Mrs. Napier was describing how she could see Tyranosaurus Rex evolving into eagles, and those big ones with long necks (sauropods?) evolving into swans, and the like. I said I didn’t think it worked like that. But it got me wondering. What I hear is that the dinosaurs evolved into the birds, which to me suggests multiple paths from multiple dinosaurs into the present day birds. This is as opposed to one particular kind of dinosaur being a common ancestor of all birds.
So, how did it happen?
No. All birds have a common ancestor, which was a single species of dinosaur. That’s how evolution works.
Yep. But there might have been more than one line of “flying dinosaurs” that didn’t survive until today. Feathers are turning out to be very common on theropods.
At any rate, the OP has it wrong in thinking, for instance, that a swan owes its long neck to a long necked dino. That long neck evolved separately, from a shorter necked bird.
No, the OP is on record for having doubted the long neck bit and similar ideas, though I do have questions.
For that matter, evolution could have brought several dinosaurs forward, couldn’t it? How different do we know ALL dinosaurs were from birds? For example if size were the only big difference for some number of later dinosaurs relative to birds, couldn’t parallel downgrading of size happened due to shared environmental pressure?
Sorry. It was the wife.
Well, “forward” isn’t a work I would use. As I noted, it’s possible that more than one line evolved flight, but all living birds share a common ancestor.
It’s only Theropods that are closely related to birds. There were lots of other non-Theropod dinos.
In theory, yes, he’s right: more than one species of dinosaur could have developed ‘bird’ adaptations independently. (Technical term, for those not familiar with the vocabulary, is polyphyletic (adj., noun polyphyly).) But as you note all modern birds (and probably all late-Cretaceous birds with them) share a single common ancestor.
Even finer tuned than that; we know that it comes from one group of theropods which either were or were closely related to the Dromaeosaurs which evolved an ankle adaptation shared only by that line of dinosaurs and birds. (Darwin’s Finch or Colibri will have to produce the sesquipedalian clade name, which I’ve forgotten, something like “Arctotarsometatarsaloidea.”
A good way to think of it is like branches on a tree. Here is a visual aid. Way back before the Triassic (Or just after it, depending on who you ask) the common ancestor of all reptiles evolved. This is one species, mind you. It split into two groups: Archosaurs, and Other Reptiles. Other Reptiles is basically things like turtles, lizards, snakes; pretty much all reptiles, except for birds and crocodiles. At some point early in the Triassic period, Archosaurs split further, into two types. One type includes crocodiles and a bunch of other extinct groups, and the other (called Avemetatarsalia) includes dinosaurs, pterodactyls, and plesiosaurs. Avemetatarsalia’s common ancestor split off into a single species that led to all dinosaurs, a single species that led to all pterodactyls, and a single species that led to all plesiosaurs. This all happened in the Triassic.
Now, the first dinosaurs were probably similar to later theropods (two-legged, meat eating dinos like t-rex or velociraptor). They quickly split into two main groups: Bird-hipped dinos, and lizard-hipped dinos. Bird hipped (Ornithischia) dinosaurs include things like duck-billed dinosaurs (Hadrosaurus), armored dinosaurs (Ankylosaurus), horned/frilled dinosaurs (Triceratops), etc. There’s a lot of variety here. By contrast, lizard-hipped dinosaurs (Saurischia) evolved into fewer main groups: Prosauropods (primitive sauropods), sauropods (Long necked giant dinos), and theropods. Surprisingly, birds evolved from theropods, who were lizard-hipped, not bird hipped.
Theropods are nearly universally carnivorous. That’s where you find things like t-rex, velociraptor, etc. Feathers appear to be pretty common here, even among the larger dinos (such as t-rex). Some time between the middle Jurassic and early Cretaceous, depending on who you ask, a group of theropods got strong enough arms and specialized feathers and began gliding. A few million years later, they developed powered flight. It’s worth noting that this is the second time vertebrates evolved powered flight, following the triassic pterosaurs. The third time vertebrates learned to fly was about 50 million years ago, with the first bats.
So, to answer your question with far more information than you probably wanted, not all dinosaurs became birds. Only one dinosaur became a bird, actually. There may have been more than one species of flying, feathered dinosaur, but all birds came from one species.
Surely this should be pterosaurs, of which pterodactyls were only one type?
Of course, of course. I did use that term later on, you’ll notice. I was just giving an example, but I suppose I should have been consistent. None of my lists of examples are exhaustive, of course.
I didn’t really go into detail about the group of non-dinosaur or non-avian Archosaurs, BTW. In case you are wondering, they are all very similar (at first glance, at least) to crocodiles. There’s one group that looks like heavily-armored plant-eating crocs, another that looks like crocodiles with straight instead of bowed legs, and a third that is formed of croc-like, bipedal crocodiles. Dyrosauridae are my favorite; marine crocodylomorphs that were around until the Eocene and include crocodiles with flippers.
T-rex had feathers? :eek:
Possibly. Theropods are split into two main types: Coelurosauria (those that are closer to Carnosaurs than birds) and… Well, the other group doesn’t really have a name. The other group includes Carnosaurs (obviously), Spinosaurids, Ceratosaurs, Allosaurus and his kin… But, oddly enough, not Tyrannosaurs. Tyrannosaurs are, in fact, closer to birds than to the other giant meat eaters. This means that Tyrannosaurus rex likely had some feathers (at least at birth), but that Allosaurus or Spinosaurus likely did not. Doesn’t mean that T-Rex was like a giant chicken, of course; it seems likely that they hatched with feathers but lost them later, or that they had feathers only on some parts of their body. Their head would likely have been bald anyhow, like modern vultures or condors.
Sure it does: Carnosauria. But really, there are more than two ‘main types’ of theropods. There are the Coelophysids and Averostra; Averostra are broken into tetanurans and ceratosauria; tetanurans are broken (primarily) into megalosaurs and Avetheropoda; and Avetheropoda is finally broken into Carnosauria and Coelurosauria. And, you have it backwards: Coelurosauria is actually closer to birds than is Carnosauria.
To continue the path from Coelurosauria to birds, we go from Coelurosauria to Maniraptora to Eumaniraptora to Avialae to Pygostylia to Ornithothoraces to Euornithes to Ornithurae to Aves. Some of those clade names are more ‘unofficial’ than others (e.g., Pygostalia is pretty much just Confuciusornithidae [Confuciusornis and friends] + Ornithothoraces).
Ignorance fought. Thank you!
So. There is a meme of sorts out there that the dinosaurs evolved into the birds, which I have been hearing in the last ten or twenty years perhaps, which sounded new. There is also the old conventional wisdom that birds descent from the single dinosaur Archaeopteryx, which I remember hearing at least forty years ago, and which when I look it up appears to have been known for 150 years now. But it sounds like this new meme is just a confused version of what we have thought for many generations.
Wiki on the origin of birds.
Includes the latest insights on shared genetics based on fossilized soft tissue.
Does that mean feathers evolved before flight? (or even, really, gliding - I can’t imagine a Tyrannosaurus gliding very far)
Does anyone have any idea what they were good for?
Same thing as fur, maybe.
Of course. It would have to be that way. Flight feathers are highly specialized feathers.
Regulating body temperature. Display.
I’d say it’s the other way around.
There was a minority argument that *Archaeopteryx *was an ancestor of birds, but it wasn’t well accepted. Science is a consensus game and consensus did not support it.
Only in the past decade or two has the lineage become well-established. Today it’s the minority group of scientists who argue for an earlier reptilian origin that’s out of the mainstream. The consensus remains that *Archaeopteryx *is the splitting point, but even that has been challenged lately.
The “confusion” is mostly that scientists now have, compared to 1861, towering piles of different kinds of evidence and large rooms full of early fossils. Counterintuitively, it’s often harder to make a consensus statement out of more evidence than less. There are many more pathways that are plausible and have to be discounted one by one. As an example, it was much easier to posit a human line of descent when there were only a handful of known species, one in each time period. Now there are more than a dozen and almost every time has several. Most scientists have simply stopped trying to draw lines between them and are waiting for more evidence to settle arguments. With birds, the evidence that they descend from dinosaurs is very strong but the pathway needs more fossils to establish.
Thanks, but how do we know that?
