I'm a paleontologist in real life. I would suggest looking at Eusthenopteron or other so called "rhipidistians" (polyphyletic old taxon). If that doesn't meet your need for age, something along the lines of cephalaspids are at least close to our lineage. If you wanna go further back, maybe just check out haikouichthys or myllokumningia. If you want even more plesiomorphic (=primative), I guess Pikaia is about the best you get. That should take you back ~520 million years and give you some starting places to look up and do your own work.
If you meant living today? Polypterus is about the best you get at the base of actinopterygii and dates back to the cretaceous. If you are butt hurting further, try the sarcopterygii, lungfish and the like. I can't do better right now, I've been in absentia from this here forum for a bit because I am doing field work.