Goodbye, Osteoglossomorpha: It’s polyphyletic in the LRT

Hilton and Lavouvé 2018
review the suspiciously varied traditional ‘clade’ Osteoglossomorpha.

From the abstract:
“The bony-tongue fishes, Osteoglossomorpha, have been the focus of a great deal of morphological, systematic, and evolutionary study, due in part to their basal position among extant teleostean fishes.”

That’s only partly true. Turns out, only some members of this traditional ‘clade’ are basal telostean taxa in the LRT. And none are the most basal. Ironically, the most derived one, Hiodon (Figs. 1, 2), looks more like a traditional fish than any of the more basal taxa.

Hilton and Lavouvé say traditional Osteoglossomorpha members include:

1. Mooneyes (= Hiodon – Hiodontidae)
2. Knifefish (= featherbacks like Notopterus – Notopteridae)
3. Abus (= African knifefish = Gymnarchus – Gymnarchidae)
4. Elephantfishes (= Mormyrus – Mormyridae)
5a. Arowanas (= Osteoglossum – Osteoglossidae)
5b. Pirarucu (= Arapaima – Osteoglossidae)
6. African butterflyfish (= Pantodon – Pantodontidae)

The traditional smaller clade, Osteoglossiformes
includes all the above sans Hiodon. The presence of teeth on the parasphenoid and tongue bones (hyoids) traditionally unite these taxa. The forward part of the gastrointestinal tract passes to the left of the esophagus and stomach distinct from all other fish. Unfortunately these traits (and apparently others not listed) are not enough to attract them together in the LRT, and apart from their LRT sisters and cousins. The LRT tests only skeletal and other hard parts that typically fossilize, like ganoid scales. The LRT tells us the presence of teeth on the parasphenoid and tongue bones are convergent. That’s why it is so important to run the scores for 238 traits and not “Pull a Larry Martin” by relying on a few to a few dozen traits.

Remember, clades are based on a last common ancestor basis,
not the possession of a short list of possibly convergent traits. (e.g. Amia, the bowfin, also has parasphenoid teeth, but is not considered a traditional osteoglossomorph).

From the abstract:
“This morphologically heterogeneous group also has a long and diverse fossil
record, including taxa from all continents and both freshwater and marine deposits. In this paper we review the state of knowledge for osteoglossomorph fishes.”

As usual, whenever you see the phrase, ‘morphologically heterogeneous’
it’s a fair bet the clade is not monophyletic. Tested in the large reptile tree (LRT, 1933+ taxa; subset Fig. 1) only two sets nest with each other (Pantodon nests with Arapaima and Mormyrops nests with Gymnarchus). The rest do not. The traditional ‘Osteoglossomorpha’ falls apart when more taxa are added. So does the traditional Osteoglossiformes and the traditional Osteoglossidae (Arapaima does not nest with Osteoglossum in the LRT).

Hilton and Lavouvé 2018 report
“Osteoglossomorpha – the bony-tongue fishes – have been the focus of a great deal of morphological, systematic, and evolutionary study, due in part to their basal position among
extant teleostean fishes.”

This is not recovered by the LRT (Fig. 1). Members of the traditional Osteoglossomorpha nest in a scattershot pattern (= not together) when more taxa are added.

Hilton and Lavouvé 2018 report
“In their pivotal classification, Greenwood et al. (1966) formally established the modern conceptualization of crown-group Osteoglossomorpha, although all families had been more or less associated with one another by ichthyologists for some time. “

Greenwood et al. wrote:
“Results indicate the necessity of a major regrouping of teleostean orders, and this also is attempted. Traditionally, studies such as ours have been based on morphology, especially the
skeleton, which is the only complete organ system available for detailed comparison with
fossils.”

Exactly. That’s why the LRT tests skeletal elements.

“However, with the variety of both primitive and advanced teleosts living today, we are most emphatically of the opinion that approaches other than morphological ones would be exceedingly fruitful in the investigation of teleostean interrelationships.”

Let’s not go with opinions. The software that recovered the LRT does not have an opinion.

For the Osteoglossomorpha,
Greenwood et al. listed 9 traits either always or often seen in member taxa. They were Pulling a Larry Martin. But in 1966, what else could one do? Back then you could not build a matrix then run the data through analysis. Science marches on.

Greenwood et al. did not employ fossil taxa.
Hilton and Lavoué did emply fossil taxa, but those taxa were cherry-picked. What you need is a wide gamut of taxa so each one will find its closest sisters, the ones sharing the most traits.

Let’s strive to minimize taxon exclusion. It’s the number one problem in paleontology. Whoever thought pterosaurs would nest with tanystropheids? Or that Vancleavea would nest with thalattosaurs? Or that bats and pangolins would be closely related? Or that toothed and baleen whales would have separate ancestries in tenrecs and desmostylians? Take the cherry-picking, textbooks and opinions out of your analyses and just keep adding taxa.

References
Greenwood PH, Rosen DE, Weitzman SH and Myers GS 1966. Phyletic studies of teleostean fishes, with a provisional classification of living forms. Bull Am Mus Nat Hist. 1966; 131(4):339-456.
Hilton EJ and Lavoué S 2018. A review of the systematic biology of fossil and living bony-tongue fishes, Osteoglossomorpha (Actinopterygii: Teleostei). Neotropical Ichthyology, 16(3): e180031, 2018 DOI: 10.1590/1982-0224-20180031

wiki/Osteoglossomorpha
wiki/Osteoglossiformes