Dinosaurs Aren't Reptiles???

This section talks about scientific classification. It makes you wonder about what a reptile really is, and when something crosses the line of reptile and mammal, or reptile and bird. This should also make you wonder: Are birds their own thing, or are they just a type of reptile?

Dinosaurs are Reptiles, Right?

We have all been told that dinosaurs are an extinct group of reptiles that birds descended from. However, birds are considered by many ornithologists and paleontologists to be dinosaurs. Birds are dinosaurs. Just let that sink in. Birds are not reptiles, but dinosaurs are. But birds are dinosaurs. How does that work? Are dinosaurs not reptiles, or are birds reptiles? Or are some dinosaurs reptiles, and others are not?

Dinosaurs: Crocs or Birds?

Currently, there are two archosaurs alive today: Crocodilians, and dinosaurs. There are two main branches of the archosaur family tree: Pseudosuchia "Crocodile-Line Archosaurs," and avemetatarsalia "Bird-Line Archosaurs." Of course, dinosaurs and pterosaurs are avemetatarsalians. The picture below will help visualize some stuff that I will be talking about.

As you can see, pterosaurs branched off of the Bird-Line archosaurs quite early. However, in order for them to have flown, and be active, they would've needed to be warm-blooded. Also, fossil evidence shows that pterosaurs had protofeathers, which were previously thought to be a trait of just birdlike dinosaurs, and birds themselves.

Because of this discovery, as well as fossil evidence of feathery Triceratopses, we think that all dinosaurs were feathered, with ankylosaurs being possible exceptions. Also, we know now that the desert that Coelophysis lived in could get quite cold, meaning a mostly/completely feathered animal could thrive, hence bringing back the feathered Coelophysis theory from the 1980's.

Therefore, dinosaurs were very birdlike, and likely do not fit the criteria of reptiles. Or do they?

So, what can we learn from this? Dinosaurs are clearly not reptiles. Birds, the only living dinosaurs, are not considered reptiles. Also, there are many differences between even primitive dinosaurs and reptiles. Dinosaurs have hollow bones, very different brains, an upright gait, and are endothermic! Therefore, I think that dinosaurs should not be considered reptiles.

But, are dinosaurs not reptiles, or are birds reptiles? There are many differences between dinosaurs and other reptiles, but we consider platypuses to be mammals, as well as dogs. Platypuses lay eggs and have poisonous ridges. Dogs produce milk from mammary glands, and give live birth to young. They do not have any venom. However, platypuses actually sweat milk! Dogs are part of the order Carnivora, whereas platypuses are part of the order Monotremata. However, they are both mammals. Other members of Monotremata lay eggs, and other members of Carnivora give live birth, do not have poison, and produce milk from mammary glands. Platypuses and dogs are on different sides of the mammalian family tree!

Therefore, dinosaurs likely can still be reptiles! Both dinosaurs and reptiles are animals, lay eggs, have scales, and are amazing. Dinosaurs are very different, but that doesn't mean that they aren't reptiles. Dinosaurs can still be reptiles, despite their differences. However, I still think that dinosaurs are not reptiles, as they are too diverse to be in a subcategory of Reptilia. Currently, Dinosauria is a clade, that is not in Reptilia, but birds are part of the order Aves, which does not have the clade listed.