During the Devonian period, the earliest lobe-finned fishes appeared and differentiated into two major categories: lungfishes (order) and lobe-finned fishes (order).
Unlike ray-finned fishes, early lobe-finned fishes had a suprafungal lobe located above the body axis on the crooked tail. Their fins have an axial skeleton and smaller bones that radiate outward on either side of the axial skeleton, and then have bony fin rays at the ends of these bones. Such fins are called protofins. Primitive ray-finned fishes had only one dorsal fin; early lobe-finned fishes had two dorsal fins. The scales of primitive lobe-finned fishes are of the tooth scale type, with a thick layer of tooth scales on the bone at the base of the scales; while the scales of primitive ray-finned fishes have very limited tooth scales, but have a thick layer of enamel. layer covers the surface.
In the evolution of fish themselves, lobe-finned fishes can be said to be a side branch of evolution. However, from the perspective of the evolution of entire vertebrates, lobe-finned fishes are a crucial group because the tetrapods that later appeared Animals evolved from lobe-finned fish.
The earliest lobe-finned fish - double-finned fish
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