Amniote Classification is currently under re-evaluation. Explain the justification behind:
1) Retaining the classical classification of Mammalia, Reptilia and Aves
2) Reducing the number of valid clades to Mammalia and Reptilia
3) Increasing the number of clades to include Mammalia, Testudines, Sphenodontia, Squamata, Crocodilia, Aves
Amniotes are generally classified as groups of vertebrate tetrapods (or animals with four limbs and spinal column) that lay eggs that contain amnions. They are one of the most diverse group of organisms which comprises mammals, birds and reptiles and their extinct relatives. The re-evaluation of amniote classification was being studied since there are gaps and questions in the genetic level of organization of species . By doing this, the classification of the fossils (or ancestors of amniotes) can be fully understood and defined.
1. The three classes (Aves, Reptillia and Mammalia) are conserved mainly because of their basic physical function or physiology. The purpose of this is to selectively identify the organism and avoid confusion.
2. Inclusion of Aves in the reptilia clade is traced back to the evolutionary evidences making the amniota to have two clades which is the mammalia and the reptilia. It was found out that birds (Aves) have a strong genetic relationship with crocodiles  and possibly with turtles as well . However, the two clades are not definite because the mammalia still have “mammal-like” reptiles which are still under investigation.
3. Increasing the number of clades is mainly due to the small number of representative samples of tuataras and turtles.
 Donoghue, et al. The Importance of fossils in phylogeny reconstruction. Annu. Rev. Ecol. Syst. 1989. 20:431-60
 Luarin and Reisz, A re-evaluation of early amniote phylogeny. Zoological Journal of the Linnean Society (1995), 113: 165–223.