Amphibia

Classification

• Infraphylum Vertebrata

  • Superclass Gnathostomata

    • class Chondrichthyes (sharks, skates, rays, ratfish)

    • class Sarcopterygii (lobe-fined fishes)

    • class Actinopterygii (ray-fined fishes)

    • class Amphibia (amphibians)

    • class Reptilia (reptiles)

    • class Aves (birds)

    • class Mammalia (mammals)

• much controversy

• many more extinct species than extant

• taxonomists agree that amphibians were the first tetrapods and predecessors to amniotes (i.e., reptiles, birds, mammals)

Class Amphibia: General

• occur on all continents except Antartica

• ~6,000 modern species

• three orders

  • order Caudata (salamanders)

  • order Gymnophiona (caecilians)

  • order Anura (frogs and toads)

Order Caudata (Salamanders)

• ~400 species

• mostly northern hemisphere

• tail throughout life (“caud”)

• both pairs of legs unspecialized

• terrestrial species live in moist litter

• aquatic larvae

• internal fertilization without copulation

Order Gymnophiona (Caecilians)

• ~160 species

• tropical

• most are worm like

• blind

Oder Anura (Frogs and Toads)

• ~4,000 species

• adults lack tails

• hindlimbs are long and muscular

• fertilization is external

• metamorphosis

Anatomy

• permeable skin

  • benefits?

    • able to absorb water

    • capable of gas exchange

      • “cutaneous respiration”

  • costs?

    • generally ties to aquatic habitat

    • susceptible to water loss

    • vulnerable to infections

      • granular gland secretions protect

    • environmental stresses threaten

      • climate change

      • environmental toxins