From this thread Lemur866 says there are no aquatic dinosaurs. Now, I’ve known plesiosaurs and mosasaurs and others are reptiles, but why aren’t there any aquatic dinosaurs? They had rule of the land for well over a hundred million years! Look how many mammals have gone into the sea in that time. Then you have the reptiles, heading back, and even ones that head back then change their mind again like tortoises. It’s not even that they’re not capable; many birds rely entirely on the water, or like penguins even spend a lot of time swimming around under it, and birds are dinosaurs, so…
On another note, why aren’t there any flying dinosaurs? Mammals have bats, reptiles have pterosaurs. Insects were the first fliers, and even fish have had go with gliding. Or is it just a matter of semantics, where any dinosaur we find that can fly we label a bird?
And one last thing, I was reading something the other day where the kakapo was brought up again, and I’m wondering if we have any cases of kakapo/dodo like incidents occurring with flying dinosaurs/birds or even flying reptiles before the KT event?
For aquatic non-avian dinosaurs, there was recently a paper suggesting that Psittacosaurus (an early ceratopsian) was semi-aquatic. I don’t think all palaeontologists would accept this, though.
Basically this. Birds were the only dinosaurs we know of to evolve powered flight, but powered flight among vertebrates isn’t that common. There are a few non-avian dinosaurs such as Microraptor that were closely related to birds may have used their feathered wings to glide.
Patagopteryx was a flightless bird from the Cretaceous period. And there is the heretical hypothesis that many Cretaceous theropods were secondarily flightless (Velociraptor, Deinonychus, Troodon, Caudipteryx, Oviraptor, etc.). No pterosaur is known to be secondarily flightless.
The OP appears to be aware that birds are dinosaurs. I guess his question is, were there any aquatic or flying true dinosaurs in the mesozoic, and if not, why not?
Iti s my understanding that, like pterosaurs, plesiosaurs are not considered dinosaurs, so it seems like a fair question. I don’t know the answer, though.
Apparently not, as it is now widely accepted that birds are dinosaurs.
Yeah, I’m pretty much wondering why there isn’t any dinosaur equivalent of bats/pterosaurs, or whales/turtles/crocodiles. I was wondering if there was anything about them that prevented them from filling those roles, when all sorts of other creatures moved in over time.
Thanks for the info heathen earthling. I knew about Microraptor, but wasn’t sure if it was a bird or dinosaur (I assumed bird, but it may just be that issue of semantics of when one turns into the other). Patagopteryx is fascinating though, kind of like a cretaceous chicken. Wonder how it came about…
Dinosaur has, since the term was coined in the early 1800s, applied to two major groups of predominantly large amniotes (‘reptiles’). A modern cladistic definition is the common ancestor of Tyrannosaurus and Triceratops and all its descendants. It does not include everything "big, fierce, and extinct’.
There were four main lineages of amniotes (vertebrates which lay shelled eggs not requiring water to survive, or give live birth after a development involving the same organs as in the amniote egg). All four had a wide variety of experimental forms during the Permian and the Erly and Middle Triassic Periods, kind of a shakedown time to see what was best fit to survive and radiate into new roles.
The Anapsids were the first to develop, but after the Permian their only survivors were the Chelonia (turtles and tortoises).
Tye Synapsids produced the sailbacks (Dimetrodon) of the Permian, the ‘mammal-like reptiles’ of the Triassic, and then evolved into the mammals, other lineages dying out by the Early Jurassic.
The Lepidosaurs included a wide assortment of creatures: the Placodonts, reptilian walruses; the Plesiosaurs; the Ichthyosaurs; the Sphenodonts (e.g., the tuatara); the Champsosaurs; and the most successful modern group, the Squamata, including five lineages of lizard plus the snakes. Note in passing one lizard lineage, the Varanoids, includes the komodo dragon and the Mosasaurs of the Cretaceous.
The Archosaurs included the Crocodilia, the Pterosaurs, and the dinosaursw, which in turn gave rise to the birds. The Crocodilians, in addition to the modern forms, developed large seagoing forms, the Geosaurs and Metriorhynchids, and active land predators, the Sebecids.
While everyone and Buddha’s great aunt seems to have evolved a gliding lineage (frogs? snakes? squirrels? marsupials? yes to all of them), powered flight seems to have evolved only four times: in the insects, the pterosaurs, the bats. and the birds. Archeopteryx is as easily termed a flying dinosaur as a primitive bird. There were a number of secondarily flightless birds (=dinosaurs) during the Cretaceous.
As for the seas? Major predators included Ichthyosaurs, Plesiosaurs (four lineages), Mosasaurs, two lineages of seagoing Crocodile plus large amphibious crocs, and a variety of smaller forms. Dinosaurs were unqiely adapted for large land-living niches, and could outcomete almost everything else for those niches. Why try to adapt to niches where the competition is already heavy? If any did, they were not successful enough to leave any fossils behind.
It’s not just that we call any dinosaur that can fly a bird. A large part of the reason is that we essentially define a dinosaur as an archosaur that isn’t adapted to swimming or flying. That means that your question becomes akin to asking why there are no flying mammals, and when someone points out that there are flying mammals, then saying that those are bats, not mammals.
The archosaurs were one group within the diapsida. That puts them at about a level of organisation somewhere between “mammal” and “marsupial”. One of the archosaur groups became specialised for aquatic existence very early on, and we call them crocodilians (near enough). Another group became specialised for aerial life, and we call them pterosaurs. Everything that didn’t go down one of those paths early on we call dinosaurs, but “dinsosaur” is a kind of scrap-heap category for everything that’s left over after the types that diverged into aquatic and aerial niches early on are removed. It’s perfectly valid cladistically but it also incidentally removed anything that was aquatic or aerial.
In mammalian terms, an analogy would be to split the carnivores into three groups: the dogs, the seals and the carnivores, which now includes only the cats and hyaenas. That’s valid cladistically, but if you were then to ask “Why aren’t there any aquatic carnivores” it would be difficult to answer your question in a meaningful way, because your cladistic scheme has actively removed the aquatic carnivores and called them seals. There’s no particular reason why other carnivores couldn’t have become aquatic, but OTOH there is no particular reason why such a transition needs to happen multiple times, especially in light of competition from close relative already occupying the niche. (Yes, I know this analogy isn’t perfect because of the otters, but I am ignoring them. Those little bastards are just being difficult). And that’s pretty much the case with the dinos. Our categorisation scheme has coincidentally also excluded the flying and swimming forms.
There probably is a reason that make it less likely for a dinosaur to ever adopt an aquatic life, and that is associated with the spine. To be able to swim with maximum efficiency an animal needs to be able to flex its spine to provide thrust to the legs. In reptiles, that means throwing the spine into an “S” shape, with the force directed sideways into legs that are splayed out from the body. In mammals it means throwing the spine into a series of humps, forcing the legs up and down. The problem that dinos had is that they had a reptile spine that bent sideways, but their legs were slung under the body, where they only force they could get was from a spine that bent into humps. Added to that, the dino spine was very inflexible, precisely because of the fact that it couldn’t provide thrust to the legs. No point weakening the spin by making it flex when that flex doesn’t do anything. It’s very hard for an animal with that configuration to become an efficient swimmer.
That doesn’t preclude them from ever adopting an aquatic lifestyle, but they need to get there from somewhere else. They can’t just enter the water hunting and expect to catch anything the way that seals or dolphins or the aquatic reptiles have done. They’d need to enter the water as slow moving herbivores as the dugongs or placodonts did. That’s not impossible obviously, but it’s difficult.
That transition is especially difficult in light of all the competition. In addition to the crocodilians, you had competition from the Placodonts, Plesiosaurs, Icthyosaurs and Mosasuars, a dozen species of human-sized amphibians and turtles in addition to a whole bunch of minor amphibious squamates and other lizard-type thingies. There really wasn’t any vacant aqautic niche for a dinosaur to enter. When mammals entered the water, their only tetrapod competition were the crocodiles and the amphibious squamates. Everything else was extinct, so there were vacant niches.
Additionally, mammals have a whole suite of features that enable them to exploit niches that other marine life can’t. The ability to chew, co-operative hunting, an ear that enables advanced hearing an echolocation, regulated body temperature and so forth. Even in the face of competition against marine reptiles, mammals probably had a good shot of making the transition. In contrast the dinos had only one feature that all the competition didn’t have: being warm blooded. In all other respects they were basically identical to every marine reptile that had already been int he water for a 50 million years. It’s kinda hard to make a niche for yourself under that sort of competition.
As for flight, well it’s not a common evolutionary trait. It’s only evolved four times in the last 4 billion years, and the archosaurs managed two of those. So it would be extraordinary if another archosaur group had managed to evolve flight. There’s not really any need to explain this. Flight is rare.
Flightlesness, sure.
Here’s the most famous birdy example but there have been at least a couple of other found.
As far as the Ptreosaurs, the jury is still out on that. There is still dispute over whether the larger types could fly or not. Look at thisand tell me that thing ever got off the ground. There have also been a few small specimens found which appear to have been flightless.
That didn’t stop other animals. Ichthyosaurs and sauropterygians (the marine reptile group including plesiosaurs) took to the water in the Triassic, but marine crocodylomorphs evolved in the Jurassic, and mosasaurs evolved in the Cretaceous.
What I wonder is whether textbooks will be revised to indicate dinosaurs survived in South America until only a few million years ago.
Yes, I know that present day canaries might be called dinosaurs too, but I wouldn’t call one a “Terror Bird” unless I happened to be in a mine at the time and it keeled over.
So the answer pretty much lies in what went into coming up with the word dinosaur. Thanks for the clarification.
Flight is rare, but aquatic adaption isn’t, and competition didn’t keep other contemporaries of the dinosaurs out. The S motion you mention doesn’t have to be the legs though; crocodiles use their tails and legs aren’t a factor at all for sea snakes. And penguins, ducks and so forth propel themselves adequately. Then you could take the hippo route of aquatic life. I do see how the combination of reptile and mammal traits might hinder them in many ways though, thanks for pointing that out.
And yet another qualifier is we’re only ever going to find a minority of what actually existed, so to us non-existent and not successful/lucky enough to appear in the fossil record are pretty much the same :-/ makes me wonder what we’ll never find or imagine.
That’s the point though, Snakes and the ancestors of crocodiles already moved by throwing their spineinto an "S’ shape to give their legs more purchase. From there it’s very easy “learn” to swim using just the spine. In the same way the ancestors of dolphins walked by throwing their spine into a series of humps, and they too “learned” how to swim using just the spine. that is why dolphins swim with an up-down motion of the spine, and have a tail that is flattened horizontally, while crocodiles swim with a side-side motion and have a tail that is flattened vertically. That’s not just random chance, it’s a direct result of the fact that their walking motion making swimming more efficient.
Dinos couldn’t do that. Because their spines flexed at right angles to their legs they couldn’t enter the water using their legs *and *spine to swim, the way that non-aquatic animals like dogs or lizards do. They could only use either their legs or their spine, not both at once. That sucks as a way to learn to swim. It doesn’t make swimming impossible, but it makes it horribly inefficient. It also locks them into an untenable evolutionary track. Either they develop webbed feet that can’t be used in conjunction with the spine, or they develop spinal swimming and have no ability to use the legs as flippers. Animals like whales and icthyosaurs lost their legs and reverted to entirely spinal swimming eventually, but they did so through intermediaries with flippers. Dinos would have had to find some way to circumvent that, and go straight from walking to efficient spinal swimming. That’s damn near impossible to do. Snakes, of course, already had spinal movement down to a fine art.
Yes, but it’s a case of “you can’t get there from here”. Those animals struggled though because they could fly. Even today, a duck is a pathetic swimmer compared to even the most basic aquatic mammal or reptile, but they compensate by their ability to fly. Penguins are great swimmers, but they got there precisely because they could fly. All those eons with the swimming ability of a tern didn’t preclude a marine lifestyle because they could fly to their food source.
How is a swimming dino in the penguin niche ever going to get to its food source? It’s going to need to dog paddle out over the open ocean full of predators. It can’t swim even vaguely effectively until it sorts out all the problems of flippers and streamlining that a penguin already has sorted out, yet it can’t fly. So it would literally be dog paddling, and not just for a while, for millions of years, because the basic requirements for being an effective swimmer just ain’t there.
Chances are that many dinos did take that route. At least some of the hadrosaurs seem to have adopted such a tactic. But it’s in many ways a dead end. Hippos eat some aquatic vegetation, but it’s not their sole food source. They still need to remain fully functional grazing animals in addition to being adapted to the water. The only real way out is to start trying to exploit marine algae, but algae is so poor in nutrients and so tough that it’s going to be a hard life.
That is true, but marine lifeforms get fossilised at rates much higher than average. So unless a marine dino managed to evolve and never spread from a tiny geographical area we would probably have found it.
No, this has never been true (though it’s often used by exasperated scientists to try to explain what dinosaurs are “not” in terms a severe layman can understand).
Traditionally dinosaurs are those archosaurs with upright hind limbs (saurischians and ornithischians). During most of the 20th century there was wide consensus that these did not even form a natural group, but this has since been overturned.
More recently, scientists define dinosaurs are the group comprising Saurischians + Ornithischians. Not necessarily by pelvic structure (if some undiscovered archosaur had non-erect limbs, but was closer to saurischians than ornithischians, it would still be a dinosaur).
All known flying and aquatic dinosaurs happen to belong to Saurischia. However we call them “birds” due to the fact that they can fly. So this is literally a No True Scotsman logical fallacy. “No dinosaurs can fly!” “But birds can fly.” “Then birds aren’t true dinosaurs!”
So asking “why no flying dinosaurs” is a bit like asking “excluding bats, why no flying mammals?”
Ok. So maybe a better question is, why no flying or aquatic ornithischians? Well, why should there be? They simply did not adapt to those niches due to competition, already evolving body plans ill suited to the task, etc. Hard to evolve flight from Triceratops.
Not as flip an answer as it sounds – when I was talking about Amniotes up above, that was Reptiles-in-the-old-sense plus the two other groups descended from them, Mammals and Birds. And defining a group to leave out its two most successful descendant lines is contrary to good taxonomic practice.
Besides which, dinosaurs appear to have been as different from lizards, snakes, tuataras, and turtles as ostriches or kangaroos are.
