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So many millions of years ago their was a lobe finned lung fish named tiktaalik that led to the evolution of all tetrapods and the diversity they hold today. And I wanna do that again, but instead of a bony fish, I wanna use a placoderm for the job. My intention in this is to have vertebrate creatures who are virtually indistinguishable from land arthropods. Yet even after all my research into fish I still cannot find my placoderm white whale, so I am asking y'all for some help.

Question

So my question is, what type of specific species placoderm would be best fit to crawl onto land?

Requirements

  • Needs to be in the order arthrodira or a simular group that has self sharpening toothplates

  • Need to have ray fins capable of evolving a form similar to a sea robbin, allowing for arthropod like legs and wings to evolve over time

  • Need color vision(not sure if they all had this or just a select few?)

  • Need to be omnivorous

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    $\begingroup$ tiktaalik is descended from placoderms thats why your having trouble. Also there is an artist who has played with this idea. deviantart.com/tag/placoderms $\endgroup$ – John Jul 29 '18 at 17:47
  • $\begingroup$ @John Thats still only a speculation, paleolgists arent sure yet, and tiktaalik isnt from the order arthrodira like I need, and thanks for the pictures, they are great!!! :) $\endgroup$ – Amoeba Jul 29 '18 at 20:34
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    $\begingroup$ @John Are you sure of that. Tiktaalik is a sarcopterygian, the placoderms are the sister clade to a group that contains all modern sharks, fish and tetrapods. Tiktaalik and the placoderms are both jawed vertebrates, but Tiktaalik is not a placoderm. $\endgroup$ – James K Jul 29 '18 at 20:45
  • $\begingroup$ Which is why I used the word descended, all of Osteichthyes, including us, are placoderm descendants. True teeth even evolved in the placoderms. $\endgroup$ – John Jul 30 '18 at 4:07
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You can evolve any features that you want, including colour vision or spines. So just take a generalist, and let (fantasy) evolution do the rest.

For example you could take Austrophyllolepis (description), which was a small arthrodire placoderm found in mid-to-late Devonian strata. Of particular interest is that it seems to have been a freshwater fish. If it has moved to fresh water, it has solved lots of the problems that land animals have. It needs a deal with different ion concentrations inside and outside its body, so it needs a skin that blocks osmosis. This is a good start for having a skin that can cope with desiccation.

Rivers are a less stable environment than the sea, so some ability to survive for short periods out of the water could be a useful adaptation. This provides a potential route to an amphibious and finally terrestrial lifestyle.

Austrophyllolepis was a detritus feeder, its digestive system could deal with a range of small prey and plants, that is a useful feature that could help it utilise the mosses and small invertebrates that were found on land.

Unfortunately, Austrophyllolepis was probably also functionally blind. It does still have all the genes for vision, so if there were evolutionary pressure for sight, this can be evolved quickly. As can spines or rays, if those are required.

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