Ammonite pavement in Lyme Regis, Dorset, Great Britain - a World Heritage Site. We went fossil hunting at Lyme Regis as kids! I took my husband a few years ago and we only found one fossil! I don't think he believed we used to find loads.
Sinomegaceros pachyosteus by ~RomanYevseyev Deer can be surprisingly dangerous as it is. I'm tempted to have the PCs-- next time they run out of food-- pass near some does that are large but not otherwise unusual. And then have the stag bust out.
Spinosaurus may be the larges Theropod to ever stalk the Prehistoric Americas and believed to be even larger than T-Rex. Recently (late it was determined to be the first and only known aquatic dinosaur.