6
widely recognised and studied because of their medical and economic importance
(Anderson 2000). Much like cestodes and trematodes discussed above, the adult
stage living in the gastrointestinal tract is very unlikely to become fossilised.
However the environmentally-resistant eggs produced by the adult parasite can be
preserved as inclusions in coprolites (e.g. Da Silva et al. 2014), survive treatment
with strong acids and/or bases (e.g. Brinkkemper and van Haaster 2012; Dufour and
Le Bailly 2013), and serve as a reliable indicator of the parasite’s presence. Fossilised
ascarid nematode eggs have so far been found in archosaur coprolites from the Early
Cretaceous to Late Cretaceous (Poinar and Boucot 2006; Cardia et al. 2018, 2019a)
and cynodont coprolites from Middle Triassic (Da Silva et al. 2014). Given the
ubiquity of parasitic nematodes in extant vertebrate hosts (Anderson 2000), the
presence of fossilised nematode eggs in the coprolites of phylogenetically distant
groups as archosaurs and synapsids, and the result by Li et al. (2018) which proposed ascaridoids had originated in terrestrial hosts during the Early Carboniferous—
close to the period when tetrapods began diversifying into various terrestrial habitats
(Dunne et al. 2018)—it can be expected that most extinct vertebrate groups were
host to ascaridoid nematodes, and their fossilised eggs may be present as inclusions
in coprolites originating from many different tetrapods.
Another group of parasitic nematodes commonly found in the gastrointestinal
tract of extant vertebrates are the Oxyurida—also known as “pinworms”. Pinworms
are found in the hindgut of many different invertebrate and vertebrate animals and
are usually associated with hosts that have hindgut bacterial fermentation because
of their bacterivorous diet (Adamson 1994). Fossils of pinworm eggs have been
found in the coprolites attributed to therapsid cynodonts from the Middle Triassic
(Hugot et al. 2014; Francischini et al. 2018), and given the taxonomic breadth of
extant pinworm hosts, it can be expected that pinworm eggs may be present in coprolites of a wide range of terrestrial vertebrates. Various aspects of these pinworm
biology also means they can provide valuable insight on the ecology and biology of
their host. Francischini et al. (2018) pointed out that pinworm egg inclusions were
found in “cylindrical” type coprolites, which were traditionally considered to be
produced by carnivorous or omnivorous therapsids. However, the presences of the
pinworm egg fossils overturn such an interpretation, as their presence implies that
the originator of those coprolites included substantial amount of plant matter in
their diet (Francischini et al. 2018). Also mentioned above, pinworms are restricted
to infecting animals that use their hindgut as a site for bacterial fermentation, furthermore their eggs have limited dispersal ability and mostly rely upon social
grooming or local contamination for transmission (Adamson 1994). Therefore, the
very presence of fossilised pinworm eggs in coprolites can provide at least three key
insights on the diet (mostly plant matter), physiology (hindgut fermentation) and
behaviour (living in social groups or colonies) of the host taxa which may not be
evident from examining the fossil of the host alone.
While all the known whole body fossils of animal-infecting parasitic nematodes
have so far been from amber fossils of insect-infecting taxa (Poinar 2015), those
fossils may nevertheless provide insight into nematodes that do infected fossil vertebrates. Some vertebrate-infecting nematodes with complex life-cycles are
T. L. F. Leung
widely recognised and studied because of their medical and economic importance
(Anderson 2000). Much like cestodes and trematodes discussed above, the adult
stage living in the gastrointestinal tract is very unlikely to become fossilised.
However the environmentally-resistant eggs produced by the adult parasite can be
preserved as inclusions in coprolites (e.g. Da Silva et al. 2014), survive treatment
with strong acids and/or bases (e.g. Brinkkemper and van Haaster 2012; Dufour and
Le Bailly 2013), and serve as a reliable indicator of the parasite’s presence. Fossilised
ascarid nematode eggs have so far been found in archosaur coprolites from the Early
Cretaceous to Late Cretaceous (Poinar and Boucot 2006; Cardia et al. 2018, 2019a)
and cynodont coprolites from Middle Triassic (Da Silva et al. 2014). Given the
ubiquity of parasitic nematodes in extant vertebrate hosts (Anderson 2000), the
presence of fossilised nematode eggs in the coprolites of phylogenetically distant
groups as archosaurs and synapsids, and the result by Li et al. (2018) which proposed ascaridoids had originated in terrestrial hosts during the Early Carboniferous—
close to the period when tetrapods began diversifying into various terrestrial habitats
(Dunne et al. 2018)—it can be expected that most extinct vertebrate groups were
host to ascaridoid nematodes, and their fossilised eggs may be present as inclusions
in coprolites originating from many different tetrapods.
Another group of parasitic nematodes commonly found in the gastrointestinal
tract of extant vertebrates are the Oxyurida—also known as “pinworms”. Pinworms
are found in the hindgut of many different invertebrate and vertebrate animals and
are usually associated with hosts that have hindgut bacterial fermentation because
of their bacterivorous diet (Adamson 1994). Fossils of pinworm eggs have been
found in the coprolites attributed to therapsid cynodonts from the Middle Triassic
(Hugot et al. 2014; Francischini et al. 2018), and given the taxonomic breadth of
extant pinworm hosts, it can be expected that pinworm eggs may be present in coprolites of a wide range of terrestrial vertebrates. Various aspects of these pinworm
biology also means they can provide valuable insight on the ecology and biology of
their host. Francischini et al. (2018) pointed out that pinworm egg inclusions were
found in “cylindrical” type coprolites, which were traditionally considered to be
produced by carnivorous or omnivorous therapsids. However, the presences of the
pinworm egg fossils overturn such an interpretation, as their presence implies that
the originator of those coprolites included substantial amount of plant matter in
their diet (Francischini et al. 2018). Also mentioned above, pinworms are restricted
to infecting animals that use their hindgut as a site for bacterial fermentation, furthermore their eggs have limited dispersal ability and mostly rely upon social
grooming or local contamination for transmission (Adamson 1994). Therefore, the
very presence of fossilised pinworm eggs in coprolites can provide at least three key
insights on the diet (mostly plant matter), physiology (hindgut fermentation) and
behaviour (living in social groups or colonies) of the host taxa which may not be
evident from examining the fossil of the host alone.
While all the known whole body fossils of animal-infecting parasitic nematodes
have so far been from amber fossils of insect-infecting taxa (Poinar 2015), those
fossils may nevertheless provide insight into nematodes that do infected fossil vertebrates. Some vertebrate-infecting nematodes with complex life-cycles are
T. L. F. Leung