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Evolution of dracosuchid flight
Topic Started: Jul 24 2013, 09:42 PM (61 Views)
DK1000
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I'm curious as to when and how dracosuchids fully develop flight. Protodracosuchus demonstrates a sort of midway phase between the fully terrestrial ancestors and the fully flighted dracosuchids, and appears at what I'm assuming is 210-208 million years ago, towards the end of the Norian*. Aetherclepthis appears to demonstrate the next step towards full flight, possessing small (crude?) wings, occurring approximately 150-120 million years ago. This leaves a rather large temporal gap of 58 million years between the gliding Protodracosuchus and the basal dracosuchid Aetherclepsis. However, it appears that flight in vertebrates develops in a relatively short amount of time, pterosaurs went from something like Scleromochlus to Preondactylus in roughly 12 million years, and bats practically come from nowhere in the fossil record. And even in eumaniraptora, flight appears to evolve quite rapidly. The 58 million year gap between Protodracosuchus and Aetherclepthis seems rather drawn out, I'd have suspected flight would have developed much quicker in the dracosuchids. That's my tuppence worth, anyway.

*I am aware the entry for Protodracosuchus says it existed 110-108 mya, but considering the apparently more advanced Aethercelpthis existed before that date, I'm willing to bet the Protodracosuchus information was a typo.
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Jack Frost
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Hmm... I wasn't aware of that, so I gave what I felt was a reasonably long enough time frame between the two. That being said, Aethercleptis is NOT the only basal dracosuchid at the time though, and is the more primitive of the two because of it's environment. The other, which I have almost ready to be posted, is farther along in flight.


And I went full retard on the time frame >_< For what ever reason I forgot the big number means later and the little number goes sooner.
Edited by Jack Frost, Jul 27 2013, 09:23 AM.
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DK1000
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Okay so I've just read something that could really affect how our dracosuchids evolve.

TL;DR read version: It's becoming increasingly unlikely that gliding is involved with the evolution of powered flight, and in fact appears to be effectively independent of it for several reasons (you can read the full post in the link to see what these are). From looking at true fliers, bats and birds, true flight comes from more unusual circumstances than just gliding around; bats appear to have "fluttered" at first to control their descent, rather than just parachuting down like gliding mammals, seemingly linked with the need to hawk aerial prey like insects. Birds too likely didn't evolve form gliding ancestors (many of the perpetuated gliders like Microraptor are actually pretty pish at gliding), and the main ideas around how birds evolved flight involve a flapping motion of the arm (WAIR, The Leaping Grapple, and the RPR), so flight appears to have come from motion of the arms in birds as well as bats.

Since the beginning of MN, our dracosuchids started out as gliders that developed powered flight, which by looking at flying and gliding animals, is a process that simply doesn't happen. We're going to need something else involved in the evolution of flight in dracosuchids, and remove the gliding stage entirely for it to work.



Now, there was an idea I had a while ago that I never got around to talking about for what could drive dracosuchids to evolve powered flight, and with this revelation I've decided to resurrect it and pitch it:

At the same time "sphenosuchians" were in the trees, there dimorphodontid pterosaurs, that were very well suited for climbing and maneuvering through trees and branches. Dimorphodontid pterosaurs also appear suited for grabbing at larger prey items then other pterosaurs of their size, and may well have been capable arboreal predators. In the presence of arboreal-sphenosuchians, we could perhaps have a group of dimorphodontids that become specialised for hunting prey items of their size, and become the sphenosuchian's main predator.
Sphenosuchians were capable of running on their hind limbs, so I don't see why they wouldn't do this in the trees as well. This would free up the arms and hands, which could be used for maneuvering to escape these predatory pterosaurs. In situations like this, gliding is often the path taken to find a means of escaping a predator, however in this case the predator itself is already capable of flight, so gliding would be useless in trying to escape from a predator that can just fly after them.
Instead, these sphenosuchians could go down a different path. By frantically flapping their arms, they might be able to maneuver as they run more easily, and give themselves an extra oomph as they do so. This could then lend itself to the evolution of being able to flutter (like bats), so instead of simply gliding away, they'd be able to control their descent far more easily, making it harder for these predatory pterosaurs to catch up with. They wouldn't be able to fly very far, but they'd be able to out manouver their predators a lot more easily. In particular, dracosuchids seem pretty capable terrestrially too (since their wing membranes aren't attached to the legs), so these early sphenosuchians could feasibly be able to reach the ground quite quickly (certainly faster than a glider) and then simply run away, as the predatory pterosaurs wuld be encumbered on the ground by their uropatagium and would no longer be able to catch up with.

This form of flapping and fluttering could then quite quickly evolve into true powered flight, without ever needing to evolve gliding at all, and is driven by a set of unique circumstances, which fits in with how powered flight appears to evolve in animals.
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