What evidence links T. rex to chickens?

[Teegvin]

That is, what distinguishes dinosaurs from other reptiles that existed at the same time, or which still exist, such as crocodiles?

People do not normally consider the crocodiles to be dinosaurs, despite the fact that they appeared before many other reptiles which have since gone extinct and which are considered dinosaurs.

Does the fact that they still exist automatically put them in a different classification?

 

[Simfish]

Morphology - dinosaurs had different morphologies than such reptiles. Classification used to go along the lines of which animals had X morphology and which animals had Y morphology. This way of classification is an arbitrary social construct, but it usually consistent with the genetic evidence (though there are notable exceptions). Nowadays we have access to genetic analysis, which could change our possible ways of classification.

 

[baywax]

Morphology - dinosaurs had different morphologies than such reptiles. Classification used to go along the lines of which animals had X morphology and which animals had Y morphology. This way of classification is an arbitrary social construct, but it usually consistent with the genetic evidence (though there are notable exceptions). Nowadays we have access to genetic analysis, which could change our possible ways of classification.

Its long been held that several of the Dinosaurids had a warm blooded system. They've evolved into birds. One documented case is the famous T-Rex which we see today as the Chicken.

An adolescent female Tyrannosaurus rex died 68 million years ago, but its bones still contain intact soft tissue, including the oldest preserved proteins ever found, scientists say.

And a comparison of the protein's chemical structure to a slew of other species showed an evolutionary link between T. rex and chickens, bolstering the idea that birds evolved from dinosaurs.

http://www.livescience.com/animals/070412_dino_tissues.html