Convergence is a process in which different species of organisms develop into one or more similar physical features in order to adapt to the same environment  The similarity between ichthyosaurs and fish is an example of convergence  Ichthyosaurs are marine reptiles and do not belong to the same class as fish  In order to adapt to the marine environment, the physical characteristics of ichthyosaurs tend to be consistent with those of fish
The most striking thing is that ichthyosaurs have fins like fish
The physical characteristics of one kind of organism are similar to those of other species, which is entirely the result of their adaptation to the living environment.