239
for some possible calibrations, largely following the guidelines by Parham et al.
(2012). However, most helminth fossils have not been included in formal phylogenetic analyses. We therefore list the characters which have been used, or could be
used, to justify their inclusion within a particular clade.
7.4.1 Fossil Record of Parasitic Annelids
The fossil record of Annelida was recently reviewed by Parry et al. (2014); Parry
et al. (2019b). The fossil record of free-living annelids can be traced back to the
early Cambrian at least (Morris and Peel 2008; Han et al. 2019), but are typically
resolved as members of the annelid stem lineage. Previously, the oldest fossils
assigned to the annelid crown group were scolecodonts that are at least Tremadocian
in age (Hints and Nõlvak 2006), but a newly discovered magelonid extends the
record of crown annelids into the early Cambrian (Chen et al. 2020).
Node. Total group Annelida
Fossil taxon. Ipoliknus avitus, Adelochaeta sinensis and at least two unnamed species
Fossil evidence. 6 carbonaceous compression fossils (Han et al. 2019).
Phylogenetic assignment. Both Ipoliknus and Adelochaeta possess biramous parapodia with capillary chaetae, constraining them to the annelid total group.
Ipoliknus avitus is resolved as the deepest lineage in the annelid stem group in
analysis only considering extinct taxa (Han et al. 2019) as well as a more comprehensive analysis of most annelid lineages and their close relatives (Parry
et al. 2019a).
Min age. 515.5 Ma. The fossils are derived from the early Cambrian Chengjiang
Biota from the Maotianshan Shales of southwest China. The maximum age of
the Chengjiang Biota has been constrained to 518.03 ± 0.69/0.71 using CA-IDTIMS U-Pb geochronology, whereas the mimimum age is constrained by correlation with the Antatlasia gutta-pluviae Zone to an age of 517.0 ± 1.5 (Yang et al.
2018). This minimum age is slightly older than minimum age based on the
Nevadella trilobite zone for the Sirius Passet Lagerstätte (Harper et al. 2019)
which has previously been considered to yield the oldest annelids (Morris and
Peel 2008).
Node. Crown group Annelida
Fossil taxon. Dannychaeta tucolus
Fossil evidence. 21 carbonaceous compression fossils (Chen et al. 2020)
Phylogenetic assignment. Dannychaeta tucolus shares morphological features
with extant Magelonidae, including a flattened prostomium, ventrolateral palps
that attach near the mouth opening and a sessile, tubicolous lifestyle (Chen et al.
2020). Phylogenetic analysis recovers this genus as a member of stem group
Magelonidae, and it is therefore a member of crown Annelida.
7 Fossil Constraints on the Timescale of Parasitic Helminth Evolution
for some possible calibrations, largely following the guidelines by Parham et al.
(2012). However, most helminth fossils have not been included in formal phylogenetic analyses. We therefore list the characters which have been used, or could be
used, to justify their inclusion within a particular clade.
7.4.1 Fossil Record of Parasitic Annelids
The fossil record of Annelida was recently reviewed by Parry et al. (2014); Parry
et al. (2019b). The fossil record of free-living annelids can be traced back to the
early Cambrian at least (Morris and Peel 2008; Han et al. 2019), but are typically
resolved as members of the annelid stem lineage. Previously, the oldest fossils
assigned to the annelid crown group were scolecodonts that are at least Tremadocian
in age (Hints and Nõlvak 2006), but a newly discovered magelonid extends the
record of crown annelids into the early Cambrian (Chen et al. 2020).
Node. Total group Annelida
Fossil taxon. Ipoliknus avitus, Adelochaeta sinensis and at least two unnamed species
Fossil evidence. 6 carbonaceous compression fossils (Han et al. 2019).
Phylogenetic assignment. Both Ipoliknus and Adelochaeta possess biramous parapodia with capillary chaetae, constraining them to the annelid total group.
Ipoliknus avitus is resolved as the deepest lineage in the annelid stem group in
analysis only considering extinct taxa (Han et al. 2019) as well as a more comprehensive analysis of most annelid lineages and their close relatives (Parry
et al. 2019a).
Min age. 515.5 Ma. The fossils are derived from the early Cambrian Chengjiang
Biota from the Maotianshan Shales of southwest China. The maximum age of
the Chengjiang Biota has been constrained to 518.03 ± 0.69/0.71 using CA-IDTIMS U-Pb geochronology, whereas the mimimum age is constrained by correlation with the Antatlasia gutta-pluviae Zone to an age of 517.0 ± 1.5 (Yang et al.
2018). This minimum age is slightly older than minimum age based on the
Nevadella trilobite zone for the Sirius Passet Lagerstätte (Harper et al. 2019)
which has previously been considered to yield the oldest annelids (Morris and
Peel 2008).
Node. Crown group Annelida
Fossil taxon. Dannychaeta tucolus
Fossil evidence. 21 carbonaceous compression fossils (Chen et al. 2020)
Phylogenetic assignment. Dannychaeta tucolus shares morphological features
with extant Magelonidae, including a flattened prostomium, ventrolateral palps
that attach near the mouth opening and a sessile, tubicolous lifestyle (Chen et al.
2020). Phylogenetic analysis recovers this genus as a member of stem group
Magelonidae, and it is therefore a member of crown Annelida.
7 Fossil Constraints on the Timescale of Parasitic Helminth Evolution