247
Most phylogenetic analyses resolve a sister relationship between Trematoda and
Cestoda (Park et al. 2007; Lockyer et al. 2003; Egger et al. 2015), both groups with
complex life cycles, although some recent phylogenomic analyses suggest otherwise (Laumer and Giribet 2014; Laumer et al. 2015b). Cestodes can be confidently
traced back to the Permian (Dentzien-Dias et al. 2013) with fossil remains yielding
cestode-like eggs based on morphology and size, the presence of a developing larva
with familiar cestode-like hooks and the arrangement of eggs in proglottids. Older
finds of eggs within shark coprolites have been attributed to cestodes (Zangerl and
Case 1976), but this identification is less convincing and in need of reinvestigation
(De Baets et al. 2015). Either way, these finds represent the oldest convincing evidence for endoparasitic helminths in the fossil record (but see Upeniece 2011 for
putative earlier finds) and also overlap with divergence time estimates for trypanorhynch tapeworms (Olson et al. 2010).
Node. Eucestoda
Fossil evidence. Eggs in Permian coprolites (Dentzien-Dias et al. 2013)
Phylogenetic justification. No formal phylogenetic analysis was performed.
However, the size and morphology of the eggs (ovoid, smooth shelled, with operculum, among others), their interpretation of hooks within one of them as well as
their association in protoglottidia speak for the assignment to Eucestoda.
Host. Shark based on spiral coprolite morphology (reflecting the spiral valve morphology of the shark intestine).
Minimum age. 259.8 Ma. The coprolite containing the fossil evidence derives from
the upper member of the Rio do Rasto Formation. The vertebrate fauna suggests
a Guadalupian (Late Wordian—Capitanian) age (Cisneros et al. 2012; DentzienDias et al. 2012; Dias-Da-Silva 2012) which yields a minimum age of 259.8 Ma
defined by the Guadalupian-Lopingian boundary (Ogg et al. 2016).
Although eggs of some lineages of Trematoda such as Dicrocoeliidae (Dufour
and Le Bailly 2013) are considered quite resistant, trematodes have so far only been
found in a Cretaceous coprolite (Poinar and Boucot 2006) and Middle Pleistocene
to younger coprolites (e.g., Jouy-Avantin et al. 1999). Most evidence in the fossil
record derives from characteristic pathologies these helminths cause in their hosts
(De Baets et al. 2015; Huntley and De Baets 2015; Huntley et al. 2021). Research
has focused particularly on characteristic pits and igloo-shaped concretions caused
today by gymnophallid trematodes in their bivalve hosts (Ruiz and Lindberg 1989;
Ituarte et al. 2001, 2005; Huntley and De Baets 2015). These structures might allow
tracing back the origin of (gymnophallid) trematodes to the Eocene (Todd and
Harper 2011) and the Cretaceous (Rogers et al. 2018), respectively. However, other
trematodes or even distantly related taxa could potentially cause similar pathologies. Superficially similar igloo-shaped pathologies in bivalves (Liljedahl 1985)
have been observed as far back as the Silurian. The only fossil vertebrate pathology
attributed to a trematode was found in Burmese amber (Poinar et al. 2017). Remains
of a lizard trapped in resin contained a cyst which could be convincingly compared
to similar metacercarian cysts found in extant lizards. Due to the sister-group relationship between Cestoda and Trematoda, the first appearance of trematodes can be
7 Fossil Constraints on the Timescale of Parasitic Helminth Evolution
Most phylogenetic analyses resolve a sister relationship between Trematoda and
Cestoda (Park et al. 2007; Lockyer et al. 2003; Egger et al. 2015), both groups with
complex life cycles, although some recent phylogenomic analyses suggest otherwise (Laumer and Giribet 2014; Laumer et al. 2015b). Cestodes can be confidently
traced back to the Permian (Dentzien-Dias et al. 2013) with fossil remains yielding
cestode-like eggs based on morphology and size, the presence of a developing larva
with familiar cestode-like hooks and the arrangement of eggs in proglottids. Older
finds of eggs within shark coprolites have been attributed to cestodes (Zangerl and
Case 1976), but this identification is less convincing and in need of reinvestigation
(De Baets et al. 2015). Either way, these finds represent the oldest convincing evidence for endoparasitic helminths in the fossil record (but see Upeniece 2011 for
putative earlier finds) and also overlap with divergence time estimates for trypanorhynch tapeworms (Olson et al. 2010).
Node. Eucestoda
Fossil evidence. Eggs in Permian coprolites (Dentzien-Dias et al. 2013)
Phylogenetic justification. No formal phylogenetic analysis was performed.
However, the size and morphology of the eggs (ovoid, smooth shelled, with operculum, among others), their interpretation of hooks within one of them as well as
their association in protoglottidia speak for the assignment to Eucestoda.
Host. Shark based on spiral coprolite morphology (reflecting the spiral valve morphology of the shark intestine).
Minimum age. 259.8 Ma. The coprolite containing the fossil evidence derives from
the upper member of the Rio do Rasto Formation. The vertebrate fauna suggests
a Guadalupian (Late Wordian—Capitanian) age (Cisneros et al. 2012; DentzienDias et al. 2012; Dias-Da-Silva 2012) which yields a minimum age of 259.8 Ma
defined by the Guadalupian-Lopingian boundary (Ogg et al. 2016).
Although eggs of some lineages of Trematoda such as Dicrocoeliidae (Dufour
and Le Bailly 2013) are considered quite resistant, trematodes have so far only been
found in a Cretaceous coprolite (Poinar and Boucot 2006) and Middle Pleistocene
to younger coprolites (e.g., Jouy-Avantin et al. 1999). Most evidence in the fossil
record derives from characteristic pathologies these helminths cause in their hosts
(De Baets et al. 2015; Huntley and De Baets 2015; Huntley et al. 2021). Research
has focused particularly on characteristic pits and igloo-shaped concretions caused
today by gymnophallid trematodes in their bivalve hosts (Ruiz and Lindberg 1989;
Ituarte et al. 2001, 2005; Huntley and De Baets 2015). These structures might allow
tracing back the origin of (gymnophallid) trematodes to the Eocene (Todd and
Harper 2011) and the Cretaceous (Rogers et al. 2018), respectively. However, other
trematodes or even distantly related taxa could potentially cause similar pathologies. Superficially similar igloo-shaped pathologies in bivalves (Liljedahl 1985)
have been observed as far back as the Silurian. The only fossil vertebrate pathology
attributed to a trematode was found in Burmese amber (Poinar et al. 2017). Remains
of a lizard trapped in resin contained a cyst which could be convincingly compared
to similar metacercarian cysts found in extant lizards. Due to the sister-group relationship between Cestoda and Trematoda, the first appearance of trematodes can be
7 Fossil Constraints on the Timescale of Parasitic Helminth Evolution