My entire childhood I was taught dinosaurs were reptiles but in recent years I’ve read that many scientists believe they are closer to birds than reptiles. Please help me understand this.
In: Biology
Well, that’s complicated.
So, the first thing to know is that we’ve actually known they were bird-like for *ages*. We’ve just now recently discovered that they were more bird-like than we originally thought.
The second thing to know is that they *were still reptiles*. But they were bird-like reptiles – reptiles on their way to becoming birds. At this time, there were also other types of reptile, same as how there are many kinds of mammal today from marsupials to placentals, from primates to felines to canines to rodents to whales to whatever the hell a platypus is. All these are mammals, but in a few tens of millions of years it’s possible that some of those will have evolved enough that we (or rather whatever intelligent civilisation takes our place – my bet is crows) would no longer classify them as mammals. Dinosaurs are just one category of all the reptiles that were around at that time. Alongside them, there also lived the reptiles that would eventually become mammals, and the reptiles that would eventually become modern lizards, snakes, turtles and crocodiles, and the flying reptiles that ended up dying out. Probably some other reptile lineages too that never made it into the fossil record (side note – the fossil record is extremely incomplete. We only know a tiny fraction of all the animals that existed at any given point in history. Everything that lived in places that aren’t good for making fossils will be forever things we can’t know about).
The third thing to know is that “dinosaur” subdivides into major groups a bit like a tree. You can see the taxonomy [here](https://en.wikipedia.org/wiki/Dinosaur#Taxonomy) but it’s a bit hard to read, so [here](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fi.stack.imgur.com%2FMM70B.gif&f=1&nofb=1) is a diagram of it. Early on in the dinosaurs, they split into two core groups: Saurischian (lizard-hipped) dinosaurs and Ornithischian (bird-hipped) dinosaurs. These categories are based on superficial observations – bird-hipped dinosaurs have hips that resemble those of birds, and lizard-hipped generally have ones that resemble those of lizards. Ornithischian dinosaurs are entirely extinct, but included most of the famous herbivores – Ankylosaurs, Stegosaurs, Triceratops. These were solidly and without a doubt very reptile-like. Meanwhile, Saurischians subdivide into Sauropods (including all the big herbivores – brachiosaurus and such), and Theropoda (including things like allosaurus, T-rex and velociraptor). As you can see, on the far left of the Theropods are true birds. Birds are dinosaurs, taxonomically, but most dinosaurs did not resemble birds. Rather, some resembled birds more than others, and if you trace them down the tree you’ll get to branch points. Other branches of the same branch point are more bird-like than ones further back. So dromaeosaurs are the most bird-like on that diagram, then Ornithornimids, then Carnosaurs, then Ceratosaurs, and everything that diverged before that point (at the theropod/sauropod split) isn’t very bird-like at all. Also yes, confusingly, birds are lizard-hipped dinosaurs, not bird-hipped dinosaurs.
Hopefully this helps. It’s not so much that dinosaurs are more birds than reptiles, but that birds are just a type of dinosaur, and now we think that many of the bird-like qualities, such as feathers, may have appeared a lot earlier than we originally thought, well before the evolution of true birds.
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