283
de León 2018). Consequently, one should assume for the Last Common Ancestor
(LCA) of diverse primate taxa that they were insectivorous to at least some extent.
In the present context though, it is of particular interest that the LCAs of the crowngroup taxa on the lineage to humans (Hominoidea, Hominidae, Homininae,
Pan + Homo, and Hominini) should also have been insectivorous to some extent (for
other character states of these LCAs, see Herlyn 2016). In expansion of this argument, insects are considered part of the diet of the Hominini genera Ardipithecus
and Australopithecus. In the case of early members of Homo and prehistoric anatomical modern humans, there is even direct evidence for insectivory—and last but
not least, in some human societies, insects continue to be part of the diet (Reinhard
and Bryant 1992; Sayers and Lovejoy 2014; van Huis 2017). To put it the other way:
There appears to be no principal reason why Ardipithecus ramidus, Australopithecus
afarensis, Homo erectus etc. should not have been infected with (archi)acanthocephalans at least sporadically. Now only their eggs have to be discovered in coprolites of the corresponding taxa (compare Sistiaga et al. 2014; Chin 2021).
8.3 Solid-Parts and Their Preservation Potential
8.3.1 Acanthocephalan Propagules: Eggs in Space and Time
In acanthocephalans, the egg-producing units are not ovaries in the traditional sense.
Instead, numerous so-called ovarian balls of unclear ontogenetic origin freely float
in the fluid-filled metasoma, and release immature eggs into the body cavity wherein
they mature (Figs. 8.3a and 8.4a; e.g., Dunagan and Miller 1991). The fluid remains
in motion through movements of the body so that the eggs sporadically pass by an
elaborated egg sorting apparatus. This so-called uterine bell is situated in the hind
trunk and allows only mature eggs to enter the terminal genital tract from where the
eggs are discharged through the genital pore into the alimentary tract or cloaca of
the definitive host (Fig. 8.4a; Herlyn and Röhrig 2003 and references therein). The
eggs are eventually released with the excrements into the environment (Fig. 8.1), a
process that can take place at high rates upon mating. Gravid females of the larger
species might even produce 82,000 eggs per day on average, and this for a patent
period of 10 months (see Dunagan and Miller 1991). Consequently, acanthocephalan eggs should be quite common in the droppings of infected gnathostomes—and
the hosts might not only have been taxa with extant members. As acanthocephalan
life cycles can be extended by post-cyclic transmission in at least some extant species (Kennedy 1999, 2006), acanthocephalan eggs may also be contained in fossilized coprolites of higher-level predators belonging to Ichthyosauria and Pterosauria
(both Sauropsida), to name just a few (compare Leung 2021). In addition, acanthocephalan eggs may be preserved in petrified sediments under favorable conditions.
The contour of acanthocephalan eggs enables a rough taxonomic diagnosis.
Thus, eggs of archiacanthocephalans and polyacanthocephalans usually have a
rounded-oval appearance. The same applies to at least some eoacanthocephalans
8 Thorny-Headed Worms (Acanthocephala): Jaw-Less Members of Jaw-Bearing…
de León 2018). Consequently, one should assume for the Last Common Ancestor
(LCA) of diverse primate taxa that they were insectivorous to at least some extent.
In the present context though, it is of particular interest that the LCAs of the crowngroup taxa on the lineage to humans (Hominoidea, Hominidae, Homininae,
Pan + Homo, and Hominini) should also have been insectivorous to some extent (for
other character states of these LCAs, see Herlyn 2016). In expansion of this argument, insects are considered part of the diet of the Hominini genera Ardipithecus
and Australopithecus. In the case of early members of Homo and prehistoric anatomical modern humans, there is even direct evidence for insectivory—and last but
not least, in some human societies, insects continue to be part of the diet (Reinhard
and Bryant 1992; Sayers and Lovejoy 2014; van Huis 2017). To put it the other way:
There appears to be no principal reason why Ardipithecus ramidus, Australopithecus
afarensis, Homo erectus etc. should not have been infected with (archi)acanthocephalans at least sporadically. Now only their eggs have to be discovered in coprolites of the corresponding taxa (compare Sistiaga et al. 2014; Chin 2021).
8.3 Solid-Parts and Their Preservation Potential
8.3.1 Acanthocephalan Propagules: Eggs in Space and Time
In acanthocephalans, the egg-producing units are not ovaries in the traditional sense.
Instead, numerous so-called ovarian balls of unclear ontogenetic origin freely float
in the fluid-filled metasoma, and release immature eggs into the body cavity wherein
they mature (Figs. 8.3a and 8.4a; e.g., Dunagan and Miller 1991). The fluid remains
in motion through movements of the body so that the eggs sporadically pass by an
elaborated egg sorting apparatus. This so-called uterine bell is situated in the hind
trunk and allows only mature eggs to enter the terminal genital tract from where the
eggs are discharged through the genital pore into the alimentary tract or cloaca of
the definitive host (Fig. 8.4a; Herlyn and Röhrig 2003 and references therein). The
eggs are eventually released with the excrements into the environment (Fig. 8.1), a
process that can take place at high rates upon mating. Gravid females of the larger
species might even produce 82,000 eggs per day on average, and this for a patent
period of 10 months (see Dunagan and Miller 1991). Consequently, acanthocephalan eggs should be quite common in the droppings of infected gnathostomes—and
the hosts might not only have been taxa with extant members. As acanthocephalan
life cycles can be extended by post-cyclic transmission in at least some extant species (Kennedy 1999, 2006), acanthocephalan eggs may also be contained in fossilized coprolites of higher-level predators belonging to Ichthyosauria and Pterosauria
(both Sauropsida), to name just a few (compare Leung 2021). In addition, acanthocephalan eggs may be preserved in petrified sediments under favorable conditions.
The contour of acanthocephalan eggs enables a rough taxonomic diagnosis.
Thus, eggs of archiacanthocephalans and polyacanthocephalans usually have a
rounded-oval appearance. The same applies to at least some eoacanthocephalans
8 Thorny-Headed Worms (Acanthocephala): Jaw-Less Members of Jaw-Bearing…