14
2013). Furthermore, the morphological traits that were initially cited by Rasnitsyn
(1992) as adaptations for parasitism—sucking mouthparts and prominent
hindlimbs—are also found in a wide range of non-parasitic insects and should not
be considered as definitive diagnostic features for ectoparasitism (Leung 2017).
Similarly, the fossil larvae of Jurassic dipteran Qiyia jurassica was interpreted by
Chen et al. (2014) as a hematophagous ectoparasite of aquatic amphibians on the
basis of its sucking mouthpart and thoracic suckers, yet as Leung (2017) pointed
out, the characteristics that Chen et al. (2014) interpreted as parasitic adaptations
are also found on many non-parasitic freshwater insects. Most importantly, none of
those fossils insects that have been interpreted as ectoparasites were ever found in
association with their postulated hosts or host material. Misattribution of parasitism
to extinct taxa is still an ongoing issue in the palaeontological literature. For example, Ponomarenko (1976) described the Early Cretaceous insect Saurophthirus as a
kind of stem flea that lived on pterosaurs on the basis of a single fossil. But as
Dittmar et al. (2015) and Zhu et al. (2015) pointed out, that interpretation is highly
questionable and inconsistent with what is known about the morphology and phylogeny of crown fleas (Dittmar et al. 2016). Despite that, recently published studies
on Saurophthirus has taken the “pterosaur ectoparasite” interpretation at face value,
so much so that every aspect of its morphology has been interpreted by some workers as that of a hematophagous pterosaur ectoparasite (Rasnitsyn and Strelnikova
2017; Shcherbakov 2017) even though (1) no Saurophthiridae fossils have ever been
found in association with pterosaur fossil material, (2) their morphological traits are
also found on insects with non-parasitic life-styles, and (3) multiple aspects of the
Saurophthirus fossil contradict this hypothesis (Rasnitsyn and Strelnikova 2018).
This should not be taken as a discouragement against searching for parasitic
insects in the fossil record, but rather, a call for a more critical appraisal of fossil
material and cultivating interdisciplinary research between palaeontologists, parasitologists and researchers from various other relevant fields. The lack of true fossil
fleas and lice prior to the Cenozoic actually raises some intriguing questions about
whether insects lived as ectoparasites of terrestrial homeotherms prior to the K-Pg
extinction event, and if so (1) were they of the same order as those of extant ectoparasites, or did they belong to entirely different or potentially extinct groups? (2)
Or perhaps the ectoparasitism niche was occupied by some other type of arthropods,
and if so (3) what were the dominant ectoparasites of terrestrial homeotherms such
as dinosaurs and mammals during the Mesozoic?
1.3 Framework for Inferring Parasite Communities
of Extinct Vertebrate Groups
Based on fossil parasites which have been described thus far, it seems that most
extinct vertebrates, at least those from the Mesozoic to recent, have similar or comparable parasites to their extant relatives (De Baets et al. 2015). While fossil
T. L. F. Leung
2013). Furthermore, the morphological traits that were initially cited by Rasnitsyn
(1992) as adaptations for parasitism—sucking mouthparts and prominent
hindlimbs—are also found in a wide range of non-parasitic insects and should not
be considered as definitive diagnostic features for ectoparasitism (Leung 2017).
Similarly, the fossil larvae of Jurassic dipteran Qiyia jurassica was interpreted by
Chen et al. (2014) as a hematophagous ectoparasite of aquatic amphibians on the
basis of its sucking mouthpart and thoracic suckers, yet as Leung (2017) pointed
out, the characteristics that Chen et al. (2014) interpreted as parasitic adaptations
are also found on many non-parasitic freshwater insects. Most importantly, none of
those fossils insects that have been interpreted as ectoparasites were ever found in
association with their postulated hosts or host material. Misattribution of parasitism
to extinct taxa is still an ongoing issue in the palaeontological literature. For example, Ponomarenko (1976) described the Early Cretaceous insect Saurophthirus as a
kind of stem flea that lived on pterosaurs on the basis of a single fossil. But as
Dittmar et al. (2015) and Zhu et al. (2015) pointed out, that interpretation is highly
questionable and inconsistent with what is known about the morphology and phylogeny of crown fleas (Dittmar et al. 2016). Despite that, recently published studies
on Saurophthirus has taken the “pterosaur ectoparasite” interpretation at face value,
so much so that every aspect of its morphology has been interpreted by some workers as that of a hematophagous pterosaur ectoparasite (Rasnitsyn and Strelnikova
2017; Shcherbakov 2017) even though (1) no Saurophthiridae fossils have ever been
found in association with pterosaur fossil material, (2) their morphological traits are
also found on insects with non-parasitic life-styles, and (3) multiple aspects of the
Saurophthirus fossil contradict this hypothesis (Rasnitsyn and Strelnikova 2018).
This should not be taken as a discouragement against searching for parasitic
insects in the fossil record, but rather, a call for a more critical appraisal of fossil
material and cultivating interdisciplinary research between palaeontologists, parasitologists and researchers from various other relevant fields. The lack of true fossil
fleas and lice prior to the Cenozoic actually raises some intriguing questions about
whether insects lived as ectoparasites of terrestrial homeotherms prior to the K-Pg
extinction event, and if so (1) were they of the same order as those of extant ectoparasites, or did they belong to entirely different or potentially extinct groups? (2)
Or perhaps the ectoparasitism niche was occupied by some other type of arthropods,
and if so (3) what were the dominant ectoparasites of terrestrial homeotherms such
as dinosaurs and mammals during the Mesozoic?
1.3 Framework for Inferring Parasite Communities
of Extinct Vertebrate Groups
Based on fossil parasites which have been described thus far, it seems that most
extinct vertebrates, at least those from the Mesozoic to recent, have similar or comparable parasites to their extant relatives (De Baets et al. 2015). While fossil
T. L. F. Leung