Why should Nessie, reported to be seen by too many people and even pictures, be extinct and not a type of dinosaur that also underwent minimal evolution.
Because there's 20 tonnes of fish (such as Arctic char) in Loch Ness. Based on the science of food chains, that would support a single monster with a mass of 2 tonnes. Now, take that monster, and think that is has to breed and produce offspring if it survived millions of years. Suddenly you don't have a two tonne monster, but a family of large fish.
What about the thermocline and the effect on the monster's food source? I'd like an answer to that too?
Now, you're slightly picking on the wrong person with the Nessie argument, as I have recently spent time around Loch Ness and visited the Loch Ness Exhibition Centre. There are many effects in the Loch that explain the sighting - swimming deer (yes), light slicks, bow waves, floating logs, upturned boats. Go and spend some time next to the Loch, and you'll see a monster each day. I did, but once you double take you'll realise it's a trick of light. If you look at every instance of the monster photographs, there's a range of different types of monsters, some with small necks, some with long necks, some that are serpent like, some that are round bodied. Are you telling me the Loch Ness monster morphs? I'd like an answer to that too.
In fact, after a thorough investigation, the Loch Ness monster is probably nothing more than a sturgeon or giant catfish that has found its way into the Loch.