The fish without a tail, part 2

Convergent with humans,
ocean sunfish (Figs. 1,2) also lack a tail. What they have instead was first called the ‘clavus‘ (= cornfield skin) by British ichthyologist, Alec Fraser-Brunner (1951),

Figure 1. Ranzania from Johnson and Britz 2004 in various degrees of dissection.

Figure 1. Ranzania from Johnson and Britz 2004 in various degrees of dissection. The clavus is where the tail used to be. Johnson and Briz determined that portions of the dorsal and anal fin migrated to produce the clavus. Compare to its relative Mola, figure 2.

From the Johnson and Britz 2004 abstract:
“Homology of the clavus has been a matter of debate since the first studies on molid anatomy in the early 1800s. Two hypotheses have been proposed:

  1. It is a highly modified caudal fin;
  2. It is formed by highly modified elements of the dorsal and anal fins.

We show that… the claval rays form from the posterior ends of the dorsal and anal fins toward the middle. We thus conclude that the molid clavus is unequivocally formed by modified elements of the dorsal and anal fin and that the caudal fin is lost in molids.”

Figure 2. The ocean sunfish (Mola) seems to be the opposite of the flying fish (Exocoetus), but these two nest with each other in the LRT based on skeletal traits.

Figure 2. The ocean sunfish (Mola) seems to be the opposite of the flying fish (Exocoetus), but these two nest with each other in the LRT based on skeletal traits.

Johnson and Britz 2009
stained tiny juveniles of the sunfish Ranzania (Fig. 1) to document their hypothesis.

Figure 4. Mola larvae ontogeny. The caudal fin appears at first, then disappears as the dorsal and anal fin ossify and the body deepens.

Figure 3. Mola larvae ontogeny. The caudal fin appears at first, then disappears as the dorsal and anal fin ossify and the body deepens.

Before finding Johnson and Britz 2009
decades older images of a hatchling and growing Mola mola (Figs. 2, 3) documented the disappearance of the tail prior to the appearance of the marginal clavus.

Figure 3. The queen triggerfish, Balistes, is related to Mola in the LRT.

Figure 4. The queen triggerfish, Balistes, is related to Mola in the LRT.

Mola mola (Linneaus 1758) is the extant ocean sunfish. As a hatchling it is similar to a pufferfish (Diodon) in shape, then undergoes metamorphosis to adulthood. It is the largest bony fish and the only one taller than long. In the large reptile tree (LRT, 1647+ taxa, subset Fig. 5) is derived from the the slow-moving queen trigger fish, Balistes (Fig. 4), and both are derived from the speedy high-fin amberjack, Seriola rivoliana apart from pufferfish. As we learned earlier, speedy flying fish (Exocoetus) and sunfish-like opah (Lampris) are also members of the amberjack + mola clade in the LRT.

Figure 1. Subset of the LRT focusing on basal vertebrates (fish).

Figure 5. Subset of the LRT focusing on basal vertebrates (fish).

That opens up a phylogenetic problem. 
The fish clade Tetraodontiformes traditionally includes trigger fish and puffer fish. In the LRT trigger fish are not related to pufferfish, except through a last common ancestor somewhere early in the genus Seriola. Both have different members of that genus in their ancestry and Seriola is not considered a member of the traditional Tetraodontiformes. This appears to be a novel hypothesis of interrelationships. If it has been published earlier, let me know so I can promote that citation.

Like Mola and Ranzania
Balistes swims by undulating those large dorsal and anal fins (see videos above) with the tail dragging without much movement behind, unlike most fish. That is why the question of clavus homology intrigued Johnson and Britz 2004.

On a side note,
sunfish have few to no pain receptors, an adaption to their diet of jellyfish. Predators sometimes take bites out of sunfish without causing a fight or flight reflex on the part of the victim.

A fossil genus traditionally aligned with Tetraodontiformes,
Plectocretacicus clarae, was earlier moved out of Tetraodontiformes to nest with the giant oarfish. Regalecus glesne. So, the clade Tetraodontiformes is likewise getting nibbled away, piece-by-piece by the LRT. Members are no longer monophyletic unless the definition or membership expands to include more taxa. 


References
Fraser-Brunner A 1951. The ocean sunfishes (Family Molidae). Bulletin of the British Museum (Natural History 1:89–121.
Johnson DG and Britz R 2004. Leis’ Conundrum: Homology of the Clavus of the Ocean Sunfishes. 2. Ontogeny of the Median Fins and Axial Skeleton of Ranzania laevis (Teleostei, Tetraodontiformes, Molidae). Journal of Morphology 266:11–21.
Linnaeus C von 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

wiki/Mola mola
wiki/Tetraodontiformes
wiki/Ranzania

Was there an EB radiation at the base of the Ichthyosauria?

Moon and Stubbs 2020 bring us a discussion on
the EB (early burst) radiation of ichthyosaurs shortly after their genesis (Fig. 1).

Unfortunately,
the authors did not know which taxon was the last common ancestor and which taxa formed the proximal outgroups.

Figure 1. Cladogram from Moon and Stubbs 2020.

Figure 1. Cladogram from Moon and Stubbs 2020.

The authors
chose as their outgroup, Hupehsuchus nanchangensis, a derived ingroup member of the ichthyosaur radiation according to the large reptile tree (LRT, 1647+ taxa; Fig. 2).

Verified outgroups not included in the cladogram
include the clades Thalattosauria, Mesosauria and Pachypleurosauria (Fig. 2).

The authors mistakenly included
Cartorhynchus and Sclerocormus as ichthyosaurs. The LRT recovered these two taxa as ichthyosaur mimics at the base of the Sauropterygia, alongside Qianxisaurus (not in the taxon list).

Other ichthyosaur basal in-groups recovered by the LRT
and not mentioned by Moon and Stubbs include Wumengosaurus and Thaisaurus.

Figure 3. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria)

Figure 2. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria).

The LRT recovered
Wumengosaurus as a basal ichthyosaur in 2011. It nested Cartorhynchus with the pachypleurosaur, Qianxisaurus in 2014. These have been available with a quick Google search for the last several years. You can say the LRT is not a recognized resource, but then you run the risk of excluding appropriate taxa and including inappropriate taxa, as Moon and Stubbs did. Their taxon list fell short of optimal and thereby opened up their study for criticism on those grounds.

The referees for this paper were more generous in their appraisal:

  1. This is an excellent, well-written, thoroughly executed and smartly illustrated study that rigorously analyses patterns of disparity and diversity throughout the evolution of ichthyosaurs. It will be of great interest to those working on marine reptiles, as well as all those interested in clade dynamics. I have nothing of any significance to criticise, and recommend publication more or less as the manuscript stands – in many ways it is a model.
  2. This is a well written, well executed and very scholarly contribution to macroevolutionary studies of ichthyosaurs…Their paper is a detailed tour-de-force through the analysis of ichthyosaur morphological diversification in a three-pronged approach to the study of evolutionary rates, disparity, and morphological space occupation… It is well written and provides ample documentation for data and result reproducibility. I have no qualms with this paper.
  3. This is a great paper with a solid and well used methodology… The authors did a great job with sharing the code and the data to reproduce this paper. Although this should be a standard in science, it is unfortunately done well and in depth way to rarely. Well done! 

Since this paper deals with comparative measurements 
the Moon and Stubbs data represent a resource that can be used for future workers, who should consider expanding their taxon set a wee bit and get rid of interlopers.

Bottom line: Was there an EB radiation at the base of the Ichthyosauria?
In the LRT it is not apparent that ichthyosaurs had an early burst (EB) radiation and disparity when Cartorhynchus and Sclerocomus are excluded, as they should be. Rather, when appropriate taxa are included and inappropriate taxa are excluded, only microevolution is apparent (i.e. a gradual accumulation of derived traits).


References
Moon BC and Stubbs TL 2020. Early high rates and disparity in the evolution of ichthyosaurs. Communications Biology 3, Article number: 68
doi: https://doi.org/10.1038/s42003-020-0779-6
https://www.nature.com/articles/s42003-020-0779-6

http://www.bristol.ac.uk/news/2020/february/ichthyosaur-evolution.html

https://phys.org/news/2020-02-boom-ancient-sea-dragons.html

 

Carboniferous taxa document the Silurian genesis of placoderms

Nailing down the origin
of the armored fish clade, Placodermi, has proven elusive. Their armored skulls and flexible tails remind most workers of jawless fish, like Arandaspis.

According to Wikipedia
“Placodermi is a class of armored prehistoric fish which lived from the (early) Silurian to the end of the Devonian period. Their head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked, depending on the species. Placoderms were among the first jawed fish; their jaws likely evolved from the first of their gill arches.”

The large paddled bottom feeder,
Stensioella
 is considered the traditional outgroup for the Placodermi (Carr et al. 2000; Early Devonian), but the large reptile tree (LRT, 1647 taxa; subset Fig. 1) nests Stensioella closer to coelacanths and lungfish. The early appearance of placoderms in the fossil record, along with the fact that some taxa have weak-to-nonexistent jaws has caused fish-paleontologists to surmise that placoderms are primitive, arising directly from jawless fish.

Figure 1. Subset of the LRT focusing on basal vertebrates (fish).

Figure 1. Subset of the LRT focusing on basal vertebrates (fish).

In counterpoint,
the LRT indicates that placoderms had a long list of ancestral taxa with jaws, and some ‘jawless’ placoderms gave rise to modern catfish, an extant clade that also lacks a maxilla. Like placoderms, some catfish retain a bony armored skull along with a long list of homologous traits.

Figure 1. Cheirodus skull compared to Austroptyctodus skull, which was reassembled by Miles and Young 1977 from disassembled bones.

Figure 1. Cheirodus skull compared to Austroptyctodus skull, which was reassembled by Miles and Young 1977 from disassembled bones. Note the quadrate attaches directly to the premaxilla. The maxilla is missing in both taxa.

In today’s news
the nesting of the heavily-scaled eurynotiform actinopterygiian Chirodus (also Cheirodus, Carboniferous) with the ptycodontid placoderm, Austracoptycodus (Fig. 2) documents the transition from scaled fish to armored placoderm. The similarities were overlooked by other workers and yours truly until recently. It’s nice to finally find a taxon similar to both of these oddballs. That it turned out to be each other was one of those wonderful moments of discovery.

Figure 2. Origin of placoderms featuring Chirodus, Austroptyctodus, Coccosteus and other pertinent taxa.

Figure 3. Origin of placoderms featuring Chirodus, Austroptyctodus, Coccosteus and other pertinent taxa. Rarely studied Eurynotus is considered a relative of Cheirodus. Let’s get some decent data on that taxon.

Basically the picture tells the story.
So does the cladogram. No other tested taxa nest closer. If Cheirodus seems a bit oddly shaped and chronologically out of place, keep in mind related taxa without those divergent traits. Note: the armored humpback of Coccosteus makes an appearance prior to the genesis of placoderms. Chronologically, the Silurian should be delivering a wider variety of taxa than it currently provides.

Once again, this appears to be a novel hypothesis
of interrelationships. If any precede this post, let me know so I can promote that citation. Taxon exclusion and traditional paradigms cemented in textbooks are issues resolved by simply adding taxa to see what the software delivers.

More later.


References
Carr RK, Johanson Z and Ritchie A 2009. “The phyllolepid placoderm Cowralepis mclachlani: Insights into the evolution of feeding mechanisms in jawed vertebrates” Journal of Morphology270 (7): 775–804. doi:10.1002/jmor.10719

https://en.wikipedia.org/wiki/Placodermi

wiki/Chirodus

Evolution at the basal dichotomy of bony fish

For a large segment of American (USA) citizens
evolution remains unbelievable (pewrsearch.org). Other than a few well-know examples that demonstrate our knowledge of transitional taxa (e.g. human ancestry; Fig. 1) the reason for this might be a general lack of diagrams demonstrating the micro-evolution between major taxa.

Figure 2. Human evolution back to the cynodonts, some 230 mya.

Figure 2. Human evolution back to the cynodonts, some 230 mya.

As a remedy, here’s one example
of micro-evolution (Fig. 2) at the base of the origin of bony fish.

Figure 1. A sister to Hybodus gave rise to a basal dichotomy in bony fish. Basal taxa immediately following this split include Trachinocephalus on the clade leading to tetrapods and Amia on the clade leading to most other traditional teleosts.

Figure 1. A sister to Hybodus gave rise to a basal dichotomy in bony fish. Basal taxa immediately following this split include Trachinocephalus on the clade leading to tetrapods and Amia on the clade leading to most other traditional teleosts.

Shown above
are transitional taxa leading to bony fish. An early Devonian sister to the traditional shark, Hybodus (Early Jurassic), gave rise to a basal dichotomy in bony fish. Taxa immediately following this split include the extant lizardfish, Trachinocephalus, a member of the clade leading to tetrapods and the extant bowfin, Amia, a member of the clade leading to most other traditional teleosts.

Figure 1. Subset of the LRT focusing on basal vertebrates (fish).

Figure 1. Subset of the LRT focusing on basal vertebrates (fish).

The large reptile tree (LRT) documents the evolution of all included taxa back to Cambrian lancelets. More transitional taxa can be seen here, here and here with more to come.

 

 

The flying fish and the ocean sunfish just became cousins in the LRT

Figure 1. Flying fish (Exocoetus) skull.

Figure 1. Flying fish (Exocoetus) skull.

This one caught me by surprise, too.
It came about because I re-examined the details.

Superficially
the speedy flying fish (Exocoetus, Fig. 1) seems to have little in common with the lethargic ocean sunfish (Mola, Fig. 2) and opah (Lampris, Fig. 3). Traditionally flying fish nest with speedy needlefish, like Tylosurus. The large reptile tree (LRT, 1647+ taxa) adds 25 more steps to move Exocoetus next to Tylosurus.

Figure 4. Mola mola is a relative of Diodon in the LRT. It has no circumorbital bones, but as a hatchling has pufferfish proportions and spines.

Figure 2. Mola mola is a relative of Diodon in the LRT. It has no circumorbital bones, but as a hatchling has pufferfish proportions and spines.

Skeletal details 
provide a different hypothesis of interrelationships. You can see a short deep mandible and a deep coracoid in these three taxa (Figs. 1-3), along with a long list of other homologous traits.

Figure 2. More traits unite the opah with the flying fish than separate these two, given the present taxon list.

Figure 3. More traits unite the opah with the flying fish than separate these two, given the present taxon list. Note the deep coracoids, as in birds and pterosaurs, here again used to flap the pectoral fins.

All three taxa are derived from
the speedy high-fin amberjack, Seriola rivoliana.

Figure 1. Subset of the LRT focusing on basal vertebrates (fish).

Figure 1. Subset of the LRT focusing on basal vertebrates (fish).

Exocoetus volitans (Linneaus 1758; up to 30cm ) is the extant blue flyingfish, here related to the much larger and nonvolant opah, Lampris (above). Exocoetus travels in schools or schoals. Sometimes they exit the water to avoid predators. Juveniles have a relatively shorter torso. Hatchlings are slow-moving and tiny. Distinctly flying fish and their relatives have a jaw joint directly below the orbit. The coracoid is larger than the scapula, raising and powering the pectoral fins.


References
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

wiki/Lampris
wiki/Almaco_jack
wiki/Exocoetus_volitans

The ‘muskie’ is a catfish without barbels

Another bit of heresy today
as a freshwater barracuda-mimic, the muskellunge (Esox masquinongy, Figs. 1, 2) now nests with the channel catfish (Ictalurus punctatus, Fig. 3) in the large reptile tree (LRT, 1647+ taxa). That makes the ‘muskie’ the only tested catfish without barbels and with eyes in the back half of the skull. This appears to be a novel hypothesis of interrelationships. If one like this was published earlier, let me know so I can provide that citation.

These corrections
also resolve a long list of unsettling cladogram issues, which are still not completely resolved in other parts of the teleost subset of the cladogram (Fig. 4). More reports like this one are ‘on deck’ to be presented shortly.

Figure 2. The muskie (Esox masquinongy) in vivo.

Figure 2. The muskie (Esox masquinongy) in vivo.

Figure 1. The muskelunge, Esox masquinongy, now nests in the LRT alongside the channel catfish (Ictalurus punctatus), Fig. 3).

Figure 1. The muskelunge, Esox masquinongy, now nests in the LRT (subset Fig. 4) alongside the channel catfish (Ictalurus punctatus), Fig. 3).

Esox masquinongy (Mitchell 1824; up to 1.2m in length) is the extant muskellunge (muskie, Figs. 1, 2). Several bones here are reidentified. Note the posterior placement of the pectoral fins, the lack of a maxilla, the multi-part premaxilla, the premaxilla/vomer tooth pad and the wider anteriorly nasals… all catfish-like traits. The split between Ictalurus and Esox is an ancient one, probably extending back to the Carboniferous or Triassic.

Figure 3. The channel catfish, Ictalurus, skull and lateral view in vivo.

Figure 3. The channel catfish, Ictalurus, skull and lateral view in vivo.

Ictalurus punctatus (Rafinesque 1818, up to 65 cm in length) is the extant channel catfish. Relative to other more primitive catfish with barbels, like Clarias and Halplosternum, the skull bones are reduced here. Note the placement of the pectoral girdle beneath the skull. This omniovore has sharp serrated spines on the leading edge of its pectoral fins.

Figure 4. Subset of the LRT focusing on basal vertebrates (fish). Esox and Ictalurus are highlighted. This cladogram reflects the latest results, which are still not completely resolving internal issues in the teleost clade. Tetrapods arise from the yellow clade at left.

Figure 4. Subset of the LRT focusing on basal vertebrates (fish). This cladogram reflects the latest results, which are still not completely resolving internal issues in the teleost clade. Tetrapods arise from the yellow clade at left.

This new nesting is only one small part of efforts
during the rewarding last two weeks of reexamining each teleost taxon and a re-scoring several skull bones as I slowly realize mistakes and make corrections to resolve internal issues in the teleost part of the LRT. As readers know, before I consider each and every taxon I know nothing about that taxon. I learn as I go… like everyone does. For those hanging on to a few mistakes I made before starting ReptileEvolution.com in 2011, these recent corrections bring my corrected mistake totals way past the 100,000 mark. More to come.

Final note:
Don’t trust what I say or what others say. Judge for yourself. Test for yourself. Then share what you found out. This is how science works. Longtime readers know a long list of published taxon exclusion issues have been resolved here. Readers also know that every so often results first presented or corrected here were ultimately replicated by others when they included the same taxa. That list can be found here.


References
Mitchell SL 1824. Mirror 1824: 297.
Rafinesque CS 1818. The American monthly magazine and critical review 4: 41.

wiki/Muskellunge – Esox
wiki/Ictalurus

The pupfish enters the LRT alongside…the wolffish

Pups nesting with wolves. Imagine that…
I googled ‘pupfish, wolffish’ looking for a prior hypothesis of relationship between these two fish. Apparently, there is none (See below), despite the obvious and overall similarities, other than size.

Today, tiny Pseudorestias, the pupfish.
(Fig. 3) enters the large reptile tree (LRT, 1646+ taxa) alongside a much larger, toothy relative, Anarhichas, the wolffish (Figs. 1, 2).

Figure 1. Skull of the wolffish, Anarhichas. Compare to the pupfish in figure 3.

Figure 1. Skull of the wolffish, Anarhichas. Compare to the pupfish in figure 3.

Figure 2. Anarhichas in vivo. Note the basic similarities between this cave dweller and its open seas cousin, Coryphaena (Fig. 1).

Figure 2. Anarhichas in vivo. Note the basic similarities between this cave dweller and its open seas cousin, Coryphaena (Fig. 1).

According to Wikipedia
Anarhichas belongs in the Anarhichadidae (nothing but wolffish and wolf eels), then the Perciformes (a huge clade of ray fin fish).

Figure 3. Tiny Pseudorestias, the pupfish, nests with the large wolffish (Figs. 1, 2) in the LRT.

Figure 3. Tiny Pseudorestias, the pupfish, nests with the large wolffish (Figs. 1, 2) in the LRT. Note the tiny pelvic fins, lost in the wolffish.

By contrast,
Pseudorestias belongs in the Cyprinodontidae (pupfish), then the Cyprinodontiformes (guppies, killifish and kin), then the ray fin fish.

Another traditional member of the Cyprinodontiformes,
Anableps, the four-eyed fish, nests elsewhere in the LRT, with sea robins, like Prionotus. Perhaps that nesting will change when I can find some guppy skulls, which seems not very likely, at present.

Pseudorestias brings new insights
into the very weird cranium of Anarhichas.

Anarhichas vomerinus (Linneaus 1758; 1.5m length) is the extant Atlantic wolffish. The marginal and vomer teeth are robust. The conjoined temporal fenestra meet dorsally along a thin ridge. Pelvic fins are absent.

Pseudorestius lirimensis (Arratia, Vila, Lam, Guerrero & Quezada-Romegialli 2017) is a tiny, newly discovered pupfish, a traditional member of the Cyprinodontiformes (killifish), but here related to the much larger wolffish. The skull is broad, as in other teleost fish. Pelvic fins are tiny.

Final note:
The teleost subset of the LRT is undergoing review and reinterpretation. This is not easy, but parts are working out. I will let you know when the whole clade is better supported at every node.


References
Arratia G, Vila I, Lam N, Guerrero CK and Quezada-Romegialli C 2017. Morphological and taxonomic descriptions of a new genus and species of killifishes (Teleostei: Cyprinodontiformes) from the high Andes of northern Chile. PLOS ONE 12(8): e0181989. doi:10.1371/journal.pone.0181989
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.

wiki/Atlantic_wolffish
wiki/Pupfish