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Foreword
The ‘fossil record’ and ‘parasites’ may seem strange bedfellows. Parasitism tends to
be overlooked by palaeontologists even though it is one of the most successful ecological strategies and an important feature of the evolutionary history and palaeoecology of many groups. One measure of the importance of parasites is their
diversity—they may account for more than 50% of all living species. Nonetheless,
parasites are largely invisible today even if the same cannot be said of their effects.
They are generally small and soft bodied, and certainly not strong candidates for
fossilisation. However, their evolutionary history is intriguing and raises issues such
as when parasitism originated and in which groups, how parasites coevolved with
their hosts, how they impacted the ecology of ancient communities, and how interactions between parasite and host changed over time. The fossil record provides the
only direct evidence of parasitism in the past, and it can contribute essential data to
answering such questions.
Parasites, of their very nature, require exceptional conditions for fossilisation,
and Konservat-Lagerstätten (conservation deposits) have proved important sources
in recent decades. Malarial parasites and trypanosomatids, for example, have been
discovered in the guts of biting insects in amber more than 100 million years old
from the Cretaceous of Burma. Eggs and cysts of intestinal parasites are present in
coprolites of late Palaeozoic elasmobranchs and Cretaceous dinosaurs, from aquatic
and terrestrial settings, respectively. Giant flea-like insects have been found in
Mesozoic lake sediments in Inner Mongolia and Liaoning Province in China. New
examples of parasitism also continue to come to light in host fossils based on the
galls, swellings and other malformations triggered by the parasite—but in this case
the perpetrator is often difficult to identify and other factors may be at work.
Molecular data provide a major new line of evidence on the evolution of parasites, even though the nature of parasite genomes can present particular challenges.
Gene sequences have allowed the phylogeny of different groups of parasites to be
analysed where morphological data are limited. The phylogeny of the free-living
relatives may also be informative. Phylogenies of parasites and of their host species,
together with dates based on fossil occurrences, can yield estimates of divergence
times (i.e. when they originated) based on molecular clocks. Such phylogenies
Foreword
The ‘fossil record’ and ‘parasites’ may seem strange bedfellows. Parasitism tends to
be overlooked by palaeontologists even though it is one of the most successful ecological strategies and an important feature of the evolutionary history and palaeoecology of many groups. One measure of the importance of parasites is their
diversity—they may account for more than 50% of all living species. Nonetheless,
parasites are largely invisible today even if the same cannot be said of their effects.
They are generally small and soft bodied, and certainly not strong candidates for
fossilisation. However, their evolutionary history is intriguing and raises issues such
as when parasitism originated and in which groups, how parasites coevolved with
their hosts, how they impacted the ecology of ancient communities, and how interactions between parasite and host changed over time. The fossil record provides the
only direct evidence of parasitism in the past, and it can contribute essential data to
answering such questions.
Parasites, of their very nature, require exceptional conditions for fossilisation,
and Konservat-Lagerstätten (conservation deposits) have proved important sources
in recent decades. Malarial parasites and trypanosomatids, for example, have been
discovered in the guts of biting insects in amber more than 100 million years old
from the Cretaceous of Burma. Eggs and cysts of intestinal parasites are present in
coprolites of late Palaeozoic elasmobranchs and Cretaceous dinosaurs, from aquatic
and terrestrial settings, respectively. Giant flea-like insects have been found in
Mesozoic lake sediments in Inner Mongolia and Liaoning Province in China. New
examples of parasitism also continue to come to light in host fossils based on the
galls, swellings and other malformations triggered by the parasite—but in this case
the perpetrator is often difficult to identify and other factors may be at work.
Molecular data provide a major new line of evidence on the evolution of parasites, even though the nature of parasite genomes can present particular challenges.
Gene sequences have allowed the phylogeny of different groups of parasites to be
analysed where morphological data are limited. The phylogeny of the free-living
relatives may also be informative. Phylogenies of parasites and of their host species,
together with dates based on fossil occurrences, can yield estimates of divergence
times (i.e. when they originated) based on molecular clocks. Such phylogenies