Firsthand observation of Gigantura vs. phylogenetic bracketing in the LRT

Konstantinidis and Johnson 2016 report:
“The goal of this paper is to provide a detailed description of the osteology of adult giganturids to resolve the identification and homology of skeletal elements, particularly those of the upper jaw. Based on topological evidence, we conclude that the premaxilla is absent and that the major tooth-bearing bone in the ‘upper jaw’ is the palatine.”

Figure 1. Gigantura indica overall. Note the pectoral fins above the gill openings and lack of pectoral fins.

Figure 1. Gigantura indica overall. Note the pectoral fins above the gill openings and lack of pectoral fins.

By contrast,
phylogenetic bracketing in the large reptile tree (LRT, 1788+ taxa) indicates the traditional interpretation of a large, toothy premaxilla in Giganturus (Figs. 1,2; Brauer 1901Konstantinidis and Johnson 2016; 20 cm long) is correct. Related taxa in the LRT, like Chiasmodon (Fig. 4) and Calamopleurus (Fig. 5) have a similar large, toothy premaxilla and no trace of a large toothy palatine.

This argument
has been going on for several decades in the fish community and will likely not be settled here. Konstantinidis and Johnson 2016 go into great detail regarding the pros and cons of previous and (then) current arguments. For instance they report, “The second problem is more complex and relates to the fact that unbeknownst to Rosen, his ‘juvenile’ Trachinocephalus was in fact still in the larval stage. The placement and arrangement of the infraorbitals undergo major changes ontogentically in synodontids, and those of Rosen’s specimen had not yet transformed.” 

This might require phylogenetic analysis of larval, juvenile and adult specimens.

Or not. Some bones and larvae may have been misidentified.

Figure 2. Gigantura skull tracings from Konstantinidis and Johnson 2016. Colors added.

Figure 2. Gigantura skull tracings from Konstantinidis and Johnson 2016. Colors added.

Konstantinidis and Johnson 2016 report,
“The systematic position of Gigantura has been problematic, in large part because of its bizarre morphological specializations and extreme reduction of many skeletal elements, especially in the skull region.”

There is no extreme reduction, especially in the skull region,demonstrated in the LRT. Sister taxa and related taxa have similar skulls. A valid phylogenetic context is essential before making pronouncements and creating hypotheses. I suspect this issue may be at the base of their arguments.

Figure 3. Konstantinids and Johnson 2016 considered this specimen to be a Gigantura larva. This is a dubious observation.

Figure 3. Konstantinids and Johnson 2016 considered this specimen to be a Gigantura larva. This is a dubious observation. No Gigantura relatives have such tiny eyes set so far back on the skull, among many other traits.

Konstantinidis and Johnson 2016
made comparisons to Bathysaurus (Fig. 6, the deep-sea lizard fish, not related to lizard fish like Trachinocephalus). Bathysaurus has not been tested in the LRT yet, but it does not appear to be related to the clade that includes Gigantura and other fish with large orbits longer than the rostrum length. Rather, Bathysaurus appears to be related to the tripod fish, Bathypterois, which nests with anglers and other taxa unrelated to Gigantura in the LRT.

Note the similarity of the purported Gigantura larva (Fig. 3) to anglers. Maybe this is part of the problem. No cladogram was presented by Konstantinidis and Johnson 2016.

Figure 2. Chiasmodon from Gregory 1938, here colorized. Compared to the lizardfish, Trachinocephalus, in figure 3.

Figure 4. Chiasmodon from Gregory 1938, here colorized. Compared to the lizardfish, Trachinocephalus, in figure 3.

Figure 5. Calamopleurus (Cretaceous) an outgroup taxon to Chiasmodon + Gigantura.

Figure 5. Calamopleurus (Cretaceous) an outgroup taxon to Chiasmodon + Gigantura.

Figure 6. Bathysaurus ferox has not been tested in the LRT, but does not appear to be similar to members of the clade that include Gigantura.

Figure 6. Bathysaurus ferox has not been tested in the LRT, but does not appear to be similar to members of the clade that includes Gigantura.

Figure 1. Bathypterois, the deep sea tripod fish, shown with diagram of jaws and palate from Sulak 2006, then colored and matched to the in vivo specimen.

Figure 7. Bathypterois, the deep sea tripod fish, shown with diagram of jaws and palate from Sulak 2006, then colored and matched to the in vivo specimen.

The clade that includes Gigantura
is among the oldest and most primitive of all bony fish, not far from hybodontid sharks. Related clades include spiny sharks (Acanthodii). The Gigantura clade precedes the major split between the Amia clade of ray fin fish and the other unnamed clade that produced lobefins and placoderms along with several other ray fin fish.


References
Brauer A 1901. Über einige von der Valdivia-Expedition gesammelte Tiefseefische und ihre Augen. Sitzungsberichte der Gesellschaft zur Beförderung der Gesamten Naturwissenschaften zu Marburg 8: 115–130.
Konstantinidis P and Johnson GD 2016. Osteology of the telescope fishes of the genus Gigantura (Brauer, 1901), Teleostei: Aulopiformes. Zoological Journal of the Linnean Society 179(2):338–353.

wiki/Telescopefish = Gigantura

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.