How do we know dinosaurs are reptiles?

Question

What part of their bone fossils tell us they are not mammals?

Answer 1

For an in depth answer, you should post this question over at

http://www.askabiologist.org.uk/

Answer 2

<<What part of their bone fossils tell us they are not mammals?>>

All existing mammals have lower jaws composed of a single bone.  Dino lower jaws are multi-boned.  (It's more complicated with some ancient mammals, as their lower jaws were multi-boned.  However, the dentary was overwhelmingly dominant.)

Mammals (and very rare fossils of close relatives) have a jaw skull joint known as the dentary-squamosal.  Dinos didn't.   Their jaw joint was the articular-quadrate.

Mammals with teeth replace them a maximum of once and, in most cases, have four distinct tooth types.  Toothed dinos had multiple replacement and, usually, a single tooth type.

Mammalian middle ears contain three ossicles for processing sound, and have a single bone contributing the bony casing; the petrosal.  Dinos had a single sound processing ossicle, and the middle ear is encased in a multi-boned complex.

Further differences occur all over the place.  Those few where merely examples of many differences.

Answer 3

the rescemblence to the reptile. dinasuars and reptiles are like alot alike and have so many bones and things in common rather than mammals.

Answer 4

Mammals have distinctive teeth where they are differentiated into different types of teeth on the same jaw.  Some of them are very closely related to birds so calling them reptiles is rather arbitrary. They are certainly not closely related to modern reptiles except more distantly to crocodiles.

Answer 5

the anatomy. they have a hole in the skull similar to reptiles. mammals do not have this feature. not to mention other things.

Answer 6

Actually we dont know they are reptiles and many scientist now believe they are a group all their own as much of their skeletal features bear resemblance to birds as opposed to reptiles but they still lack the basic features of a bird.  If you compare a chicken skeleton to say a compy skeleton you wouldnt find too many diffrences in basic setup besides the tail and beak.

Its in much of the hip, tooth, and vetrebare stucture.  Many also have hollow bones.

Answer 7

Dinosaurs are not reptiles. Evidence actually points to them being ancestors to modern birds. There is also evidence of them being homeothermic (warm-blooded), which is not characteristic of reptiles.