Concept 34.4: Tetrapods are gnathostomes that have limbs

Flashcards from Concept 34.4 of Pearson's Campbell Biology, Twelfth Edition.

Tetrapods

Gnathostomes that have limbs via the evolution of a lineage of lobe-fins 365 mya, leading to great diversification

• Have four limbs and feet with digits

• A neck, enabling independent head movement

• Fusion of the pelvic girdle to backbone

• The absence of gills

• Ears for detecting airborne sounds

Tiktaalik

A fossil species with characteristics of both fish and tetrapods

• Fish traits include fins, gills, lungs, and scales

• Tetrapod traits include ribs, a neck and shoulders, front fins with similar bone patterns, and a pelvis and rear fin more robust than those found in fish

• Likely could walk in water, but is unlikely that it walked in land

Amphibians

A class with 6,150 species in three clades:

• Salamanders (Urodela or “tailed ones”)

• Frogs (Anura or “tail-less ones”)

• Caecilians (Apoda or “legless ones”)

Name means “both ways of life,” referring to the life stages of many frog species first in water and then on land

• Usually found in damp environments; these have skin that function in gas exchange

• Eggs lack a shell and must be laid in water or moist environments on land

Salamanders (Urodela)

A clade under amphibians with about 550 species; these have tails

• Some are aquatic

• Exhibit paedomorphosis, or the retention of larval features when mature

• Typically carniverous

Paedomorphosis

The retention of larval features when mature enough to reproduce; this is common in aquatic salamanders

Frogs (Anura)

A clade under amphibians with about 5,420 species; these lack tails but have powerful hind legs for locomotion on land

• These with leathery skin are called “toads”

• Larvae are herbivoeres with gills, a lateral line system, and long, finned tails; this eventually is grown out of and a carnivorous diet persists

Caecilians (Apoda)

A clade under amphibians with about 170 species; these are legless and nearly blind, resembling earthworms

• Legs were lost as a secondary adapation

• These inhabit moist forest soils in tropical areas