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
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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