249
2014). In the meantime, various new discoveries of parasitic nematodes have been
made in Triassic to Cretaceous coprolites (Da Silva et al. 2014; Hugot et al. 2014;
Francischini et al. 2018; Cardia et al. 2018) and in Miocene coprolites (DentzienDias et al. 2018).
We herein map fossil finds in the phylogeny (Fig. 7.5) to demonstrate that several
constraints on nematode evolution may be derived from the fossil record.
Based on trace fossils suggestive of free-living nematodes, and therefore also
their sister-group Nematomorpha, Nematoida must have been around at least since
the Late Ordovician (Knaust and Desrochers 2019; Balinski et al. 2013). Older sinusoidal trace fossils have been reported from the Ordovician (Balinski et al. 2013)
and even the Cambrian-Ediacaran (e.g., Parry et al. 2017). Such sinusoidal trace
fossils are caused by the specific movement of vermiform animals (possibly nematodes) in waves as their body wall comprises only longitudinal muscles but no ring
muscles—an apomorphy for Nematoida (Maas 2013). Confident assignment to
Nematoda remains difficult because distantly related forms with similar behavior
could potentially also have created such burrows (Collins et al. 2000; Seilacher
2007; Metz 1987). One can be more confident when such traces are associated with
worm-like body fossil remains (Knaust 2010; Knaust and Desrochers 2019), but
even then it is quite difficult to identify the particular lineages of nematodes that
created these traces. Many nematodes lack rich distinguishing external features,
which makes them even more difficult to identify in a fossil state, particularly when
poorly preserved (Schram 1973; Muir et al. 2014). This is ably illustrated by putative carboniferous nematode remains (Størmer 1963) that have now been reidentified as scorpion spines (Poinar 2011). Well-preserved compression or
impression fossils have been attributed to free-living nematodes since the
Carboniferous. Schram (1973, 1979) described various specimens of a putative
nematode Nevamermis mackeei, considering it to be the remains of a free-living
form with affinities to modern species of Chromadorida which have comparable
cuticular ornamentation and structures possibly identifiable as papillae or cirri (an
opinion shared by Poinar 2011). However, these characters are plesiomorphic for
Nematoda and are not necessarily helpful for their taxonomic assignment (Maas
2013). According to Poinar (2014), no other fossil nematodes could so far be attributed to Chromadorida.
Node. Nematoida
Fossil evidence. Trace fossils associated with worm-like fossils (Knaust and
Desrochers 2019)
Phylogenetic justification. The sinusoidal trace associated with worm-like fossils
suggest a nematode or at least a nematoid caused these traces
Minimum age. The rocks of the Vaureal Formation have been assigned to the Late
Katian (Knaust and Desrochers 2019), which yield a minimum age of 445.2 Ma
according to GTS 2016 (Ogg et al. 2016).
Additional free-living nematode remains include the Jurassic Eophasma jurasicum (Arduini et al. 1983), the Early Cretaceous Captivonema cretacea (Manum
7 Fossil Constraints on the Timescale of Parasitic Helminth Evolution
2014). In the meantime, various new discoveries of parasitic nematodes have been
made in Triassic to Cretaceous coprolites (Da Silva et al. 2014; Hugot et al. 2014;
Francischini et al. 2018; Cardia et al. 2018) and in Miocene coprolites (DentzienDias et al. 2018).
We herein map fossil finds in the phylogeny (Fig. 7.5) to demonstrate that several
constraints on nematode evolution may be derived from the fossil record.
Based on trace fossils suggestive of free-living nematodes, and therefore also
their sister-group Nematomorpha, Nematoida must have been around at least since
the Late Ordovician (Knaust and Desrochers 2019; Balinski et al. 2013). Older sinusoidal trace fossils have been reported from the Ordovician (Balinski et al. 2013)
and even the Cambrian-Ediacaran (e.g., Parry et al. 2017). Such sinusoidal trace
fossils are caused by the specific movement of vermiform animals (possibly nematodes) in waves as their body wall comprises only longitudinal muscles but no ring
muscles—an apomorphy for Nematoida (Maas 2013). Confident assignment to
Nematoda remains difficult because distantly related forms with similar behavior
could potentially also have created such burrows (Collins et al. 2000; Seilacher
2007; Metz 1987). One can be more confident when such traces are associated with
worm-like body fossil remains (Knaust 2010; Knaust and Desrochers 2019), but
even then it is quite difficult to identify the particular lineages of nematodes that
created these traces. Many nematodes lack rich distinguishing external features,
which makes them even more difficult to identify in a fossil state, particularly when
poorly preserved (Schram 1973; Muir et al. 2014). This is ably illustrated by putative carboniferous nematode remains (Størmer 1963) that have now been reidentified as scorpion spines (Poinar 2011). Well-preserved compression or
impression fossils have been attributed to free-living nematodes since the
Carboniferous. Schram (1973, 1979) described various specimens of a putative
nematode Nevamermis mackeei, considering it to be the remains of a free-living
form with affinities to modern species of Chromadorida which have comparable
cuticular ornamentation and structures possibly identifiable as papillae or cirri (an
opinion shared by Poinar 2011). However, these characters are plesiomorphic for
Nematoda and are not necessarily helpful for their taxonomic assignment (Maas
2013). According to Poinar (2014), no other fossil nematodes could so far be attributed to Chromadorida.
Node. Nematoida
Fossil evidence. Trace fossils associated with worm-like fossils (Knaust and
Desrochers 2019)
Phylogenetic justification. The sinusoidal trace associated with worm-like fossils
suggest a nematode or at least a nematoid caused these traces
Minimum age. The rocks of the Vaureal Formation have been assigned to the Late
Katian (Knaust and Desrochers 2019), which yield a minimum age of 445.2 Ma
according to GTS 2016 (Ogg et al. 2016).
Additional free-living nematode remains include the Jurassic Eophasma jurasicum (Arduini et al. 1983), the Early Cretaceous Captivonema cretacea (Manum
7 Fossil Constraints on the Timescale of Parasitic Helminth Evolution