Reptilian and amphibian cryptids encompass alleged unknown cold-blooded vertebrates, from large sauropod-like creatures reported from the Congo Basin to giant salamander analogues from North America. This category also overlaps with fossil-survivor hypotheses, as the most prominent cases (Mokele-Mbembe, Kasai Rex) are often interpreted as evidence for surviving Mesozoic-era lineages. The Central African rainforest basin, due to its size, ecological complexity, and limited scientific exploration, is considered by some zoologists a plausible refuge for large undescribed animals.
Mokele-Mbembe — a term in the Lingala and related Bantu languages usually translated as "one who stops the flow of rivers" or "blocker of rivers" — is reported from the Congo River basin, Lake Tele, and the Likouala swamp region of the Republic of Congo, covering an area of approximately 55,000 square miles of largely unexplored rainforest and swamp. Descriptions from multiple ethnic groups independently converge on a large, long-necked, semi-aquatic creature with a rounded body and heavy tail, comparable in silhouette to a sauropod dinosaur, though the most common descriptions would be consistent with a large reddish-brown animal approximately the size of a small elephant or hippopotamus.
The modern Western record begins with missionary accounts from the eighteenth and nineteenth centuries. Systematic investigation was initiated by Roy Mackal (University of Chicago biologist) and James Powell, who led two expeditions into the Likouala region in 1980 and 1981. Mackal's A Living Dinosaur? In Search of Mokele-Mbembe (1987) documents extensive witness interviews and the difficulty of reaching the core habitat zone. During the 1981 expedition, Congolese guides reportedly became visibly frightened when shown silhouettes of various animals; the sauropod silhouette produced the strongest recognition response while the hippo silhouette produced no recognition.
A 1992 Japanese expedition led by Fujiwara Redmond filmed unusual water disturbance on Lake Tele; the footage was broadcast on Japanese television but proved inconclusive on analysis. Subsequent expeditions by William Gibbons (2000, 2001) and others have collected additional accounts but no physical specimens. The primary zoological objection is that a surviving sauropod lineage would require an extraordinarily large breeding population to persist, with no fossil record from the region in the relevant geological period and no skeletal remains.
Nguma Monene ("large serpent") is a distinct cryptid from the Likouala swamp region, described as an enormous serpentine creature without the long neck of Mokele-Mbembe, capable of capsizing canoes and cutting a broad swath through riparian vegetation. Some researchers classify Nguma Monene as a giant, undescribed constrictive snake, which is zoologically more plausible than a surviving sauropod. The largest known snake, the reticulated python (Malayopython reticulatus), reaches 6–7 metres; an analogue of 10–15 metres would require significant ecological resources but is not inherently implausible for an unexplored swamp ecosystem.
Kasai Rex is based primarily on accounts from Swedish plantation manager John Johanson, who claimed to have witnessed a large bipedal reptile killing and feeding on a rhinoceros in what is now the Democratic Republic of Congo in 1932. The account, circulated in cryptozoological literature, includes alleged photographs; the photographs are widely considered fraudulent, and the Kasai Rex is regarded by most researchers as a hoax or misidentification. It is documented here as a commonly cited but evidentially weak category entry.
Reports of monitor lizards greatly exceeding the known maximum size of the Komodo dragon (Varanus komodoensis, maximum approximately 3 metres) exist from several regions. The Megalania (Varanus priscus) — a giant monitor lizard reaching an estimated 5–7 metres — is known from the Australian Pleistocene fossil record, with the youngest specimens dated to approximately 40,000 years ago. Given the coincidence of this date with human arrival in Australia, some researchers have proposed hunting drove the species to extinction relatively recently, with the possibility of relic populations in remote areas. Australian indigenous accounts of a large monitor-like creature (Burrunjor) persist in some communities. In Papua New Guinea, the Artrellia or "tree crocodile" — a large, arboreal lizard with a reputation for killing pigs — may represent an undescribed large varanid; several sightings by credible witnesses exist in the herpetological literature.
The Loveland Frogman is a bipedal, humanoid entity with frog- or lizard-like features reported from the Loveland, Ohio, area near the Little Miami River, with documented police encounters in March 1972. Officer Ray Shockey reported encountering a 3–4 foot, bipedal lizard-like animal on the roadside; a second officer reported a similar encounter two weeks later. The Loveland Frogman occupies an overlap zone between the reptilian cryptid and hybrid/humanoid categories. It is documented here under reptilian due to the cold-blooded morphology described in the police reports. A 2016 Pokémon Go player reportedly filmed a large bipedal lizard at the same location, though the footage quality was insufficient for analysis.
North America has a documented history of unusually large salamander reports beyond the known range of the hellbender (Cryptobranchus alleganiensis, maximum approximately 74 cm). Folk accounts of "mud devils" and "devil dogs" from Ozark and Appalachian river systems describe animals of 1–2 metres, significantly exceeding the known maximum. Japanese giant salamanders (Andrias japonicus) reach nearly 1.5 metres, suggesting that North American relatives in unexplored tributary systems may have been misidentified or undescribed. The South China giant salamander complex, recently revised into multiple species, demonstrates that cryptic diversity in the genus is real and unresolved — strengthening the case that large undescribed salamanders are possible in suitable habitats.
This page presents documented research and reported phenomena without endorsement. All classifications represent researcher categorisation of witness accounts and physical evidence. No conclusions about species identity or palaeontological survival are made herein.