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
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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.
Generally speaking, dinosaurs are Still reptiles.
That hasn’t changed.
What the big change was people discovering that a lot of, specially smaller velociraptor like ones, probably had feathers, or some kind of grandfather to feathers. And that birds evolved from these small dinosaurs that first started using these special scales, which become feathers, to glide around and eventually fly.
So, all modern birds and descended from dinosaurs, and some call them the last remaining dinosaurs.
But not all dinosaurs were the kind that gave rise to birds, for example, the super huge dinosaurs with the long necks and tails, brachiosaurus, those are still considered reptiles. And definitely are not birds. And are still dinosaurs.
The discovery was that birds are descended from dinos, and that some, not All, probably looked more like birds than we previously imagined.
Just to reiterate what everyone else is saying—
Dinosaurs are reptiles. Birds, having descended from a specific type of dinosaur, are also considered reptiles, based on what we now know about cladistics and the fossil record.
‘Reptile’ is not a technical term, unless you mean lizards, snakes and such. That group (the lepidosaurs) is more closely related to the dinosaurs than the mammals are, but is still on a different branch. The crocodiles are more close to dinosaurs than the snakes, and turtles and tortoises more distant – about as distant as mammals. Birds descent from one group of dinosaurs.
Better to think of the dinosaur groups as a major branch, one fork going on to birds, and various reptile groups as other major branches.
TL;DR: Birds are related to dinosaurs in the same way that bats are related to mammals.
The source of this confusion is a change in how biologists name things. In the old days, we used to name things based on shared traits: does it live in the water and have gills and things? It’s a fish. Does it have scales and cold blood etc? It’s a reptile. Is it fuzzy? It’s a mammal. Feathers? It’s a bird. This is also how people talk about animals in everyday non-scientific terms…things that look similar get lumped together.
It’s fine for everyday use, but becomes less useful when trying to get well defined scientific terms, because sometimes not everything in a group has the same traits (for example, not all mammals are fuzzy) and the things that “look alike” to us sometimes hide deeper or more important similarities and differences. So instead biologists started naming things by relationships…by families. Including any weird black sheep of the family. So for example, elephants are mammals, platypuses are mammals, the last common ancestor of elephants and platypuses was a mammal, and _all_ its descendants were mammals.
So, where does this get us with dinosaurs? Take the classic dino duo, Triceratops and Tyrannosaurus. Both dinosaurs, their last common ancestor was a dinosaur too. And so were all its descendants. Some of those descendants (from a branch not that far from T. rex) are birds. They don’t look much like the famous big extinct dinos, but they are right there in the middle of the dino family tree. And actually there were a lot of little dinos that had feathers and looked more like birds.
For comparison, imagine if you lived in a future when all mammals had gone extinct…except for bats (and you are like, an intelligent squid or something). You kinda take bats for granted, bats are these teeny little fuzzy flying things. You don’t think of bats as mammals, mammals are these big fossil extinct critters like the mighty elephant and lion. You probably don’t even realize that lots of mammals had fur, or that there were a bunch of smaller ones that looked a bit more like bats.
So birds are a kind of dinosaur, but what about reptiles? Well, “reptile” in common language is a pretty imprecise term, just being a general word we call a bunch of animals that are mostly similar because they aren’t anything else..not a fish or an amphibian or a mammal or bird. Really, turtles, lizards and snakes, and crocodiles are three very distinct groups. All three are (probably) more closely related to each other than any are to mammals, so you can basically split the branch of the vertebrate family tree up into “mammals and extinct ancestors/relatives” and “reptiles”. But where does this leave dinosaurs? Well, dinos and crocodiles are closely related, so dinosaurs fall solidly within reptiles. And so do birds, because they sit on the “dinosaurs” branch.
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