The paddlefish (Polyodon) and basking shark (Cetorhinus) are closely related

The ‘key trait’: having one gill cover or several gill covers
(as in sharks, Fig. 1) turns out to be a trivial trait in a matrix of 235 traits in the large reptile tree (= LRT, subset Fig. 2). Only one gene has to change to make one type of gill or the other as recently documented (see below).

Figure 1. The basking shark (Cetorhinus) compared to the paddlefish (Polyodon). Note the gelatinous rostrum in the paddlefish juvenile. That trait is retained in mako sharks, as we learned earlier.

What does ‘closely related’ actually mean?
No other tested taxon shares as many traits with paddlefish (Polyodon) as the basking shark (Cetorhinus, Fig. 1) in the LRT. Someday a taxon might be added that nests between them. At present such taxa remain unknown and untested. Both taxa are derived from the Polyodon hatchling taxon (Fig. 3), which has a shorter rostrum and a more basking shark-like appearance overall. Back in the Silurian, pre-paddlefish hatchlings were likely much smaller and adults were likely the size of present day hatchlings, but that’s not a requirement. No other analysis that I am aware of has ever included paddlefish hatchlings as taxa, but that morphology is key to understanding various lineages within Chondrichthyes. So, here’s a case where adding a taxon is much more important than adding a character.

Figure 2. Adding Debeerius to the LRT helped revise the shark-subset. Note the shifting of the basking shark, Cetorhnus within the paddlefish clade.

Note the gelatinous rostrum
in the paddlefish juvenile (Fig. 1). That trait is retained from mako sharks (Figs. 3, 6, as we learned earlier here. The rostrum of the adult basking shark is likewise filled with gelatin supported by a thin frame of cartilage (Fig. 4). The shark-like appearance of paddlefish has been noted previously. Previously the presence of one enormous gill cover in paddlefish has excluded them form prior shark studies. The LRT minimizes such taxon exclusion by simply adding taxa.

We’ve always known
that ratfish (with one gill cover, Fig. 3) nest with sharks (with several gill covers separating slits). No one has complained about that yet.

Then we learned
that sturgeons and Chondrosteus (with one gill cover, Fig. 3) nest basal to whale sharks and mantas (with several gill covers). The pattern of gill covers was presented and revised recently here.

Figure 3. Shark skull evolution according to the LRT. Compare to figure 1.

Now
paddlefish (Polyodon) nests with basking sharks (Cetorhinus, Fig. 1) in the large reptile tree (LRT, 1785+ taxa, subset Fig. 2). Evolution is full of such trivial exceptions.

Paddlefish inhabit rivers. Basking sharks inhabit the sea.
They both feed the same way. Basking sharks reach 30 feet in length. Paddlefish reach 7 feet in length. The two likely went their separate ways in the Silurian (prior to 420mya), so they had plenty of time to evolve on their own since then.

Figure 4. Skull of Cetorhinus adult and juvenile showing differences in the rostrum and fusion of skull elements in the adult.

A recent study on gill covers by Barske et al. 2020
“identify the first essential gene for gill cover formation in modern vertebrates, Pou3f3, and uncover the genomic element that brought Pou3f3 expression into the pharynx more than 430 Mya. Remarkably, small changes in this deeply conserved sequence account for the single large gill cover in living bony fish versus the five separate covers of sharks and their brethren.”

Figure 5. Skull of Polyodon from a diagram published in Gregory 1938, plus a dorsal view and lateral photo.

While comparisons to the feeding technique in paddlefish and basking sharks
appear in the literature (Matthews and Parker 1950, Haines and Sanderson 2017), these were presumed to be by convergence based on the single gill cover vs. multiple gill cover difference.

Figure 6. Skull of the dogfish shark, Squalus, superimposed on a graphic of the invivo shark. Yellow areas added to show the extent of the gelatinous material that fills the empty spaces above and below the cartilaginous rostrum (nasal homolog).

Relying on one, two or a dozen traits
to trump the other 234, 233 or 213 is called “Pulling a Larry Martin.” You don’t want to do that. Put aside your traditions, add taxa and let the unbiased software figure out where your taxon nests using the widely accepted hypothesis of maximum parsimony (= fewest changes) over a large set of character traits.

The present hypothesis of interrelationships
(Fig. 2) appears to be novel. If not, please advise so I can promote the earlier citation.

---

References
Barske L et al. (10 co-authors) 2020. Evolution of vertebrate gill covers via shifts in an ancient POU3f3 enhancer. PNAS 117(40):24876–24884.
Haines GE, Sanderson SL 2017. Integration of swimming kinematics and ram suspension feeding in a model American paddlefish, Polyodon spatula. The Journal of Experimental Biology, 10.1242/jeb.166835, 220, 23, (4535-4547), (2017).
Matthews LH, Parker HW 1950. Notes on the anatomy and biology of the basking shark (Cetorhinus maximus (Gunner)). Proceedings of the Zoological Society of London 120(3):535–576.

USC-led study traces the evolution of gill covers

The juvenile enantiornithine STM-34-1 nests with Chiappeavis in the LRT

In a paper on Early Cretaceous fossilized feather molting,
O’Connor et al. 2020 presented several specimens, among them an unnamed juvenile STM-34-1 (Figs. 1–3). The specimen originally appeared in part in Zheng et al. 2012 in their study on sternum ontogeny. O’Connor was a co-author then, too.

Figure 1. STM-34-1 in situ along with select elements.

Note the shorter forelimb
and longer hind limb in the juvenile, which has no tail feathers preserved as well as those elsewhere on the body and limbs. Birds, like other archosaurs, develop allometrically, changing in shape as they mature. By contrast, pterosaurs, like other lepidosaurs, develop isometrically, not changing in shape as they mature, contra traditional thinking.

Figure 2. STM-34-1 skull in situ and reconstructed.

STM 34-1 is from
Liutiaogou, Ningcheng, Chifeng, Inner Mongolia, Lower Cretaceous.

Chiappeavis is from 
Jianchang, Liaoning Province, northeastern China. Jiufotang Formation, Lower Cretaceous

Figure 3. Chiappeavis, Pengornis and STM-34-1 to scale.

Added to
the large reptile tree (LRT, 1785+ taxa, subset Fig. 4) STM-34-1 nested with Chiappeavis (Fig. 3).

Figure 4. Subset of the LRT focusing on the bird clade, Enantiornithes.

A phylogenetic analysis that tested STM 34-1
was not presented by O’Connor et al. 2020, nor by Zheng et al. 2012.

---

References
O’Connor JK, Falk A, Wang M and Zheng X-T 2020. First report of immature feathers in juvenile enantiornithines from the Early Cretaceous Jehol avifauna. Vertebrata PalAsiatica 58(1):24–44. DOI: 10.19615/j.cnki.1000-3118.190823
Zheng XT, Wang XL, O’Connor JK et al., 2012. Insight into the early evolution of the avian sternum from juvenile enantiornithines. Nat Commun, 3: 1–8.

wki/Chiappeavis

Name-calling in the Twitterverse

Earlier we looked at Ezcurra et al. 2020 (December 09, 2020)
who made a chimaera of a lagerpetid and a protorosaur and called it a pterosaur precursor that walked on two toes close to dinosaurs. Ezxurra et al. cited Peters 2000, who recovered four pterosaur precursors using four previously published analyses, but Ezcurra et al. omitted those four taxa from their analysis.

On December 09, 2020
PhD Darren Naish (@Tetzoo) posted notice of the Ezcurra et al. 2020 paper to Twitter (Fig. 1). Several responses followed. Naish responded to one that referenced this blogpost (toward the bottom of Fig. 1).

Figure 1. Copy and paste from @Tetzoo Twitter.com account December 09, 2020.

Some definitions
Pseudoscientist: “a person who falsely or mistakenly claims to be a scientist.”

Scientist: “a person who is studying or has expert knowledge of one or more of the natural or physical sciences.”

Pseudoscience: “consists of statements, beliefs, or practices that are claimed to be both scientific and factual but are incompatible with the scientific method.”

The Scientific Method:  “a process for experimentation that is used to explore observations and answer questions.” There are seven steps in the Scientific Method:”

1. Question
2. Research
3. Hypothesis
4. Experiment
5. Observe
6. Conclude
7. Report results

I would add eighth, ninth and tenth steps, but they must be done independently by others: 8. Repeat the experiment to confirm or refute findings. 9. Report any material omissions in the original study. And finally, getting back to the original authors: 10. Have the guts to publicly admit error, omission and oversight when appropriate. If possible, everyone, readers and authors alike, should do these in a precise, timely and public manner, while the original report is still in the news cycle. Not letting a myth proliferate is everyone’s responsibility. Not falling behind the cutting edge of research is also everyone’s responsibility.

I would not add the following steps to the scientific method: 1. ad hominem remarks, 2. name-calling. 3. prejudicial remarks, 4. hyperbole or 5. other middle-school pranks. People who decide future opportunities and book sales for all of us judge all of us on everything we do, including publicly visible tweets.

References
Click here for a list of topics characterized as pseudocience. Creation science is on that list. Phylogenetic analysis is not.

Debeerius: enters the LRT basal to Rhinochimaera

Figure 1. Debeerius reconstruction from Grogan and Lund 2000. Compare the skull to Figure 2.

Figure 2. Debeerius skull, colors added here.

Debeerius ellefseni 
(Grogan and Lund 2000; Mississipian, 320 mya) was originally considered intermediate betweeen sharks and ratfish, but here nests between Chimaera and Rhinochimaera (Figs 3–5).

Figure 3. The long-nosed chimaera (Rhinochimaera africana?).

Figure 4. Fused cartilage skull of Rhinochimaera lacking the tactile/sensory probe supports. Compare to diagram in figure 6.

Figure 5. Diagram of Rhinochimaera pacifica from Didier 1995. Inverted area and colors added to show interpretations of element boundaries based on Callorhinchus (Fig. 7) and other related taxa.

Rhinochimaera pacifica
(Mitsukuri 1895, 130cm in length) is the extant Pacific spookfish. A long nasal bone greatly extends the rostrum, creating a larger sensory surface, as in sawfish, hammerheds and paddlefish by convergence.

Figure 6. Adding Debeerius to the LRT helped revise the shark-subset. Note the shifting of the basking shark, Cetorhnus within the paddlefish clade.

Revisions to the LRT
(Fig. 6) shift the second largest living fish, the basking shark (Cetorhinus) with paddlefish (Polyodon). Both are filter feeders with huge gapes. Among the few differences is the presence of gill slits vs. gill covers. Turns out to be a trivial trait in the scheme of things. The basking shark is a giant hatchling paddlefish.

Figure 7. Polyodon hatchling. Compare to the Polyodon adult (figure 8) and Cetorhinus (figure 9).

Figure 8. Skull of Polyodon from a diagram published in Gregory 1938, plus a dorsal view and lateral photo. compare to figures 7 and 9.

Figure 9. The basking shark, Cetorhinus maximus, in lateral and ventral views. Compare to figures 7 and 9.

References
Grogan ED and Lund R 2000. Debeerius ellefseni (Fam. Nov.,Gen. Nov., Spec Nov.), an autodiastylic chondrichthyan from the Misssissippian Bear Gulch limestone of Montana (USA), the relationships of the Chondrichthyes, and comments on gnathostome evolution. Journal of Morphology 243:219–245.

wiki/Debeerius

Harpagofututor enters the LRT with the moray eel, Gymnothorax

Lund 1982 described an eel-like specimen with almost no scales
Harpagofututor volsellorhinus (Figs. 1, 3, 5), as a type of bradyodont shark.

Figure 1. Harpagofututor female from Lund 1982.

Added to 
the large reptile tree (LRT, 1782+ taxa) Harpagofututor nested with another eel-like bony fish close to sharks with no scales, Gymnothorax (Figs. 2, 4). Both were derived from the traditional chimaera, Gregorius (Fig. 6). and the scaleless incertae sedis, Prohalecites. These nest as basalmost bony fish in the LRT, derived from the shark, Hybodus. Lund did not mention these taxa in his paper on Harpagofututor.

Figure 2. Moray eel skeleton. Note the two gray dots represent absent fins.

From the Lunds 1982 abstract:
“A new chondrenchelyoid bradyodont, Harpagofututor volsellorhinus is described from the Namurian Bear Gulch limestone beds, Bear Gulch member of the Heath Formation, of Montana. It has a bladelike body form with a low, continuous dorsal fin, segmental vertebral arcualia, and a biserial archipterygial pectoral fin, as does Chondrenchelys problematica. There are two paired flat upper tooth plates, and a symphysial plus two paired crushing lower tooth plates. Males have large paired, distally biramous ethmoid claspers.”

Figure 3. Harpagofututor skull colored and reconstructed here. Compare to Gymnothorax in figure 4. Note the different upper and lower teeth. This taxon is likely basal to Helicoprion based on the morphology of the teeth that are present.

Figure 4. The skull of the moray eel, Gymnothorax, in 3 views. Colors added as homologs to tetrapod skull bones. The nares exit is above the eyes.

Like Harpagofututor,
the much larger and more derived, Helicoprion vessonowi (Figs. 5; Karpinsky 1899; Bendix-Almgreen 1966; Tapanila et al. 2013; Permian, 290-270 mya; possibly 12m in length) had a symphysial (central) tooth whorl and two lateral tooth plates arising from the dentary. In the more primitive, Harpagofututor, those three tooth plates arose one in front, two in back. In Helicoprion the two now toothless plates support the much larger central tooth whorl. The other elements resemble Harpagofututor to such an extent that a relationship seems to be present, reducing the mystery surrounding Helicoprion. Harpagofututor was not mentioned in the Tapanila et al. 2013 redecription of Helicoprion. They referred Helicoprion to the Euchondrocephali, which includes Gregorius (Fig. 6).

Figure 5. Harpagofututor male and female skulls. Added here is the best partial skull of the buzz tooth shark, Helicoprion.

The facial claspers of a male Harpagofututor
(Fig. 5) are similar to, but different from similar additional nasal bones arising from ratfish.

Figure 6. Tiny Gregorius rexi nests basal to moray and gulper eels and also basal to all bony fish in the LRT.

The present hypothesis of interrelationships appears to be a novel one.
If there are similar prior hypotheses, please bring them to my attention so I can promote them.

---

References
Bendix-Almgreen SE 1966. New investigations on Helicoprion from the Phosphoria Formation of south-east Idaho, USA. Biol. Skrifter udgivet af det Kongelige Danske Videnskabernes Selskab 14, 1–54.
Lund R 1982. Harpagofututor volsellorhinus new genus and species (Chondrichthyes, Chondrenchelyiformes (from the Namurian Bear Gulch limestone, Chondrenchelys problematica Traquair (Visean), and their sexual dimorphism. Journal of Paleontology 56(4):938–958.
Tapanila L et al. (6 co-authors) 2013. Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helcoprions. Biology Letters 9, 20130057, http://dx.doi.org/10.1098/rsbl.2013.0057

When Helicoprion was first discussed here
the only other tested taxa with a central tooth whorl were the unrelated forms Ischnagnathus and Onychodus.

https://pterosaurheresies.wordpress.com/2019/11/05/tooth-whorls-helicoprion-ischnagnathus-and-onycodontus/

wiki/Harpagofututor

hwiki/Euchondrocephali

Strange Squaloraja has a new sister in the LRT: Scapanorhynchus

Earlier one of the the strangest of all bottom-dwelling vertebrates,
Squaloraja (Fig. 1), nested in the LRT with paddlefish (= Polyodon) and goblin sharks (= Mitsukurina), rather than the traditional ratfish (= Chimaera).

Figure 1. Squaloraja is not the chimaerid everyone thinks it is, but nests with Scapanorhynchus and Mitsukurina in the paddlefish clade.

Today
a traditional relative of Mitsukurina, Scapanorhynchus (Davis 1887, Woodward 1889, 1899; Figs. 2, 3) nests closer to Squaloraja (Fig. 1) in the paddlefish clade.

Figure 2. Skull of Scapanorhynchus traced and reconstructed using DGS. Note the large eyes as in Squaloraja.

Scapanorhynchus lewisii
(originally Rhinognathus lewisii David 1887; Woodward 1889; NHMUK PV P 4774; Early Cretaceous; 65cm to 1m in length) is widely considered a relative of Mitsukurina, the goblin shark, but here nests closer to Squaloraja. Here the gill basket is much longer, the eyes are midway in size and two dorsal fins are retained.

Figure 3. Scapanorhynchus, and Early Cretacous goblin shark.

Squaloraja polyspondyla (Agassiz 1843, Woodward 1866, Early Jurassic) is traditionally considered a relative of Chimaera, but here nests with Scapanorhynchus from the Cretaceous.

Figure 4. Adding Debeerius to the LRT helped revise the shark-subset. Note the shifting of the basking shark, Cetorhnus within the paddlefish clade.

This appears to be
another  novel hypothesis of interrelationships. If not, please supply the citation so I can promote it.

---

References
Agassiz L 1843. Recherches sur les Poissons Fossiles, III (IV), Imprimerie de Petitpierre, Neuchatel, pp. 157-390.
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.
Woodward AS 1886. On the anatomy and systematic position of the Liassic selachian Squaloraja polyspondyla Agassiz. Proceedings of the Zoological Society of London, 1886: 527–538.
Woodward AS 1889. Catalogue of the Fossil Fishes in the British Museum. Part 1. London: British Museum of Natural History, 1-474.
Woodward AS 1899. Note on Scapanorhynchus, a Cretaceous shark apparently surviving in Japanese seas. Annals and Magazine of Natural History, (Series 7), 3 (18): 487–489.

Other references online here and here.

wiki/Squaloraja
wiki/Scapanorhynchus

 

Gill covers vs gill slits above and below the pectoral fins

Rays, sawfish and skates have gill slits on their flat undersides. 
White and mako sharks have gill slits on their lateral sides. Sturgeons, ratfish and most bony fish, have an operculum. Lampreys have a series of lateral gill holes. Ostracoderms have a series of holes on their flat ventral surface. Moray eels and their deep sea relatives have a single lateral hole without an operculum.

Those are the observations.
What do the evolutionary patterns tell us?

Put into a phylogenetic context, 
(Fig. 1) patterns emerge, but reversals are apparent.

Figure 1. Subset of the LRT showing the pattern of gill slits and opercula in basal vertebrates.

What you don’t want to do
is get caught “Pulling a Larry Martin” (= defining a clade by a short list of traits, like the type of gill openings present). Some clade members don’t follow all of ‘the rules’, but all clade members follow most of ‘the rules.’ If they don’t, they go to another clade.

What you do want to do
is let all the traits and all the taxa fight it out, out of sight, deep in the 0s and 1s of your unbiased software and see what patterns emerge.

For this situation I was curious to see
what patterns emerged, given the present cladogram. Sharp-eyed readers will note this portion has been corrected since the last time it was presented, and probably not for the last time as each new taxon sheds new light on various subsets of the LRT. It’s an ongoing project in real time. It’s never finished.

PS You’ve heard that ontogeny recapitulates phylogeny. 
Here’s a series of paddlefish larvae at weekly intervals.

Figure 2. Paddlefish larvae change as they grow. Adults have an enormous gill cover that starts off much smaller in hatchlings. Note the shark-like stage and the earlier bowfin-like stage, not so much recapitulating phylogeny, but predicting it in descendant taxa.

Note the shark-like stage
and the earlier bowfin-like stage, not so much recapitulating phylogeny, but predicting it in descendant taxa.

Happy holidays.
Thank you for your readership. Be good.

Making a living in paleontology

So, you want to be a paleontologist?
How much you earn depends on what sort of paleontologist you are.

For the title: ‘Paleontologist’ salary estimates 
in the USA range from $20,000 to $110,000 per year. I’m guessing the high end goes to tenured professors and geologists in the oil industry. The low end probably goes to preparators. Volunteers, of course, love their work. They just want to be in and around museums, fossils and projects. Salary estimates in the UK average: £32,414 = $43,000 per years. 

According to Indeed.com/palentologist
“Paleontologists can make an average of $90,000 per year and must undergo extensive training in addition to completing a doctorate level of education.”

“Paleontologists working in the coal and petroleum manufacturing industry make the highest salary, whereas paleontologists who teach at universities typically make the lowest average salary.”

What is a paleontologist?
“A paleontologist is a scientist who studies the history of the earth and how evolution has affected life through the examination of fossils and other historical data. These professionals may find and preserve animal and plant traces, fossilize bones and other data and use these findings to make conclusions about the evolution of life and the history of our planet. They often spend their time at worksites where they perform fieldwork projects to uncover fossils or collect samples that they study in a laboratory.

Common duties that a paleontologist may perform include:

• Discover the location of fossils
• Perform excavations to uncover fossils
• Gather information about fossils found during excavations and digs
• Use specialized computer programs to analyze discoveries made
• Compare new data to existing information
• Perform various tasks within a laboratory setting related to analyzing fossils and other related findings
• Determine in which time period fossils originated
• Communicate findings to colleagues and other individuals within the scientific field”

Of course, if you are in the right university or museum,
then the fossils come to you.

Figure 1. The cover of Giants, the book that launched my adult interest in dinosaurs, pterosaurs and everything inbetween.

Some artists and writers
specialize in paleontology, I was one for a while. An advance to write and illustrate a dinosaur book was $15,000 back in the 1990s. That gets split in half if the author or illustrator is someone else. Thereafter increased sales provide royalty payments, IF there are more sales. For Giants (Fig. 1) I received only one royalty check worth a nice year’s salary, even though it had been featured in The New York Times, Newsweek and other publications on their 10-Best-for-Christmas Books. The publisher let it stay on the shelves for only one year due to rising printing costs at the time. Several other books that followed did not make back their advance. They tell me ‘novelty’ is the key to positive reviews and big sales. So keep that in mind when you come up with your book idea.

Big selling paleontology books of the past all broke new ground.

Jurassic Park author Michael Crichton made millions in book sales and movie rights. Of course, the timing could not have been better.

Dinotopia author and artist, James Gurney, also did well in his fantasy book that also became a movie.

The Dinosaur Heresies author and artist, Robert T. Bakker, stirred the imagination of readers and workers who followed and built upon his new views.

The Princeton Field Guide to Dinosaurs author and artist, Greg Paul, likewise filled a niche that made the book a perennial good-seller.

Some writers and artists work for science oriented popular magazines.
They depend on the paleontologists for their news and artwork. I’ve never seen them question results and they cannot use images under Fair Usage because they are in business for profit.

According to MakeaLivingWriting.com
freelancers can make $100 to $2500 per article. That’s when the editor likes your idea. Much time can be spent pitching ideas and striking out.

• Discover Magazine — $2/word
• New Scientist — $300+ per assignment
• Popular Science — $2/word
• Smithsonian — $1 to $3.50/word
• Scientific American — $2/word to start according to  Whopays.tumbler
• National Geographic — $1.50/word according to WhoPaysWriters
• Science or Nature — academic publications don’t pay contributors and they send back 95% of all submissions.

Sculpture and Discovery
Some paleontologists are in the businesses of providing fossils and models of fossils to museums, universities and wealthy individuals.  They also hire workers.

Triebold Paleontology digs fossils and creates casts for museum and home display. All of my pterosaur skeletons are now casts available there. It was fun to go to a European museum in 2007 with my girlfriend and say, “Hey, I did that Pteranodon!”

Figure 2. Pteranodon model based on the Triebold specimen

Staab Studios creates models for museums, film and private collectors

Black Hills Institute supplies prepared fossils, casts and mineral specimens for research, teaching and exhibit.

CMStudio is a small shop that also produces full-size sculptures for dinosaur lovers, museums and businesses around the world.

Paleoartists on Pintrest include Raul Martin, Mark Hallett, and many others.

If you don’t need to make a salary or commission,
but have a keen interest in paleontology, you can be a blogger or create your own website, like ReptileEvolution.com. That way you can document the progress of your studies, invite comments and catch hell from irate PhDs.  :  )

Figure 3. Left: Pteranodon. Right: Diomedea (albatross).

Orthocormus: a bony fish with an odd reversal: a shark face

Everyone agrees
that Orthocormus roeperi (Weitzel 1930; Arratia and Schultze 2013; Early Jurassic; 45cm; BSPG 1993 XVIII-VFKO B1) is a pachycormiform fish. In the large reptile tree (1781+ taxa) Orthocormus nests with a more derived, Late Jurassic pachycormiform with a longer snout, Aspidorhynchus (Figs. 3, 4), the famous Rhamphorhynchus nibbler.

For reasons unknown,
Aspidorhynchus (Figs. 3, 4) is not traditionally considered a pachycormiform fish.

Arratia and Schultze 2013 consider 
“The fish described here is the best-preserved pachycormiform from Bavaria, Germany, as well as from the Upper Jurassic worldwide.”

Figure 1. Orthocormus, a small, bony fish with a shark-like face. Shown 1/3 actual size on a 72dpi screen.

According to Wikipedia
“Pachycormiformes were characterized by having serrated pectoral fins (though more recent studies demonstrated that fin shape diversity in this group was high, reduced pelvic fins and a bony rostrum.”

Figure 2. The shark-like skull of Orthocormus, a ray-fin bony fish. The extended rostrum is a reversal from shark ancestors.

As you can see, this is less than accurate description.
The pelvic fins are not reduced in Orthocormus nor are the pectoral fins serrated. Pachycormus does not have a bony snout. Wikipedia lists several synapomorphies (“Pulling a Larry Martin“) and does not list Aspidorhynchus as a pachycormiform. Better to just run the analysis and find the last common ancestor to determine clade membership.

Figure 3. Rhamphorhynchus entangled with Aspidorhynchus. Both complete and articulated. Inside the belly of Rhamphorhynchus are several smaller fish. Inside its throat is another. Image from Frey and Tischlinger (2012).

Dentition according to Arratia and Schultze 2013:
“There are small conical teeth on the upper jaw, a large tooth on the posterior part of the premaxilla, and both large and small teeth on the maxilla; the lower jaw carries large teeth anteriorly and smaller ones posteriorly.”

Notochord
“The vertebral column is formed by a persistent notochord without chordacentra,”

The tail
“The scaly caudal apparatus, formed by large modified scales with a precise arrangement, is interpreted as an adaptation to fast swimming comparable to that of modern tunas.”

Spiral valve
Another apparent reversal is the presence of a soft tissue spiral intestine, as found in sharks and several other various taxa without apparent pattern, including sarcopterygians. This is the only time Arratia and Schultze 2013 mention the term, ‘shark’ in their text.

Figure 4. The face of the Wyoming Dinosaur Center CSG 255 specimen of Asphidorhynchus + Rhamphorhynchus with facial bones identified using DGS.

Wkipedia reports on Pachycormiformes,
“Their exact relations with other fish are unclear, but they are generally interpreted as stem-teleosts.”

By adding taxa, the LRT provides exact relations with other fish, in this case, within bony fish, close to the base, not in the stem. Again, a wider view provided by the LRT supplements and aids the more focused view of those describing the fossil firsthand. Reversals and convergent traits can be tricky. Let the unbiased software do the decision-making.

---

References
Arratia G and Schultze H-P 2013. Outstanding features of a new Late Jurassic pachycormiform fi sh from the Kimmeridgian of Brunn, Germany and comments on current understanding of pachycormiforms. Pp. 87–120 in Mesozoic Fishes 5 – Global Diversity and Evolution, Arratia G, Schultze H-P and Wilson MVH (eds.).
Weitzel K 1930. Drei Riesenfische aus den Solnhofener Schiefern von Langenaltheim. – Abh. Senckenberg. Naturforsch. Ges. 42 (2): 85-113.

wiki/Orthocormus
wiki/Pachycormiformes

What do larval sturgeons eat (when they have teeth)?

Updated May 31, 2023 with the news that
sturgeons are basal vertebrates in the large reptile tree (LRT, 2264 taxa) splitting off prior to the lineage of gnathostomes. Sturgeons are in the lineage of conodonts and lampreys. The tiny teeth of hatchlings are not dentine and enamel but similar in chemistry to those of conodonts and lampreys. At 3cm sturgeons shed their teeth.

Yesterday I learned
that larval sturgeons (like larval paddlefish) have small sharp teeth. These are lost when hatchlings grow more than 3cm in length. At this point their diet changes from open water microscopic copepods to river bottom macroscopic arthropods. At the same time their mouth parts become extensible vacuum cleaner tubes, usually carried inside, sometimes everted (Fig. 2b).

Figure 1. Medial section of Acipenser larva with temporary teeth from Sewertzoff 1928. Looks more like a shark than a sturgeon here because this is where sharks come from in the LRT.

Zarri and Palkovacs 2018 described
larval green sturgeon diets. “Fish smaller than 30 mm had teeth on the oral jaws and showed a strong reliance on zooplankton prey. The developmental loss of teeth in fish greater than 30 mm was associated with decreased zooplankton consumption and increased richness of benthic macroinvertebrates in diets.”

Figure 2. Growth stages in Acipenser transmontanus, a species of white sturgeon. First the yolk sac is absorbed, then external feeding begins. Adult armor is derived from ostracoderm armor.

According to the online The Fish Report
“The study found that the most common larval sturgeon prey included copepods (a kind of tiny zooplankton), and macroinvertebrates such as mayflies, midges, and blackflies. The scientists also noted an interesting diet shift: larval sturgeon consumed zooplankton and macroinvertebrates in roughly equal amounts until they grew to 30 millimeters in total length, at which point their macroinvertebrate consumption increased. This shift coincided with the young sturgeon losing their teeth (fun fact: unlike humans, sturgeon start out life with teeth and lose them as they grow older).”

Zooplankton prey
include copepods (a kind of tiny zooplankton) that floats freely in open waters.

Benthic macroinvertebrates
such as larval mayflies, midges, and blackflies that live in river sands and muds.

Figure 2b. Sturgeon mouth animated from images in Bemis et al. 1997. This is similar to ostracoderms and basal to sharks. The barbels are retained buccal cirri.

Muir et al. 2000 report
a burrowing river amphipod about 1 cm long, Corophium spp., is the most important prey for bottom-feeding juvenile and sub-adult white sturgeon. In adult sturgeons,small bottom-dwelling fish, larvae, crayfish, snails, clams and leeches are on their prey list.

So the loss of teeth and the change in diet
reflects a change from open water predation of microscopic forms that other fish would filter to visible worms and larvae living in river bottoms.

This somewhat mirrors more primitive behavior in lancelets
that feed in open waters as juveniles, then burrow tail first in river bottoms and become sessile feeders. One branch of lancelets kept evolving to become crinoids and later, starfish. The other branch, the one that kept active as adults, became vertebrates.

Given the above gathered data points,
now I’m looking for a juvenile osteostracan. Wonder what it looks like? If less bony, as in sturgeons, they might be hard to find.

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References
Muir WD, McCabe GT Jr, Parsley MJ and Hinton SA 2000. Diet of first-feeding larval and young-of-the-year white sturgeon in the Lower Columbia River. Northwest Science 74(1):25–33.
Sewertzoff AN 1928. The head skeleton and muscles of Acipenser ruthensus. Acta Zoologica 13:193–320.
Zarri LJ and Palkovacs EP 2018. Temperature, discharge and development shape the larval diets of threatened green sturgeon in a highly managed section of the Sacramento River. Ecology of freshwater fish 28(2): https://doi.org/10.1111/eff.12450

https://fishbio.com/field-notes/the-fish-report/diets-baby-giants-feeding-habits-larval-green-sturgeon.