Evolution of the Dinosaurs YouTube video by Manabu Sakamoto PhD

One of Dr. Sakamoto’s major interests is
“How did major groups of animals radiate?” So we have similar interests. This slide show lecture apparently on ZOOM (or a similar format) is 56 minutes in duration and was streamed live March 12, 2021.

Sakamoto received his PhD from the U of Bristol in England,
which does not bode well. That’s where too many recent myths about pterosaurs and dinosaurs had their genesis.

In his slide labeled ‘Birds are dinosaurs’
Sakamoto includes an illustration of Microraptor (Fig. 1), which has wings and feathers, but is not a bird in the large reptile tree (LRT, 1817+ taxa), but a bird mimic arising from Ornitholestes  (Fig. 1). Sakamoto had so many birds to choose from, but chose a non-bird.

Figure 1. Changyuraptor to scale with Ornitholestes, Scriurumimus and Microraptor.

Figure 1. Changyuraptor to scale with Ornitholestes, Scriurumimus and Microraptor.

In his slide labeled ‘What makes a dinosaur?’
Sakamoto includes four illustrations and photos of four traits he reports are common to dinosaurs. That’s called a “Pulling a Larry Martin” because it is fraught with convergence in various non-dinosaurs. He should have used the “Last Common Ancestor (LCA) hypothesis.

In his slide labeled ‘Dinosauromorphs’
Sakamoto includes lagerpetids and notes reduced toes 1 and 5. That’s not true of sauropods, which have a huge toe 1. Lagerpetids are not related to dinosaurs when more taxa are added. Lagerpetids are proterochampsids convergent with dinosaurs. He lists Marasuchus among the dinosauromorphs. In the LRT it nests as a basal theropod even though the acetabulum is 90% not-perforated, as in ankylosaurs (see “Pulling a Larry Martin” above).

So far, not so good,
and we’re only 16 minutes into the video. So glad I did not waste time and money getting an education at the University of Bristol, like Dr. Sakamoto did. The professional academic Bristol program in dinosaurs is evidently behind the times.

In his slide labeled ‘A modern definition of Dinosauria’
Sakamoto correctly reports, dinosaurs are “members of the least inclusive clade containing Triceratops horridus and Passer domesticus (house sparrow),” but incorrectly includes ‘Dinosauromorphs’ as outgroup taxa between Crocodylomorpha and Dinosauria. In the LRT there are no taxa between Crocodylomorpha and Dinosauria.

In his slide labeled ‘major dinosaur groups’
Sakamoto reaches into the past to divide dinosaurs into Saurischia and Ornithischia. By contrast the LRT, with more taxa, divides dinosaurs into Theropoda and Phytodinosauria (Fig. 2) with a set of herrerasaurids preceding this split. So far Sakamoto is extending the reputation of U of Bristol for perpetuating myths.

Figure 2. Subset of the LRT focusing on the Phytodinosauria with Buriolestes at its base.

Figure 2. Subset of the LRT focusing on the Phytodinosauria with Buriolestes at its base.

In his slide labeled ‘…but there is only one true tree!’
Sakamoto presents his best estimate from data: an unresolved branching of Sauropodomorpha, Theropoda and Ornithischia. Based on what Sakamoto has presented thus far, the problem in Sakamoto’s presentation appears to be due to taxon exclusion. The LRT fully resolves the origin of dinosaurs by including more taxa. So why go to Bristol when you can learn with complete resolution online here?

In his slide ‘Dating dinosaur origins’
Sakamoto attempts to time the origin of dinosaurs, but without resolution or precise timing. In the LRT the dino-croc split occurred prior to the Ladinian (Late Middle Triassic) when the most primitive LCA of Dinosauria, PVL 4597 roamed South America.

 

Figure 4. The PVL 4597 specimen nests at the base of the Archosauria, not with Gracilisuchus.

Figure 3. The PVL 4597 specimen nests at the base of the Archosauria, not with Gracilisuchus.

In his slide ‘Early dinosaurs spread across the globe,
but started out just in the Southern hemisphere’ Sakamoto graphically considers Ladinian Lagerpeton and Asilisaurus ‘Basal Dinosauromorpha’, but verbally calls them early dinosaurs. Neither are dinosaurs in the LRT. Asilisaurus is a poposaur, the proximal outgroup for the Archosauria. Like many of his contermporaries, Sakamoto completely ignores the basal bipedal crocodylomorphs that the LRT nests as the proximal outgroup to the Dinosauria.

At this point we’re 30 minutes in
and very little Sakamoto has reported so far is verified by the LRT.

So we’re going to stop here.
The ratio of myth to fact is way too high. The ratio of missing taxa to included taxa is also way to high. Sakamoto now teaches at the U of Lincoln. If you are thinking of spending tuition money there, you have this preview to help you in your decision.

 

 

 

 

 

 

 

 

 

 

You heard it here first: Ichthyostega and Acanthostega were secondarily aquatic

In this YouTube video from 2018
Dr. Donald Henderson starts his online slide video presentation by repeating the traditional fin-to-finger story (Fig. 1).

Unfortunately
that story was already out-of-date in 2018 due to taxon exclusion in comparison to and competition with the phylogenetic analysis found in the large reptile tree (LRT, 1817+ taxa; subset Fig. 5).

Not surprisingly, Dr. Henderson thought it was “very peculiar”
that Middle Devonian tetrapod trackways preceded the Late Devonian fossils of tetrapods by tens of millions of years. The LRT solves this problem. Acanthostega and Ichthyostega are not transitional taxa, but dead end taxa with polydactyly not found in other tetrapod taxa. Their phylogenetic ancestors filled the gap between the Middle and Late Devonian, but those fossils have not been found yet in those strata, only in later strata as late survivors of those earlier radiations.

In the middle of the presentation
Dr. Henderson presented his alternative view: that Ichthyostega and Acanthostega were secondarily aquatic tetrapods. His YouTube video is dated January 11, 2018. Only a short month earlier the LRT recovered Ichthyostega and Acanthostega as secondarily more aquatic tetrapods, time-stamped here.

Evidently that was an idea whose time had come.
Or else Dr. Henderson read that hypothesis here and embraced it. Either way, Dr. Henderson did not employ phylogenetic analysis, but came to his solution as a notion to reconcile the Middle Devonian tracks to the late Devonian fossils.

Otherwise
Dr. Henderson’s presentation was mundane. Henderson’s customary family tree of vertebrates (Fig. 1) indicates he had no idea how clades of fish are related to one another at a species level (Fig. 2). He never tested traditional hypotheses, but accepted them without reservation.

Figure 1. Slide from Henderson's YouTube video with connections between clades highlighted in frame 2.

Figure 1. Slide from Henderson’s YouTube video with connections between clades highlighted in frame 2.

The fish phylogeny problem was resolved
here in 2019 and continues to evolve with every added taxon.

Figure 4. Shark skull evolution according to the LRT. Compare to figure 1.

Figure 2. Shark skull evolution according to the LRT. Compare to figure 1.

Dr. Henderson also presents a traditional lineup
of tetrapods (Fig. 3) that was improved by the LRT by simply adding overlooked taxa (Fig. 4).

Figure 3. Slide from Henderson YouTube presentation modified in frame 2 to reflect the order of basal tetrapods in the LRT. Missing here is Trypanognathus (Fig. 3) and kin, basal tetrapods in the LRT.

Figure 3. Slide from Henderson YouTube presentation modified in frame 2 to reflect the order of basal tetrapods in the LRT. Missing here is Trypanognathus (Fig. 4) and kin, basal tetrapods in the LRT.

Henderson’s traditional lineup is lacking several taxa,
like Trypanognathus (Fig. 4), that are also long, low and with tiny limbs, like Tiktaalik and Panderichthys, but are traditionally never included in fin-to-finger cladograms, other than here in the LRT.

Figure 6. Dorsal and ventral views of Panderichthys and several basal tetrapods demonstrating the low, flat skulls and bodies with small limbs and relatively straight ribs.

Figure 4. Dorsal and ventral views of Panderichthys and several basal tetrapods demonstrating the low, flat skulls and bodies with small limbs and relatively straight ribs.

It’s nice to have a notion, like Dr. Henderson had.
After all, that’s where all scientific inquiry has its genesis. But you can’t beat a good old, wide gamut phylogenetic analysis to make your notion into a testable hypothesis that covers all the other competing hypotheses. Let’s hope that someday PhDs will adopt a taxon list comparable to the LRT and then let the taxa and their taxonomy tell the tale.

Figure 4. Subset of the LRT focusing on basal tetrapods. Colors indicate number of fingers known. Many taxa do not preserve manual digits.

Figure 5. Subset of the LRT focusing on basal tetrapods. Colors indicate number of fingers known. Many taxa do not preserve manual digits.

Colleagues,
follow up those notions with testable analyses. It’s hard work, but it’s the professional thing to do.


References
https://pterosaurheresies.wordpress.com/2017/12/15/ichthyostega-and-acanthostega-secondarily-more-aquatic/

Cretaceous Aquilolamna nests with Devonian Palaeospondylus in the LRT

Summary for those in a hurry
The authors excluded related taxa that would have helped them identify their strange, new 1.6 m shark with elongate pectoral fins. The authors also failed to identify the correct mouth, eyes, nasal capsules and gill slits.

Vullo et al. 2021 bring us a wonderful new 1.6m Turonian elasmobranch
with graceful, really long, pectoral fins, Aquilolamna milarcae (INAH 2544 P.F.17, Figs. 1, 2). The authors tentatively assigned (without a phylogenetic analysis) their fossil shark to lamniformes, like the mako shark, Isurus, which has a standard underslung mouth and overhanging rostrum. Vullo et al. thought Aquilolamna was a filter-feeder by assuming that it had a wide, ‘near-terminal mouth’ without teeth, as in the manta ray (genus: Manta). That morphology is distinct from lamniformes like Isurus.

This is a difficult fossil to interpret.
More than the fins make Aquilolamna different than most other fossil and extant sharks.

Unfortunately
Vullo et al. put little effort (Fig. 2 diagram) into their attempt to understand the many clues Aquilolamna left us. Those clues are documented here (Fig. 2) by using DGS (= color tracings) and tetrapod homologs for skull bones.

Figure 1. Aquilolamna in situ from Vullo et al. 2021. Colors added here.

Figure 1. Aquilolamna in situ from Vullo et al. 2021. Colors added here.

For proper identification, it didn’t help that Vullo et al. 

  1. imagined the mouth wide and in front, instead of small and below the occiput
  2. imagined the eyes on the sides, instead of on top
  3. imagined the gill slits on the sides, instead of ventral
  4. did not perform a phylogenetic analysis with a wide gamut of taxa
  5. did not consider Middle Devonian Palaeospondylus (Figs. 3, 4) as a taxon worthy of their time and consideration
  6. did not consider the torpedo ray, Tetronarce (Fig. 5), or the hammerhead, Sphyrna, taxa worth comparing in analysis (as in Fig. 4).
Figure 2. Skull of Aquilolamna and diagram from Vullo et al. 2021. Colors and new labels applied here. The mouth (magenta) appears under the occiput, overlooked by Vullo et al.

Figure 2. Skull of Aquilolamna and diagram from Vullo et al. 2021. Colors and new labels applied here. The mouth (magenta) appears under the occiput, overlooked by Vullo et al. White lines indicate symmetries. The hyomandibulars are small with fused quadrates at the new jaw corners and link to the intertemporals, as in all other vertebrates.

Despite these issues, Vullo et al. thought there was enough of Aquilolamna
that was strange, new and easy to understand to make it worthy of publication. And it is. And that’s okay. In science it’s okay to leave further details to other workers. Keeps us busy and feeling helpful! It’s okay to make mistakes. Others will fix those. That’s all part of the ongoing process.

From the abstract:
“Aquilolamna, tentatively assigned to Lamniformes, is characterized by hypertrophied, slender pectoral fins. This previously unknown body plan represents an unexpected evolutionary experimentation with underwater flight among sharks, more than 30 million years before the rise of manta and devil rays (Mobulidae), and shows that winglike pectoral fins have evolved independently in two distantly related clades of filter-feeding elasmobranchs.”

By contrast, in the LRT filter-feeding manta rays are more primitive than sharks that bite for a living.

Unfortunately the authors omitted important sister taxa recovered by the LRT from their comparison studies. They looked at other elamobranchs, but not the electric torpedo ray, hammerhead and Palaeospondylus (Figs. 3, 4).

By focusing on just a few traits the authors are trying to “Pull a Larry Martin.” Instead they should have performed a wide-gamut phylogenetic analysis with hundreds of traits.

Figure 1. A specimen of Palaeospondylus in situ with colors added here. This appears to be a ray in the hammerhead shark, Sphyraena family.

Figure 3. A specimen of Palaeospondylus in situ with colors added here. This appears to be a ray in the hammerhead shark, Sphyrna family, that also includes the electric torpedo ray, Tetronarce.

Figure 4. Palaeospondylus diagram from Joss and Johanson 2007 who mistakenly considered Palaeospondylus a hatchling lungfish.

Figure 4. Palaeospondylus diagram from Joss and Johanson 2007 who mistakenly considered Palaeospondylus a hatchling lungfish.

From the taphonomy section of the SuppData:
“No teeth can be observed in INAH 2544 P.F.17, possibly due to rapid post-mortem disarticulation and scattering affecting the dentition.”

Turns out the authors were looking for teeth in the wrong place. The real jaws with tiny teeth were partly hidden below the occiput, as in Middle Devonian Palaeospondylus (Fig. 4), not at the anterior skull rim of Aquilolamna.

Figure 4. Subset of the LRT focusing on the shark clades related to Aquilolamna and Palaeospondylus.

Figure 4. Subset of the LRT focusing on the elasmobranch clades related to Aquilolamna and Palaeospondylus.

The reported lack of pelvic fins in Aquilolamna
is unexpected in sharks, which otherwise always have pelvic fins. This lack of pelvic fins could turn out to be a synapomporphy of taxa descending from Palaeospondylus. We’ll have to have more taxa for that.

From the Vullo et al. 2021 diagnosis of the ‘family, genus and species’:
“Medium-sized neoselachian shark that differs from all other selachimorphs in having hypertrophied, scythe-shaped plesodic pectoral fins whose span exceeds the total length of the animal. High number (~70) of anteriorly directed pectoral radials. Head short and broad, with wide and near-terminal mouth. Caudal fin markedly heterocercal. Caudal fin skeleton showing a high hypochordal ray angle (i.e., ventrally directed hypochordal rays). Caudal tip slender with no (or strongly reduced?) terminal lobe. Squamation strongly reduced (or completely absent?).”

Figure 1. Tetronarce fairchildi (originally Torpedo fairchildi Hutton 1872, 1m)

Figure 5. Tetronarce fairchildi (originally Torpedo fairchildi Hutton 1872, 1m). Note the robust caudal fin. The hyomandibular links the jaw joint to the braincase.

Aquilolamna has more vertebrae than Palaeospondylus,
but the former is much larger, an adult and geologically younger by 280 million years. We looked at Palaeospondylus just three days ago here. Very lucky timing to have Palaeospondylus for comparison prior to studying Aquilolamna.

Figure 6. Ontogenetic growth series of an electric torpedo ray. Pectoral fins in green.

Figure 6. Ontogenetic growth series of an electric torpedo ray from Madl and Yip 2000. Pectoral fins in green. Pectoral fins enlarge with maturity. Eyes migrate dorsally. Perhaps the same occurred with Aquilolamna and Palaeospondylus.

Taxon exclusion
continues to be the number one problem in paleontology. Phylogenetic analysis with a wide gamut of hundreds of taxa continues to be the number one solution to nesting all new and enigma taxa. Contra the assertions of dozens of PhDs, first-hand examination of the fossil is not required, nor is a degree or doctorate. This is the sort of profession where you learn on the job with every new taxon that comes along. This one was not in any textbooks, so everyone started like a September freshman with Aquilolamna.

And finally, if you can’t find the mouth where you think it should be,
look somewhere else.


References
Madl P and Yip M 2000. Essay about the electric organ discharge (EOD) in Colloquial meeting of Chondrichthyes head by Goldschmid A, Salzberg, January 2000. Online here.
Vullo R, Frey E, Ifrim C, Gonzalez Gonzalez MA, Stinnesbeck ES and Stinnesbeck W 2021. Manta-like planktivorous sharks in Late Cretaceous oceans. Science 371(6535): 1253-1256. DOI: 10.1126/science.abc1490
https://science.sciencemag.org/content/371/6535/1253

Online Publicity for Aquilolamna:

  1. sciencemag.org/news/2021/03/eagle-shark-once-soared-through-ancient-seas-near-mexico
  2. phys.org/news/2021-03-discovery-winged-shark-cretaceous-seas.html
  3. nationalgeographic.com/science/article/shark-like-fossil-with-manta-wings-is-unlike-anything-seen-before
  4. livescience.com/ancient-shark-flew-through-dinosaur-age-seas.html

Haikouichthys: an Early Cambrian galeaspid in the LRT, not a basal lamprey

Haikouichthys is supposed to be
a lamprey ancestor, but after testing in the LRT nests as an Early Cambrian galeaspid with a small head.

Either way,
Shu et al. reported on the importance of this fossil, “These finds imply that the first agnathans may have evolved in the earliest Cambrian, with the chordates arising from more primitive deuterostomes in Ediacaran times (latest Neoproterozoic, ,555 Myr BP), if not earlier.”

If Haikouichthys is a galeaspid,
ancestral, soft, worm-like chordates, like the more primitive lamprey, emerged in the Ediacaran, “if not earlier.”

Figure 1. Haikouichthys in situ and skull closeup, colors added.

Figure 1. Haikouichthys in situ and skull closeup, colors added. The oral  cavity on both lampreys and galeaspids is ventral.

Haikouichthys ercaicunensis
(Luo, Hu & Shu 1997; Shu et al.1999; HZf-12-127; 2.5cm) is an Early Cambrian galeaspid in the LRT. It has an appropriately much smaller skull than later galeaspids. The pectoral fin (green) is not separate from the body. The gill openings are invisible here, likely beneath the skull, as in galeaspids, not on the sides, as in lampreys. A prominent dorsal fin is present. So is a heterocercal tail. The series of posterior green diamonds are likely armored scales… like those in later sturgeons and osteostracans and those in early thelodonts, like Thelodus (Fig. 3). They are likely not gonads, but overlaid the area where the gonads are in related taxa.

Figure 2. Skull of Dunyu with tetrapod homolog colors applied here.

Figure 2. Skull of Dunyu with tetrapod homolog colors applied here.

The only other tested galeaspid in the LRT,
Dunyu (Fig. 2), is from the Late Silurian andhas a larger skull. We looked at Dunyu earlier here. It is close to the Early Devonian osteostracan, Hemicyclaspis (Fig. 3), which is basal to the extant sturgeon in the LRT. Note that galeaspids arise from soft-bodied thelodonts like Thelodus (Fig. 3), in the LRT.

Figure 3. Subset of the LRT focusing on basal chordates, including Dunyu.

Figure 3. Subset of the LRT focusing on basal chordates, including Dunyu.

Some thelodonts,
like Furcacauda, have a relatively small head, a ventral oral cavity, a dorsal fin and no lateral fins.

Figure 1. Galeaspids from Halstead 1985.

Figure 4. Galeaspids from Halstead 1985.

No prior authors
have attempted to put tetrapod homologs on the skull of Haikouichthys or any other galeaspid (Fig. 4).

Shu et al. 1999 wrote,
The theory of lateral fin folds has had considerable signiificance, but of the fossil agnathans only the anaspids and Jamoytius have such paired fn-folds. The possible occurrence of this condition in these Lower Cambrian agnathans indicates, however, that fin-folds may be a primitive feature within the vertebrates. The occurrence of close-set dorsal fin-radials in Haikouichthys, on the other hand, may be a relatively advanced feature.”


References
Luo H. et al. 1997. New occurrence of the early Cambrian Chengjiang fauna from Haikou, Kunming, Yunnan province. Acta. Geol. Sin. 71, 97-104.
Shu D-G et al. (8 co-authors) 1999. Lower Cambrian vertebrates from China. Nature 402:42-46.

wiki/Haikouichthys

Your 500-million year family tree YouTube video

From Paleocast in September 2017.
This YouTube video parallels the large reptile tree (LRT, 1816+ taxa) by describing a wide gamut of vertebrate taxa. Dr. Joseph Keating of the University of Manchester School of Earth of Environmental Science is the professor of this 38-minute PowerPoint presentation.

https://www.youtube.com/watch?v=usiPFZ352Dg

Some critical thoughts:
The presentation starts off with the statement: “You are a fish.” That’s exciting and odd, but there is no monophyletic clade called ‘fish’. Keating’s presentation shows a ladyfish (genus Elops), which is not in the lineage of humans. More accurately:

  1. You are a chordate
  2. You are a craniate
  3. You are a vertebrate
  4. You are a gnathostome, etc.

Comparing shark jaw and pharyngeal ‘bones’ to human counterparts
Keating omitted the upper jaw counterpart in the human of the upper gill element in the shark. Missing elements in the human include the lacrimal, maxilla and premaxilla.

Keating continues with the out-dated tradition
that placental mammals diverged from one another 80 to 90 million years ago. This is falsified by the presence of Maiopatagium, Rugosodon and other members of Glires (= rodents, rabbits and kin) in the Early Jurassic, some 200 million years ago.

Figure 1. Keating's out-dated cladogram of mammals.

Figure 1. Keating’s out-dated cladogram of mammals.

Worse yet,
Keating has elephants splitting from edentates (Fig. 1), and dolphins splitting from cattle, neither of which is confirmed by the LRT. But that’s what you get with gene studies. Gosh, I’d hate to spend tens of thousands of dollars on tuition and several years at these universities to be forced to regurgitate these myths.

Keating gets the Archosauromorph/Lepidosauromorph split correct
at about 330 million years ago, but incorrectly puts birds in the Lepidosauromoph clade.

Keating incorrectly marks the genesis of tetrapods
at about 360 million years ago. We have tetrapod trackmakers in the Middle Devonian, at 390 million years ago.

Figure 2. Keating's illustration of vertebrate skulls with tetrapod homologs colored, as is done here.

Figure 2. Keating’s illustration of vertebrate skulls with tetrapod homologs colored, as is done here.

To his credit,
Keating colors fish bones with tetrapod homologs (Fig. 2). Everyone knows now how easy that makes comparisons.

Keating correctly reports
that we (and bony fishes) share a last common ancestor with sharks about 450 million years ago, deep in the Ordovician. Keating does not indicate which shark was ancestral to bony fish. (It was Hybodus).

Figure 3. Keating's photo of human teeth. Maybe I'm missing something here, but those don't look like human molars.

Figure 3. Keating’s photo of human teeth. Maybe I’m missing something here, but those don’t look like human molars.

Keating’s image of human teeth
(Fig. 3) look unlike any human teeth I have ever seen.

Keating’s favorite group
is the jawless fishes, splitting from sharks at 500 million years. Sturgeons and paddlefish are not mentioned. Neither are Birkeniathelodonts, osteostracans and heterostracans.

There are lots of pictures
of lampreys and hagfish,  if that’s your thing, including how they fit into human cuisine.

When lancelets are introduced,
the concept of ‘Vertebrates’ is introduced. Keating reports that gills, brain, eyes, liver, heart, gall bladder, not vertebrae, are characters of vertebrates. Perhaps he is mixing up ‘craniates’ with ‘vertebrates. I think hagfish are inappropriate vertebrates, contra tradition. Call me old-fashioned, but vertebrae should be present in vertebrates.

Figure 4. Keating's illustration of shark and human facial bones. Labels and dark skull image at lower right added here.

Figure 4. Keating’s illustration of shark and human facial bones. Labels and dark skull image at lower right added here.

According to Keating, 
heterostracans document the earliest evidence of mineralized bone, the exoskeleton. Keating studied this material in detail with a µCT scanner. As everyone knows, heterostracans have a robust exoskeleton. Birkenia documents a much more primitive state of bone development.

Osteostracans
have paired fins, the first taxa do this, according to Keating. Thelodus is the most primitive fish with paired fins in the LRT. The osteostracan, Hemicyclaspis, evolves later as a derived thelodont.

Placoderms are discussed with an emphasis on Dunkleosteus.
Due to taxon exclusion Keating has no idea how placoderms originated within the bony fish. Keating mistakenly reports placoderms were the first to develop jaws. Actually paddlefish did this, just following sturgeons.

The talk concludes
with Tiktaalik. Having a neck is a key trait according to Keating. Another unrelated fish with a neck capable of bending the skull left and right is the Lepidogalaxias, the salamander fish, nesting at the base of the bony ray-fin fish.

Here’s a bonus video
for those who have followed the ongoing clash between certain PhDs and this blogsite as it represents the website RepitleEvolution.com on a daily basis. The speaker, Julia Galef, describes the various mindsets involved and the psychological reason for their separate points-of-view.

 

 

 

 

Middle Devonian Paleospondylus nests with extant torpedo rays

Summary for those in a hurry:
a traditional enigma fish taxon, Paleospondylus (Figs. 1, 2) nests in the large reptile tree (LRT, 1815+ taxa) with the electric torpedo ray (Fig. 3) genus = Tetronarce), a taxon overlooked by all prior studies.

Before the addition of Paleospondylus,
the closest relative of the torpedo ray in the LRT was the hammerhead shark, Sphyraena. Both contributed to understanding the taxonomy and anatomy of Paleospondylus, a tiny juvenile ray with a relatively big, shark-like tail (Fig. 1). The LRT is the first wide gamut phylogenetic analysis attempt for Paleospondylus. Earlier studies compared only a few traits and few taxa, thereby “Pulling a Larry Martin” in the process.

Figure 1. A specimen of Palaeospondylus in situ with colors added here. This appears to be a ray in the hammerhead shark, Sphyraena family.

Figure 1. A specimen of Palaeospondylus in situ with colors added here. This appears to be a juvenile ray in the hammerhead shark (Sphyraena) family. The torpedo ray, Torpedo, is also a member of this clade. Shown twice life size.

According to Wikipedia:
“Palaeospondylus gunni (Gunn’s ancient vertebrae, Traquair 1890) is a mysterious, fish-like fossil vertebrate. The fossil as preserved is carbonized, and indicates an eel-shaped animal up to 6 centimetres (2 in) in length. The skull, which must have consisted of hardened cartilage, exhibits pairs of nasal and auditory capsules, with a gill apparatus below its hinder part, and ambiguous indications of ordinary jaws.”

The phylogeny of this bizarre fossil has puzzled scientists since its discovery in 1890, and many taxonomies have been suggested. In 2004, researchers proposed that Palaeospondylus was a larval lungfish. Previously, it had been classified as a larval tetrapod, unarmored placoderm, an agnathan, an early stem hagfish, and a chimeraThe most recent suggestion is that it is a stem chondrichthyan.”

Palaespondylus diagram from Joss and Johanson 2007, colorized here.

Figure 2. Palaespondylus diagram from Joss and Johanson 2007, colorized here with tetrapod homologs. The authors considered Paleospondylus a larval lungfish. Late Johanson et al. 2017 no longer supported this hypothesis of interrelationships. The lungfish, Dipterus, occurs in the same fossil beds.

From Wikipedia continued,
“Most recently, Palaeospondylus has been identified as a stem-group hagfish (Myxinoidea). However, one character questioning this assignment is the presence of three semicircular canals in the otic region of the cartilaginous skull, a feature of jawed vertebrates.”

Figure 1. Tetronarce fairchildi (originally Torpedo fairchildi Hutton 1872, 1m)

Figure 3. Tetronarce fairchildi (originally Torpedo fairchildi Hutton 1872, 1m)

From Wikipedia continued,
“According to Johnson et al. 2017, “Previously, Palaeospondylus has been assigned to almost every major jawless and jawed vertebrate group and identified as both larval and adult. Most recently, Palaeospondylus has been identified as a stem-group hagfish (Myxinoidea). However, one character questioning this assignment is the presence of three semicircular canals in the otic region of the cartilaginous skull, a feature of jawed vertebrates.”

“Additionally, new tomographic data reveal that the following characters of crown-group gnathostomes (chondrichthyans + osteichthyans) are present in Palaeospondylus: a longer telencephalic region of the braincase, separation of otic and occipital regions by the otico-occipital fissure, and vertebral centra. As well, a precerebral fontanelle and postorbital articulation of the palatoquadrate are characteristic of certain chondrichthyans.”

Johnson et al. 2017 conclude, “the absence/non-preservation of teeth, scales and fins continues to be problematic in determination of Palaeospondylus as a jawed vertebrate. Also problematic with regards to a chondrichthyan association is the composition of the Palaeospondylus cartilaginous skeleton that includes hypertrophied chondrocyte lacunae surrounded by mineralized matrix, previously interpreted as representing an early stage in endochondral bone development, a type of bone found in bony fishes (Osteichthyes).”

Figure 2. Skull of Sphyrna tutus in three views from Digimorph. org and used with permission. Colors added.

Figure 4. Skull of Sphyrna tutus in three views from Digimorph. org and used with permission. Colors added.

When Palaeospondylus was added to the LRT,
it nested with the torpedo ray while retaining many traits (like a precerebral fontanelle) found in hammerhead sharks,  Palaeospondylus lived in the Middle Devonian, so transitional and primitive precursors that look like a ray with a shark tail are to be expected. Lack of fusion in the skull elements, the overall small size and the appearance of several specimens in a small area suggesting a nursery, combine to indicates a juvenile status.

Figure 1. The small hammerhead shark, Sphyrna tutus, is best appreciated in dorsal or ventral view.

Figure 5. The small hammerhead shark, Sphyrna tutus, is best appreciated in dorsal or ventral view.

In the most recent paper on Palaeospondylus
(Johnson et al. 2017) the following taxa were not found in the text, but at times appear in the citations: 1) shark; 2) ray; 3) torpedo. The authors reported, “The presence of
centra within the synarcual of Palaeospondylus is reminiscent of the synarcual in batoid chondrichthyans.” They did not follow up on that clue. Contra tradition, in the LRT members of the traditional batoid clade are split apart and distributed among other chondrichthyans and basal gnathostomes.

In their conclusion Johnson et al. 2017 reported,
“Palaeospondylus gunni has been a perplexing vertebrate fossil since Traquair first described it in 1890; here X-ray tomography provides new data and morphological characters demonstrating that Palaeospondylus is a jawed vertebrate. Characters that associate Palaeospondylus with chondrichthyans are a precerebral fontanelle, foramina for lateral dorsal aorta in the chondrocranium, and the articulation of the palatoquadrate to the ventral postorbital process. Palaeospondylus also lacks bone and instead manifests an entirely mineralized cartilage in the endoskeleton.”

Taxon exclusion is the number one problem affecting paleontology today
and for several prior decades. The LRT minimizes taxon exclusion by testing a wide gamut of extant and extinct taxa in a trait-based phylogenetic analysis. If only prior workers had included hammerheads and torpedos in their own phylogenetic analysis, Paleospondylus would not have been the enigma it remained until today.


References
Hirasawa T, Oisi Y and Kuratani S 2016. Palaeospondylus as a primitive hagfish. Zoological Letters. 2 (1): 20.
Joss J and Johanson Z 2007. Is Palaeospondylus gunni a fossil larval lungfish? Insights from Neoceratodus forsteri development. J Exp Zool B Mol Dev Evol. 2007 Mar 15;308(2):163-71.  https://pubmed.ncbi.nlm.nih.gov/17068776/
Johanson Z et al. 5 co-authors 2017.
Questioning hagfish affinities of the enigmatic Devonian vertebrate Palaeospondylus. Royal Society Open Science. 4 (7): 170214.
Thomson KS 2004. A Palaeontological Puzzle Solved?. American Scientist. 92 (3): 209–211.
Traquair RH 1890. On the fossil fishes at Achanarras Quarry, Caithness. Ann Mag
Nat Hist 6th Ser. 1890;6:479–86.

wiki/Palaeospondylus

Coryphaenoides, the deep-sea rat-tail, is a deep sea cod

No controversy here
as the deep sea rat tail, Coryphaenoides carapinus, enters the large reptile tree (LRT, 1814 taxa) between  the cod, Gadus (Fig. 3) and the mahi-mahi, Coryphaena (Fig. 2) plus its Antarctic relative, Notothenia (Fig. 4).

Figure 1. The rat tail Coryphaenoides, is close to the cod, Gadus, in the LRT.

Figure 1. The rat tail Coryphaenoides, is close to the cod, Gadus, in the LRT.

Coryphaenoides carapinus (Gunnerus 1765) is the extant rat tail, a deep sea fish close to Gadus with dorsal fins, anal fins and caudal fins merged into a straight tail. Like some sharks, the nasal extends beyond the premaxilla. The circumorbital series is robust. The parietals are unknown in this image.

FIgure 1. Mahi-mahi (Coryphaena) mounted as if in vivo.

Figure 2. Mahi-mahi (Coryphaena) mounted as if in vivo.

Coryphaena hippurus (Linneaus 1758; 1.5m length) is the extant open seas predator mahi-mahi or dolphinfish, here related to the similar, but deeper sea Notothenia (Fig. 4). The dorsal fin starts at the skull. The caudal fin is deeply forked. The teeth are needle-like. Males have a tall fleshy forehead supported by a bony crest. A smaller-crested female is also shown above.

Figure 5. Atlantic cod, Gadus morhua, in lateral view.

Figure 3. Atlantic cod, Gadus morhua, in lateral view.

Gadus morhua (Linneaus 1758) is the Atlantic cod, nesting between the mahi-mahi (Coryphaena) and the cobia, Rachycentron. The anal fin is split in two. The chin has a barbel. The postparietal forms a long crest that divides the parietal. The naris is divided in two by the lacrimal. An antnarial opening precedes the naris. Note the elongate intertemporal and hyomandibular.

Figure 3. Notothenia is a Coryphaena sister of the deepest oceans.

Figure 4. Notothenia is a Coryphaena sister of the deepest oceans.

Notothenia coriiceps (Richardson 1844; 50cm) is the extant Antarctic yellowbelly rockcod. It lacks a swim bladder and the bones are dense, accounting for its reduced buoyancy. The body is adapted to sub freezing temperatures. Here it nests with the mahi-mahi, Corphaena (above), not with traditional perch.


 

References
Gunnerus JE 1765. Efterretning om Berglaxen, en rar Norsk fisk, som kunde kaldes: Coryphaenoides rupestris. Det Trondhiemske Selskabs Skrifter 3: 50-58.
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/Gadus_Atlantic_cod
wiki/Coryphaenoides
wiki/Notothenia_coriiceps
wiki/Mahi-mahi

 

Hollow-cheeked Euchambersia nests alongside puffy-cheeked Charassognathus

Unique among synapsids, Euchambersia
(Broom 1931, Benoit et al. 2017; Fig. 1) had an antorbital fenestra (= maxillary fenestra and fossa, Fig. 1) that may have housed a venom gland posterior to the canine root.

Reported by Brian Switek in Scientific American online,
“Because of the uniqueness of its skull anatomy,” Benoit and coauthors conclude, “Euchambersia mirabilis is and will remain a puzzling species.”

The ability to be unique in a world of gradual accumulations of derived traits 
made this taxon interesting. I wondered, which taxon did Euchambersia nest alongside? And did that taxon have anything like the antorbital fenestra found in Euchambersia?

The two answers are 1) Charassognathus and 2) yes.

Figure 1. Euchambersia skull with colors and shifting bones added.

Figure 1. Euchambersia skull with colors and shifting bones added.

Turns out Euchambersia was not unique among synapsids
for reasons stated above because its sister in the Therapsid Skull Tree (TST, 75 taxa) Charassognathus (Fig. 2) has a skull bulge posterior to the canine root.

Figure 4. Charassognathus does not share more traits with Abdalodon than other taxa, like Bauria and Promoschorhynchops in the TT.

Figure 4. Charassognathus (SAM-PK-K10369) does not share more traits with Abdalodon than other taxa, like Bauria and Promoschorhynchops in the TST. Note the bulge posterior to the canine root.

According to Wikipedia, citing Botha, Abdala and Smith 2007
Charassognathus is a basal cynodont.

By contrast, in the TST, Charassognathus is a cynodont-mimic nesting with therocephalians. Given the state of taphonomy documented in Euchambersia, the possibility that the unique maxillary fenestra was in life covered by a thin bulge of bone, as in Charassognathus, should be considered a possibility.

Wikipedia notes,
“Charassognathus has a snout that makes up slightly less than half of the total length of its skull and a long facial process on its septomaxilla. Other than these two features its skull is that of a typical cynodont. The odd shape of its septomaxilla is more typical of therocephalians than other cynodonts indicating that it may be close to a common ancestor between the two groups.”

The same is true of Euchambersia.

Figure 4. Therapid Skull Tree with the addition of Euchambersia and Charassognathus apart from cynodonts.

Figure 4. Therapid Skull Tree with the addition of Euchambersia and Charassognathus apart from cynodonts.

Nomenclature tidbit.
According to Wikipedia, “Broom named the genus Euchambersia, which he considered “the most remarkable therocephalian ever discovered”, after the eminent Scottish publisher and evolutionary thinker Robert Chambers, whose Vestiges of the Natural History of Creation was considered by Broom to be “a very remarkable work” though “sneered at by many.”

Chambers was probably happy to get the honor and compliment from Dr. Broom, while others sneered.


References|
Benoit J, Norton LA, Manger PR and Rubidge BS 2017. Reappraisal of the envenoming capacity of Euchambersia mirabilis (Therapsida, Therocephalia) using μCT-scanning techniques. PLoS ONE 12(2): e0172047. doi:10.1371/journal.pone.0172047
Botha J, Abdala F and Smith R 2007. The oldest cynodont: new clues on the origin and diversification of the Cynodontia. Zoological Journal of the Linnean Society. 149: 477–492.
Broom R 1931. Notices of some new Genera and species of Karroo Fossil Reptiles. Rec Albany Mus. 1931; 41: 161–166.

It’s not often that all the references fall within the range of one letter. The odds against that are approximately one in 26 cubed or 17.576.

https://blogs.scientificamerican.com/laelaps/did-this-protomammal-have-a-venomous-bite/

wiki/Euchambersia
wiki/Charassognathus
wiki/Akidnognathidae

Hagfish and nematodes side-by-side in detail for the first time

Summary for those in a hurry
After this comparison, nematodes and hagfish need to be added to the base of the vertebrate/ echinoderm/ deuterostome family tree as outgroup taxa. In other words, hagfish are big nematodes with a notochord. And in turn, so are we.

Figure 1. The hagfish Myxine in vivo patrolling the sea floor.

Figure 1. The hagfish Myxine in vivo patrolling the sea floor. Note the nematode-like tentacles surrounding the mouth end at lower left.

Hagfish (clade: Myxini)
are very low on the vertebrate family tree. According to Wikipedia, They are the only known living animals that have a skull but no vertebral column, although hagfish do have rudimentary vertebrae.”

With origins in the Cambrian or Ediacaran,
we know of only one fossil hagfish, Gilpichthy greenei (Bardack and Richardson 1977, FMNH PE18703, 5cm; Fig. 2) from the famous Mazon Creek Formation, Late Carboniferous, 307 mya.

Figure x. Gilpichthys, a Pennsylvanian hagfish, enlarged and full scale.

Figure 2. Gilpichthys, a Pennsylvanian hagfish, enlarged and full scale.

Without vertebrae,
the Atlantic hagfish (genus Myxine, Linneaus 1758, 50cm, other genera up to 127cm) nest between Vertebrata and more basal taxa. (Not yet added to the LRT).

Outgroup taxa include
lancelets and nematodes (= round worms).

Yesterday
one of those insightful bells rung when I realized nematodes have eversible teeth made of keratin, as in hagfish. Something obvious had, once again, been overlooked. Peters 1991 listed nematodes as vertebrate ancestors based on overall morphology. Hagfish were not included then.

Now
let’s see what other details link nematodes to hagfish, a relationship overlooked by all prior authors, probably due to the great size difference (most nematodes are <2.5mm long), or perhaps due to taxon exclusion. According to Wikipedia, “Taxonomically, they [nematodes] are classified along with insects and other moulting animals in the clade Ecdysozoa,”

Figure x. Nematodes and hagfish side-by-side, focusing on the eversible mouth parts and keratin teeth.

Figure 3. Nematodes and hagfish side-by-side, focusing on the eversible mouth parts and keratin teeth.

Classification
According to Wikipedia, “The classification of hagfish had been controversial. The issue was whether the hagfish was a degenerate type of vertebrate-fish that through evolution had lost its vertebrae (the original scheme) and was most closely related to lampreys, or whether hagfish represent a stage that precedes the evolution of the vertebral column (the alternative scheme) as is the case with lancelets. Recent DNA evidence has supported the original scheme.”

We have learned time and again, you can never trust DNA evidence, especially when taxon exclusion is in play. Instead, look at the traits of the taxa under study. And look at lots of taxa to make sure none of them share more traits.

Smithsonian Magazine listed 14 (edited to 7) fun facts about hagfish.

  1. Hagfishes live in cold waters around the world, from shallow to 1700 m.
  2. Hagfish can go months without food.
  3. Hagfish can absorb nutrients straight through their skin.
  4. Hagfish have two rows of tooth-like structures made of keratin they use to burrow deep into carcasses. They can also bite off chunks of food. While eating carrion or live prey, they tie their tails into knots to generate torque and increase the force of their bites.
  5. No one is sure whether hagfish belong to their own group of animals, filling the gap between invertebrates and vertebrates, or if they are more closely related to vertebrates.
  6. The only known fossil hagfish, [Gilphichthys, above] looks modern.
  7. Hagfish produce slime. When harassed, glands lining their bodies secrete stringy proteins that, upon contact with seawater, expand into the transparent, sticky slime.
Figure x. Illustration of a nematode with labels.

Figure 4. Illustration of a nematode with labels from corodon.com. This model has been based on the fresh-water nematode Ethmolaimus. Compare to the hagfish in figure 1.

How does the hagfish compare to an aquatic nematode?

  1. Tail — The post-anal region forms a tail in both
  2. Mucus — Moens et al. 2005 report, “Many aquatic nematodes secrete mucus while moving.” The authors did not mention hagfish, which are famous for mucus. Some nematodes also exude adhesive from post-anal, tail tip glands.
  3. Sensory tentacles — The mouth is in the centre of the anterior tip and may be surrounded by 6 lip-like lobes in primitive marine forms, three on each side. Primitively the lips bear 16 sensory papillae or setae.
  4. Burrowing into their prey — Both hagfish and nematodes attach their lips to larger prey, make incisions and pump out the prey’s contents with a muscular pharynx.
  5. Swimming — In water nematodes swim by a graceful eel-like motion as they throw their stiff but elastic bodies into sinusoidal curves by contracting longitudinal muscles (the elasticity of the cuticle and hydrostatic skeleton more or less returns the body to its original straight shape). The notochord in the hagfish gives the same sort of elasticity to the famously wriggly body capable, as in nematodes, to form corkscrews and knots.
  6. Niche — Nematodes represent 90% of all animals on the ocean floor, not counting hagfish. Both play important roles in dead vertebrate decomposition.
  7. Embryo development — An alternative way to develop two openings from the blastopore during gastrulation, called amphistomy, appears to exist in some animals, such as nematodes.
  8. Size –– some species of hagfish and nematode reach 1m in length, though most nematodes are <2.5mm
  9. Eyes — A few aquatic nematodes possess what appear to be pigmented eye-spots, but most are blind. So are hagfish.
  10. Reproduction — Usually male and female, sometimes hermaphroditic
  11. Tough skin and subcutaneous sinus — largely separated from underlying tissue

Evolution from nematode to hagfish

  1. Head — radially symmetrical evolves to bilaterally symmetrical
  2. Mouth — three or six lips with teeth on inner edges reduced to two
  3. Skin and skeleton — Hydroskeleton and cuticle evolve to notochord and ‘eelskin’
  4. Nerve chord —Dorsal, ventral and lateral in nematodes, reduced to just dorsal in hagfish
  5. Brain – circular nerve ring in nematodes, dorsal concentration in hagfish

Pikaia gracilens
(Walcott 1911, Middle Cambrian, Fig. Z) has been compared to lancelets and hagfish. Like hagfish, Pikaia retained twin tentacles, but also had cirri instead of rasping eversible teeth.

Figure z. Pikaia gracilens from Mallatt and Holland 2013 showing hagfish and lancelet affinities.

Figure z. Pikaia gracilens from Mallatt and Holland 2013 showing hagfish and lancelet affinities.

Added 24 hours later
as the question of mouth and anus origin from the original blastopore (Fig. zz) arises again in the comments section.

Figure z. Blastopre evolution to produce an anus and mouth at the same time in a marine nematode. This is the transitional taxa from protostome nematodes to deuterostomes.

Figure zz. Blastopre evolution to produce an anus and mouth at the same time in a marine nematode. This is the transitional taxon from protostome nematodes to deuterostomes. This is how it happened. This is how it was ignored in many Western textbooks.

Malakov 1997 writes,
“The blastopore initially has a spherical Caenorhabtitis sp. (Ehrenstein & Schierenberg, shape, but then stretches to become an elongated 1980). oval-shape (Fig. 2). Subsequent development results Embryogenesis in enoplids appears to have several in the lateral edges ofthe blastopore approaching and u.nusual features. Firstly, variability occurs in the eventually connecting with the centre. Two openblastomere arrangement in the stages of early cleavings, one at the anterior end the other at tl1e posterior age. At the four-cells stage various configurations end of the embryo, are persistent remnants of the have been observed, viZ., tetrahedral, rhombic, Tblastopore. The anterior opening provides the beginshaped. These configurations have been variously ning of the definitive mouth, and the posterior one, encountered in the development of nematodes bethe definitive anus.”

See figure z (above). Hagflish and vertebrates arose form marine nematodes exhibiting this form of early cell division. This is how deuterostomes arose.

Malakov 1997 reports, “From these results it may be concluded that enoplids represent an early evolutionary branch, which seperated (sic) from the ancestral nematode stem prior to all other groups of nematodes.”

Figure x. Medial section of Acipenser (sturgeon) larva with temporary teeth from Sewertzoff 1928.

Figure 5. Medial section of Acipenser (sturgeon) larva with temporary teeth from Sewertzoff 1928. Note this specimen has marginal teeth and deeper teeth.

Getting back to baby sturgeon teeth…
Several months ago I cited Sewertzoff 1928 (Fig. 5) who found tiny teeth in the tiny lava of the large sturgeon, Acipenser. Those tiny teeth disappear during maturity, as you might recall. The question is: are those teeth homologs of keratinous hagfish + nematode teeth? Or homologs of enamel + dentine shark and bony fish teeth? McCollum and Sharpe  2001 in their review of the evolution of teeth reported, “The aim of this review is to see what this developmental information can reveal about evolution of the dentition.”

Unfortunately McCollum and Sharpe 2001 delivered the usual history of citations that indicate teeth started with sharks, overlooking sturgeon, nematode, lamprey and hagfish teeth. Phylogenetic bracketing indicates that baby sturgeon teeth are keratinous, not homologous with dentine + enamel shark teeth, which phylogenetically evolve later, first in sharks and later retained by bony fish. Let me know if this is incorrect.

Figure 3. Ventral view of the GLAHM V830 specimen of Thelodus. This appears to have fang-like teeth, but these may be sharp cilia. The mandible appears to be a dead end experiment convergent with the mandible of all other vertebrates.

Figure 6. Ventral view of the GLAHM V830 specimen of Thelodus. This appears to have fang-like teeth, but teeth are too soon. These are barbels = cirri.

Sturgeon barbels:
Are they homologs of hagfish + nematode barbels? Soft tissues, like barbels, are unlikely to fossilize, but one intervening bottom-dwelling taxon, Thelodus (Fig. 6), preserves barbels anterior to the ventral oral opening. Open water thelodonts do not preserve barbels. Catfish barbels appear to be a reversal because a long line of more primitive taxa do not have barbels. The same can be said of the catfish-mimic eel ancestor, the cave fish Kryptoglanis.

The relationship between hagfish and nematodes
should have been known for decades, but apparently this hypothesis of interrelationships has been overlooked, ignored or set to the side until now. If someone else recovered this hypothesis of interrelations previously, let me know so I can promote that citation.


References
Bardack D and Richardson ES Jr 1977. New aganathous fishes from the Pennsylvanian of Illinois. Fieldiana Geology 33(26):489–510.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Malakov VV 1998. Embryological and histological peculiarities of the order Enoplida, a primitive group of nematodes. Russian Journal of Nematology 6(1):41–46.
Mallatt J and Holland ND 2013. Pikaia gracilens Walcott: stem chordate, or already specialized in the Cambrian? Journal of Experimental Zoology, Part B, Molecular and Developmental Evolution 320B: 247-271.
McCollum M and Sharpe PT 2001. Evolution and development of teeth. Journal of Anatomy 199:153–159.
Moens T et al. (6 co-authors) 2005. Do nematode mucus secretions affect bacterial growth? Aquatic Microbial Ecology 40:77–83.
Morris CS, Caron JB 2012. Pikaia gracilens Walcott, a stem-group chordate from the Middle Cambrian of British Columbia. Biological Reviews 87: 480-512.
Nielsen C, Brunet T and Arendt D 2018. Evolution of the bilaterian mouth and anus. Nature Ecology & Evolution 2:1358–1376.
Nielsen C 2019. Blastopore fate: Amphistomy, Protostomy or Dueterostome. In eLS (eds) John Wiley & Sons Ltd.  DOI: 10.1002/9780470015902.a0027481
Peters D 1991. From the Beginning – The story of human evolution. Wm Morrow.
Sewertzoff AN 1928. The head skeleton and muscles of Acipenser ruthensus. Acta Zoologica 13:193–320.

wiki/Hagfish
wiki/Nematode
wiki/Pikaia
cronodon.com/BioTech/Nematode.html
pterosaurheresies.wordpress.com/2020/08/07/chordate-origins-progress-since-romer-1971/
Hagfish Day, occurs every year on the third Wednesday of October:
smithsonianmag.com/science-nature/14-fun-facts-about-hagfish-77165589/

Hagfish YouTube video 

Jones et al. 2021: Reptile backbone divisions and mobility

From the Jones et al. 2021 In brief:
“Jones et al. disprove the long-held idea that mammal backbone evolution involved a transition from reptile-like lateral bending to sagittal bending.”

Unfortunately, the study was conducted without a proper phylogenetic context. Outgroups included three salamanders (taxa unrelated to reptiles in the large reptile tree (LRT, 1811+ taxa).

Diadectes (Fig. 1) was cherry-picked as a ‘stem amniote‘ and ‘the ancestral condition for amniotes‘, but in the LRT Diadectes is a deeply nested lepidosauromorph amniote (= reptile) derived from Milleretta and not far from limnoscelids, pareiasaurs, procolophonids and turtles. This is a traditional mistake still taught at the university level due to taxon exclusion. At least two of the co-authors are from Harvard. So, kids, don’t go there. Harvard is not up-to-date!

In their results section
Jones et al. report, “there is less phylogenetic signal than expected under a Brownian motion model of evolution and that vertebral shape varies substantially within clades.”

That’s because they did not employ enough pertinent taxa. More taxa = more understanding of reptile phylogeny, just like a larger mirror collects more light and increases resolution in telescopes.

Figure 2. Diadectes (Diasparactus) zenos to scale with other Diadectes specimens.

Figure 1. Diadectes (Diasparactus) zenos to scale with other Diadectes specimens.

The whole concept of a transition from lateral undulation
to dorso-ventral undulation in the synapsid ancestors of mammals has been known for several decades. It was even included in Peters 1991, and not as an original hypothesis.

From the Jones et al. abstract:
“We show that the synapsid adaptive landscape is different from both extant reptiles and mammals, casting doubt on the reptilian model for early synapsid axial function, or indeed for the ancestral condition of amniotes more broadly. Further, the synapsid-mammal transition is characterized by not only increasing sagittal bending in the posterior column but also high stiffness and increasing axial twisting in the anterior column. Therefore, we refute the simplistic lateral-to-sagittal hypothesis and instead suggest the  synapsid-mammal locomotor transition involved a more complex suite of functional changes linked to increasing regionalization of the backbone.”

This was well-known decades ago.

Given this hypothesis, where do Jones et al. draw the transition zone?
Jones et al. indicate that dinocephalian synapsids walked like lizards by matching tracks (Fig. 1) and citing Smith 1993. They should have looked at dinocephalians more closely to see if Smith 1993 was correct. Turns out Smith 1993 was either incorrect or inaccurate.

Figure 2. Gaits illustrated by Jones et al. 2021. Compare the 'dinocephalian' to figure 3. It does not match.

Figure 2. Gaits illustrated by Jones et al. 2021. Compare the ‘dinocephalian’ to figure 3. It does not match.

This purported dinocephalian trackway
(Fig. 2, Smith 1993, Jones et al. 2021) does not match the hypothetical trackmaker (Fig. 2). The Smith 1993 trackway is so narrow the thumb prints overlapping the midline, something sprawling dinocephalians were unable to replicate (Fig. 3). That should have been checked, not just used ‘as is’ by Jones et al. 2021.

In similar fashion, too often workers use prior cladograms without checking for veracity. Science should be all about testing, checking, verifying. Too often it is about borrowing, trusting, accepting.

Figure 3. Dinocephalian in ventral view showing a widely splayed trackmaker.

Figure 3. Dinocephalian in ventral view showing a widely splayed trackmaker. Compare to figure 2 and 4.

Perhaps a better trackmaker
can be found for the Smith 1993 track in a larger relative to Hipposaurus (Fig. 4), a basal therapsid with the required 1) narrow pectoral girdle, 2) long slender limbs and 3) extremities that match the narrow-gauge tracks in size and configuration.

Figure 3. Image from Smith 1993, reprinted in Jones et al. 2021 falsified using their own data, then compared to a lithe large Hipposaurus with narrow toros and long limbs enabling a parasaggital gait matching the manus and pes.

Figure 4. Image from Smith 1993, reprinted in Jones et al. 2021 falsified using their own data, then compared to a lithe, large Hipposaurus with narrow toros and long limbs enabling a parasaggital gait matching the manus and pes.

Jones et al. 2021 discuss cervical, dorsal and lumbar regionalization,
without reporting that regionalization begins with Gephyrostegus (Fig. 5), a basalmost amniote (= reptile) in the LRT. This amphibian-like reptile was not mentioned by Jones et al. 2021. Smaller Diplovertebron (Fig. 5), a basal archosauromorph reptile, inherited and emphasized this regionalization.

Figure 1. Diplovertebron, Gephyrostegus bohemicus and Gephyrostegus watsoni. None of these are congeneric.

Figure 5. Diplovertebron, Gephyrostegus bohemicus and Gephyrostegus watsoni. None of these are congeneric.

 

 

Regionalization of the vertebral column
diminishes in some lepidosauriformes (Fig. 6) reaching a minimum in snakes. Regionalizaton increases in some owenettids, macrocnemids (including fenestrasaurs and pterosaurs) and iguanids.

Figure 6. Saurosternon, the first taxon in the lepidosauromorph lineage with sternae. Note the lack of differences between cervical, dorsal and there are no lumbar vertebrae.

Among archosauromorphs
regionalization did not diminish as much, as shown by Ophiacodon (Fig. 7) a basal synapsid in the lineage of therapsids.

Figure 1. Varanosaurus, Ophiacodon, Cutleria and Ictidorhinus. These are taxa at the base of the Therapsida. Ophiacodon did not cross into the Therapsida, but developed a larger size with a primitive morphology. This new reconstruction of Ophiacodon is based on the Field Museum (Chicago) specimen. Click to enlarge.

Figure 7. Varanosaurus, Ophiacodon, Cutleria and Ictidorhinus. These are taxa at the base of the Therapsida. Ophiacodon did not cross into the Therapsida, but developed a larger size with a primitive morphology. This new reconstruction of Ophiacodon is based on the Field Museum (Chicago) specimen. Click to enlarge.

By contrast, 
a basal archosauromorph diapsid, Archaeovenator (Fig. 8) reduces regionalization to a minimum. Lepidosauromorph turtles minimize lateral undulations when they evolve a carapace. So regionalization comes and goes.

Figure 2. Archaeovenator, a sister to Orovenator, is a protodiapsid.

Figure 8. Archaeovenator, a sister to Orovenator, is a protodiapsid.

 

 

One good reason for a lack of ribs in the lumbar region
was to make room for larger amniote eggs in the Earliest Carboniferous that even today greatly distends the abdomen of gravid lizards (Fig. 9).

Figure 4. Extant lizards, A. gravid, B. in the process of laying eggs, C. with egg clutch.

Figure 9. Extant lizards, A. gravid, B. in the process of laying eggs, C. with egg clutch.

Giving credit where credit is due
Jones et al. measured and graphed vertebral dimension across a wide swath of taxa, many closely related to one another. Expanding the taxon list to a wider gamut might have helped them see beyond the synapsids, a clade already well-studied for this factor.


References
Jones KE, Dickson BV, Angielczyk and Pierce SE 2021. Adaptive landscapes challenge the ‘‘lateral-to-sagittal’’ paradigm for mammalian vertebral evolution. Current Biology https://doi.org/10.1016/j.cub.2021.02.009
Peters D 1991. From the Beginning – The story of human evolution. Wm Morrow.
Smith RM 1993. Sedimentology and ichnology of floodplain paleosurfaces in the Beaufort Group (Late Permian), Karoo sequence, South Africa. Palaios 8, 339–357.