I had a domain ranked 1 or 2 for a phrase for about 6 years!1 SIX YEARS Little black/white penguin comes along and i did not have icy water for him so i get wacked I did not do any SEO on that site other than general onpage seo but have not changed anything to it for years and been doing great. little traffic but very targetted. phrase was domain name, now i dont even rank for the phrase as one word only i i add .com i get the site. Whats up with that!!!!!!?? This makes no sense and proves that it is not related to overoptimization.
What's your URL? I will have a look if you want. Maybe your link building inconsistency is the problem here.
I am not being ridiculous! Take a look at all of the main keywords: Example: keyword: "DINOSAURS" 9/10 of the sites ranked are sites listed in wikipedia as a resource...... Oh, take a look at 7th position: Dinosaurs (TV series 1991-1994 - Internet movie database) Are you going to seriously tell me that they did not BUY that position and you are going to say that google search claims that when people want to know about dinosaurs they really want to know about some old show that aired for 3 years........
Don't much worry! Google is updating it. You can try with NeatPeak Checker. Checking the whole backlink profile nowadays is worthwhile. In the mean time, please be patient and remove low quality links and wait for new updates. I believe that new linkbuilding techniques/tool to cheat new algorithm change.
Chances are the fact that you have not done any off page SEO is whats dropped your site. On page is is GREAT and VERY important but you need to combine this with an effective Off page SEO strategy. You need to focus on link diversity, quality HIGH PR links, relevant and contextual links.