A little piranha sister, Hoplerythrinus, enters the LRT

And like its deep-bodied, big-toothed sister,
the aimara, trahira, gold wolf fish, etc. (genus: Hoplerythrinus unitaeniatus (hop-ler-rie-thry-nus) originally Erythrinus) also swims in South American rivers.

Figure 1. The araimaia, Hopolerythrinus, enters the LRT with the piranha, Serrasalmus.

Figure 1. The araimaia, Hopolerythrinus, enters the LRT with the piranha, Serrasalmus.

The aimara is longer and leaner than the piranha,
more like their giant Cretaceous Niobrara cousins (Fig. 5), Portheus and Xiphactinus.

Figure 3. Araimaia (Hoplerythrinus) skull.

Figure 2. Araimaia (Hoplerythrinus) skull.

The Gregory 1938 diagram of the skull
(Fig. 2) clarifies and corrects several elements of the skull in the piranha (Serrasalmus), and the Niobrara taxa, Portheus and Xiphactinus.

Figure 1. Skeleton of the red eye piranha, Serrasalmus rhombeus, in lateral view. Distinct from its bottom foraging predecessor, Alma, the skull and torso of this more agile swimmer are deeper and narrower.

Figure 3. Skeleton of the red eye piranha, Serrasalmus rhombeus, in lateral view. Distinct from its bottom foraging predecessor, Alma, the skull and torso of this more agile swimmer are deeper and narrower.

Hoplerythrinus unitaeniatus (originally Erythrinus unitaeniatus Spix and Agassiz 1829) is the extant gold wolf fish or aimara, found in South American rivers. Here this smaller, more primitive, less toothy taxon nests with the highly derived piranha. Like Amia, this taxon does well with stagnant, oxygen-poor water by gulping air.

Figure 4. Piranha (Serrasalmus) skull.

Figure 4. Piranha (Serrasalmus) skull. Some skull bones re-identified here.

Figure 2. Xiphactinus fossil. The famous fish-within-a-fish. Note the posterior pelvic fins.

Figure 5. Xiphactinus fossil. The famous fish-within-a-fish.

Figure 4. Subset of the LRT focusing on basal ray fin fish.

Figure 4. Subset of the LRT focusing on basal ray fin fish. The clear resemblance to Amia hints at a series of similar transitional taxa leafing to inteventing clades.

The clear resemblance of Hoplerythrinus to the bowfin, Amia
(Fig. 5), hints at a series of similar transitional taxa leafing to inteventing clades.

Figure 4. Skull of the extant bowfin (Amia). Compare to figure 3.

Figure 5. Skull of the extant bowfin (Amia). Compare to figure 2.

The atypical contact between
the premaxillary ascending processes and the frontals (splitting the nasals, Fig. 2) in Hoplerythrinus recalls a similar morphology in Amia (Fig. 5), several nodes away (Fig. 4). This similarity hints at a transitional series of taxa that look more like Amia and Hoplerythrinus basal to the intervening clades including Elops, Megalops, Salmo and Hydrolycus .


References
Spix JB von and Agassiz L 1829. Selecta genera et species piscium quos in itinere per Brasiliam annis MDCCCXVII-MDCCCXX jussu et auspiciis Maximiliani Josephi I…. colleget et pingendso curavit Dr J. B. de Spix…. Monachii.

 

Enigmatic Jamoytius enters the LRT

Sansom et al. 2010 studied and discussed
Jamoytius kerwoodi (White 1946; Early Silurian; Fig. 1) an early eel-like taxon originally considered to be the most primitive known vertebrate, then a sister to lampreys, then a sister to Euphanerops (the subject of yesterday’s post). Turns out, it is none of these.

Sansom et al write:
“The study of the anatomy of problematic organisms can be aided by the use of a methodology designed to separate topological and morphological reconstruction from anatomical interpretation and to gather as much information as possible about the preserved features through taphonomic analyses.”

Unfortunately the authors did not trace the skull bones (Fig. 1) and those of several related taxa (Figs. 3, 4) and so missed the ability to score Jamoytius more completely and accurately.

“Interpretations of paired fins remain equivocal. Analyses of the phylogenetic affinity of Jamoytius identify a sister taxon relationship with Euphanerops. This clade, the Jamoytiiformes, is a primitive group of stem-gnathostomes and does not form a clade with the Anaspida.”

By contrast, the large reptile tree (LRT, 1718+ taxa, subset Fig. 2) nests Jamoytius not with lampreys, nor with Euphanerops, but between Birkenia (Fig. 3) and Thelodus (Fig. 4), taxa ignored by Sansom et al.

Figure 1. Jamoytius photo and diagram from Sansom et al. 2020. Colors and new labels added here.

Figure 1. Jamoytius photo and diagram from Sansom et al. 2020. Colors and new labels added here. Note the lack of skull bone tracings on the diagram. It looks like each gill opening has a little opercular flap. Note the new identification for the left eye. The ‘notochord’ is here a dorsal ridge, a precursor to dorsal armor.

Jamotius kerwoodi (White 1946, Sansom et al. 2010; Early Silurian; 10+cm in length) shares a tiny circular mouth and naris at the tip of its short snout with closely related taxa along with a similar set of skull bones, plus a dorsal ridge!

Figure 2. Subset of the LRT focusing on basal chordates and Jamoytius.

Figure 2. Subset of the LRT focusing on basal chordates and Jamoytius.

 With a small circular oral cavity,
Jamoytius and its sisters could not have been open sea predators, or blood suckers, but likely scoured sea muds and lake sands for tiny buried prey, like young lancelets and This extant sturgeons. Sturgeons (Fig. 4) feed on a spectrum of small benthic prey. Larger  sturgeons are known to suck in larger prey, like salmon, into their toothless, nearly jawless oral cavity.

BTW,
these taxa are all buried deep in the human lineage. So, say ‘hello’ to your ancestors.

Figure 3. Birkenia skull for comparison to Jamoytius.

Figure 3. Birkenia skull for comparison to Jamoytius.

Paleontologists of all stripes are fond of saying,
‘first-hand examination of the fossil is essential’. Sansom et al. had several fossils to look at firsthand and did not trace skull bones (Fig. 1). As I’ve been saying for nine years, the computer monitor and a digitally scanned photo can be superior to a binocular microscope because the monitor can trace elements in color, thereby reducing the apparent chaos into discrete segregated units. That opens up a whole new world of data that can be used to confidently nest enigmatic taxa, like Jamoytius (Fig. 2).

Figure 7. Top to bottom: Thelodus a soft jawless fish with a ventral oral opening and gill slits, perhaps a hint of diamond-shaped armor laterally. Hemicyclaspis, adds extensive armor. Euphaneropsps, a late survivor of an Ordovician radiation basal to sturgeons. Acipenser, a sturgeon with a protrusible tube for a mouth and reduced armor. Chondrosteus, a fish with jaws, but no marginal teeth.

Figure 4. Top to bottom: Thelodus a soft jawless fish with a ventral oral opening and gill slits, perhaps a hint of diamond-shaped armor laterally. Hemicyclaspis, adds extensive armor. Euphaneropsps, a late survivor of an Ordovician radiation basal to sturgeons. Acipenser, a sturgeon with a protrusible tube for a mouth and reduced armor. Chondrosteus, a fish with jaws, but no marginal teeth.

Taxon exclusion, once again. 
Sansom et al. did not mention, trace and test either Birkenia (Fig. 3) or Thelodus (Fig. 4). So taxon exclusion is also an issue resolved here by the LRT using character traits originally designed for reptiles and still working in basal chordates. It’s that simple. Just add taxa and enigmas get confidently nested.


References
Sansom RS, Freedman K, Gabbott SE, Aldridge RJ and Purnell MA 2010. Taphonomy and affinity of an enigmatic Silurian vertebrate, Jamoytius kerwoodi White. Palaentology 53(6):1393–1409.
White EI 1946. Jamoytius kerwoodi, a new chordatefrom the Silurian of Lanarkshire. Geological Magazine, 83, 89–97.

wiki/Jamoytius

Euphanerops: basal to sturgeons with tiny new pelvic fins

Janvier and Arsenault 2007 took another look at
Euphanerops longaevus (Woodward 1900; Late Devonian, Figs. 1, 2) comparing it uncertainly to living lampreys and extinct jawless, finless fish. They report, “The anatomy of Euphanerops longaevus is reconstructed here on the basis of 17 specimens, 14 of which were hitherto undescribed. Practically all the mineralized elements that can be observed in the largest individuals of E. longevous display the same structure, which strikingly recalls that of lamprey cartilage, despite the uncertainty as to the origin of its mineralization.”

Elongated and confluent paired fins
“The new material of E. longaevus described here provides strong support for the presence of ventrolateral, ribbon-shaped, paired fins armed with numerous parallel radials. These fins extend from the anus to the anterior part of the branchial apparatus anteriorly, and are the first instance of paired fins with radials, whose anteroposterior extension largely overlaps that of the branchial apparatus in a vertebrate.”

Mostly true, but let’s not forget in manta rays and guitarfish, skates and rays, paired pectoral fins indeed do overlap the branchial apparatus (= gill basket), IF that is happening in Euphanerops (see below).

From the abstract
“Owing to the uncertainty as to the biogenic or diagenetic nature of the anatomical features described in E. longevous, no character analysis is proposed. Only a few possible homologies are uniquely shared by euphaneropids and either lampreys or anaspids, or both.”

Phylogenetically, the authors note:
“Euphanerops longaevus has been referred to as an anaspid, chiefly because of its distinctive hypocercal tail and anal fin. However, since it apparently has no mineralized dermal skeleton, E. longaevus lacks evidence for the tri-radiate postbranchial spine, which Forey (1984) proposed as the defining character of the Anaspida. Consequently, it is now often treated in recent phylogenetic analyses as a separate terminal taxon, alongside other scale-less (or “naked”) jawless vertebrate taxa also once regarded as anaspids, namely Endeiolepis and Jamoytius.”

Figure 1. Several basal chordates: Branchiostoma, Euphanerops, Jamoytius and Birkenia. The middle image of Euphanerops is the tracing. The others are freehand interpretations not supported here.

Figure 1. Several basal chordates: Branchiostoma, Euphanerops, Jamoytius and Birkenia. The middle image of Euphanerops is the tracing. The others are freehand interpretations from Janvier and Arsenault 2007.

Here 
(Fig. 2) individual skull bones and tiny overlooked pectoral and pelvic fins are identified. Adding a missing (unossified?) rostrum (= nasal) restores the original profile. In the large reptile tree (LRT, 1717+ taxa) Euphanerops nests basal to sturgeons, like Pseudoscaphirhynchus (FIg. 3), a clade not mentioned by Janvier and Arsenault 2007. A previously enigmatic element in front of the mouth is here identified as a pair of barbels, as in sturgeons. The tiny dorsal spines of Euphanerops are also found as larger dorsal armor in Birkenia, osteostracans and sturgeons.

Figure 2. Euphanerops skull region showing tetrapod homolog bones and displace fin. See Birkenia for closer homologs. Image from Janvier and Arsenault 2007. Colors added here.

Figure 2. Euphanerops skull region showing tetrapod homolog bones and displace fin. See Birkenia for closer homologs. Image from Janvier and Arsenault 2007. Colors added here.

According to Wikipedia
Euphaneropidae have, “greatly elongated branchial apparatus which covers most of the length of the body.”

Here that area is identified as a typical subdivided and flattened ventral surface, as in Birkenia, sturgeons and osteostracans.

Figure 1. Skull of Pseudoscaphorhynchus. Note the mouth is created by the lacrimal and surangular, not the maxilla and dentary, which are tooth-bearing bones in more derived fish.

Figure 3. Skull of Pseudoscaphorhynchus. Note the mouth is created by the lacrimal and surangular, not the maxilla and dentary, which are tooth-bearing bones in more derived fish.

The hypocercal tail of Euphanerops
has heterocercal elements and this taxon nests between taxa with a heterocercal tail. With an Ordovician genesis, Late Devonian Euphanerops likely developed a dipping tail and larger propulsive dorsal fin secondarily, as a reversal. An ancestor, Birkenia, has a similar dipping tail.

Figure 4. Euphanerops caudal fin with elements re-identified.

Figure 4. Euphanerops caudal fin with elements re-identified.

Small enigmatic squares of rod-like elements near the cloaca
are here identified as primitive pelvic fins or vestiges of the same. More primitive taxa do not have pelvic fins. More derived taxa do.

Figure 3. Euphanerops with elements here identified as tiny pectoral fins just anterior to the cloaca.

Figure 5. Euphanerops with elements here identified as tiny pectoral fins just anterior to the cloaca and posterior to the ventral armor. Images from Janvier and Arsenault 2007.

Primitive pectoral fins
are known in ancestral and descendant taxa, so Euphanerops should have them, too. Here (Fig. 6) they are identified as vestiges.

Figure x. Euphanerops plate and counter plate with colors added identifying elements.

Figure 6. Euphanerops plate and counter plate with colors added identifying elements.

Traditionally sturgeons have not been tested with osteostracans
(Fig. 7) and other jawless fish. The LRT tests a wide gamut of competing candidates and nests sturgeons prior to the advent of jaws and teeth in vertebrates, close to osteostracans and Euphanerops. Do not let one or two traits, like a dipping (hypocercal) tail, steer you off course in your wide-gamut analysis.

Figure 7. Top to bottom: Thelodus a soft jawless fish with a ventral oral opening and gill slits, perhaps a hint of diamond-shaped armor laterally. Hemicyclaspis, adds extensive armor. Euphaneropsps, a late survivor of an Ordovician radiation basal to sturgeons. Acipenser, a sturgeon with a protrusible tube for a mouth and reduced armor. Chondrosteus, a fish with jaws, but no marginal teeth.

Figure 7. Top to bottom: Thelodus a soft jawless fish with a ventral oral opening and gill slits, perhaps a hint of diamond-shaped armor laterally. Hemicyclaspis, adds extensive armor. Euphaneropsps, a late survivor of an Ordovician radiation basal to sturgeons. Acipenser, a sturgeon with a protrusible tube for a mouth and reduced armor. Chondrosteus, a fish with jaws, but no marginal teeth.

The ‘paired fin ridges’ observed by Janvier and Arsenault
may be ray-like ossifications that gathered to produce the ventrolateral armor on sturgeons (Fig. 7) or were vestiges thereof. Additionally, that’s where basal chordate gonads are located.

A set of lamprey-like gill openings appear near the skull
of Euphanerops. This appears to be a retention of or reversal back to similar multiple openings seen in Birkenia (Fig. 1). Again, don’t judge a taxon by one or two traits. Test them all against a wide gamut of taxa, like the LRT. We may be seeing what happens a the transition from multiple gill openings to a sturgeon-like operculum here.


References
Janvier P, Desbiens S, Willett JA and Arsenault 2006. Lamprey-like gills in a gnathostome related Devonian jawless vertebrate. Nature 440:1183–1185.
Janvier P and Arsenault M 2007. The anatomy of Euphanerops longaevus Woodward, 1900, an anaspid-like jawless vertebrate from the Upper Devonian of Miguasha, Quebec, Canada. Geodiversitas 29 (1) : 143-216.
Woodward AS 1900. On a new ostracoderm fish (Euphanerops longaevus) from the Upper Devonian of Scaumenac Bay, Quebec, Canada. Magazine of Natural History ser. 7, 5: 416-419.

wiki/Euphaneropidae

Platysomus sheds new light on placoderms

Short one today.
One more fish enters the LRT. Some changes (like a prefrontal) are added to previously nested taxa.

Adding the Carboniferous fish,
Platysomus (Fig. 1) , to the large reptile tree (LRT, 1713+ taxa; Fig. 2) to no one’s surprise nests it with Cheirodus (= Chirodus, Amphicentrum; Fig. 1), a less stretched-out version.

The heresy is
these two taxa nest with catfish and placoderms (Fig. 2) when allowed to do so by taxon inclusion, as we’ve seen previously. Placoderms evolve from ordinary fish.

Figure 1. Platysomus and Cheirodus are both platysomids, related to catfish and placoderms. All these taxa lack maxillae.

Figure 1. Platysomus and Cheirodus are both platysomids, related to catfish and placoderms. All these taxa lack maxillae. Note the relabeling on Platysomus.

None of these taxa
have a maxilla and they share a long list of other synapomorphic traits.

Figure 3. Subset of the LRT focusing on fish and updated here.

Figure 3. Subset of the LRT focusing on fish and updated here. Catfish and placoderms are located in the center of this diagram.

Another traditional platysomid, 
Eurynotus (Fig. 4), is even closer to the placoderms Coccosteus (open sea predators) and Entelognathus (bottom dwellers).

Figure 2. Eurynotus is another platysomid, basal to the placoderms Coccosteus and Entelognathus.

Figure 2. Eurynotus is another platysomid, basal to the placoderms Coccosteus and Entelognathus. Sharp-eyed readers will notice several skull identity changes in placoderms based on what was learned from this taxon.

Platysomus parvulus (Agassiz 1843, Carboniferous to Permian; 18cm long) is a taller, more disc-like fish related to Cheirodus. Note the reduction of the mandible. Considered a plankton eater.

Apologies for the bone ID changes.
I’m learning as I go and revising the naming system so homologies with tetrapods can be more readily understood. Someone had to do it. Why wait until 2021 or thereafter?


References
Agassiz L 1833, 1837 in Agassiz L 1833-1843. Recherches sur les Poissons fossiles-I, I, III, Neuchatel, pp 1420.

 

The goblin shark (Mitsukurina) enters the LRT

Often hailed as ‘the most bizarre shark’,
the goblin shark, Mitsukurina owstoni (Jordan 1898; Figs. 1, 2) nests with the guitarfish (Rhinobatos) in the large reptile tree (LRT, 1710+ taxa). These two are sister to Isurus, the mako shark.

Figure 1. The skull of the goblin shark, Mitsukurina.

Figure 1. The skull of the goblin shark, Mitsukurina. Red arrow points to naris. The extended nasal region is full of ampullae that sense electrical activity produced by prey twitching muscles while hiding in the sea floor.

Figure 2. Classic diagram of the goblin shark, Mitsukurina.

Figure 2. Classic diagram of the goblin shark, Mitsukurina.

Mitsukurina owstoni (Jordan 1898; 3-4+m long) is the extant goblin shark, a transitional form leading from the mako shark to the guitarfish. This is a sluggish swimmer feeding on sea floor prey, sensing their electrical fields, snatching them with protrusible jaws, (as in guitarfish).

FIgure 3. Scapanorhynchus, and Early Cretacous goblin shark.

FIgure 3. Scapanorhynchus, and Early Cretacous goblin shark.

Scapanorhynchus lewisii (Davis 1887; 65cm to 3m long; Early Cretaceous) is a fossil goblin shark.

Figure 2. Rhinobatos, the guitarfish, and Rhina the bowhead guitarfish, are transitional to skates and rays, but not mantas. Note the ventral mouth and pectoral fins extending anterior to the orbits.

Figure 4. Rhinobatos, the guitarfish, and Rhina the bowhead guitarfish, are transitional to skates and rays, but not mantas. Note the ventral mouth and pectoral fins extending anterior to the orbits.

Rhinobatos rhinobatos (Linneaus 1758; up to 1.47m) is the extant common guitarfish, a transitional taxon between sharks and skates. The mouth and gills are below the pectoral fins that extend forward anterior to the eyes, which rise to the top of the skull.

Rhina anclystoma (Bloch and Schneider 1801) is a type of guitarfish. Still waiting for skull data to score this fish.


References
Bloch MC and Schneider JG 1891. Systema anclystoma.
|Davis JW 1887. The fossil fishes of the chalk of Mount Lebanon, in Syria. Scientific Transactions of the Royal Dublin Society, 2 (3): 457–636, pl. 14–38.
Jordan DS 1898. Description of a species of fish (Mitsukurina owstoni) from Japan, the type of a distinct family of lamnoid sharks. Proceedings of the California Academy of Sciences, Zoology. Series 3. 1 (6):199–204.
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/Common_guitarfish
wiki/Mitsukurina
wiki/Goblin_shark
wiki/Scapanorhynchus

Sturgeon + Paddlefish = Sturddlefish?

Galdy et al. 2020 bring us results of a mistake.
These gene scientists ‘accidentally’ mixed sturgeon (Figs. 1, 2) eggs with paddlefish (Fig. 3) sperm. Genetic hybrids (Figs. 4, 5 ) resulted.

From the abstract
“Two species from the families Acipenseridae and Polyodontidae, Russian sturgeon (Acipenser gueldenstaedtii, Brandt and Ratzeberg, 1833; functional tetraploid; Fig. 1) and American paddlefish (Polyodon spathula, Walbaum 1792, functional diploid; Fig. 2) were hybridized. The hybridization was repeated using eggs from three sturgeon and sperm from four paddlefish individuals.

Survival in all hybrid family groups ranged from 62% to 74% 30 days after hatching. This was the first successful hybridization between these two species and between members of the family Acipenseridae and Polyodontidae. Many individuals reached a size of approximately 1 kg by the age of one year under intensive rearing conditions.”

Figure 1. Acipenser, a sturgeon.

Figure 1. Acipenser, a sturgeon. I don’t see differences between the hybrids and this illustration created years ago.

Figure 1. Skull of Pseudoscaphorhynchus. Note the mouth is created by the lacrimal and surangular, not the maxilla and dentary, which are tooth-bearing bones in more derived fish.

Figure 2. Skull of Pseudoscaphorhynchus. Note the mouth is created by the lacrimal and surangular, not the maxilla and dentary, which are tooth-bearing bones in more derived fish.

Figure 4. Skull of Polyodon from a diagram published in Gregory 1938, plus a dorsal view and lateral photo.

Figure 3. Skull of Polyodon from a diagram published in Gregory 1938, plus a dorsal view and lateral photo. Note the real jaws here.

Figure 1. Photos from Kaldy et al. 2020, re-scaled to the scale bars.

Figure 4. Photos from Kaldy et al. 2020, re-scaled to the scale bars. Note the growth of the snout with size/age. Note the hybrids really do look like sturgeons, not paddlefish. No

Chondrosteus nests between sturgeons and paddlefish
in the large reptile tree (LRT, 1709+ taxa). So the sturgeon and paddlefish are not sisters.

  1. Sturgeons retain osteostracan armor. Paddlfeish lack armor.
  2. Sturgeons lack jaws. Paddlefish have jaws.
  3. Hybrids have armor and lack jaws, as in sturgeons, not paddlefish.
Figure 4. Principal component analysis (PCA) plot for morphometric characters from Kaldy et al. 2020.

Figure 5. Principal component analysis (PCA) plot for morphometric characters from Kaldy et al. 2020. Note the strong skew toward sturgeon traits in the hybrids.

Kaldy et al. provided a principal component analysis
for sturgeon traits, paddlefish traits and hybrid traits (Fig. 5). Their PCA showed a strong tendency toward sturgeon traits in the hybrid juveniles, as reflected in the morphology of theiir photos (Fig. 4).


References
Kaldy J et al. (12 co-authors) 2020.
Hybridization of Russian Sturgeon (Acipenser gueldenstaedtii, Brandt and Ratzeberg, 1833) and American Paddlefish (Polyodon spathula, Walbaum 1792) and Evaluation of Their Progeny. Genes 2020, 11, 753. https://www.mdpi.com/2073-4425/11/7/753

Online NYTimes article (click to view):

The above photo looks weird, but this specimen is little to no different from typical sturgeons.
Article by Annie Roth, NY Times writer, July 15, 2020

Figure x. Subset of the LRT, focusing on fish for July 2020.

Figure x. Subset of the LRT, focusing on fish for July 2020.

 

 

The silver sweep (Scorpis) enters the LRT basal to flatfish

No new heresies to report here.
Scorpis is widely considered basal to flatfish (= halibut, flounder and sole; Friedman 2008). As reported earlier with piranha, I needed to add a taxon to the large reptile tree (LRT, 1709+ taxa; Fig. x) to clarify issues, and flounders needed a non-flounder at their base. Not surprisingly, this gambit worked!

Figure 2. Scorpis skull from Gregory 1938. Colors added here. No asymmetry is present on this outgroup to the flatfish.

Figure 1. Scorpis skull from Gregory 1938. Colors added here. No asymmetry is present on this proximal outgroup to the flatfish.

Scorpis lineolata (Kner 1865; 30cm) is the extant silver sweep or false pompano. This deep, but narrow oceanic fish has a mouthful of sharp teeth, a deep lacrimal and a tall post parietal (= ‘soc’ here). This denizen of Australian waters feeds on plankton over rock reefs. Distinct from related taxa, the postfrontal (orange in Fig. 1) contacts the prefrontal (brown in Fig. 1).

Figure 2. Flatfish evolution from Scorpis to Psettodes and Cynoglossus.

Figure 2. Flatfish evolution from Scorpis to Psettodes and Cynoglossus.

The evolution of flatfish
(Fig. 2) finds Scorpis at the base and swimming upright with symmetrical left and right eyes.

When flatfish evolve to hug the sea floor
and bury themselves in loose sand note the forward progress of the pelvic fin and the rotation of the eyes to the top side.

Note the loss of teeth
in the basal flatfish, Heteronectes, followed by a taxon with extra long teeth in Psettodes.

Figure x. Subset of the LRT, focusing on fish for July 2020.

Figure x. Subset of the LRT, focusing on fish for July 2020.

According to the heretical LRT,
Scorpis was derived from the mackeral, Scomber. Sister taxa include the perch (Perca) and its descendants. Beyond that clade comes the threadfin (Polydactylus) and its descendants.

On a somewhat separate note:
Several paleontologists (most recently Nick Gardiner on Facebook) have noticed that homologous bones in fish, classic reptiles and mammals sometimes do not share the same name. This can stop immediately if biologists and paleontologists want that to happen. Just give all the bones the names found in reptiles. No more circumorbital series. No more zygoma. Now just call the cheekbone the jugal. Or at least use matching (= homologous) colors. At present the jugal is traditionally a bright cyan (Fig, 1). The benefits to such a change are self-evident.


References
Friedman M 2008. The evolutionary origin of flatfish asymmetry. Nature 454:209–212.
Kner R 1865. Reise Novara, Fische, 1865: 108, Sydney.

http://reptileevolution.com/hippoglossus.htm
wiki/Silver_sweep

One little ‘fix’ on the piranha premaxilla resolves phylogenetic issues

Confession time!
Now that I have discovered this error, the piranha (Serrasalmus, Figs. 1, 2) no longer disrupts the ‘flow’ of evolution in that corner of the large reptile tree (LRT, 1709+ taxa; Fig. x).

The mistake:
Previously I misidentified the upper tooth-bearing bone in Serrasalmus as the premaxilla. That I.D. matches the majority of bony fish in which the sutured premaxilla retains teeth and the loose maxilla sometimes lacks teeth.

Figure 1.  On the piranha, Serrasalmus, the premaxilla (yellow) does not extend to the tooth row. Instead the maxilla (green) carries all the upper teeth. Serrasalmus skeleton image courtesy of ©Steve Huskey and used with permission.

Figure 1.  On the piranha, Serrasalmus, the premaxilla (yellow) does not extend to the tooth row. Instead the maxilla (green) carries all the upper teeth. Serrasalmus skeleton image courtesy of ©Steve Huskey and used with permission.

The correction: 
As the anterior view of Serrasalmus shows (Fig. 2), the premaxilla (yellow) does not extend to the tooth row, distinct from all other fish. The upper teeth arise from the sutured maxilla (green), which meet anteriorly, distinct from all other fish. This uncorrected error vexed the resolution of the fish portion of the LRT for several months.

Figure 2. Anterior view of the piranha, Serrasalmus, showing the premaxilla does not extend to the tooth row.

Figure 2. Anterior view of the piranha, Serrasalmus, showing the premaxilla does not extend to the tooth row.

Serrasalmus rhombeus (Lacepède 1803) is one of the extant piranhas, predatory fish restricted to the Amazon River.  A deep, narrow and short body with a propensity to school distinguish this genus from its sisters. Note the sagittal crest.

Figure 1. Xiphactinus skull revised using Portheus as a guide. The 'shadow' area in the reconstruction indicates a lack of cheek bones, exposing the large pterygoids and quadrate.

Figure 1. Xiphactinus skull revised using Portheus as a guide. The ‘shadow’ area in the reconstruction indicates a lack of cheek bones, exposing the large pterygoids and quadrate.

Xiphactinus audax (Leidy 1870; Late Cretaceous; up to 6m in length) was a large traditional ray-fin fish.  The teeth are longer and stronger in this clade. Like the piranha a parasagittal crest is present. The torso is much longer.

Portheus molossus (Cope 1872; Late Cretaceous; is considered a junior synonym for Xiphactinus. However, note the expanded jugal and postorbital and different shapes for several other facial bones, included the tabular (red).

Figure 4. The skull of Portheus from Gregory 1938. Many workers consider this a junior synonym of Xipactinus.

Figure 4. The skull of Portheus from Gregory 1938. Many workers consider this a junior synonym of Xipactinus.

According to Schwimmer, Stewart and Williams 1997,
“Joseph Leidy and Edward D. Cope independently described the taxon as Xiphactinus audax Leidy 1870 and Portheus molossus Cope, 1871. Although Cope’s type specimen was a finely preserved individual, whereas Leidy’s type was an isolated pectoral fin spine, the rules of priority (Ride, et al. 1985) require that the widely-known name Portheus molossus be suppressed as a junior synonym. In their early descriptions of Xiphactinus and Portheus, Leidy and Cope followed prevailing practice and recognized numerous species, all of which, at least for North America, were subsequently subsumed into the single species X. audax by Bardack (1965). which was the last substantive taxonomic
analysis of the genus.”

Among living taxa,
Bardack (1965) allied Xiphactinus to the overall similar modern wolf-herring, Chirocentrus (Fig. 5) based on eyeballing it. That hypothesis predated MacClade and PAUP. By contrast, the LRT nests Chirocentrus with the lizardfish, Trachinocephalus and the viperfish, Chaulidos apart from Xiphactinus and Serrasalmus. 

Figure 1. The wolf herring (Chirocentrus) enters the LRT.

Figure 5. The wolf herring (Chirocentrus) enters the LRT.

Apparently the connection between
Xiphactinus and the piranha, Serrasalmus, was never made in the academic literature. While Googling I was able to find connections only in the popular press which promoted Xiphactinus as a giant fish with ‘piranha-like jaws’. Let me know if there is an earlier citation in the literature so I can promote it.

Figure x. Subset of the LRT, focusing on fish for July 2020.

Figure x. Subset of the LRT, focusing on fish for July 2020.

References
Bardack D 1965. Anatomy and evolution of Chirocentrid fishes. The University of Kansas Paleontological Contributions 10:1-88.
Cope ED 1871. Account of a journey in the valley of the Smoky Hill River in Kansas. Proceedings of the American Philosophical Society 12:174-176
de Lacepéde BG 1803. Histoire naturelle des poissons. Tome Cinquieme. 5(1-21):1-803 + index.
Leidy J 1870. [Remarks on ichthyodorulites and on certain fossil Mammalia]. Proceedings of the Academy of Natural Sciences, Philadelphia 22:12–13.
Schwimmer DR, Stewart JD and Williams GD 1997. Xiphactinus vetus and the distribution of Xiphactinus species in the Eastern United States. Journal of Vertebrate Paleontology 17(3):610–615.

wiki/Piranha
wiki/Serrasalmus
wiki/Xiphactinus

https://pterosaurheresies.wordpress.com/2020/02/02/the-wolf-herring-chirocentrus-enters-the-lrt/

Toothy Calamopleurus enters the LRT, but not with Amia

Short one today.
If you like fish with big teeth,
you’ll like Calamopleurus (Agassiz 1841, Early Cretaceous; Figs. 1, 2), a taxon typically considered a relative of the bowfin, Amia.

Figure 1. The skull of Calaomopleurus from Long 1995 and reconstructed using DGS methods.

Figure 1. The skull of Calamopleurus from Long 1995 and reconstructed using DGS methods.

When you add in a few more taxa,
Calamopleurus moves over a few nodes to nest with Trachinocephalus, the extant blunt-nosed lizardfish (Fig. 3) in the large reptile tree (subset Fig. x). That’s only one or two nodes away from Amia. That means the resemblance is homologous, not convergent.

Figure 2. Another specimen diagram of Calamopleurus.

Figure 2. Another specimen diagram of Calamopleurus. Looks like a bowfin, but it is closer to lizardfish.

Nesting where it does in the LRT,
(Fig. x) Calamopleurus is basal to virtually all other bony fish, including ray fins and lobefins, and that means this toothy fish if close to our own direct ancestry… and also sea horses, sailfish, catfish, spiny sharks and placoderms. That means this fish and this clade of fish had its genesis and initial radiation 300 million years earlier, in the Silurian.

Figure 3. The extant blunt-nosed lizardfish, Trachinocephalus, nests with Calamopleurus in the LRT.

Figure 3. The extant blunt-nosed lizardfish, Trachinocephalus, nests with Calamopleurus in the LRT.

It should come as no surprise
that this clade of fish also includes several hyper-toothy taxa, including Chiasmodon (Fig. 4) and Malacosteus (Fig. 5).

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

Figure 4. Chiasmodon from Gregory 1938, here colorized.

Based on the preponderance of big teeth
at the base of the big bony fish split (Fig. x), evidently ‘long, sharp teeth’ was a primitive trait later sometimes lost in both lineages.

Figure 2. Chauliodus, the viperfish, skull. Compared to the wolf herring in figure 1.

Figure 5. Chauliodus, the viperfish, skull.

The LRT proposes a hypothesis of interrelationships
previously untested with extant and extinct taxa from several traditional clades here (Fig. x) tested together for the first time.

Figure x. Subset of the LRT, focusing on fish for July 2020.

Figure x. Subset of the LRT, focusing on fish for July 2020.

LRT change:
The enigmatic wide-mouth, big-eyed fish, Doliodus, now nests with the spiny sharks, Homalacanthus and Acanthoides. a few nodes apart from Xenacanthus, which also has twin-spiked teeth.


References
Agassiz L 1833-43. Recherches sur les poissons fossiles. Imprimerie de Petitpierre et Prince, Neuchâtel.

Vaškaninová et al. 2020 test placoderms to describe the origin of marginal teeth

Vaškaninová et al. 2020 
employ several partial placoderms from Czechoslovakia to demonstrate the antiquity of lingual tooth growth (= from the inside out as in modern fishes; Fig. 1).

Unfortunately taxon exclusion mars this study.
Following tradition, the team thought derived placoderms (in the process of losing their teeth) were primitive taxa just gaining teeth (Fig. 1). Like other workers before them, they omitted too many taxa.

By contrast and using a wider gamut of taxa,
we looked at the origin of marginal teeth earlier here. Marginal teeth first appeared in the late-surviving basal paddlefish, Tanyrhinichthys (Fig. 2). The outgroup taxon, late-shriving Chondrosteus, (Fig. 3) lacked teeth and tooth-bearing bones (the premaxilla, maxilla and dentary).

From the Vaškaninová et al. 2020 abstract:
“The dentitions of extant fishes and land vertebrates vary in both pattern and type of tooth replacement. It has been argued that the common ancestral condition likely resembles the nonmarginal, radially arranged tooth files of arthrodires, an early group of armoured fishes. We used synchrotron microtomography to describe the fossil dentitions of so-called acanthothoracids, the most phylogenetically basal jawed vertebrates with teeth, belonging to the genera Radotina, Kosoraspis, and Tlamaspis (from the Early Devonian of the Czech Republic).

Note: In the LRT these taxa are placoderms in the process of losing their teeth. Teeth developed much earlier in the family tree (Fig. 4).

“Their dentitions differ fundamentally from those of arthrodires; they are marginal, carried by a cheekbone or a series of short dermal bones along the jaw edges, and teeth are added lingually as is the case in many chondrichthyans (cartilaginous fishes) and osteichthyans (bony fishes and tetrapods). We propose these characteristics as ancestral for all jawed vertebrates.”

Figure 3. Omitting many pertinent taxa, Vaskaninova et al. constructed this cladogram of tooth evolution. The LRT uses a wider gamut of taxa and recovers a different tree topology.

Figure 1. Omitting many pertinent taxa, Vaskaninova et al. constructed this cladogram of tooth evolution. The LRT uses a wider gamut of taxa and recovers a different tree topology. See figure 4.

In the Vaškaninová et al. 2020 study
basal fish, both jawless and not, are all armored.

Here
in the large reptile tree (LRT, 1707+ taxa) the origin of jaws lacking teeth is close to Chondrosteus (Fig. 3), a derived sturgeon (Fig. 10). In Chondrosteus the upper jaw is the lacrimal. The premaxilla and maxilla have not appeared yet. The lower jaw likewise lacks a dentary and is composed of the surangular and angular.

Figure 2. Skull of Tanyrhinichthys (above) with two bones relabeled. The other fish, Saurichthys, is clearly unrelated.

Figure 2. Skull of Tanyrhinichthys (above) with two bones relabeled. The other fish, Saurichthys, is clearly unrelated. The origin of tiny marginal teeth is close to Tanyrhinnichthys, a basal paddlefish (Fig. 2), the next moreb derived clade in the LRT. The tooth bearing bones (premaxillla, maxilla and dentary) originate as slender dermal layers on the lacrimal and surangular carrying tiny teeth, not much larger than skin denticles.

Adding taxa in the LRT
separates armored Devonian placoderms from armored Silurian jawless fish.

Figure 1. Chondrosteus animation (2 frames) in situ and reconstructed in lateral view. This is the transitional taxon linking sturgeons to bony fish + sharks.

Figure 3. Chondrosteus animation (2 frames) in situ and reconstructed in lateral view. This is the transitional taxon linking sturgeons to bony fish + sharks.

Chronology is not as helpful as phylogeny
in figuring out these transitions, so much so that extant taxa need to be added to fill out the tree topology (Fig. 4).

Figure x. Subset of the LRT, focusing on fish for July 2020.

Figure x. Subset of the LRT, focusing on fish for July 2020.

Members of the Placodermi
like their relatives the catfish, are relatively derived taxa in the LRT (Fig. 4). Marginal teeth are missing in catfish and placoderms because they both have lost the maxilla along with their last common ancestor, taxa near late-surviving Diplacanthus.

Figure 5. Radotina is a basal taxon in the Vaskaninova et al. cladogram (Fig. 1).

Figure 5. Radotina is a basal taxon in the Vaskaninova et al. cladogram (Fig. 1). Compare to Romundina (Fig. 6) another basal taxon in Vaskaninova et al.

Basal taxa in the Vaskaninova et al. cladogram,
Romundina (Fig. 6) and Radotina (Fig. 5) are rather specialized terminal taxa in the LRT, leaving no descendants. Chondrosteus and Tanyrhinichthys are more generalized and primitive. All living fish, other than sturgeons (Fig. 10), whale sharks and mantas, are derived from Silurian sisters to these two taxa in the LRT.

Figure 10. What little we know of Radotina and where the same bone appears on the more complete Romundina, a terminal taxon in the Placodermi.

Figure 6. What little we know of Radotina and where the same bone appears on the more complete Romundina, a terminal taxon in the Placodermi.

Vaškaninová et al. provide the parts for Kosoraspis
(Fig. 7), a basal taxon without resolution in figure 1. Here (Fig. 8) I provide a possible restoration in which the large curved green bone identified as the ‘preopercular’ is re-identified as a postfrontal (orange in Fig. 8) based on similarities to Clarias, the walking catfish (Fig. 9).

Figure 8. From Vaškaninová et al. 2020, the parts for Kosoraspis. See figure 9 for a reconstruction where the largest bone here (green preopercular) is relabeled a postfrontal.

Figure 7. From Vaškaninová et al. 2020, the parts for Kosoraspis. See figure 9 for a reconstruction where the largest bone here (green preopercular) is relabeled a postfrontal.

Figure 9. Kosoraspis restored as a Devonian catfish like Clarias (Fig. 10).

Figure 8. Kosoraspis restored as a Devonian catfish like Clarias (Fig. 10). Those tooth plates are similar to those in catfish.

FIgure 1. Clarias, the walking catfish is a living placoderm with skull bones colorized as homologs of those in Entelognathus (Fig. 2). Here the mandible shifts forward and the opercular shifts backwards relative to Entelongnathus in the Silurian.

FIgure 9. Clarias, the walking catfish is a living placoderm with skull bones colorized as homologs of those in Entelognathus (Fig. 2). Here the mandible shifts forward and the opercular shifts backwards relative to Entelongnathus in the Silurian.

Determining when teeth and jaws first appeared
in basal vertebrates has been a contentious issue largely because pertinent taxa have been left out of the solution. Apparently Vaškaninová et al. left out several taxa key to understanding this transition from toothless jaws to toothy jaws. They considered taxa in the process of losing teeth, but placed them at the genesis of developing teeth.

Once again,
more taxa resolve problems like this better than more characters do.

Figure 1. Top to bottom: Thelodus a soft jawless fish with a ventral oral opening and gill slits, perhaps a hint of diamond-shaped armor laterally. Hemicyclaspis, adds extensive armor. Acipenser, a sturgeon with a protrusible tube for a mouth and reduced armor.

Figure 10. Top to bottom: Thelodus a soft jawless fish with a ventral oral opening and gill slits, perhaps a hint of diamond-shaped armor laterally. Hemicyclaspis, adds extensive armor. Acipenser, a sturgeon with a protrusible tube for a mouth and reduced armor.

If this helps,
here again (Fig. 10) are three taxa preceding the origin of jaws with marginal teeth. These interrelationships have gone unnoticed by fish workers who continue to nest sturgeons with jawed fishes. The next taxon following these three had large jaws: Chondrosteus (Fig. 3).

Figure 11.  Manta compared to Thelodus (Loganellia) and Rhincodon. All three have a terminal mouth essentially straight across, between the lateral eyes, distinct from most fish. Note the lack of teeth. 

Figure 11.  Manta compared to Thelodus (Loganellia) and Rhincodon. All three have a terminal mouth essentially straight across, between the lateral eyes, distinct from most fish. Note the lack of teeth.

Here again are whale sharks and mantas
(Fig. 11) on their own branch derived from Silurian sisters to Thelodus and LoganelliaThese taxa have jaws, but lack marginal teeth, similar to Chondrosteus (Fig. 3).

As mentioned above,
it is so important to include a wide gamut of taxa, including extant taxa.


References
Vaškaninová V, Chen D, Tafforeau P, Johanson Z, Ekrt B, Blom H and Ahlberg PE 2020. Marginal dentition and multiple dermal jawbones as the ancestral condition of jawed vertebrates. Science 369(6500): 211-216 DOI: 10.1126/science.aaz9431
https://science.sciencemag.org/content/369/6500/211

placoderm jaws

News:
https://phys.org/news/2020-07-advanced-technology-evolution-teeth.html