Ostrich the Flightless Bird - African Wildlife Documentary Film with Narration

[Anomalocaris]

Reptiles have legs extending from their sides. Dinosaurs have legs under their torso. The above is reptile.

Not all animals that have traditionally considered to be members of the reptiles class Under Linnean classicifcatkom have legs extending out from their sides.  There were many extinct groups traditionally considered reptiles,  besides the dinosaurs, that also had legs Partially or entirely under their bodies.   Living Crocodiles actually walk and run with their legs partially under their bodies, about half way between a lizard and a cow.

Reptile as most people use the term is based on a Linnean classification derived from superficial comparative anatomy.   Modern genetic and cladistic analysis suggest there is Actually no sensible grouping based on genetic relationship and descent that corresponds to traditional reptile group.    Usually the extinct “mammal like reptile” group has to be expelled form the reptile group, while birds brought under the umbrella of “reptiles” to make it conform to modern ideas of what makes a sensible grouping. 

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Well, you said Z-prime actually.  All dinos were reptiles, but not all reptiles are dinos.

Boru

Dinos are no longer reptiles. They were warm blooded and feathered, characteristics no reptile should have. Or you can say dinos and mammals are reptiles. That would be fun to watch.

Warm bloodedness have been shown to be a poor way to organize animals because it evolves easily and are lost easily amongst many different groups of animals.   For example, many pelagic fish and some sharks are warm blooded.  Some mammals have little ability maintain a constant body temperature and are for all practical purposes not warm blooded.   

Feathers are just mutated scales.   Many, if not most, reptiles have horny skin scales somewhere on their bodies.  Birds still have lizard like scales on their legs and feet.