The article below can be obtained freely in the next link
http://www.biolreprod.org/cgi/content/abstract/46/1/39

Alligators provide evidence for the evolution of an archosaurian mode
of oviparity

BD Palmer and LJ Guillette Jr
The female reproductive tract of birds is different from that of other
oviparous amniotes in that the eggshell membranes and calcareous layer
are formed in separate regions of the uterus; the isthmus and shell
gland, respectively. Phylogenetically, birds are included among the
archosaurs, along with crocodilians and dinosaurs. Many dinosaurs were
oviparous, producing hard-shelled eggs, yet the reproductive system of
dinosaurs has proven difficult to investigate, due to poor
preservation of soft anatomy. In this study, we examined functional
morphology and eggshell formation in a reptilian archosaur, the
American alligator, and demonstrated that the crocodilian reproductive
tract has separate uterine regions for formation of the eggshell
membranes and calcareous layer. These uterine regions are
ultrastructurally comparable to the isthmus and shell gland of birds,
and may be homologous. This similarity of reproductive functional
morphology between crocodilians and birds may implicate the evolution
of an archosaurian mode of oviparity that may shed light on dinosaur
reproduction.