GMAT Critical Reasoning (CR) | Biologists suspect that feathers are modified scales.

Biologists suspect that feathers are modified scales. Ancient reptiles developed feathers as a way to insulate their bodies from the cold and regulate their body temperatures. However, many of these early feathered reptiles were unable to fly. Thus, today’s flightless birds probably developed their feathers as a way to manage their body temperatures.

Scope of the question stem : flightless birds
We have to prove :

today’s flightless birds didn't developed their feathers as a way to manage
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