Corrections galore are illustrated here
as further study and better data (from Grande and Poyato-Ariza 1999) resolve earlier issues.
According to Wikipedia,
“The hingemouth (Phractolaemus ansorgii) is a small freshwater fish that is found only in west central Africa, the sole member of the subfamily Phractolaeminae of the family Kneriidae. The mouth can extend like a small trunk, thus the name, and has just two teeth, both in the lower jaw. The swim bladder has two compartments, and can function as a lung, allowing the hingemouth to survive in oxygen-poor environments.”
The hingemouth (Phractolaemus) no longer nests alone.
The family Kneriidae traditionally includes the unrelated bonefish, Chanos.
So this has been a wastebasket clade.
Note sure about those ‘two teeth, both in the lower jaw’ since the dentary is missing.
Traditionally Phractolaemus is also considered a member of the larger clade, the Gonorhychiformes, which includes Gonorhynchus (a sturgeon relative) and Chanos (a bonefish relative). So this has been another wastebasket clade for strange fish. Extinct taxa, like Middle Triassic Marcopoloichthys (Fig 4), have been traditionally omitted or misinterpreted.
The phylogenetic loss of the dentary
is the key factor in helping to understand the hingemouth problem. Previously I reported, “Unlike any other gnathostome, the ‘premaxilla’ rotates on the front axis of the ‘dentary’, acting like a vacuum cleaner sweeper to fling small bottom detritus into the tiny dorsal mouth.” Now the traditional ‘dentary’ is absent, and the primitively loose upper jaw elements act more like those found in the suction feeders Fundulus (Fig 3) and Marcopoloichthys (Figs 3, 5), only exaggerated. The preopecular (light yellow) is broken/split into a horizontal piece and a vertical piece. Compare to Marcopoloicthys and Fundulus.
igure 2 Marcopoloicthys compared to Phractolaemus in several views.
Phractolaemus ansorgii
(Boulenger 1901; 20cm) is the hingemouth, or mud minnow, an extant African freshwater fish not previously associated with Fundulus and Marcopoloicthys. Two catfish-like barbels probe and sense the substrate as this fish swims head down, tail up over the substrate. The swim bladder can act as a lung. The opercula (cyan) wrap over each other ventrally. Branchials appear to be absent, but could be hidden.
Another look at the mandible of Marcopoloicthys
(Fig 4) indicates a transitional morphology in which the articular kept its shape, but extended anteriorly. The vestigial dentary can still be observed on the ‘chin’ of the down-turned articular. Compare this transitional mandible to that of Fundulus (Fig 3). and Phractolaemus (Fig 3).
Figure 4. Marcopoloicthys with colors updated. Note the reduction of the blue dentary and increase of the violet angular. The two upper jaw elements (yellow and green are loose, held together by skin.
These corrections resulted in an apparent novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here.
References
Boulenger GA 1901. Diagnoses of new fishes discovered by Mr. W. L. S. Loat in the Nile. Annals and Magazine of Natural History, Including Zoology, Botany and Geology, Being a Continuation of the ‘Magazine of Botany and Zoology’, and of Louden and Charlesworth’s ‘Magazine of Natural History’, Series 7 8: 444-446.
Grande T and Poyato-Ariza FJ 1999. Phylogenetic relationships of fossil and Recent gonorynchiform fishes (Teleostei: Ostariophysi). Zoological Jounial of the Linnean Society (1999), 125: 197-238.
Poyato-Ariza FJ, Grande T and Diogo R 2010. Gonorynchiform Interrelationships: Historic Overview, Analysis, and Revised Systematics of the Group.In: Grande, T., F. Poyato-Ariza & R. Diogo (eds.), Gonorynchiformes and ostariophysan relationships – a comprehensive review, Science Publishers and Taylor & Francis (Oxford, UK): 221-231.
The Pterosaur Heresies 