There are many questions that are studied in the name of science that are not useful but we study them anyway to satisfy our curiosity. I admit I am woefully ignorant of the mechanics of flight and evolution thereof, however I remember a program on one of the “science” channels a couple years back where a leading proponent of each theory argued passionately and convincingly for their viewpoint or theory.
So from my layperson point of view if the Archaeopteryx turns out not be a bird or its lineage never became capable of flight, then there is reason to theorize the evolution of feathers must have been important to animals who were never in a position to need flight. I could be wrong but it seems like this is reason enough to take another look at the existing theories (she opined in an MPSIMS kind of way).
But it was considered a bird (at least, according to How to Build a Dinosaur). I understand that an ancient bird could not be the direct ancestor of modern birds, but it was still really cool.
I also understand the argument that birds are dinosaurs - there’s nothing unique about birds - every birdish trait is present in some dinosaurs - but it still just seems wrong. Amphibians evolved from fish, but aren’t fish. And sure, there are several species around the edges that you don’t know which side to put them on, but amphibians are no longer fish.
I’d say the same holds true for birds. Biepdal theropods had every recognizable trait in common with birds, except powered flight (for now), but bipedal theropods are a small part of the dinosaur class.
Of course, I’m a dilletante talking to a professional - what percentage of dinosaurs had feathers? Beaks? Lost their tail vertebrae? Had the hyperextended finger thingy?
Well, sure, but we’ve known about non-bird, feathered dinosaurs for some time; it’s pretty much a given at this point that feathers predate flight capabilities. Basically, feathers are no longer diagnostic of birds, and this was true before this latest critter was discovered.
Is A. conclusively not a flier? I thought the consensus was that it was a poor flyer, perhaps on the level present-day fowls that live mostly on the ground.
(I want to say “chicken” here, except some of them can fly surprisingly well if their wing feathers are allowed to achieve their natural size and profusion.)
Aves is typically defined as a crown group these days: the most recent common ancestor of all extant birds, and their descendants; Archaeopteryx would be excluded from such a definition. A node-based definition may or may not include Archie, depending on the placement of the node. Typically, Archy is included as an Aviale, which is a node or two below Aves. So it depends on which node you want to call “birds” if you want to define it that way.
Feathers or feather-like features have now been found to be well-distributed among the theropod dinosaurs, including in the tyrannosaur lineage. I am not aware of feathers being found in the other main saurischian group, the sauropods (“brontosaurus” types).
Recently filaments have been found in a ceratopsian dinosaur, a member of the other main group of dinosaurs (ornithischians). This suggests that the precursors to feathers could have been present in the ancestors of all dinosaurs.
And even further afield, it has long been known that some pterosaurs had a hair-like or filamentous covering. Pterosaurs are not dinosaurs, but like dinosaurs are members of a group called the archosaurs. If these filaments are homologous to those in dinosaurs, this would push their evolution back to within or before the archosaurs.
Since crocodiles are also archosaurs, we are presented with the possibility that the ancestors of crocodiles might have been fuzzy and crocs have secondarily lost their filaments.
Archaeopteryx had asymmetrical wing feathers, which generally indicates capability for flight. I think the weight of the evidence still indicates it could fly; I haven’t seen any convincing evidence that would exclude it.
The new research suggests Archaeopteryx belongs to the Deinonychosauria, the group to which Velociraptor belongs. If Archie could fly, it brings up the possibility that Velociraptor was a flightless descendant of flying ancestors, like modern ostriches.
If Archaeopteryx is excluded from the bird clade, it wouldn’t be the only flying non-avian dinosaur. There is also the bizarre four-winged Microraptor gui.
Just to be clear, I was asking for my own education and not questioning your expertise. And now that this has moved to GQ I’ll probably be bowing out, though I would still be interested in your answer.
The great majority of fossils, across the board, probably are not literally lineal ancestors of any living species. It’s easy to overlook or forget, but the total of all fossils discovered is really only a minuscule fraction of all the species that must have existed in the almost incomprehensible depths of evolutionary time.
But modern bird species are all descended from flying species, correct? And it’s still believed that the common ancestor of Archaeopteryx and modern birds also flew, right? I’d feel comfortable calling the first feathered critter that flew the first bird, and calling it and all of its descendants “birds”.
I don’t know what the state of play is on that. According to same analysis that knocked Archaeopteryx out of the bird clade, the non-flying Epidexipteryx is the earliest member of the clade that led to birds. If Archeopteryx flew, while the ancestors of Epidexipteryx didn’t (it’s possible that the thing could be secondarily flightless), that means flight arose separately in Archaeopteryx and true birds.
Given that Microraptor evidently flew, and it is generally regarded as a non-avian dinosaur, whether a species flew or not doesn’t help define it as bird any more than feathers do. There may have been multiple acquisitions of flight and reversions to flightlessness in diferent lineages.
There is a true dichotomy between ascending and descending, because it’s one or the other. And quite clearly it’s descending. There’s no plausible explanation for how an animal would acquire the otherwise useless set of characteristics for flight, and then suddenly leap into the air and start flying. It’s also testable based on enough fossil and DNA evidence, but it may be an impossible test because we may never find that much evidence.
If birds are dinosaurs, humans are fish. All modern birds descended from flying species, and there’s no evidence of flying dinosaurs (unless you include pterosaurs, which do not seem to be the ancestors of modern birds).
‘Ground up’ is not plausible. The justifications are things that are not ‘ground up’, or nonsense. For example, the theory that animals with wing-like feathered limbs running uphill and then taking flight are ridiculous. Long before ever flying, these animals would have been jumping and then gliding in descent, eventually gaining flight capability. That’s not ‘ground up’. The false dichotomy would be saying ‘tree down’ opposed to ‘ground up’, and excluding everything but trees as the source of initial altitude. The ‘down’ path could be from rocks instead of trees, or even jumping into the air, but there’s no plausible means of having a ground based animal starting to flap it’s arms and taking flight.
Imagine this: animal is being chased by a predator. Just before the last lunge, the prey jumps up in the air, escaping the jaws. The higher it jumps and the longer it can stay up from flapping, the more successful the species and the better the flyer. That’s ground up.
