Final answer:
The question describes lobe-finned fishes, a group that includes lungfishes and coelacanths, which have fins with skeletal structures similar to terrestrial vertebrates. Dolphins, seahorses, crocodiles, and turtles do not fit this description.
Step-by-step explanation:
The description provided in the question best matches sarcopterygian fish, specifically the lobe-finned fishes. Neither dolphins (mammals), seahorses (teleost fishes), crocodiles (reptiles), nor turtles (reptiles) are sarcopterygian fish. Lobe-finned fishes, like the coelacanth, are characterized by fleshy fins with bones that resemble the limb bones of terrestrial vertebrates. Among the modern representatives of this group, lungfishes and coelacanths have fins supported by skeletal structures homologous to those in the limbs of terrestrial vertebrates.
These prehistoric tetrapods are a significant part of evolutionary history as their limb-like appendages facilitated the transition from life in water to life on land, leading to diverse terrestrial vertebrate lineages such as amphibians, reptiles, and mammals.