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Alternate sea reptiles
Topic Started: Jan 21 2010, 05:35 PM (1,160 Views)
Carlos
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As you al know, the Mesozoic oceans were ruled by plesiosauroids (both plesiosaurs and pliosaurs), mosasaurs, ichthyosaurs, turtles and sea dweeling crocs. However, during the Triassic several other linages of marine reptiles existed, and I was wondering of how the Jurassic and Cretaceous oceans would look like if things were different.

For starters, the nothosaurs, which would produce later the plesiosaurs, would have gone extinct, or at least the pistosaurs (the appearent direct ancestors of plesiosauriods) would have gone dead; most likely the thalattosaurs would have gone into power, first maybe as mosasaur like creaturs before gradually becoming more streamlined like in ichthyosaurs, which would either be gone at the T/J event or gradually decline. In fact, while the post-Triassic Mesozoic had two main groups of sauropsids taking the cetacean niches (plesiosauroids and ichthosaurs, and later plesiosauroids and mosasaurs), most likely thalattosaurs would take most niches by the end of the Cretaceous.

The Triassic was also inhabited by sea going temnospondyl "amphibians" and hupehsuchians (ichthtyosaur like reptiles with an armour instead of dorsal fin, an eel like tail and fins that were mostly clawless webbed digits than perhaps true flippers), the first occupying a gharial like niche and the later appearently being bottom filter feeders akin to grey whales; maybe both groups would survive quite some time afterwards, though the marine temnospondyls would probably had been replaced by phytosaurs, proterochampsids or crocodillians (in fact I'd prefer either of the first two than the last). The seal niches most likely would had been occupied by phytosaurs, if they survived, or by choristoderes, which could take the sea by the Cretaceous. Maybe, instead of mosasaurs, there would be sea dweeling sphenodontians, albeit not probably not as marine and probably able to pass through the KT event alongside choristoderes.

Marine turtles perhaps would take longer to appear if placodonts had survived; most likely only by the end of the Cretaceous would turtles have been a presence in marine biomes. In our world, pterosaurs never took an aquatic niche, perhaps due to competition due to aquatic sauropsids and because of their wing membranes, though if there's not enough competition I'd assume a "pterosaurian penguin" could evolve. Maybe birds will take that niche first and create hesperornithid like forms though.
Lemuria:
http://s1.zetaboards.com/Conceptual_Evolution/topic/5724950/

Terra Alternativa:
http://s1.zetaboards.com/Conceptual_Evolution/forum/460637/

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Rick Raptor
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I doubt it would stand a chance against the better adapted marine life forms, if penguine-like pterosaurs had already evolved the Compsognathid wouldn´t have any other chance than to stay out of the water because it would not be able to compete with them.
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ATEK Azul
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While I don't know every group mentioned that timeline is great and greatly helps my picture of your world so thank you.
I am dyslexic, please ignore the typo's!
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Margaret Pye
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On non-avian aquatic dinosaurs: remember Specworld duckgongs, ornithopods in sirenian niches? Swam by kicking, came ashore to nest? I thought they were a good idea.

(And making the most common species bright yellow, so that it looked like a ginormous rubber ducky, was hilarious. Bit silly, but there's no evolutionary reason it shouldn't be yellow after all..)
My speculative dinosaur project. With lots of fluff, parental care and mammalian-level intelligence, and the odd sophont.
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Carlos
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Sadly, I think marine ornithopods would only work after sea grass evolved...
Lemuria:
http://s1.zetaboards.com/Conceptual_Evolution/topic/5724950/

Terra Alternativa:
http://s1.zetaboards.com/Conceptual_Evolution/forum/460637/

My Patreon:

https://www.patreon.com/Carliro

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Margaret Pye
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Kelp?
My speculative dinosaur project. With lots of fluff, parental care and mammalian-level intelligence, and the odd sophont.
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Carlos
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Maybe. Or corals (we never had a coral eating tetrapod, but parrot fish show its possible to eat corals)
Lemuria:
http://s1.zetaboards.com/Conceptual_Evolution/topic/5724950/

Terra Alternativa:
http://s1.zetaboards.com/Conceptual_Evolution/forum/460637/

My Patreon:

https://www.patreon.com/Carliro

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