Why? Because we are intelligent enough to take what we see in extant organisms and apply that consistency of morphology to fossils? Why would something that reliably applies to today's organisms not apply equally to extinct organisms?
Was there some point in the past where the morphological relationship between features and functions changed drastically? When would that have been? During some time period or event that has no physical evidence?
Or were you just barking at the moon?
Your tagline says it all. Have fun.