First of all, as some here have already mentioned, is the problem presented with the creature’s breathing as size increases. Arthropods do not have a closed circulatory system and this means that their “blood” (actually called hemolymph in this case) doesn’t carry oxygen the way ours does. For arthropods, oxygen comes in through pores (called spiracles) connected to the outside of the exoskeleton and the oxygen is then diffused into the body through tubes called tracheae. At a certain point, an arthropods size is physically limited because these pores and tubes become too big to effectively exchange oxygen and carbon dioxide. At a certain size, an arthropod will physically not be able to breathe and will die from a build up of carbon dioxide. Prehistoric arthropods were able to become somewhat larger in size because of the more oxygen rich atmosphere they lived in.

Even if this respiratory problem was somehow overcome, there is a second problem to contend with that limits size. There is a long drawn out scientific explanation for this, but I will try to make this as concise as possible. Basically, arthropods have muscles inside their bodies and so the exoskeleton becomes a major limitation as size increases. The power of the muscle fibers are a function of their thickness, and as an arthropod grows larger in three dimensions, its muscles only get bigger in two. In other words, the weight of the exoskeleton increases at a faster rate than muscular strength. To maintain strength, the arthropod’s muscles would have to grow larger at a faster rate than the actual limbs and exoskeleton around it. At a certain point, two things can happen. The creature can either burst, or it will become unable to move at all since because its weight increases faster than its muscular strength, the exoskeleton becomes to heavy to lift. Insects can perform great feats of strength precisely because they are small. The reason underwater arthropods can get so large is because the water helps support them and makes it easier to lift around the exoskeleton. This is physics and it applies to all creatures with an exoskeleton, even land crabs.

There are solid, scientific reasons why a terrestrial arthropod’s size is limited. I do not believe it to be possible for a terrestrial spider to attain the extreme 4 to 6 foot range described simply because there are certain well established biological and physical restrictions that apply to all arthropods, and I am not about to ignore these because some people claim to have seen them.

I believe that the forest rhino theory is by far the most promising possibility for the Mokele-mbembe. Or maybe it could be a tapir-like animal, or some kind of giant hog, or even a rare, previously unknown proboscidean. There are several possibilities that I think would be much more likely than any kind of dinosaur. I just do not believe that any dinosaurs survived the K-T extinction – unless you count birds.

A spider THAT big? Sheesh!!!

Like I said on another thread—

I think locals would know (for the most part) the difference between a rhino and something else.

SOMETHING big and reptile-like is present in darkest Africa. I tend to agree with SOCALcryptid. Triceratops or Sauropod sounds more like it.