Juvenile xenacanth

[izak_]

While preparing a large xenacanth tail from a new site south of Sydney I noticed this juvenile of the same species within the nodule. Xenacanths are very common in this horizon of the Ashfield Shale but are often poorly preserved, so this example offered a unique opportunity to photograph certain features such as the denticles. Unfortunately, both specimens are incomplete since half the nodule was missing, but that is just the nature of this site! 

 

Here is the whole nodule with the partial xenacanth tail, three poorly preserved Cleithrolepis and juvenile xenacanth towards the right:

 

The juvenile xenacanth. Towards the top middle section is the base of the dorsal spine which never seems to preserve on adult specimens, and towards the left are impressions of denticles and the vertebrae. Towards the right, the lower jaws with teeth are preserved and there even seems to be an impression of the eye.

 

Ammonium chloride images of a latex peel showing the whole specimen and closeups of the jaw and teeth:

 

Closeups of denticles:

 

 

 

Edited March 18 by izak_

[Yoda]

@izak_

 

Fantastic find. 

And those extreme close ups are really interesting 

[Al Dente]

1 hour ago, izak_ said:

I noticed this juvenile of the same species within the nodule. Xenacanths are very common in this horizon of the Ashfield Shale

Interesting find. I’m not seeing the typical double cusps seen on Xenacanth teeth. Could this be some other type of shark?

[rocket]

wow, incredible find! Rare to see some from outside Europe. 

[izak_]

1 minute ago, Al Dente said:

Interesting find. I’m not seeing the typical double cusps seen on Xenacanth teeth. Could this be some other type of shark?

I did consider that and you may be right, however no other sharks have been reported from the Sydney Basin to my knowledge. One possibility is that the cusps themselves are in the counterpart and the structures left in the jaw aren't the crowns of the teeth, the latex is of the natural split so it's hard to say. I think this option is unlikely but what are your thoughts?

 

All of the adult xenacanths from this formation do not possess the dorsal spines which seem to be consistently present on the "juveniles", so perhaps there actually are two species here? 

[Al Dente]

24 minutes ago, izak_ said:

I did consider that and you may be right, however no other sharks have been reported from the Sydney Basin to my knowledge. One possibility is that the cusps themselves are in the counterpart and the structures left in the jaw aren't the crowns of the teeth, the latex is of the natural split so it's hard to say. I think this option is unlikely but what are your thoughts?

 

All of the adult xenacanths from this formation do not possess the dorsal spines which seem to be consistently present on the "juveniles", so perhaps there actually are two species here? 

You may want to send your photos to an expert. I was looking at several papers online and a researcher named Gary Johnson has published quite a bit on Xenacanth teeth. He is from the University of South Dakota. He would probably be interested in seeing your photos.

[rocket]

might be this is interesting, some papers about europaen xenacanthids with teeth and denticles

 

Mitt-Pollichia_90_0019-0028.pdfMitt-Pollichia_70_0065-0086.pdf

[izak_]

@Al Dente @rocket

 

Thank you both!

24 minutes ago, rocket said:

might be this is interesting, some papers about europaen xenacanthids with teeth and denticles

 

The figures in these papers are excellent, especially the beautiful skeletal reconstructions. Thank you for sharing. 

[Tidgy's Dad]

Beautiful photographs of a fascinating specimen.

[deutscheben]

What an interesting find! I agree with others that the teeth do not resemble typical xenacanth teeth, either in crown or root shape. I hope you can discover more about what it may be. I wonder if @jdp has any thoughts as well. 

[ThePhysicist]

Spectacular fossil and awesome imagery. The dentition is certainly not of any xenacanth I'm aware of. I believe a far more likely candidate is a hybodont like Lissodus. Is this going to a private collection or museum?

 

^ de Lange, Bart et al. “Fish Remains from the Rhaetian (Late Triassic) of Winterswijk, the Netherlands (Pisces: Chondrichthyes and Actinopterygii).” Netherlands Journal of Geosciences 102 (2023): e10. Web.

[izak_]

9 minutes ago, ThePhysicist said:

Spectacular fossil and awesome imagery. The dentition is certainly not of any xenacanth I'm aware of. I believe a far more likely candidate is a hybodont like Lissodus. Is this going to a private collection or museum?

Fantastic, that looks like a close match! Thank you for that. We donate a lot of our finds from here to the Australian Museum so this can go there if it's of interest. Maybe lots more of the "xenacanths" from this formation are actually hybodonts but just assumed to be xenacanth due to a lack of teeth...

[ThePhysicist]

3 hours ago, izak_ said:

Fantastic, that looks like a close match! Thank you for that. We donate a lot of our finds from here to the Australian Museum so this can go there if it's of interest. Maybe lots more of the "xenacanths" from this formation are actually hybodonts but just assumed to be xenacanth due to a lack of teeth...

That's great to hear, I'm certain it would be of great interest to them.

Edited March 19 by ThePhysicist

[izak_]

1 minute ago, ThePhysicist said:

That's great to hear, I'm certain it would be of great interest to them. It's got the articulated dentition, denticles, dorsal spine, and looks like indications of soft tissue with a body outline and eye.

Unfortunately there are very few people working on Triassic fish in Australia so I doubt it'll be published for a long time. I'll try to contact some people who have published on Australian palaeozoic sharks, there's probably the most overlap with those groups. The fish of the Sydney Basin (especially the Ashfield Shale) really need to be worked on but very few people seem to be interested!

[Jared C]

12 minutes ago, izak_ said:

Unfortunately there are very few people working on Triassic fish in Australia so I doubt it'll be published for a long time. I'll try to contact some people who have published on Australian palaeozoic sharks, there's probably the most overlap with those groups. The fish of the Sydney Basin (especially the Ashfield Shale) really need to be worked on but very few people seem to be interested!

There's always the opportunity of independent research  

It sounds like you might have the opportunity to take it on yourself. If one is enthusiastic about the subject, reading the relevant literature to round out your understanding of your finds will be enjoyable and fulfilling. Folks can unintentionally become the experts in their niche fields this way.

 

Plus, when it comes time to jot your ideas/observations down on paper, you can talk with paleontologists working on other types of critters and they will help you construct your paper. That, and email correspondence, zoom calls etc. with people more versed with your finds will assist you further. Plus, some journals are free or very cheap to publish in (ex: paleontologica electronica, which has no fees for authors). 

[izak_]

2 hours ago, Jared C said:

There's always the opportunity of independent research  

It sounds like you might have the opportunity to take it on yourself. If one is enthusiastic about the subject, reading the relevant literature to round out your understanding of your finds will be enjoyable and fulfilling. Folks can unintentionally become the experts in their niche fields this way.

 

Plus, when it comes time to jot your ideas/observations down on paper, you can talk with paleontologists working on other types of critters and they will help you construct your paper. That, and email correspondence, zoom calls etc. with people more versed with your finds will assist you further. Plus, some journals are free or very cheap to publish in (ex: paleontologica electronica, which has no fees for authors). 

Hopefully one day! There are some papers I will co-author in the future, so it will be a good opportunity to learn about the process

 

Here is another specimen. The air scribing became challenging towards the tail since there was little separation between the fossil and matrix, so there is still some matrix stuck to it. Air abrasion may be a better method for cleaning it up further. Anyway, it is clearly not a xenacanth either!

[doushantuo]

Unfortunately; theré is a bit of a paywall surrounding this one:

FIRSTPAGELINK

IZAK: good photography, good journalism , once again

( the link is to the first page of :

Recent Advances in the Origin and Early Radiation of Vertebrates
G. Arratia, M. V. H. Wilson & R. Cloutier (eds.): pp. 533-562, 13 figs., 1 tab.

Development and growth in xenacanth sharks:
new data from Upper Carboniferous of Bohemia
Rodrigo SOLER-GIJÓN

Edited March 19 by doushantuo

[Yoda]

3 hours ago, izak_ said:

Hopefully one day! There are some papers I will co-author in the future, so it will be a good opportunity to learn about the process

 

Here is another specimen. The air scribing became challenging towards the tail since there was little separation between the fossil and matrix, so there is still some matrix stuck to it. Air abrasion may be a better method for cleaning it up further. Anyway, it is clearly not a xenacanth either!

 

Another interesting specimen 

[izak_]

17 hours ago, doushantuo said:

Unfortunately; theré is a bit of a paywall surrounding this one:

FIRSTPAGELINK

IZAK: good photography, good journalism , once again

( the link is to the first page of :

Recent Advances in the Origin and Early Radiation of Vertebrates
G. Arratia, M. V. H. Wilson & R. Cloutier (eds.): pp. 533-562, 13 figs., 1 tab.

Development and growth in xenacanth sharks:
new data from Upper Carboniferous of Bohemia
Rodrigo SOLER-GIJÓN

Thank you! I will try to track a copy down, it sounds quite interesting  

[jdp]

Amazing specimen. The small shark is definitely a hybodontiform, not a xenacanthid. As for getting this looked at, you might want to try reaching out to John Long. He mostly works in the Devonian, but he might be interested in this fossil.

[izak_]

6 hours ago, jdp said:

Amazing specimen. The small shark is definitely a hybodontiform, not a xenacanthid. As for getting this looked at, you might want to try reaching out to John Long. He mostly works in the Devonian, but he might be interested in this fossil.

Thank you! I have been talking to John about this already, he is sending photos to a European hybodont expert. Will update you on what they say  

[izak_]

An update, John's expert is very excited by this find, apparently it is quite unique and definitely a first for Australia! We will hopefully publish it soon. Thank you to everyone for their help, I probably wouldn't have posted it yet if I knew it would be published! 

[ThePhysicist]

16 hours ago, izak_ said:

An update, John's expert is very excited by this find, apparently it is quite unique and definitely a first for Australia! We will hopefully publish it soon. Thank you to everyone for their help, I probably wouldn't have posted it yet if I knew it would be published! 

That is great news! I'll look forward to the paper.