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Pladcoderm evolution; Remember the armored fish?
Topic Started: Sep 11 2008, 08:37 AM (3,173 Views)
Spartan Delta
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I had a thought. Does anybody remember the pladcoderm fish from the Devonian, like Dunkleosteus?
Well, what if they were able to get on land first? I imagined a T-Rex like biped with fins for this...
What do you think?
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Jurassic-Gothic
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That would be likely at all. Several Placoderms lived in freshwater environments, so water-land transition could even occur as for Crossopterygians.
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Spartan Delta
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Jurassic-Gothic
Oct 3 2009, 03:22 PM
JohnFaa
Sep 11 2008, 01:31 PM
Placoderms couldn't possibly become land dweelrs; they lacked every single adaptayion our ancestors had for such evolutionary step, like bony skeletons and a swimming bladder that could become a lung. Plus, will all that armour...

However, if the other fish groups had died out instead of them, they could very well dominate the seas. I imagine several species of placoderms occupying the niches of modern fish: shark like placoderms, ray-like placoderms, marlin-like placoderms, etc.
Actually fossil placoderms known show several similarities with chondrichthyans.
Though not taxonomically related, their features resemble those of modern cartilagineous fishes:

- Flat-body Rhenanids showed interesting stingray affinities

- Coccosteids showed shark-like features (except well-known dorsal fin), although not active and specialized predators, whereas Dunkleosteids were

- Rolfosteids showed long noses alike marlins and swordfishes

- Rhamphodospids were quite chimaera-like creatures (see also Materpiscis, ovoviviparous too)

- Phlyctaeniids were a bit different, but Antiarchs quite broke the rule someway, showing independent autapomorph features.


Imagining land-dwelling Placoderm is surely an interesting speculative work, though, as for me, I would likely imagine more Placoderm specialize as Chondrichthyans have done up to modern times.

I would see giant whale-size plankton-eater dunkleosteids, Manta-ray rhenanids, mako-shark coccosteids, marlin-nose rolfostedis and abyss-dwelling rhamphodopsids.

Plus If I remember correctly, Antiarchs showed lung prints at fossil state. We don't know if those were actually lungs of homologue features and employed in dessication events too, but it's certain Antiarchs were both marine both freshwater dwellers.

Well, an Ichthyostega-like bothriolepid wouldn't be unlikely at all, according to these assumptions...
First off, thank you for enjoying my work. ^^

Second, I just have one question for that idea - how could they change their diet? Dunkleosteids, anyway.
As far as I know, the dunkleosteids and other large, carnivorous placoderms were....well, carnivorous. And their jaw structure had sharpened bony scissors, essentially, instead of teeth. It seems quite a transition from a bony-jawed carnivor to a filter-feeding giant.
I'm not saying it's a bad idea - in fact, that idea actually sounds cool - ,but I don't quite see how Dunkleosteids in particular could chnge to fit that. To be honest, I actually thought that sharks could've well kept that slot filled in, keeping those armored fish to either smaller filter-feders or carnivores.
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Yeah. See, my thoughts went basically like this:

-"Dunkleosteus is huge, bloodthirsty, and reeally mean-lookin'! Totally awesome, dood!"

--"That jaw design is really unique; it looks like an armored T-Rex!"
---"Hey, what if there was a land predator with a similar type of jaw? That'd be sweet!"

----"OMG, what if it was Dunkleosteus?! He could've possibly gotten on land, and since he only had two well-defined flippers, he could evolve into a predator alot like T-Rex!"

-----"Hey, whay if not just Dunkleosteus, but all the placoderms made it on land? What would they change into?"
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