4 ms·

They've always looked like large reptiles to me, what are the main features that implies modern birds instead?

ghaff 9y ago
As the sibling comment notes, there's incredible variation. But look at, say, large flightless birds like an ostrich and a therapod dinosaur (three-toed limbs, hollow bones, etc.) and--with the benefit of hindsight--you're left shaking your head and asking why it took so long for someone to draw the connection.
- eponeponepon 9y ago
  It really didn't take long for the connection to be drawn - Archaeopteryx was discovered in the 1860s or so, if I remember rightly. What took a long time was for the idea to reach the public and stick.
logfromblammo 9y ago
I think it's in the hips and pelvic bones, mainly. Reptiles and some dinosaurs have a sprawling, splayed-out posture. Other dinosaurs, birds, and mammals have independently-evolved upright postures. The birds apparently evolved from the splayed-hip dinosaurs rather than from the upright-hip dinosaurs, so a change in hip structure could be a decent dividing line. But strictly speaking, birds (Aves) have wings as their forelimbs, rather than arms. The (extinct) moa is an exception in that it had no wings, but that is because it had no forelimbs at all. It is very likely that other theropods besides the birds also had feathers, but it is rare for soft tissues to fossilize, so it can be hard to say what the scale and feather coverage was like for a given species when all you have is a partial skeleton. Determining coloration is almost impossible, though it has been estimated from especially well-preserved fossilized impressions of feathers that showed different spacing between the microstructures on the feather.
- ghaff 9y ago
  >Reptiles and some dinosaurs have a sprawling, splayed-out posture. Other dinosaurs, birds, and mammals have independently-evolved upright postures. The birds apparently evolved from the splayed-hip dinosaurs rather than from the upright-hip dinosaurs, so a change in hip structure could be a decent dividing line. The traditional categorization is the forward (Saurischian) and backward (Ornithischian) facing pubic bones. But, the categorization isn't perfect and some theropods including birds, which are Saurischians, evolved backward facing pubic bones. (And apparently some Ornithischians evolved pubic bones that at least somewhat forward facing.)

As the sibling comment notes, there's incredible variation. But look at, say, large flightless birds like an ostrich and a therapod dinosaur (three-toed limbs, hollow bones, etc.) and--with the benefit of hindsight--you're left shaking your head and asking why it took so long for someone to draw the connection.

eponeponepon 9y ago
It really didn't take long for the connection to be drawn - Archaeopteryx was discovered in the 1860s or so, if I remember rightly. What took a long time was for the idea to reach the public and stick.

logfromblammo 9y ago

I think it's in the hips and pelvic bones, mainly. Reptiles and some dinosaurs have a sprawling, splayed-out posture. Other dinosaurs, birds, and mammals have independently-evolved upright postures. The birds apparently evolved from the splayed-hip dinosaurs rather than from the upright-hip dinosaurs, so a change in hip structure could be a decent dividing line. But strictly speaking, birds (Aves) have wings as their forelimbs, rather than arms. The (extinct) moa is an exception in that it had no wings, but that is because it had no forelimbs at all. It is very likely that other theropods besides the birds also had feathers, but it is rare for soft tissues to fossilize, so it can be hard to say what the scale and feather coverage was like for a given species when all you have is a partial skeleton. Determining coloration is almost impossible, though it has been estimated from especially well-preserved fossilized impressions of feathers that showed different spacing between the microstructures on the feather.

ghaff 9y ago
>Reptiles and some dinosaurs have a sprawling, splayed-out posture. Other dinosaurs, birds, and mammals have independently-evolved upright postures. The birds apparently evolved from the splayed-hip dinosaurs rather than from the upright-hip dinosaurs, so a change in hip structure could be a decent dividing line. The traditional categorization is the forward (Saurischian) and backward (Ornithischian) facing pubic bones. But, the categorization isn't perfect and some theropods including birds, which are Saurischians, evolved backward facing pubic bones. (And apparently some Ornithischians evolved pubic bones that at least somewhat forward facing.)