Two small tales of two small tails: Onychodus and Aphanopus

Small tail #1:
Earlier the whirl-toothed Late Devonian Onychodus (Fig. 1) entered the LRT (subset Fig. 3) based on skull traits only. Today a small straight tail is added to the known anatomy of this moray eel-like predator, confirming it as a taxon close to the ancestry of living moray eels and several deep sea predators (Fig. 2). Until further notice, this remains a novel hypothesis of relationships heard here first.

Figure 1. The tail tip is added to Onychodus and a body is added based on phylogenetic bracketing. Interesting comparing the much larger body of Gymnothorax given the relatively similar-sized skulls in Onychodus and Gymnothorax.

Figure 1. The tail tip is added to Onychodus and a body is added based on phylogenetic bracketing. Interesting comparing the much larger body of Gymnothorax given the relatively similar-sized skulls in Onychodus and Gymnothorax.

 

Interesting note:
despite the great increase in size shown by Gymnothorax (Fig. 1) its jaws are no larger than the presumably much smaller Onychodus.

Figure 2. The ancestry of Eurypharynx extends to moray eels and rhizodontid lobe fins, like Onychodus (Fig. 1)

Figure 2. The ancestry of Eurypharynx extends to moray eels and rhizodontid lobe fins, like Onychodus (Fig. 1)

Phylogenetic analysis
(Fig. 3) does not shift the nesting of Onychodus given this new data. So, phylogenetic bracketing could have predicted a tail like this.

Figure 2. Subset of the LRT focusing on basal lobefin fish and kin.

Figure 3. Subset of the LRT focusing on basal lobefin fish and kin.

Onychodus sigmoides (Newberry 1857; Onychodus jandemarra Andrews et al. 2006; Late Devonian; 10cm skull, 47 cm length with larger specimens up to 2m in length; Fig. 1) is a sister to the much smaller Strunius. Both are considered members of the Onychodontida. The large, rotating tooth whorl at the dentary and long premaxilla extending below the orbit are key traits. The jugal and postorbital are fused. The nasal contact the orbit.


Small tail # two:
In an earlier post (now deleted) I wondered why the Northern pike (genus: Esox) did not nest with the muskellunge (genus: Esox). A sharp-eyed reader reported the skull I employed for the pike (and mistakenly labeled Esox lucius)was actually the skull of the black scabbardfsih (genus: Aphanopus) resolving the problem. Thank you for the correction!

Figure 3. Meter-long Aphanopus, the black scabbard fish, has a long, eel-like torso tipped with a tiny diphycercal tail.

Figure 3. Meter-long Aphanopus, the black scabbard fish, has a long, eel-like torso tipped with a tiny diphycercal tail.

Aphanopus, known to some a the vampire fish for its long sharp anterior teeth
nests with the much deeper bodied Lampris in the LRT. I will continue to seek taxa transitional or basal between these two distinctly different morphologies.

Oddly,
despite the long eel-like body, Aphanopus retains a tiny diphycercal tail (Fig. 3). This trait readily distinguishes the scabbard fish from other similar deep water fishes.

Apanopus carbo (Lowe 1839, up to 1.1m) is the extant black scabbardfish, close to the eel-like cutlassfish. The body is extremely elongate with an odd little diphycercal tail. The pelvic fins are vestiges in juveniles, absent in adults. In the LRT, Lampris, the opah, is a sister at present.


References
Andrews M, Long J, Ahlberg P, Barwick R and Campbell K 2006. The structure of the sarcopterygian Onychodus jandemarrai n. sp. from Gogo, Western Australia: with a functional interpretation of the skeleton. Transactions of the Royal Society of Edinburgh. 96 (3): 197–307.
Lowe RT 1839. A supplement to a synopsis of the fishes of Madeira.; Proceedings of the Zoological Society of London, 7: 76–92.
Newberry JS 1857. Fossil fishes from the Devonian rocks of Ohio. Geological
Survey of Ohio: Bulletin National Institute: 1–120.

wiki/Onychodus

wiki/Aphanopus (aka: black scabbard fish)

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