‘The most radical revision of early actinopterygian evolution since the late 1980s’

Coates 2017, describing Giles et al. 2017 in Nature,
reported, “This is the most radical revision of early actinopterygian evolution since the late 1980s: it offers new data, evolutionary trees and timescales, and provides newly populated stem lineages where none existed before for polypterids and the Actinopterygii as a whole.”

Giles et al. 2017 report,
“Polypterids (bichirs and ropefish) represent the earliest-diverging lineage of living actinopterygians…. Here we show that scanilepiforms, a widely distributed radiation from the Triassic period (around 252–201 million years ago), are stem polypterids

One of the scanilepiforms (= stem polypterids) key to the Giles et al. cladogram is Middle Triassic Fukangichthys (Fig.1). Giles et al. hypothesize it shares more traits with extant Polypterus (Fig. 4) than to Early Triassic Pteronisculus (Fig. 2).

Figure 1. Middle Triassic Fukangicthys from Su 1978, Xu et al. 2014; Giles et al. 2018) is not a basal fish taxon in the LRT.

Figure 1. Middle Triassic Fukangicthys from Su 1978, Xu et al. 2014; Giles et al. 2018) is not a basal fish taxon in the LRT.

Radical is one thing… but is the Giles et al. cladogram correct?
With more outgroup taxa the large reptile tree (LRT, 1673+ taxa) nests derived polypterids with derived lungfish. More primitive scanilepiforms, like Fukangichthys, nest with more primitive Pteronisculus and other Triassic fish. Both have tall narrow oval morphologies distinct from the low wide shape of Polypterus and lungfish. That’s just for starters.

Figure 2. Pteronisculus nests with Fukangichthys in the LRT apart from Polypterus.

Figure 2. Pteronisculus nests with Fukangichthys in the LRT apart from Polypterus.

Another error in the Giles et al. 2017 study
was subjectively and arbitrarily choosing outgroup taxa (the placoderms Dicksonosteus and Entelognathus) rather than expanding the taxon list and letting software choose valid bony fish outgroups. That’s what the LRT does (Fig. 3) going back to Cambrian chordates.

Figure x. Updated subset of the LRT, focusing on basal vertebrates = fish.

Figure 3. Updated subset of the LRT, focusing on basal vertebrates = fish.

Giles et al. 2017
are unaware of the bask dichotomy splitting bony fish, and that placoderms and spiny sharks nest within one of those clades. Polypterus and other lungfish nest close to tetrapodomorphs.

Figure 1. The Nile bichir (Polypterus), skull, skeleton and bones colorized for ease of comparison. Compare to the placoderm, Entelognathus, (Fig. 2) and the stem tetrapod Tinirau (Fig. 3).

Figure 4. The Nile bichir (Polypterus), skull, skeleton and bones colorized for ease of comparison.

For their basalmost bony fish,
Giles et al. nest Dialipina (Early Devonian). By contrast the LRT nests Dialpina in a much more derived node, with the extant coelacanth, Latimeria, which it greatly resembles. We’ll look at that nesting tomorrow, but the links above will give the anxious reader a sneak preview.

Contra Coates 2017,
the LRT has become the most radical revision of early actinopterygian evolution since the late 1980s. If you come across a more radical one, or one that includes more outgroup taxa complete with reconstructions (to check scoring accuracy), let me know and I will promote that citation.


References
Coates M. 2017. 
Plenty of fish in the tree. Nature 549:167–169.
Giles S, Xu G-H, Near TJ and Friedman 2017.
Early members of ‘living fossil’ lineage imply later origin of modern ray-finned fishes. Nature 549:265–268.
Xu G-H and Gao K-Q 2011. A new scanilepiformfrom the Lower Triassic of northern Gansu Province, China, and phylogenetic relationship of non-teleostean Actinopterygii. Zoological Journal of the Linnean Society 161:595–612.

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