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ZoPteryx — Ornithocetids
Published: 2014-03-26 21:16:03 +0000 UTC; Views: 17662; Favourites: 262; Downloads: 46
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Description
Quite possibly the most derived archosaurs that have ever lived, the discovery of cetacean-like dinosaurs in the Saurocene shocked the scientific community. Though scientists were initially cautious to classify them, genetic and skeletal evidence has made it abundantly clear that the ornithocetids are nested well within the aquaraptoriformes along with the better known aquaraptorids. Ornithocetids emerged in the late Oligocene and quickly spread across the world's oceans, filling the gap left by the sudden disappearance of many large marine reptiles in the late Eocene, including other more archaic types of aquaraptoriformes.Skeletally, ornithocetids are highly abnormal, much more so than the aquaraptorids. There bones are thick-walled and relatively solid; the naris and antorbital fenestra have combined into a nasoantorbital fenestra (similar to some pterosaurs) to accommodate the retracted nostrils; digits II and III of the hand are completely fused and usually clawless; the pubis and ischium are massively constructed and elongated to form a keel along the underside; the dorsal spines of the sacral vertebrae are elongated and often form a dorsal fin; the hind limbs are extremely reduced, but still functional; the hallux is vestigial and, unusually, lies on the outer side of the foot; and finally the last few caudal vertebrae have fused into a massive pygostyle to support the feathered tail fluke.
Physiologically, their most peculiar feature, the one that sets them apart from all other archosaurs, is their ability to give live birth. They are ovoviviparous, meaning the hard-shelled eggs are retained inside the mothers body but there is little to no connection between them and the mother. The egg shells dissolve away and are excreted shortly before the young are due to be born. Dissected specimens have allowed scientists to determine that, for most species, eggs are rather large and usually number between 5 and 10. Young stay with their mothers for an extended period of time, though how long various between genera with some becoming independent at only a few months old, while others may remain with their family group for years. There is a high mortality rate amongst newborns.
Locomotion is a simple cetacean-like undulation of the body and tail, occasionally accompanied by flapping with the forelimbs. Their most flexible points are their necks and the base of the tail, unlike aquaraptorids which also have a flexible lower back. Like all aquaraptoriformes, the feathers of the forelimbs and tail are unique, stiff, interlocking, and plate-like. The feathers that form the tail fluke are fixed in position, but those of the arm are a bit looser allowing the arm to flex normally, this lends them great maneuverability. These feathers are also detachable and may be shed at will (such as when they have been grasped by a predator!), similar to how some lizards can drop their tails; like the lizards' tail, the feathers will regenerate in time.
Though webbed, the tiny hind limbs serve no purpose in locomotion and are used mainly during mating, hence their large claws. In receptive females, the feet may become brightly colored to advertise to the males. Ornithocetids rely mainly on sight and sound, though they do not use any form of echolocation. The gular pouches of males can become brightly colored in the breeding season and extended like the dewlap of anole to display to females and rivals. Most species are rather social and some even form large flocks. They are fairly large creature, on average being about 4-5 meters long and weighing over 700 pounds; some are much larger, while others are smaller. Behaviorally, they are quite similar to cetaceans in habits, but not in intelligence.
There are four genera: Ornithocetus (O. callipeplus is pictured), Pelagisaurus, Ichthyoraptor, and the peculiar Mantaraptor. Small examples have been maintained in captivity, but they are nervous animals that must be given lots of space. The tank must also be covered, otherwise they will attempt to jump out (being stranded on land, via jumping out of tank or beaching themselves, almost always leads to a broken pelvis and certain death). Large individuals in the wild should be treated with caution, they are very inquisitive, sometimes too inquisitive.
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Sorry about all that text, genera descriptions will come next time.
Ornithocetid Genera
Aquaraptoriformes Intro
Saurocene Intro
Related content
Comments: 65
Lovely! I find these alternate natural history science materials to be absolutely delightful!
I really find it something exceedingly well-done, thank you!
Sincerely;
Adalack.
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Thanks! It's a descendant of unenlagiine dromaeosaurs like Austroraptor.
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I love how you made the pubis and sacral spines the ventral and dorsal fins
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Thanks! Glad you like the design!
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In many ways, they are more like aquatic birds, even though they are descended from non-avian dinosaurs.
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I've been rethinking about the creatures, and I've found some more things that feel off about it.
1: Why would they evolve that kind of feathering for propulsion? Flightless marine-birds like penguins never had to evolve these kind of feathering, nor did (as far as we know) other extinct flightless marine-birds. These aren't birds, but I would imagine it would still hold the same. Penguin-like wings would be more possible.
2: Aren't the tails of paravians too stiff to act as means of propulsion? I know they are comparable to fishing rods in terms of flexibility, which means it would be highly implausible for it to be used effectively for propulsion. In face it would be more likely that the wings and hind limbs would be the form of propulsion. The tail would probably shrink down or simply become flat and a tool to become more manoeuvrable.
3: I know you haven't discussed their evolution, although these seem unlikely to evolve in general. What kind of events and pressures would allow the ornithocetids to evolve with these traits? I'm still sceptical about the eggs, how would such a thing evolve? How would a lot of these adaptations appear? Couldn't there be alternate traits that could be more plausible and easier to evolve? Also what about other lineages that could become fully marine as well in less time that the ornithocetids evolve (and become fully marine). Remember, whales only evolved in around 15 million years (from land to fully marine mind you). How long did take for these to evolve. So much questions.
That's all I have to complain so far. You might think I'm being rude here, but that's not what I'm trying to do. If I am, them I apologize. I think the forelimbs would be better as penguin-like (with the claw too). The tail would probably (to me at least) make more sense as a flat and flexible and not used as a method of propulsion, and more of a organ that aids manoeuvrability in the sea.
Also sorry for the continued criticism, it's just that these creatures seem a bit implausible.
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No need to apologize, I like discussing these things.
1. The answer is two fold and stems from their ancestry. They evolved from quadrupedal ancestors that needed to be able to cling to rocks in the surf zone (more explained in #3). Penguins may cross this zone in their travels, but they don't spend much time here because they are so ungainly. Under these conditions, a flexible clawed forearm was beneficial rather than a stiff flipper, but then what to do for a lifting surface? Specially reinforced primary feathers were the answer. These could be derived either from typical primary feathers or from EBFFs, both of which were possessed by deinonychosaurs. The advantages to these are a) allows for more maneuverability on land in in water because the forearm because the lifting surfaces' area can e changed (same reason flying birds or so successful), and b) they are expandable, replaceable, and can be scuffed up without injury, unlike a flipper, thus allowing them to spend more time in the ruff and tumble surf zone (remember, we're talking about their ancestors here, which can be though of as "diving rock herons").
2. The tails of maniraptors, as a rule, are stiff like you described. However, they are quite flexible at their base, particularly in the vertical range (Senter et al, 2012). Also, quote: "it appears to represent part of a trend in within Dromaeosauridae that couples an increase in tail flexibility with increasing size". Likewise, the tails of aquaraptorids are quite stiff and used mainly as a rudder and counterbalance, while those of ornithocetids are more flexible.
3. Aquaraptoriformes are descended from South American unenlagine dromaeosaurids. Buitreraptor, or a similar form, may be the direct ancestor of all aquaraptoriformes. The reasons for this are as follows: a piscivorous lifestyle, long arm capable of a wide range motion, unusually short hand, small but sharply curved pedal claws, and shorter toes than would be expected if these were heron-like waders. It is that these "protoaquaraptoriformes" were essentially diving herons that inhabited rocky coastlines (away from the competition of the new "pelecanimorphs") that pursued fish with a flapping motion of the forelimbs. This form existed in the late Cretaceous through the Paleocene (a time when the Andes were experiencing uplift, resulting in the rocky coastlines along the interior seaway that existed at the time). By the Eocene, selective pressure had enlarged the forelimbs, reduced the hand further, reinforced the feathers, shortened the snout, and expanded and webbed the feet. Tails and legs were still relatively long in these "cormorant raptors", but unlike cormorants, these swam with a flapping motion. These species lived in the cool coastal waters off the Tierra del Fuego and possibly adjacent Antarctica; some grew fairly large (a few meters). In the wake of the PETM in the late Eocene and resulting marine fauna turnover, aquaraptoriformes spread across the globe to fill the void and grew massive on it. They thrived in the cooler polar waters that other marine reptiles had struggled to conquer. Why go to such extremes you ask? Simple, because they could, because, like all species, they evolved to fill their niche to the fullest extent possible (and without much competition, they were able to go pretty far). By the late Oligocene, aquraptorids and ornithocetids had diverged from one another and followed evolutionary paths roughly similar to pinnipeds and cetaceans, respectively, while the older forms perished at the hands of advanced seabirds and fluctuating sea levels. Egg laying appears to have abandoned by ornithocetids some time early in their evolution, at least by the early Miocene.
With regards to eggs, I personally see no other viable option other than the one we discussed earlier. A pouch with air would have too great an effect on buoyancy, hard shelled eggs can't be laid in water (at least not for long), so the best place for them is to stay within the placenta. The dissolving egg shell method could have evolved to reduce stress on the mother during pregnancy, so the egg could be expelled sooner, but after all calcium had been used in bone development of course. After this point, the protective egg shell is no longer necessary and its removal makes it easier for the embryo to absorb nutrients from the placenta (the leathery inner shell is still present).
That's all for now.
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The keel helps them stay stable when resting at the service, where they spend much of their time while scanning for prey.
Mantaraptor: a very unusual genus with reduced tail feathers and enlarged forelimbs, it swims in a stingray-like fashion. It has a short skull and feeds mainly along the bottom.
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Give it a long neck and you have the perfect sea serpent with the feathers and all.
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I sort of have something like that already planned, but it won't evolve for another 100 million years!
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I agree, though it would make me think twice before going surfing!
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Awesome! This has to be one of my favorite concepts ever
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I have a concern, and that concern is the eggs, wouldn't the egg shells kinda hurt the mother after the eggs hatch? Which means that the cuts could give the female a infection, leading to death. Also the eggs do need air, if not they asphyxiate. Beside that the concept seems plausible.
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I'll assume the eggs are leathery like those of a crocodilian, that should solve the "egg shrapnel" problem. As for gas exchange, ovoviviparous sharks can do it, and leathery egg shells should help.
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But aren't dinosaur eggs hard-shelled? So far no known dinosaur (avian or not) have evolved leathery eggs. Also shark eggs are very different compared to those of amniotes. Amniote eggs have holes in them, which means they would drown in water, while sharks can actually breath the water (although to be honest, my knowledge on shark-egg anatomy is rather poor).
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Your right about dinosaurs, but pterosaurs had leathery shelled eggs and they're some of dinosaurs' closest relatives (along with crocs of course), so I suppose ornithocetid reproduction could've experienced and evolutionary reversal. You bring up a good point about the sharks. However, it's a problem faced by all live-bearing amniotes (there's no bubble of air for the embryo to breath). Presumably, whatever fluid the uterus contains would supply the oxygen needs of the embryo by diffusing through leathery shell. If not, uteruses can produce all sorts of extra secretions, maybe they can make one rich in dissolved oxygen.
Hmm, maybe it'd just be easier to make them placental!
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While yes, pterosaurs did have leathery eggs, dinosaurs didn't. The thing about hard-shelled eggs is that it is really hard to reverse, and a "evolutionary reversal" seems rather unlikely. That would be as likely as placental mammal laying eggs again. Also, amniote embryos obviously don't have a air bubble, the pores on the egg shell essentially allow the embryo to "breath". This could be solved by the uterus having dissolved oxygen, however the thing with (dinosaur) eggs is that the eggs are supposed to be laid as soon as the egg shell is developed. Which means that the eggs are specialized to absorb air, rather then oxygen in a liquid.
Also it's pretty much impossible for a dinosaur to develop a placenta-based development. The eggs are too specialized for such a system to evolve, compared to mammals where their eggs aren't calcified (like in turtles, and crocodilians and dinosaurs).
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Well to be honest, this is all rather unlikely! But still, I'm not so sure an evolutionary reversal reverting back to leathery eggs is that unlikely; they way I see it, the leathery shell hasn't been lost so much as modified, unlike in most mammals where it is well and truly gone. The right mutation could stop the calcification process or prevent it from going to completion. As for the pores and dissolved oxygen absorption, sounds like a number-of-pores-to-surface-area issue, which should be an "easy fix" in evolutionary terms.
Regarding all of this I'd like to bring up skinks of the genus Trachylepis, which exhibit every mode of reproduction from hard-shelled egg laying to full blown viviparity, complete with placentation. These are of course lepidosaurs, but skinks as a rule tend to lay hard shelled eggs, so that's probably an ancestral condition for the group, and yet some have become viviparous to varying degrees. It appear in most of these, that there is a hard shell at first, but it dissolves away before fully forming, either going away completely or being left as a thin membrane. Archosaurs don't appear to be as flexible as lepidosauromorphs in terms of reproduction strategy, but then again, 65 million years of evolutionary pressure can have strange effects on a body.
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Sorry for going into this discussion but HybriRex is right, birds and dinosaurs need a hard shell for the developement of their bones.
My solution for this problem in my Cetosornis clade was to make the shell able to absorb oxygen from a liquid enviroment. The mother nest a single egg within it's padded uterus until shortly before the baby hatches. Than it lays its egg into the water. The contact with saltwater trigger the hatching and a new small Cetosornis fight its way out of the shell.
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I've changed the text reflect that they have hard shelled eggs, the shell just dissolves shortly before birth (presumably, the offspring are done building up bone mass by this time).
I do like the idea of water triggering the hatching process though. I believe there's a turtle that uses this strategy, isn't there?
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Indeed, the australian softshell turtle when I remember correctly
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If it's unlikely, then why even bother with the concept? I'm a real stickler when it comes to plausibility in spec evo. To be honest; lizards, (already marine) turtles, and mammals are more likelier to be "whale" analogues. Maybe even marine birds like the already existing sphenisciformes or anseriformes could go in a niche, all they need to do is evolve a pouch of some kind.
I did exaggerated on the claim, but it essentially is. Archosaurs have shown to be very inflexible in terms of eggs. They are either leathery or hard. Archosaur shells seem to calcified, and no evidence that they switched between. It seems that once they had hard-shelled, it was permanent. The fossil record supports this, and it probably would follow the same in a alternative timeline. The likeliness that the "right mutation" of occurring is pretty slim. Also I don't think it would be as easy as "the number of pores", and it's definitely not a "easy fix". You are changing the morphology of an egg that was originally adapted and specialized to be laid on the surface, and changing it to be laid in a liquid medium.
For the skink part; skinks, like all lepidosaurs, evolved from a ancestor with leathery eggs. And unlike archosaurs, had uncalcified eggs (although many lineages have developed calcified eggs. Also can you link a source for the skink egg-shell development, I can't find much information on the subject.
And yes, archosaurs seem to be not as inflexible, as I said. Although I doubt 65 million years would do that. The Trassic period in general was almost as long as the Cenozoic. If we include both the Mesozoic and Cenozoic, no known archosaur has developed live-birth or reverting back to leathery eggs.
Sorry if I sound a bit rude, I'm just a tired.
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What about marine crocodiles like dakosaurus , I find it hard to belive that they laid eggs...
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I find that it's way overstated that Dakosaurus "had" to give birth to live young. It was only about 4.5 meters long at most, saltwater crocodiles can grow even larger (5.2 meters). If a saltwater crocodile can go on land, I don't see why Dakosaurus couldn't. A better example would be Plesiosuchus, which could grow up to 6.8 meters long. That's pretty big. However some other extinct crocodilians could get even bigger, at almost 11 meters in length Deinosuchus was a lot bigger.
They had flippers though, so I would imagine the only reason they would return to land is to lay egg like a sea turtle.
Also Dakosaurus wasn't a crocodile, it was a metriorhynchid
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No problem, I want my creations to be as plausible as possible, so any help/refinement is appreciated!
I'm not sure how marine birds or sea turtles would be more likely to evolve to give live birth, they all have the calcified egg problem. I'm not sure a pouch would solve the problem, would it be air tight? Why not just retain the eggs in the uterus (a special compartment perhaps). When the egg is first developing it's there anyway, and embryo can obviously breath, so why not just stay there?
I agree whole heartedly, but this is a new evolutionary pathway, one that obviously never happened thanks to a pesky series of unfortunate events a long time ago. My point is, there's no telling what natural selection and adaptive radiation will do. If I were an extraterrestrial given a live Tiktaalik to study, I doubt I would be able to predict all of tetrapod diversity. Point is with these aquaraptoriformes, I was really trying to avoid the whole "K with a new hat syndrome" that often plagues similar projects, by making something totally novel.
As for skink links: The animals section here, breeding section here, but most of what I know comes second hand from one of my professors who has worked extensively on the subject (though nothing published as far as I know). I brief google search for more yielded surprisingly little.
My only point to the final paragraph would be the Cenozoic's climate was a lot less stable than the Mesozoic, colder and drier in particular. These conditions could've encouraged the evolution of this reproductive strategy, particularly if there was a niche to be filled as other marine reptiles began to decline in the late Eocene.
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Well, a marine turtle could give birth to live young, they're leathery. Marine birds however, are different story. A pouch could work because all you need to do is keep the pouch tight underwater, and open it when it's exposed to the air.
Well, of course they wouldn't know. They would also have to know the geography and geology of Earth, and the other flora and fauna to at least get a good idea for what they could evolve into. The "K with a new hat syndrome" is nonsense, especially with the marine fauna. The Mesozoic didn't have marine mammals, or fully marine birds (maybe besides hesperornithiformes). So you have a lot of room to work with.
I guess that method of egg development might work, although the likeness of that happening is not that high. Although I admit my knowledge on eggs isn't that high either.
If I can add, the marine reptiles (or at least most of them) would probably go extinct during the PETM (Paleocene-Eocene thermal maximum).
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I've been thinking, maybe instead making these ornithocetids re-evolve leathery eggs, perhaps I just make the egg shell dissolve away at some point late in development shortly before birth. It works for some of those skinks, and would seem to be a lot "easier" in evolutionary terms. What do you think?
As for the PETM, yes, I haven't had a chance to thoroughly explain the Saurocene's timeline yet, but lots of marine things do die out at that point (and a lot of terrestrial stuff shortly after) including some of the dominant marine reptiles of the time, leaving many niches to be filled.
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Actually the dissolving shell could work. As you said skinks do it, and they don't have to turn their hard shelled eggs into leathery ones. I think it's probably more plausible too.
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It's settled then! I'll change the text accordingly.
Thanks for helping me iron out these kinks!
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