Besides lacking thumbs, dolphins would also have a pretty hard time harnessing fire as a tool. This probably truncates their tech tree severely.

> Besides lacking thumbs, dolphins would also have a pretty hard time harnessing fire as a tool.

I keep reading about this, and I don't see it as a major problem.

Sure, it might take a while for them to even grasp the concept of fire. Much like it took us a while to grasp relativity.

However, once they know it to be possible, it's an engineering problem. They can build their forges above water. Holding breath to operate them (until they can do it remotely) is inconvenient but they are pretty good at it.

There's also a fair bit of construction they could do without even resorting to that. Humans can weld underwater. They could too.

> Holding breath to operate them (until they can do it remotely) is inconvenient but they are pretty good at it.

Nitpick: Dolphins breathe air.

Humans can weld underwater - with equipment that they built on dry land, using materials that they created on dry land. Could they have created the materials underwater? It would have been hard, even knowing how.

Dolphins are mammals like us. They're holding their breath when they're underwater like us :P

It would truncate the human tech tree. It's anybody's guess what a Dolphin-based tech tree would look like, given their environmental constraints.

True, but perhaps they could harness technology we never thought of as valuable. Perhaps they could build structures around sea vents, or use sticks and weeds to build pens in which to farm fish. Many possibilities exist. They could even be doing agriculture right now and we wouldn't even know it.

I like your ideas but without dexterous extremities it at least a very versatile mouth it seems you'd be very limited in your capacity to control or shape your environment.

Dolphins do have a versatile mouth. Even seals have been trained to do fancy things with their mouths. But staying on the dolphin theme, check out these dolphins blowing air rings: https://www.youtube.com/watch?v=bT-fctr32pE

I'm endlessly grateful that Raccoons aren't more intelligent.

Yet. Coexisting near humans, it's likely that the environment will incentivize smarter raccoons.

I think it’s the opposite. Any idiot raccoon can raid a trash can and get lots of calories. And unlike rats we are generally not out there looking to kill them.