How do lobe-finned fishes differ from ray-finned fishes, and why were the ray- finned forms unlikely to give rise to terrestrial animals?

First, let's define these two types of fishes: - Lobe-finned fishes (Sarcopterygii) are a group of bony fishes that possess fleshy, lobed, paired fins, which are connected to the body by a single, sturdy bone. - Ray-finned fishes (Actinopterygii) are the other group of bony fishes that have fins comprising webs of skin supported by bony or horny spines called rays.

The main difference between these two types of fishes lies in their fins' structure: - Lobe-finned fishes have fleshy, muscular fins supported by a central "lobe" of bones, allowing more maneuverability and strength. - Ray-finned fishes have fins supported by slender rays, which provides them with greater flexibility but lack the strength and stability found in lobe-finned fishes.

Apart from their fins, other characteristics differentiate lobe-finned and ray-finned fishes: - Lobe-finned fishes have a more complex skull structure, with more bones involved in the jaw, which allows for greater biting strength. - The two groups also have slightly different types of scales, with lobe-finned fishes having cosmoid scales and ray-finned fishes having either ganoid or cycloid/ctenoid scales.

Lobe-finned fishes, such as the Coelacanth and Tiktaalik, had strong, muscular fins supported by robust bones. These adaptations allowed them to navigate shallow waters and even to move on land for short periods. This made them more capable of adapting to terrestrial environments, and eventually giving rise to four-limbed animals (tetrapods) such as amphibians, reptiles, birds, and mammals.

Ray-finned fishes are unlikely to give rise to terrestrial animals due to the structure of their fins. Their slender rays, which give their fins greater flexibility, do not provide enough support or strength for movement on land. This lack of structural stability significantly reduces the chances of ray-finned fishes evolving into terrestrial animals. Additionally, their skull structure and scales do not offer the same advantages as lobe-finned fishes for adapting to the terrestrial environment. In conclusion, lobe-finned fishes differ from ray-finned fishes by having fleshy, muscular fins supported by a central "lobe" of bones, a more complex skull structure, and cosmoid scales. These characteristics allowed lobe-finned fishes to evolve into terrestrial animals, whereas the ray-finned fishes' adaptations limited their potential for life on land.