One of my favorite theories is that dinosaurs never truly died out, not completely, and sightings of dinosaurs or dinosaur like beings have been reported for ages, mostly in tropical areas but sometimes in more rural ones. Here I'll briefly outline some of the reported dinosaur cryptids.
Kasai Rex- African Congo
Size differs on this one, most reports say about 40 feet long though. Most reports also seem to stay with the same coloration, red with black stripes. Many meat eating dinosaurs have been suggested including the T-rex, Allosaurus, Spinosaurus and others. Some even suggest it's a creature known as the Chepekwe, a giant monitor lizard reported to weigh 4 tons, but most experts claim it's nothing by local myth.
Emela-ntouka- Central Africa
Described as similar to a Rhino, having a long white horn, this beast is said to gore elephants and has a tail like a crocodile. Some descriptions seem to fit the ceratopsian Monoclonius.
The last reported sighting of this creature was in 1982 but aboriginals have reported seeing a 25 foot two legged creature with short forelimbs for many years. New Guinea and South America have similar sightings.
Mbielu-Mbielu-Mbielu- Republic of the Congo, Africa
This creature has always been described as having "planks" along it's back, suggesting to most researchers that it's part of the Stegasauridae family. Only a few sightings have been recorded but all agree it's herbivorous and mostly harmless.
Kongamato- Jiundu swamps of Western Zambia, Angola and Congo
A pterodactyl-like creature said to have been seen by natives and explorers but most likely to be a mistaken bird like a stork or perhaps an undiscovered large species of bat. Flying creatures of the size the Kongamato is reported, 3-5 feet wingspan, are hard to hide for long. Creatures matching the description of the Kongamato have been reported in America as well but not as frequently.
Described as having heavy armor all over it's body and a thick club on it's tail, this creature most closely resembles the Ankylosaurid family. Some scientists think that the Muhuru might be an evolved species of stegasaur though the description doesn't really fit that.
Probably the most famous of the Living Dinosaurs, the Mokele-Mbembe is described as a long necked, thick bodied animal that's mostly aquatic and has a mean temper. Sauropods most closely resemble these descriptions, though this species is apparently a micro version of them, being only about 15-30 feet long. Though most tribes describe it as said above, some have identified it as a Rhino, which is not native anymore to that area and may be a mix of racial memory and folklore from when they were plentiful in the jungles. Many expeditions have been made to find proof of this creature, but nothing conclusive has ever been found.
Now, all of these creatures can be argued against, stating wrongfully identified creatures or myths so ingrained in local minds that they believe them. But we're discovering new species all the time and in the areas these animals are said to frequent as dense forest and mostly unexplored areas, so it is not unthinkable that they may exist. Until we have concrete proof however, everything remains a mystery.
(Pictures taken from Google and info taken from many sources.)