Did shark skeletons evolve from bony ancestors?

Did bone precede cartilage in sharks? 
Or did shark-like cartilage precede bone in bony fish?

Good question.
A good answer will come from a cladogram that accurately mirrors evolutionary events.

Brazeau et al. 2020 bring us
a new, partial placoderm skull, Minjinia turgenensis (Fig. 1), that preserves a great deal of internal bone, and not a lot of dermal bone. Brazeau et al. think their specimen answers the above questions because they think placoderms phylogenetically precede sharks + bony fish.

Figure 1. Minjina in 4 views, mirror-image and colors added.

Figure 1. Minjina in 4 views, mirror-image, tail, pectoral fins and colors added for clarity.

From the Brazeau et al. 2020 text:
“Chondrichthyans (sharks and their kin) are the living sister group of osteichthyans and have primarily cartilaginous endoskeletons, long considered the ancestral condition for all jawed vertebrates (gnathostomes). Phylogenetic analyses place this new taxon [Minjinia turgenensis] as a proximate sister group of the gnathostome crown. These results provide direct support for theories of generalized bone loss in chondrichthyans. Furthermore, they revive theories of a phylogenetically deeper origin of endochondral bone and its absence in chondrichthyans as a secondary condition.”

What came first? The large reptile tree (LRT, 1733+ taxa; subset Fig. x) supports the hypothesis that the absence of endochondral bone in sharks and ratfish is a primitive trait retained from more primitive sturgeons (Pseudoscaphorhynchus) and paddlefish (Polyodon).

According to Wikipedia, sturgeons “are unique among bony fishes because their skeletons are almost entirely cartilaginous.”

According to the Caddo Lake Institute, “The only bone in the [paddle] fish’s body is the jawbone.”

What about placoderms? The LRT nests placoderms deep within one branch of osteichtheys close to catfish. The internal and external placoderm skeleton is made of strong bone. Not sure why this major item of evidence has been traditionally overlooked.

Brazeau et al. continue:
“The absence of bone in modern jawless fishes and the absence of endochondral ossification in early fossil gnathostomes appear to lend support to this conclusion.”

Not really. Sturgeons are pre-gnathostomes in the LRT (subset Fig. x). They are at the genesis of jaws, rather than derived taxa losing their jaws, as commonly thought.

Unfortunately,
extensive taxon exclusion ruins the basics of Brazeau et al. 2020.

Instead
the LRT nests Minjinia with the small, unnamed and better preserved bottom-feeding placoderm ANU  V244 specimen (Fig. 2), a more complete taxon not mentioned by Brazeau et al. 2020. Both nest between the more famous bottom-dwelling placoderms Entelognathus and Bothriolepis.

Figure 1. The tiny ANU V244 specimen in various views. Note the scale bars.

Figure 2. The tiny ANU V244 specimen in various views. Note the scale bars.

Considering the fact that sturgeons and paddlefish have so little bone,
sharks and ratfish don’t have that much bone to lose. We just have to remember to take sturgeons and paddlefish out of the clade of bony fish and put them where the LRT (Fig. x) indicates they nest.

Like other fish workers,
Brazeau et al. 2020 used an out-dated traditional cladogram missing so many pertinent taxa that placoderms nested basal to jawed fish. In the LRT (Fig. x) placoderms nest alongside catfish deep within one branch of the Osteichthyes.

Figure x. Subset of the LRT focusing on fish.

Figure x. Subset of the LRT focusing on fish.

The publicity for Minjinia has been extraordinary.
Sci-News.com reported,
“This discovery suggests the lighter skeletons of sharks may have evolved from bony ancestors, rather than the other way around.”

While true, as shown by the LRT (Fig. x), the phylogenetic context of this placoderm fossil was greatly in need of additional taxa.

From cosmosmagazine.com:
“This 410-million-year-old fossil with a bony skull uncovered in Mongolia may force a rethink of how sharks evolved. Minjinia turgenensis, a new species, is an ancient cousin of both sharks and animals with bony skeletons, the researchers say – and that suggests the lighter skeletons of sharks may have evolved from bony ancestors, rather than the other way around.”

Too few taxa mar this study. In the LRT Minjinia does nest with placoderms, but placoderms nest far from sharks, closer to catfish.

Co-author Martin Brazeau was reported as saying,
“Conventional wisdom says that a bony inner skeleton was a unique innovation of the lineage that split from the ancestor of sharks more than 400 million years ago, but here is clear evidence of bony inner skeleton in a cousin of both sharks and, ultimately, us.”

Not related to sharks. Add taxa and placoderms move close to catfish.

“M. turgenensis belongs to a broad group of fish called placoderms, out of which sharks and all other jawed vertebrates – animals with backbones and mobile jaws – evolved.”

False. The loss of the mandible in one branch of the placoderms should not be confused with the genesis of the mandible in the clade Gnathostomata following sturgeons, a clade at the genesis of jaws in the LRT.

Again, from cosmosmagazine.com:
“The new find suggests the ancestors of sharks first evolved bone and then lost it again, rather than keeping their initial cartilaginous state for more than 400 million years, the researchers say.”

Not exactly true.  Sturgeons and paddlefish are more primitive and have very little bone. Placoderms, like Minjinia (Fig. 1) have lots of bone and nest deep within bony fish.

Sometimes scientists rush off to get publicity
BEFORE waiting a suitable amount of time for feedback (confirmation or refutation). In this case the peer-review process apparently failed because everyone was working from an old playbook. So did the publicity process.


References
Brazeau et al. (7 co-authors) 2020. Endochondral bone in an Early Devonian ‘placoderm’ from Mongolia. Nature Ecology & Evolution. https://doi.org/10.1038/s41559-020-01290-2
Hu Y, Lu J and Young GC 2017. New findings in a 400 million-year-old Devonian placoderm shed light on jaw structure and function in basal gnathostomes. Nature Scientific Reports 7: 7813 DOI:10.1038/s41598-017-07674-y

https://cosmosmagazine.com/nature/evolution/new-thoughts-on-how-sharks-evolved/
http://www.sci-news.com/paleontology/minjinia-turgenensis-08823.html

 

Tiny Janusiscus enters the LRT in the lungfish clade

Giles et al. 2015 looked at
the tiny (1cm wide) fossil skull roof of Janusiscus schultzei (Fig. 1) and nested it between placoderms and bony fish + spiny sharks + sharks. This represents yet another example of taxon exclusion in a traditional family tree of fossil fish.

From the abstract:
“The phylogeny of Silurian and Devonian (443–358 million years (Myr) ago) fishes remains the foremost problem in the study of the origin of modern gnathostomes (jawed vertebrates). A central question concerns the morphology of the last common ancestor of living jawed vertebrates, with competing hypotheses advancing either a chondrichthyan-or osteichthyan-like model. Here we present Janusiscus schultzei gen. et sp. nov., an Early Devonian (approximately 415 Myr ago) gnathostome from Siberia previously interpreted as a ray-finned fish, which provides important new information about cranial anatomy near the last common ancestor of chondrichthyans and osteichthyans.”

Five years ago, when Giles et al. 2015 was published,the LRT included few to no fish. Today that problem has been rectified (subset Fig. x).

Figure 1. Tiny Janusiscus compared to the much larger lungfish relative, Uranolophus.

Figure 1. Tiny Janusiscus compared to the much larger lungfish relative, Uranolophus.

The large reptile tree (LRT, 1733+ taxa; subset Fig. x) employs a much wider gamut of taxa than traditional fish cladograms, like those used by Giles et al. 2015. Here tiny Janusiscus nests with the much larger and coeval Uranolophusknown since 1968.

Figure x. Subset of the LRT focusing on fish.

Figure x. Subset of the LRT focusing on fish. Here Janussicus (not listed) nests with Uranolophus and other lungfish.

Given the tiny size of Janusiscus
one wonders if it is a hatchling or juvenile of a larger genus, like Uranolophus?


References
Giles S, Friedman M and Brazeau MD 2015. Osteichthyan-like conditions in an Early Devonian stem gnathostome. Nature 520(7545):82–85.

The lamprey (Pteromyzon) enters the LRT, but not as a fish

Is the lamprey,
Pteromyzon (Fig. 1), the basalmost fish? Or is it a large, derived lancelet (Fig. 2) with eyes, external gill openings and parasagittal fins?

Figure 1. Lamprey adult (Pteromyzon) and larvae in vivo and sagittal section.

Figure 1. Lamprey adult (Pteromyzon) and larvae in vivo and sagittal section.Pteromyzon marinus (Linneaus 1758) is the extant lamprey, a large lancelet in which some metamorphiosized adults attach themselves to fish to suck their blood. Others do not feed as adults, but live off reserves obtained by filter feeding while young. The gill openings open to the outside, not into an atrium.

The answer might come down to the question,
is a skull present in lampreys? Fish have a skull (Fig. 4). Lancelets (Fig. 2) do not.

Figure 2. Extant lancelet (genus: Amphioxus) in cross section and lateral view. The gill basket nearly fills an atrium, which intakes water + food, sends the food into the intestine and expels the rest of the water.

Cambrian lancelets
like Metaspriggina (Fig. 3) have eyes, but no skull. So do flatworms, lampreys and conodont animals. Transitional taxa between flatworms and lampreys, like nematodes and extant lancelets, lack eyes. So do all the closest relatives of basal chordates: echinoderms, crinoids, tunicates. The loss of eyes appears to be a derived trait in hagfish (Fig. 3) and, by convergence, chordate relatives derived from lancelets. Lamprey eyes are complex structures that took a long time to evolve. Apparently blindness is a derived trait on generally sessile chordate cousins, starting with lancelets.

Figure 1. Hagfish and lamprey cranial organs compared to the lancelet, Metaspriggina.

Figure 3. Hagfish and lamprey cranial organs compared to the lancelet, Metaspriggina. No dermal skull material, other than the nasal, is present in the lamprey.

Perhaps now is a good time to consider definitions
to help decide the lamprey ‘fish or lancelet’ question.

According to Wikipedia (Lamprey),
Lampreys are an ancient extant lineage of jawless fish of the order Petromyzontiformes, placed in the superclass Cyclostomata.

According to Wikipedia (Fish),
Fish are gill-bearing aquatic craniate animals that lack limbs with digits.”

Note that both definitions rely on traits,
not phylogenetic placement.

Even so,
does the lamprey skull (= cranial and annular cartilage) have homologs in the dermal skull of craniates?

Not really, except perhaps, the nasal,
which is the largest bone/cartilage in many basal fish. The appearance of more dermal cranial bones would have been phylogenetically gradual. We wait until Drepanaspis, Drepanolepis and Birkenia for cranial homologs of many bones to appear in these valid jawless craniates.

You might think the loss of eyes in lancelets
resulted in the loss of primitive cartilage structures that held the eyes, as in large-eyed conodonts, but even in lampreys, such dermal skull structures are not present (Fig. 1).

It’s always phylogeny, not a short list of defining traits.
In the large reptile tree (LRT, 1729+ taxa; subset Fig. 5) the last common ancestor of lampreys (genus: Pteromyzon; Fig. 1), is the lancelet Metaspriggina (Fig. 3) The last common ancestor of all extant fish is Euphanerops, another jawless fish from the Late Devonian with an earlier radiation in the Silurian. Middle Silurian Birkenia (Fig. 4) is the most primitive fish with skull bones homologous with those of extant fish. A less primitive, Early Silurian Jamoytius (Fig. 5) has been considered a sister to lampreys, but in the LRT nests between Birkenia and Thelodus.

Figure 3. Birkenia skull for comparison to Jamoytius.

Figure 4. Birkenia skull has bones still found in derived craniates, including fish, birds and mammals. Here the nasal is still the largest skull bone.

Armored lancelets
Arandaspis
, and Porapsis have an armored gill chamber with few to no bone homologs with those of living craniates. Yes, that armor forms a sort of skull, but it is not the same skull as in Birkenia and its craniate descendants. Arandaspis, and Porapsis have been called primitive fish, but phylogenetically precede valid craniates, which means they cannot be ‘fish’, by definition. For the same reason, neither can the lamprey, Pteromyzon, be called a fish.

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

Figure 5. Subset of the LRT focusing on basal chordates and Jamoytius (at right).

Lamprey origins
go back to the early Ordovician. 38 extant and 5 extinct species are known. Like other lancelets and basal fish, primitive and young lampreys are filter feeders. The closest living relatives of lampreys are hagfish (Fig. 2) and lancelets.

As hypothesized earlier
here, the lack of a lens, iris and eyeball in lancelets was retained by derived taxa including tunicates and echinoderms, distinct from the order proposed by Romer and others.

Another point-of-view, according to Gregory 1933:
“The profound researches of Stensio (1927) and Kiser (1924) have left no reasonable doubt however, that one or another of the ostracoderms gave rise to the modern class of cyclostomes, including the lampreys and hags, thus confirming the earlier views of Cope and others.”

Gregory 1933 continues:
“Both Gaskell and Stensio have shown the striking similarities of the larval lamprey head to that of the cephalaspid ostracoderms and in the light of much evidence it seems highly probable that the lamprey skull type has been derived from a cephalaspid-like type in the following way:

  1. “the bony exoskeleton has lost its bone cells and become membranous; 
  2. thorny epidermal teeth have developed around the sucker-like mouth;
  3. rasping apparatus has developed out of the so-called tongue, which is a specialized part of the branchial apparatus;
  4. the rest of the branchial arches have been displaced backward;
  5. the cartilages that support the sucker and its teeth have also been enlarged; 
  6. the originally continuous cartilaginous septa between the gill-pouches have become fenestrated, giving rise to the branchial basket;
  7. a special hydraulic organ, described by T. E. Reynolds (1931) has been developed in the oral chamber to assist in the sucking action of the mouth.”

LRT arguments to Gregory’s 1933
ostracoderm ancestry for lampreys based on the LRT:

  1. Gregory has it backwards: the bony exoskeleton had not developed yet;
  2. Agreed. Lamprey ‘teeth’ are not homologous with those of gnathostomes;
  3. Or the tongue is a new medial organ not associated with paired lateral branchials;
  4. Not displaced relative to LRT sisters;
  5. Agreed;
  6. Or the fenestrations are derived from sisters to Metaspriggina, unknown in 1933;
  7. Agreed, but only a few lampreys are blood suckers and no juveniles are bloodsuckers.

This is not the first time the LRT has been in the minority.
In the LRT(subset Fig. 5) the lamprey is several nodes more primitive than the ostracoderm, Hemicyclaspis, a sturgeon ancestor with pectoral fins, armor and a heterocercal tail. Again, the best way to find out what a taxon is, is to nest it in a wide gamut cladogram like the LRT.


References
Gregory WK 1933. Fish skulls. A study of the evolution of natural mechanisms. American Philosophical Society 23(2) 1–481.
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/Branchiostoma
wiki/Lamprey_Pteromyzon
wiki/Birkenia
wiki/Jamoytius

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