasnov, Boris R. |title=Functional and Evolutionary Ecology of Fleas: A Model for Ecological Parasitology |url=https://books.google.com/books?id=tkvr8h8zxFwC&pg=PA3 |year=2008 |publisher=Cambridge University Press |isbn=978-1-139-47266-1 |pages=3–9}}</ref>

Many of the known species are little studied. Some 600 species (a quarter of the total) are known from single records. Over 94% of species are associated with [[mammal]]ian hosts, and only about 3% of species can be considered to be specific parasites of [[bird]]s. The fleas on birds are thought to have originated from mammalian fleas; at least sixteen separate groups of fleas switched to avian hosts during the evolutionary history of the Siphonaptera. Occurrences of fleas on reptiles is accidental, and fleas have been known to feed on the [[hemolymph]] (bloodlike body fluid) of [[tick]]s.<ref name=Krasnov3/>