Why do you say this is so? There are still prokaryotes. There are still eukaryotes. There are still primitive multicellulars. There are still primitive chordates that look a lot like the Burgess-Shale Pikaia. There are still fish, the first true vertebrates in the fossil record. One of the surviving fish species still looks a lot like the kind of lobe-finned fish that gave rise to amphibians. There are still amphibians. There are still reptiles. There are still primitive primates. There are still monkeys. There are still apes.
Our line comes through all of the above, albeit maybe not exactly through any still-extant species that we can be sure. So what was your point?
Is there doubt about this? Are you refering to something like Big Foot?
Truth of the matter is that even the simplest species in the evolutionary tree are still around. There is absolutely no reason why the evolutionists are not able to show common descent from existing species. The only reason they cannot do that is because there is no common descent. The three simplest forms of living organisms - the archaea, the prokaryotic bacteria and the eukaryotic bacteria did not descend from one another and there are no intermediate species to show how such a thing might have happened. There are likewise no intermediate species between the major families and orders of nature.