The lancet fish (Alepisaurus): a swordfish with fangs and no sword

According to Wikipedia
The lancet fish (Alepisaurus) is a traditional member of the Aulopiformes, the clade of lizardfish and their allies. Lizardfish, as you might remember, have eyeballs as far anteriorly as possible, the opposite of lancet fish.

Figure 1. Alepisaurus, the lancet fish nests with swordfish and eels in the LRT.

Figure 1. Alepisaurus, the lancet fish nests with swordfish and eels in the LRT.

By contrast,
in the large reptile tree (LRT, 1810+ taxa) the lancet fish nests close to European eels (Anguilla), but closer to swordfish (Xiphias). All three have similar skulls with a straight rostrum and very little (if any) post-orbital region anterior to the massive hyomandibular. Of course, neither eels nor swordfish have anything like those massive fangs found in the lancet fish. All three had a last common ancestor (LCA) distinct from other fish, and each evolved from that LCA their own special way leaving few clues, other than a similar skull, as evidence of their relationship to one another. That’s the way the LRT recovered it.

Figure 1. Extant swordfish (Xiphias) to scale with Eocene swordfish (Blochius).

Figure 2. Extant swordfish (Xiphias) to scale with Eocene swordfish (Blochius), which looks more like Alepisaurus overall.

That’s why we run all taxa through phylogenetic analysis. 
To do otherwise, to cherry-pick one trait or a dozen, is to “Pull a Larry Martin” which we are cautioned (for good reason) never to do. Professor Martin taught us well.

Figure 5. Skull of Anguilla, the European eel, compares well with that of Bavarichthys. Note the loss and reduction of preorbital bones.

Figure 3. Skull of Anguilla, the European eel, compares well with that of Bavarichthys. Note the loss and reduction of preorbital bones.

Alepisaurus ferox
(Lowe 1833, 1835a b, 215cm) is the extant lancetfish. Traditionally considered a aulopiform (= lizard fish. likeTrachinocephalus) here Alepisaurus nests as a swordfish sister without a rostrum sword, but with giant fangs and vestigial pelvic fins. During prey capture the fangs pierce swimming muscles, stopping the struggle. This hermaphrodite taxon can descend more than a mile into deep unlit seas.

Figure 4. Swordfish ontogeny (growth series). Hatchings have teeth, a short bill and an eel-like body still lacing pelvic fins.

Figure 4. Swordfish ontogeny (growth series). Hatchings have teeth, a short bill and an eel-like body still lacing pelvic fins.

It’s worth noting
that swordfish hatchlings have teeth and a long dorsal fin, like lancet fish. So the resemblance is closer in younger swordfish. It’s also worth noting that fossil swordfish precursors, like Blochius (Fig. 4, Eocene; 60-150cm) also had proportions closer to lancet fish.

Fierstine 2006, in his history of billfishes,
mistakenly included the convergent sailfish, Istophorus, and excluded the European eel and the lancet fish. This is what I mean when we talk about “Pulliing a Larry Martin.” It looks right. It feels right. It gets published. However, whenever you cherry-pick taxa, you are less likely to get the big picture you are chasing: an accurate hypothesis of interrelationships that models real evolutionary events. Instead you should  employ lots and lots of taxa. Then the big picture (= the accurate model) will come to you. The cladogram will recover the correct tree topology.


References
Fierstine HL 2006. Fossil history of billfishes (Xiphoidei). Bulletin of Marine Science 79(3):433–453.
Lowe RT 1833. Description of a new genus of acanthopterygian fishes, Alepisaurus ferox. Proc. zool. Soc. Lond ,1:104.
Lowe RT 1835a. Description of a new genus of acanthopterygian fishes, Alepisaurus ferox. Trans. zool. Soc. Lond., 1: 123-128, pl. 19.
Lowe RT 1835b. Additional observations on Alepisaurus ferox. Trans. zool. Soc. Lond., 1: 395-400, pl. 59.

wiki/Aulopiformes
Alepisaurus_ferox

14 thoughts on “The lancet fish (Alepisaurus): a swordfish with fangs and no sword

  1. So you assume them to be related just because of the position of their eyes? I don’t see how that matters, as there are other fish genera with similarly positioned eyes.

    • Speaking of fish, I thought that this blog was dedicated to pterosaurs…
      How are fish related to pterosaurs again?

      • Some fish are pterosaur ancestors, going waaaaay back. Those same fish are human ancestors. This blogpost is the daily news for ReptileEvolution.com, an online phylogenetic analysis that has grown from fewer than 300 taxa ten years ago to its present size of 1810 taxa, plus therapsids, plus pterosaurs. The large reptile tree documents the ancestry for any included taxon back to headless chordates in the Cambrian. Apparently you are new here, Jonathan. Hope this helps.

    • Assumption is not good science. These are results recovered after testing in phylogenetic analysis using hundreds of characters and 1810 taxa. Phylogenetic analysis is a standard method in paleontology for recovering an hypothesis of interrelationships.

  2. I appreciate the time and dedication that you have put into your LRT and other phylogenetic trees, but, if you use too many characters from sometimes irrelevant /or basal genera to classify newer /or more derived genera, there will be a few things that don’t quite line up with what others have said about said genera. An example might be the inclusion of placoderms in the assessment of fish taxa, and, as a result, we now have them related to catfish. Placoderms are now closer to cartilaginous fish like sharks and chimaeras thanks to new evidence from recent studies, and catfish are Actinopterygians, AKA ray-finned fish. I think that not just your LRT, but all of your phylogenies can benefit from the removal of the basal genera. To refine your phylogenies in the previously stated way, I think that you might be able to take some time off from new articles and to refine your phylogenies.
    P.S. Please don’t misunderstand, I love the fact that your phylogenies include all these taxa, but the thing is that all those taxa are not always relevant to the more derived genera included in the phylogenies.

    • I simply report results. That those results don’t line up with genomic results or those that have excluded pertinent taxa in the past is an issue best resolved by asking others to add pertinent taxa to match the LRT to confirm or refute results. Scientific method: repeatable results come from repeatable methods and materials.

      • Might I also add that Manta is now invalid, but has been lumped into Mobula as of 2009?

      • While I am adding, I would also like to point out that basking sharks and paddlefish are in two totally different classes (Elasmobranchii for the sharks and Actinopterygii for the paddlefish)

      • That’s traditional thinking. When tested in the LRT the two taxa nest closer to one another than to any other taxon. If you can cite another phenomic study that includes both taxa and nests them apart, please send that citation and I will review it and promote it.

      • The thing you did with Ubirajara is just nuts from the get-go. Those “leg bones” couldn’t even support the weight of a dog. They have the structural integrity of a stick, and you expect us to believe that they used to hold a 500-odd pound dinosaur?

      • Remember only the possible impressions of an ankle and knee are visible in the fossil. The rest is “connecting the dots”. The scale bar indicates the 14cm graphic would enlarge 3x, to 42cm tall. That’s in the range of a green heron, which weighs 8.5 oz, far short of 500 pounds.

      • And about the stargazer/frogfish thing, there is a difference between convergent evolution and mimicry.

      • Agreed. There is a difference between convergence and homology. Mimicry is a different concept. Given the present taxon list, the stargazer and frogfish are presently separated by only two taxa, Periophthalmus and Elactinus. Pertinent taxa will probably separate them further. Always check the LRT for the latest updates. Earlier posts might represent shorter taxon lists lacking newly added taxa. This online study started with fewer than 300 taxa, now at 1811 for the LRT, 74 for the TST and 256 for the LPT.

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