Animal Diversity: Chordata

The following alternate classification of amphibians is as given by Parker and Haswell:
Table 2: Classification of amphibia
Subclass 1:
Apsidospondyli
Super order 1:
Labyrinthodontia
Order 1:
Ichthyostegalia
Order 2:
Rhachitomi
Order 3:
Stereospondyli
Order 4:
Embolomeri
Order 5:
Seymouriamorpha
Super order 2:
Salientia
Order 1:
Eoanura
Order 2:
Proanura
Order 3:
Anura
Subclass 2:
Lepospondyli
Order 1:
Aistopoda
Order 2:
Nectridia
Order 3:
Microsauria
Order 4:
Urodela
Order 5:
Apoda
Labyrinthodonts The oldest amphibians were the swamp-dwelling labyrinthodonts.
Ichthyostega was the earliest specimen appearing in the Devonian. Labyrinthodonts were a
large, widely dispersed and diverse assemblage. On the basis of the morphology of their
vertebrae, paleontologists have been of the opinion that fossil amphibians with
stereospondylous and embolomerous vertebrae were not in the amniote line. Labyrinthodonts
had many features seldom seen in modern amphibians. These included minute bony scales in
the skin dermis; a fishlike tail supported by dermal fin rays; and skull similar to those of
rhipidistian fishes. Labyrinthodonts, like their aquatic ancestors, had a sensory canal system
of neuromast organs. One or another of the labyrinthodonts was ancestral to the first amniote.
Temnospondyls was a group that was common in the Permian with its fossil record
extending back to the Mississippian. Members of the temnospondyls have achieved skeletal
similarities to modern frogs and salamanders, suggestive of their close relationship. A
number of lissamphibian skeletal features and their relatively smaller size can be explained as
the retention of juvenile ancestral temnospondyl features. The condition in caecilians does
not fit easily into this scenario, possibly suggesting an independent origin from microsaurs.
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