Amazichthys, a placoderm with fins preserved

[Halichoeres]

A beautiful new fossil from Morocco (although, troublingly, with no Moroccan authors included on the paper) preserves both the armor and outline of an arthrodire placoderm in the family Selenosteidae. While people have predicted for many years (see Kaiyodo's 2001 Dunkleosteus figure) that many arthrodires would have had lunate (shark- or tuna-like) tails based on ecology, this confirms that prediction. Meet Amazichthys trinajsticae, named for the Amazigh people of North Africa (although the coincidental resemblance to the word "amazing" was probably not lost on the authors).

Fossil:


Reconstruction:


The paper appears to be open-access, but if you can't see it, pm me for a pdf: https://www.frontiersin.org/articles/10.3389/fevo.2022.969158/full

[Faelrin]

Once again lost everything I had typed up, because it logged me out the moment I went to post what I had typed up. So frustrating. Guessing I'll need to start using that draft button (and copy) for every post now as a precaution. Ugh. Going to retype up an approximation of what I had earlier.

Anyways this is an incredible find, and not with one specimen, but several as well. I haven't been this excited about a newly published find since the Lystrosaurus mummy this year. Really glad we finally got another arthrodire with extensive soft tissue remains (the only other one coming to mind is Coccosteus). I also really like the artwork, and I'm fascinated by the invertebrate fauna in it as well. Wondering what those are?

Obligatory want a figure of this now comment.

I also agree the lack of Moroccan authors is troubling. I think this is unfortunately par for the course in this field however.

Also worth mentioning that Dunkleosteus and Titanichthys are more related to this then Coccosteus, as all three fall under the clade Pachyosteomorphi, although it does diverge from there. Though both the family Amazichthys is in, the Selenosteidae, and Titanichthys, falls under the clade Aspinothoracidi. Dunkleosteus is in the superfamily Dunkleosteoidea, which diverged from the clade Aspinothoracidi.

[andrewsaurus rex]

wow, so it's been confirmed.  Very interesting find. Most complete specimen is about 3 feet long.  So that indicates that probably all placoderms had lunate tails, not just the larger ones.   Boy was i wrong about this....lol.

[Newt]

Super cool. I'm impressed that it even has a tuna-style lateral keel - this puppy was built for serious swimming. I'm used to thinking of Devonian vertebrates as a ponderous bunch, but there were definitely some exceptions.

A @andrewsaurus - don't get too carried away, the placoderms were an ecologically and morphologically diverse group. Other placoderms with preserved tails are known, including the aforementioned Coccosteus and everybody's favorite antiarch, Bothriolepis, whose tails were not lunate and were quite different from one another and from Amazichthys. 

[andrewsaurus rex]

oh I see.....but it does seem clear now that larger placoderms, like Eastmanosteus and Dunkleosteus certainly had lunate tails, doesn't it?

[Halichoeres]

It seems pretty likely that they did. My takeaway from this is that if we're trying to guess a given placoderm's tail shape, its environment and lifestyle might be more important clues than which of the few taxa with known tails it's most closely related to. The same is true of sharks; whereas I lazily said "shark-like" above, that ignores a lot of variation among sharks in different settings.

@Faelrin I wouldn't mind a figure myself!

[Faelrin]

That really would make the most sense. And thankfully there's no shortage of marine animals to learn from that might have comparable morphologies. Like if something had a similar lifestyle to a leopard or zebra shark, I imagine it would have had a similar tail (Coccosteus which does have its tail preserved, comes to mind). Where as a large pelagic hunter like Dunkleosteus may have had a tail like a Great White shark. 

Adding on to both what @Newt and @Halichoeres said, it's worth noting that Placodermi is also paraphyletic, much like Ostracodermi. And in this particular case, narrowing it down to the order Arthrodira, even there's quite a bit of variation, and the current examples we have of this does include at least Coccosteus and now Amazichthys, if not others.

[Halichoeres]

@Faelrin I missed your question on the invertebrates before. The arthropods are thylacocephalans, probably Concavicaris. I don't know the genus of the cephalopods, but the fish is the stem-ratfish Ferromirum: https://dinotoyblog.com/forum/index.php?topic=9110.0

[Faelrin]

@Halichoeres Thank you very much. TIL about those.