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

Lobe-finned fishes and ray-finned fishes are two different groups of fishes. Lobe-finned fishes, known as Sarcopterygii, have fleshy, lobed paired fins, while ray-finned fishes, called Actinopterygii, have fins supported by thin, elongated bony structures called rays.

Apart from the differences in their fins, lobe-finned fishes have a series of characteristics that are not present in ray-finned fishes. Some of these differences are: 1. Lobe-finned fishes have a single dorsal fin located closer to the tail, while ray-finned fishes usually have two dorsal fins. 2. Lobe-finned fishes have a different arrangement of skull bones compared to ray-finned fishes. 3. Lobe-finned fishes have a significantly reduced number of fin rays and possess a more muscular and robust structure in their fins, which facilitates movement on different types of substrates, such as the bottom of rivers or ocean floors.

Lobe-finned fishes are believed to be the ancestors of terrestrial vertebrates. This is due to the unique features that are absent in ray-finned fishes. The fleshy, muscular fins of lobe-finned fishes enabled them to move around on different types of surfaces more easily compared to ray-finned fishes. This locomotory adaptation is crucial for the evolutionary transition from aquatic to terrestrial environments.

Ray-finned fishes were less likely to give rise to terrestrial animals because: 1. Their fins, made up of thin bony rays, were not suitable for the locomotory requirements of the terrestrial environments, as they provided less support and were not as robust. 2. Most ray-finned fishes lack the anatomical features that allowed lobe-finned fishes to evolve into terrestrial vertebrates, such as the robust, muscular fins and specific bone arrangement in the skull. In conclusion, lobe-finned fishes differ from ray-finned fishes mainly in the structure of their fins, having fleshy lobed paired fins rather than fins supported by slender bony rays. The unique set of characteristics in lobe-finned fishes made them more suitable for the transition from aquatic to terrestrial environments, while ray-finned fishes lacked the necessary features to evolve into land-dwelling animals.