12
Fossil ticks are usually found in isolation from host material, however, their morphology resembles that of extant ticks closely enough to infer their parasitic, hematophagous life-style, in some case can even be identified to extant genera (e.g.
Amblyomma birmitum—Chitimia-Dobler et al. 2017). While only a few fossils of
ticks have been described, they are likely to have been blood-feeding ectoparasites
of many extinct terrestrial vertebrate taxa. This is supported by fossils that indicate
such ticks were also hosts for vector-borne pathogens which are similar to those that
infect extant vertebrates (Poinar 2019). A molecular phylogeny study found the
divergence of hard and soft ticks to have occurred during the Early Permian, which
indicates a Carboniferous origin for ticks (Mans et al. 2012). This was also during
an important period in the evolution and diversification of terrestrial vertebrates and
amniote animals (Clack 2002), therefore it is possible that ticks coevolved with terrestrial tetrapods.
Recent discoveries of dinosaur body parts or even entire hatchlings with intact
plumage in amber (Xing et al. 2016, 2017) presented exceptional opportunities to
investigate potential dinosaur ectoparasites such as ticks. Such amber fossils not
only preserve the parasite in detail, but also in situ with host material, thus providing
direct evidence for their parasite-host relationships. As an illustrative example,
recently some tick fossils were described by Peñalver et al. (2017) from Middle
Cretaceous Burmese amber. The ticks were found in association with loosely vaned
pennaceous feathers which are found on penneraptoran dinosaurs, but not crown
birds (Peñalver et al. 2017), thus providing unequivocal evidence of ectoparasites
on non-avian theropod dinosaurs. Furthermore, some of the fossil ticks have morphology which indicates they belonged to families that no longer exist, such as
Deinocroton draculi which was assigned to the family Deinocrotonidae (Peñalver
et al. 2017). This indicates that there are families of ticks which have become coextinct with their hosts, indeed this should be expected as many extant parasite
groups had lineages that have become extinct with their hosts during various extinction events, indeed the potential co-extinction of parasites with their endangered
hosts has recently emerged as a key issue in conservation biology (e.g. Campião
et al. 2015; Strona 2015; Thompson et al. 2018).
1.1.10 Ectoparasitic Insects (Fleas and Lice)
While insects originated in the Devonian (Misof et al. 2014), evidence for insect
feeding on the blood of vertebrates did not appear until the mid-Mesozoic
(Lukashevich and Mostovski 2003). Nagler and Haug (2015) provided an extensive
review on fossils of parasitic insects including those that are ectoparasites of vertebrates. There are at least seven orders of insects that have evolved to associate with
vertebrates with their relationships ranging from commensalism to parasitism, with
some feeding non-invasively on host secretion to those that actively feed on host
tissue such as integumentary growth or blood (Waage 1979). It is worth noting that
the major groups of ectoparasitic insects are usually associated with hosts that have
T. L. F. Leung
Fossil ticks are usually found in isolation from host material, however, their morphology resembles that of extant ticks closely enough to infer their parasitic, hematophagous life-style, in some case can even be identified to extant genera (e.g.
Amblyomma birmitum—Chitimia-Dobler et al. 2017). While only a few fossils of
ticks have been described, they are likely to have been blood-feeding ectoparasites
of many extinct terrestrial vertebrate taxa. This is supported by fossils that indicate
such ticks were also hosts for vector-borne pathogens which are similar to those that
infect extant vertebrates (Poinar 2019). A molecular phylogeny study found the
divergence of hard and soft ticks to have occurred during the Early Permian, which
indicates a Carboniferous origin for ticks (Mans et al. 2012). This was also during
an important period in the evolution and diversification of terrestrial vertebrates and
amniote animals (Clack 2002), therefore it is possible that ticks coevolved with terrestrial tetrapods.
Recent discoveries of dinosaur body parts or even entire hatchlings with intact
plumage in amber (Xing et al. 2016, 2017) presented exceptional opportunities to
investigate potential dinosaur ectoparasites such as ticks. Such amber fossils not
only preserve the parasite in detail, but also in situ with host material, thus providing
direct evidence for their parasite-host relationships. As an illustrative example,
recently some tick fossils were described by Peñalver et al. (2017) from Middle
Cretaceous Burmese amber. The ticks were found in association with loosely vaned
pennaceous feathers which are found on penneraptoran dinosaurs, but not crown
birds (Peñalver et al. 2017), thus providing unequivocal evidence of ectoparasites
on non-avian theropod dinosaurs. Furthermore, some of the fossil ticks have morphology which indicates they belonged to families that no longer exist, such as
Deinocroton draculi which was assigned to the family Deinocrotonidae (Peñalver
et al. 2017). This indicates that there are families of ticks which have become coextinct with their hosts, indeed this should be expected as many extant parasite
groups had lineages that have become extinct with their hosts during various extinction events, indeed the potential co-extinction of parasites with their endangered
hosts has recently emerged as a key issue in conservation biology (e.g. Campião
et al. 2015; Strona 2015; Thompson et al. 2018).
1.1.10 Ectoparasitic Insects (Fleas and Lice)
While insects originated in the Devonian (Misof et al. 2014), evidence for insect
feeding on the blood of vertebrates did not appear until the mid-Mesozoic
(Lukashevich and Mostovski 2003). Nagler and Haug (2015) provided an extensive
review on fossils of parasitic insects including those that are ectoparasites of vertebrates. There are at least seven orders of insects that have evolved to associate with
vertebrates with their relationships ranging from commensalism to parasitism, with
some feeding non-invasively on host secretion to those that actively feed on host
tissue such as integumentary growth or blood (Waage 1979). It is worth noting that
the major groups of ectoparasitic insects are usually associated with hosts that have
T. L. F. Leung