Arms and Legs first evolved so that fish, by crawling onto land, could escape predators: over 375 million years ago and the Paddlefish

 As described about 1 hour in

 New genetic data overturn long-held theory of limb development

 Study reveals genes present long before fish needed hands, feet

https://www.uchicagomedicine.org/forefront/news/new-genetic-data-overturn-long-held-theory-of-limb-development 

So the genes were "already there" but needed the environmental pressure to trigger the genes.

 This finding overturns a long-held, but much-debated, theory that limb acquisition was a novel evolutionary event, requiring the descendents of lobed-fin fish to dramatically alter their genes to adapt their bodies to their new environments of streams and swamps.

The paper, "An autopodial-like pattern of Hox expression in the fins of a basal actinopterygian fish," shows that the genetic and developmental toolkit that builds limbs with fingers and toes was around long before the acquisition of limbs, according to the scientists, and that this toolkit exists in some primitive form in a living primitive bony fish, the paddlefish.

 Tetrapods have a second phase of Hox gene expression that happens later in development. During this second phase, hands and feet develop. Although this second phase is not known in zebrafish, the scientists found that it is present in paddlefish, which reveals that a pattern of gene activity long thought to be unique to vertebrates with hands and feet is in fact much more primitive.

 Paddlefish are an ancient species of fish. Fossils of this odd-looking fish date back 400 million years

 The irony being that modern science human civilization has almost made the Paddlefish EXTINCT - they have to be bred now. So their wild populations are not sustainable on their own...