AMPHIBIANSfirst terrestrial

vertebrates

CLASSIFICATIONKingdom: Animalia Phylum: Chordata Subphylum: Vertebrata

Class: Amphibia (anamniote tetrapods) Subclass: Labyrinthodontia (earliest

tetrapods) Subclass: Lepospondyli Subclass: Lissamphibia

- They diversified and became dominant during the Carboniferous and Permian periods, but were later displaced by reptiles and other vertebrates. - Over time, amphibians shrank in size and decreased in diversity, leaving only the modern subclass Lissamphibia.

CLASS AMPHIBIA

- The earliest amphibians evolved in the Devonian Period from sarcopterygian fish with lungs and bony-limbed fins, features that were helpful in adapting to dry land.

SUPERCLASS LABYRINTHODONTIA

→ Ichthyostegalia—primitive ancestral forms Late Devonian only.

→ Temnospondyli—common, small to large, flat-headed forms with either strong or secondarily weak vertebrae and limbs; mainly Carboniferous to Triassic. May or may not be ancestral to all modern amphibians

→Anthracosauria—deep skulls, strong vertebrae but weak limbs, evolving towards and ancestral to reptiles; Carboniferous and Permian (Now considered to be reptile-like tetrapods separate from true amphibians)

SUPERCLASS LABYRINTHODONTIA

SUPERCLASS LABYRINTHODONTIA

→ oldest amphibians; earliest tetrapods→ considered to include the first vertebrates known to

live on solid ground, and to have been ancestral to at least some of the groups of modern amphibians and a bridge to the reptiles.

→ constituted some of the dominant animals of Late Paleozoic and Early Mesozoic times (350-210 mya).

SUBCLASS LABYRINTHODONTIA

→ Greek for "maze-toothed," → up to four meters long. → They were short-legged and large headed→ skulls were deep and massive→ jaws lined with small, sharp, conical teeth. There was

a second row of teeth on the roof of the mouth.→ vertebrae made of four pieces: an intercentrum, two

pleurocentra, and a neural arch/spine.

SUBCLASS LABYRINTHODONTIA

→ special sense organs in the skin, that formed a system for perception of water fluctuations

→ some of them possessed well developed gills and many seemingly had primitive lungs.

→ labyrinthodonts were probably similar to fishes. They laid eggs in the water.

SUBCLASS LABYRINTHODONTIA

Cross-section of a labyrinthodont tooth

Strongly folded tooth surface, involving infolding of the dentin and enamel of the teeth, so that a cross section resembles a classical labyrinth (or maze), hence the name of the group.

LIMBS

LIMBS

→ vertebral column was strengthened, notochord replaced by bony rings

→ limbs developed (more adapted for terrestrial habitat)→ development of lung structures→ terrestrial ear

→ anamniotic eggs→ tail fins→ lateral line system

SIMILARITIES TO FISHES

SIMILARITIES TO REPTILES

Lepospondyls

Small salamander-like amphibians from the Carboniferous.

• Cardiocephalus Salamander (Eastern Mud)

What are Lepospondyls?

having simple, spool-shaped vertebra, which were not preformed as cartilage, but rather grew as bony cylinders around the notochord

Six different groups are known, the  Acherontiscidae,  Adelospondyli,  Aïstopoda,  Lysorophia,  Microsauria and  Nectridea,

between them they include newt-like, eel- or snake-like, and lizard-like forms,

Various species were aquatic, semi-aquatic, or terrestrial

• BRIEF OVERVIEW OF THE DIFFERENT ORDERS

•  is an order of elongate, presumably aquatic,  Carboniferous amphibians.

• skull is solidly roofed, and elongate, with the orbits located very far forward

Order Adelospondyli

• limbs are well developed

• Adelospondylus.

• an order of highly specialized snake-like amphibians.

• no trace of limbs or even limb girdles in any known fossil

• the tail was short and primitive

Order Aïstopoda

• bones at the back of the skull were reduced or absent.

• resembled modern newts or aquatic salamanders.

• long flattened tails to aid in swimming,

• and well-developed hind limbs, with a full set of five toes each. 

Order Nectridea

Diplocaulus

• short tails and small legs• group included lizard-like animals that were relatively well-adapted

to living on dry land, burrowing forms, and others that.

• possible ancestors of the newts and salamanders

Order Microsauria

• resembled small snakes, as their bodies are extremely elongate.

• are usually considered to be related to the Microsauria, although the pattern of bones of the skull is very different.

Order Lysorophia

• Some features prompt the concept that at least some specimens classified as lepospondyls may have arisen directly from crossoptergian ancestor.

• Some Urodeles may be descendants of those specific lepospondyls.