Taxonomy
The Archaeobatrachians are the most primitive of frogs. These frogs have morphological characteristics which are found mostly in extinct frogs, and are absent in most of the modern frog species. Most of these characteristics are not common between all the families of Archaeobatrachians, or are not absent from all the modern species of frog. However all Archarobatrachians have free vertebrae, whereas all other species of frog have their ribs fused to their vertebrae.
The Neobatrachians comprise the most modern species of frog. Most of these frogs have morphological features which are more complex than those of the Mesobatrachians and Archaeobatrachians. The Neobatrachians all have a palatine bone, which is a bone which braces the upper jaw to the neurocranium. This is absent in all Archaeobatrachians and some Mesobatrachians. The third distal carpus is fused with the remaining carpal bones. The adductor longus muscle is present in the Neobatrachians, but absent in the Archaeobatrachians and some Mesobatrachians. It is believed to have differentiated from pectineus muscle, and this differentiation has not occurred in the primitive frogs.
The Mesobatrachians are considered the evolutionary link between the Archaeobatrachians and the Neobatrachians. The families within the Mesobatrachian suborder generally contain morphological features typical of both the other suborders. For example, the palatine bone is absent in all Archaeobatrachians, and present in all Neobatrachians. However, within the Mesobatrachians families, it can be dependent on the species as to whether the palatine bone is present.
Due to the many morphological features which separate the frogs, there are many different systems for the classification of the Anuran suborders. These different classification systems usually split the Mesobatrachian suborder.
Read more about this topic: List Of Anuran Families