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Ptychodus is a lamniform


ThePhysicist

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Today a study was published on many exceptional body fossils of the durophagous shark Ptychodus, revealing it to be a lamniform - the same order as the great white, megalodon, etc. For a long time this shark's taxonomic placement was uncertain. The authors also conclude it was a high-speed predator that preferred animals like turtles and ammonites for prey rather than benthic mollusks and crustaceans.

 

Vullo R et al. 2024. Exceptionally preserved shark fossils from Mexico elucidate the long-standing enigma of the Cretaceous elasmobranch Ptychodus. Proc. R. Soc. B 291: 20240262. https://doi.org/10.1098/rspb.2024.0262

 

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Figure 6. Life reconstruction of the tachypelagic lamniform shark Ptychodus in the early Turonian open marine environment of Vallecillo. Two individuals are shown preying on nektonic shelled organisms (i.e. an ammonite and a sea turtle) in a trophic hotspot. Artwork by Frederik Spindler.

 

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Figure 1. Fully articulated Ptychodus specimens from the early Late Cretaceous (Turonian) of Vallecillo showing the general morphology and anatomy of the genus. (a,b) Photograph (a) and interpretative line drawing (b) of MMSP CPC 3063, adult specimen of Ptychodus sp. (c,d) Photograph (c) and interpretative line drawing (d) of MMSP CPC 3064, juvenile specimen of Ptychodus sp. All to the same scale.

 

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Figure 3. Anatomical details of Ptychodus. (a) Scleral capsule showing tesserae, specimen MUDE CPC 3065. (b) Portion of articulated dentition, specimen MMSP CPC 3063. (c) Close-up on two teeth of the lower dentition (box in (b)), specimen MMSP CPC 3063. (d) Precaudal vertebral centrum showing parallel lamellae (white arrow), specimen MMSP CPC 3067. (e) precaudal vertebral centra and muscle remains (well-preserved myomeres plus scattered isolated myofibres), specimen MMSP CPC 3067. (f) Close-up on muscle tissues (box in (e)) showing myospeta (white arrows) and myomeres composed of myofibres (black arrows), specimen MMSP CPC 3067. (g) First dorsal fin, specimen MMSP CPC 3063. (h) Pectoral fin, specimen MMSP CPC 3063. (i) Tail portion showing second dorsal fin (white arrow indicating its origin), anal fin (black arrow indicating its origin) and proximal caudal fin skeleton, specimen MMSP CPC 3063.

 

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Figure 4. Cladogram (strict consensus tree estimated from the 6349 most parsimonious trees) showing the placement of Ptychodus within Elasmobranchii. Numbers in nodes follow the arrangement ‘node number: jackknife support/Bremer support’. Clades of interest for the relations of Ptychodus are colour coded.

 

 

Edited by ThePhysicist
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“The most incomprehensible thing about the world is that it is comprehensible.” - A. Einstein

 

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Very interesting indeed.

Life's Good!

Tortoise Friend.

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Now that is a bombshell article! Wonder what other Ptychodus experts think about these conclusions because this turns things completely upside down.

 

This reminds me about the time I had first learned of Ptychocorax, the Anacoracid (Lamniformes) that has typical Squalicorax teeth in the front and Ptychodus-like teeth in the back. I wonder if some day they will determine that Ptychodontidae was an early offshoot of Anacoracidae. That family already seems to have a head start for high bite force so maybe to bridge that gap is not as difficult as we previously thought.

 

The stuff about them being high speed swimmers that ate turtles and ammonites instead of benthic animals is also interesting. It throws a wrench into the traditional explanation for why oysters and clams of the Late Cretaceous got such big shells (higher durophagus predation from Ptychodus namely).

 

Thanks for sharing this

 

 

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2 hours ago, Mikrogeophagus said:

Now that is a bombshell article! Wonder what other Ptychodus experts think about these conclusions because this turns things completely upside down.

 

Holy ####! Bombshell indeed. 

Mexico has some incredible Cretaceous lagerstätten that I feel will get international attention in next couple decades, as it absolutely should. The paleontology of the country is very underrated. Can't wait to see what our southern neighbors continue to discover :) 

Edited by Jared C
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“Not only is the universe stranger than we think, it is stranger than we can think” -Werner Heisenberg 

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Wow!  Being a fan of Ptychodus sharks, this is very interesting.  Thank you so much for sharing!

-Jay

 

 

 

''...science is eminently perfectible, and that each theory has constantly to give way to a fresh one.''

-Journey to the Center of the Earth, Jules Verne

 

 

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3 hours ago, Mikrogeophagus said:

I wonder if some day they will determine

or maybe you? :whistle:

Dentistry while doing paleo research at the side doesn't sound like a bad gig to me. I definitely think you're cut out for some shark research if you ever decided to mess with that :)  

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“Not only is the universe stranger than we think, it is stranger than we can think” -Werner Heisenberg 

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BTW I can PM the article if anyone is interested.

 

3 hours ago, Mikrogeophagus said:

Now that is a bombshell article! Wonder what other Ptychodus experts think about these conclusions because this turns things completely upside down.

Ya would be curious to see, but with how complete these are, I doubt a phylogenetic analysis will produce much different results. I'm wanting to understand the algorithms behind these trees - this was done via parsimony, but another method (that may subvert it) is a Bayesian approach which utilizes a similar class of algorithm we use in gravitational-wave astronomy.

 

3 hours ago, Mikrogeophagus said:

This reminds me about the time I had first learned of Ptychocorax, the Anacoracid (Lamniformes) that has typical Squalicorax teeth in the front and Ptychodus-like teeth in the back. I wonder if some day they will determine that Ptychodontidae was an early offshoot of Anacoracidae. That family already seems to have a head start for high bite force so maybe to bridge that gap is not as difficult as we previously thought.

Interesting thought that might be worth pursuing, I would think convergence is more likely, similar to molariform posteriors in the bonnethead. 

 

3 hours ago, Mikrogeophagus said:

The stuff about them being high speed swimmers that ate turtles and ammonites instead of benthic animals is also interesting. It throws a wrench into the traditional explanation for why oysters and clams of the Late Cretaceous got such big shells (higher durophagus predation from Ptychodus namely).

The diversity of tooth forms within the genus might suggest a diversity of trophic roles? After all we're only seeing the form of one species. A modern analogue might be Carcharhinus which occupy both reefs and the open ocean, so maybe some species of Ptychodus indeed may have specialized on benthic prey. 

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“The most incomprehensible thing about the world is that it is comprehensible.” - A. Einstein

 

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incredible..., never thought this. We have had some nearly complete jaws of Ptychodus in the german turonian, one was published. But, never thought that it is a lamniform shark.

Fantastic find! I will pm you, @ThePhysicist, for the paper

 

lets wait what @Ptychodus04 says, to be a lamniform shark now :D

 

e.g. I attach the paper (I am not the author) about the german ptychodus jaw  

GuP_Heft_70_Seite_55-63.pdf

Edited by rocket
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:popcorn: Interesting topic. I’m generally skeptical of conclusions from a single study that overturn years of understanding. It takes time for them to be debated and validated.

 

I’m sure the arguments are already forming in the shark-paleo circles.

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Very interesting paper, thanks for the heads up on this.

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7 hours ago, ThePhysicist said:

The diversity of tooth forms within the genus might suggest a diversity of trophic roles?

That is probably true. There's like 6 or 7 Ptychodus species known from the Kamp Ranch. You'd think there has to be some sort of niche partitioning at play if that is for sure the case (unless there are other weird things such as sexual dimorphisms being counted as diff species etc.).

 

I haven't gotten to read their reasoning for why they assigned these to Ptychodus sp. (and there's multiple specimens so maybe multiple species?). Just from that pic of the partially exposed tooth and the age of the fm, it kinda looks like P. marginalis or maybe P. decurrens. Both of those are low crowned species and if any taxon of Ptychodus was eating benthic organisms, I for sure would've thought it was one of those. Now I'm even more curious as to what oddballs like P. whipplei were doing!

 

Also, I just noticed Aquilolamna (?Cretomanta) in the background of the art. I hadn't made the connection that that amazing specimen came from the same quarry. They must have a lot of amazing sharks waiting to be published... :popcorn:

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1 hour ago, Mikrogeophagus said:

Also, I just noticed Aquilolamna (?Cretomanta) in the background of the art. I hadn't made the connection that that amazing specimen came from the same quarry. They must have a lot of amazing sharks waiting to be published... :popcorn:

 

That same area (and probably same quarry) also produced the holotype for Mauriciosaurus, which is also pictured.

Mauriciosaurus_fernandezi.jpg.0262b55b44b00c4533197e8e9fe08452.jpg

 

 

And the primitive mosasauroid Vallecillosaurus

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“Not only is the universe stranger than we think, it is stranger than we can think” -Werner Heisenberg 

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15 hours ago, Ptychodus04 said:

:popcorn: Interesting topic. I’m generally skeptical of conclusions from a single study that overturn years of understanding. It takes time for them to be debated and validated.

 

I’m sure the arguments are already forming in the shark-paleo circles.

Certainly, we need more skepticism in this world. I too look forward to independent analyses.

 

I think this apparent "leap" in understanding is due to a leap in evidence; we went from naught but teeth and denticles to complete articulated body fossils with soft tissue. 

 

A specimen of a similar caliber that should be included in future work is the articulated specimen in the Texas Through Time museum, which I'm sure you all know about and may have seen. It too looks to be a low-crowned species.

 

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“The most incomprehensible thing about the world is that it is comprehensible.” - A. Einstein

 

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31 minutes ago, ThePhysicist said:

Certainly, we need more skepticism in this world. I too look forward to independent analyses.

 

I think this apparent "leap" in understanding is due to a leap in evidence; we went from naught but teeth and denticles to complete articulated body fossils with soft tissue. 

 

A specimen of a similar caliber that should be included in future work is the articulated specimen in the Texas Through Time museum, which I'm sure you all know about and may have seen. It too looks to be a low-crowned species.

 

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I've often wondered about the actual provenance of this fossil. It's said it came from near Uvalde, in the Buda limestone... but I'm extremely skeptical of a Buda limestone origin. Apart from this, I've never seen nor heard of Ptychodus out of that formation. I've been told Shawn Hamm saw this specimen and guessed an ID of P. decurrens. 

 

The preservation and matrix of the Mexican specimens reminded me of this one instantlyand the only ID that the authors on the above paper made with confidence was P. decurrens on one of the specimens. 

The Texas through time specimen has no work done on it that I'm aware of, I hope someone spends some time with it and looks at the matrix. I have a suspicion it might be a wayward mexican specimen, but for now who knows.

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“Not only is the universe stranger than we think, it is stranger than we can think” -Werner Heisenberg 

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7 hours ago, ThePhysicist said:

A specimen of a similar caliber that should be included in future work is the articulated specimen in the Texas Through Time museum, which I'm sure you all know about and may have seen. It too looks to be a low-crowned species.


I have seen that specimen. It is amazing. Texas Through Time is a cool little museum and Andre, the directer of the museum, is a great guy.

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On 4/25/2024 at 12:28 AM, ThePhysicist said:

this was done via parsimony, but another method (that may subvert it) is a Bayesian approach which utilizes a similar class of algorithm we use in gravitational-wave astronomy.

Bayesian inference relies on having an understanding of the relative likelihood of various character changes, which is really hard to establish for fossil morphology. It’s typically applied for genetic-based phylogenies, such as the common K80 model for SNPs. I would love to see Bayesian phylogenetics applied more to paleontology, but there’s a lot more groundwork to be done before it’s anything short of highly controversial.

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“The worse the country, the more tortured it is by water and wind, the more broken and carved, the more it attracts fossil hunters, who depend on the planet to open itself to us. We can only scratch away at what natural forced have brought to the surface.”
- Jack Horner

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6 hours ago, Opabinia Blues said:

Bayesian inference relies on having an understanding of the relative likelihood of various character changes, which is really hard to establish for fossil morphology. It’s typically applied for genetic-based phylogenies, such as the common K80 model for SNPs. I would love to see Bayesian phylogenetics applied more to paleontology, but there’s a lot more groundwork to be done before it’s anything short of highly controversial.

Very interesting discussion!

 

I don’t really have a grasp of how Bayesian methods work - despite sitting in on a few lectures :heartylaugh:

 

Maybe I do?

 

But if I understand correctly you can start to incorporate prior knowledge of how a system works into your calculations?

 

I’ve used software to create radiocarbon age-depth models before and you can include prior knowledge/assumptions on how the sediments were deposited (e.g. constant vs pulses of sediment). 

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8 hours ago, Opabinia Blues said:

Bayesian inference relies on having an understanding of the relative likelihood of various character changes, which is really hard to establish for fossil morphology. It’s typically applied for genetic-based phylogenies, such as the common K80 model for SNPs. I would love to see Bayesian phylogenetics applied more to paleontology, but there’s a lot more groundwork to be done before it’s anything short of highly controversial.

Right, but what I'm needing to learn is how to write down a likelihood for a cladogram, but sounds like that's the point of contention in paleontology. Perhaps we're lucky in physics to have such precise models haha. I'm planning to devote some time this Summer to studying this, do you have any useful pedagogic references?

 

2 hours ago, Doctor Mud said:

But if I understand correctly you can start to incorporate prior knowledge of how a system works into your calculations?

Yes, Bayesian inference can be viewed as an expression of the scientific method, where you update your prior beliefs based on new data.

 

Schematically, we wish to know the conditional probability of our model given the data, the "posterior". Bayes' theorem allows us to relate the posterior to a prior distribution multiplied by another conditional probability distribution, the probability of the data given the model, the "likelihood", all normalized by something called the "evidence" (the likelihood marginalized over all model parameters - though this isn't always necessary to compute in Bayesian inference, it is in nested sampling which I'm less familiar with). A class of algorithms, Markov Chain Monte Carlo (MCMCs), allow one to produce approximately independent samples of the posterior by "exploring" the likelihood space. How this is actually done is not something I can explain very concisely in a TFF post, if you're curious, a popular method is the Metropolis-Hastings algorithm. There are multiple additional layers on top of this including differential evolution and parallel tempering (aka simulated annealing) to address issues with efficiency and exploration like local maxima. 

“The most incomprehensible thing about the world is that it is comprehensible.” - A. Einstein

 

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I am late to the discussion. Very cool to see two more completely articulated Ptychodus! Based on just one tooth, this larger one looks like Ptychodus marginalis. It appears to be about 5' long. Before Shawn saw the one in Hillsboro (which he thought was Ptychodus anonymous), he said the following in his NMMNH Bulletin 81 extract:

"Based on all available data, the systematic position of the 
Ptychodontidae should be placed within its own order, the Ptychodontiformes within the Neoselachii at the base 
of the Superorder Galea."

 

In that paper he concludes that Ptychodus rugosus and other younger species were likely fast swimmers and ate ammonites and squids. So, that "fast swimmer" part is not new. The position in the hierarchy is slightly different. He had them in Galeamorphii also, but as a separate order (Ptychodontiformes) not under Lamniformes.

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I'm just relieved that ptychodus isn't a ray, after I've been imagining them as sharks all this time :)

-Jay

 

 

 

''...science is eminently perfectible, and that each theory has constantly to give way to a fresh one.''

-Journey to the Center of the Earth, Jules Verne

 

 

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  • 4 weeks later...

FYI - One more little tidbit to add. Vullo R et al 2024 did not cite Shawn Hamm for the dietary preferences based on tooth morphology and tropic levels of available prey that were put out in Shawn's 2019 and 2020 papers. Instead, they claimed that as their own. Therefore, I think that this is not a professionally sound paper. There was some guy that wrote a paper on European species that also basically used Shawn Hamm's conclusions as their own to sound like they really knew the European species that were common with the WIS species. It seems that in the scientific community, it is respectful to notate someone that has previously come to similar conclusions that you now agree with. It's also possible that the analysis in this paper was a little too far out in "left field".

 

One thing that was really clear in the 2020 NMMNH Bulletin 81 from Shawn Hamm was how the ammonites modified their shell thicknesses and armored spines during the period of Ptychodus reign. It would make sense that the Ptychodus teeth would also change form to still be able to crush and eat those mollusks. One extreme example is Ptychodus whipplei.

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