You, ahem, didn't.
Lamarck was the guy who came up with a proto-theory of evolution, the theory of use-and-disuse, and the idea that as giraffes stretched their necks to eat high leaves, they not only physically changed their own necks, but the necks of their children as well.
The guy who invented biological taxonomy was Linneus.
But it's not fair to characterize Lamarck as a pseudoscientist. He was, for his day (which was nearly a century before Darwin, remember), a top-flight biologist. He invented the $%^& theory of evolution, for Pete's sake! In an age when everyone else believed not only in special creation and spontaneous generation, but also in the immutability of species since their creation in the Garden, he suggested the almost heretical idea that no, species can change over time and here's one suggestion of a mechanism for how something like a horse can turn into something like a giraffe.
He also wasn't an amateur. He was a curator at the French Museum of Natural HIstory, as close as one could come in the 18th century to being a professional scientist.
This isn't confined to the past, nor has it ever been confined to pseudoscientists. If I can, in my career, achieve a single insight as brilliant as Lamarck's, I can die happy. I don't even care (much) if I'm wrong. All scientists are wrong, eventually -- even Newton didn't get gravity right, and Einstein is on the ropes. I'd like to be Darwin. I would be happy being Lamarck. I expect that I'll just end up being drkitten, though....
Long day? Still not a good enough excuse.