AD transition to land

Question 1

Transition to Land: from the bony fish to the amphibians

What do key transitions include?

Answer 1

Air-breathing (lungs or lung derivatives)

Walking on land (legs)

bony fish have lungs, however, land-living doesn’t evolve until much later.
So, its bony limbs not lungs which are needed to lift the body up and over land

Question 2

What are the 3 groups of vertebrate fish?

Answer 2

Ray-finned fishes (teleosts)
Lungfishes
The lobe-fins

Question 3

Describe ray finned fishes

Answer 3

Dominant fishes on the planet - main line of fish evolution
Possess fin rays

Characterized by
cycloid or ctenoid scales
increased cranial complexity
swim bladders (usually)

Question 4

What is a swimbladder?

Answer 4

In modern fish it’s a buoyancy organ located in the body cavity.
Developed from an outpocket of the pharynx or esophagus.
Contains gas (usually oxygen) which allows the fish to maintain depth without floating or sinking

Homologous (closely related) to the lungs

Question 5

There are 2 ways of inflating the swim bladder. What are these?

Answer 5

Physostomus swim bladder: retains connection to pharynx via pneumatic duct. Fish gulps/releases air to control volume. THEREFORE: air gulping is useful even in aquatic habitats & evolved independently of life on land

Physoclistous swim bladder: pneumatic duct is lost. Gas is released into the bladder at the knot of capillaries (rete mirabile)

Question 6

Describe lungfishes

Answer 6

They generally inhabit stagnant ponds and swamps

an example of an organism where air gulping is useful without living on land

In lungfishes and tetrapods, the primary function of swimbladders is respiration

Question 7

Describe the lobe fins

Answer 7

Characterized by muscular, fleshy fins with bony, leg-like supports

Coelacanths

Tetrapods !

Question 8

What is the origin of tetrapods?

Answer 8

In one lineage of lobe-fins

The fins became progressively more limb-like while the rest of the body retained adaptations for aquatic life

One of the most significant events in vertebrate history was when the fins of some lobe-fins evolved into the limbs and feet of tetrapods

Question 9

What is special about Tiktaalik roseae?

Answer 9

Tiktaalik roseae is an extremely important fossil link in the origin of tetrapods

Unlike a fish it has a mobile neck and the ear is structured so that it can hear both in and out of water.

Most strikingly, in addition to the other tetrapod limb bones Tiktaalik has a wrist. Tiktaalik’s elbow could bend like ours and the wrist could bend too, which allowed the animal to make its “palm” lie flat