Tetrapod Origins & Terrestrial Adaptations

Bio Unit 2

Osteolepiform fishes

Extinct lobe-finned fishes with many morphological similarities to tetrapods

†Eusthenopteron

Sarcopterygian with limb-like fins, transition between fish and amphibians.

†Panderichthys

Flattened, shallow-water fish showing tetrapod-like features

†Ichthyostega

One of the earliest known tetrapods, had limbs with digits

†Tiktaalik

Known from Devonian, transitional “fishapod” with both fish and tetrapod traits

†Acanthostega

Well developed branchial skeleton, early tetrapod with limbs and digits but primarily aquatic

Sacral connection

Link between pelvic girdle and vertebral column for weight support on land

Polydactyly

Having more than 5 digits per limb, common in early tetrapods

Axial skeleton

Skull, vertebral column, and ribs

Appendicular skeleton

Limbs and limb girdles

Synovial fluid

Lubricating fluid in movable joints

Walking-trot

Ancient motor pattern

Positive pressure buccal pump

Raise and lower floor of the buccal cavity to force air into lungs

Negative pressure aspiration pump

Use axial muscles to expand chest cavity to draw air into lungs

Vomeronasal (Jacobson’s) organ

Chemosensory organ detecting pheromones

Keratin

Tough protein forming skin, scales, claws, and other protective structures

Cloaca

Common opening for digestive, urinary, and reproductive tracts