Natural Science Forum / Biology / Paleontology / September 2006

Hey, see this paper. Even in 2006 not everybody agrees with that.

Kurochkin E N, Parallel evolution of theropod dinosaurs and birds,
Zoologicheskii Zhurnal 2006; 85: 283-297

Abstract

In recent years, the hypothesis of an origin of birds from theropod
dinosaurs has been widely spread.  Direct sisterly relations between
theropods and birds are established based on such casual and formal
synapomorphies, as the number of tail vertebrae, relative length of the
humerus, flatness of the dorsal edge of the pubis, etc.  In essence, this
hypothesis is developed on such characters (recognized as homologies), as
feathers, furcula, uncinate processes, pygostyle, double-condyled cranial
joint of quadrate, and inverted back pubic bone, which are discovered in
various groups of Coelurosauria.  Not so long ago, they were considered as
apomorphies in birds.  Nevertheless, all these characters are mosaically
distributed among dromeosaurids, troodontids, oviraptorosaurids,
therizinosaurids, and tyrannosaurids.  There is no Theropoda group, where
they would occur together.  This fact testifies to parallelism in the
evolution of theropods and birds. Theropod dinosaurs and Sauriurae
(Archaeornithes with Enantiomithes) have a number of important system
synapomorphies that demonstrate their close relationships.  Ornithurine
birds do not have such synapomorphics, but their monophyly is established
according to a great number of diagnostic characters.  The hypothesis of
independent origin of Sauriurae and Ornithurae is substantiated. According
to this hypothesis, Sauriurae originated from Theropoda in the Jurassic
period and Ornithurae from basal Archosauromorpha in the Late Triassic
one.  Findings of small avian footprints in the upper Triassic and lower
Jurassic deposits on different continents support the existence of birds
in the Early Mesozoic era.

Only if you are tracking evolution. Cladistics is no good for habitat
analysis, such as benthic and pelagic.

Cladistically, of course, what you meant to say is that birds are theropods.

Damn, I thought you were going to say something controversial...