Mapinguari belongs to a complex family of traditions distributed through the Brazilian Amazon rather than to one neatly standardized monster story. Descriptions recorded from different communities and regions vary, but recurring characteristics include a human-sized or larger hairy being, extraordinary strength, enormous claws, a penetrating odor and a powerful vocalization compared with a human scream or thunder. Some traditions give the creature feet that appear reversed or strangely formed, while more elaborate folkloric versions describe a single eye, a huge mouth extending down the body, or skin resistant to weapons. Those variations are important: combining every attributed feature into one anatomical description creates a creature that may never have existed in precisely that form in any one tradition.

Brazilian folklorist Luís da Câmara Cascudo documented Mapinguari material by the mid-twentieth century, and the tradition was already understood as part of Amazonian folklore rather than a newly emerging cryptozoological claim. The name itself has been connected with Tupi-Guarani roots interpreted as referring to a twisted or backward-turned foot. Different Indigenous and rural traditions use additional names or describe beings that later writers have sometimes grouped together as Mapinguari, although those correspondences should not automatically be treated as exact cultural equivalents.

For many tellers, Mapinguari functions as more than an unidentified animal. The forest being may act as a source of danger, a warning against entering remote forest carelessly, or an entity connected with hunting and proper conduct in the landscape. Accounts in which the being is invulnerable to bullets, possesses impossible anatomy or behaves as a supernatural guardian belong naturally within that folkloric framework. Reducing those traditions to an undiscovered species can preserve certain physical details while discarding much of their original cultural meaning.

The case took a striking turn when zoologist and ornithologist David C. Oren of the Museu Paraense Emílio Goeldi began considering whether some reports might contain a zoological component. Oren initially regarded Mapinguari as legendary, but testimony from Amazonian residents persuaded him that at least some witnesses believed they had encountered a physical animal. In 1993 he published "Did Ground Sloths Survive to Recent Times in the Amazon Region?" in Goeldiana Zoologia, arguing that selected descriptions were surprisingly compatible with a relatively small forest-dwelling mylodontid ground sloth.

The proposal was extraordinary but not biologically arbitrary. Large ground sloths were genuine members of South America's prehistoric fauna. Their anatomy included powerful limbs and large claws, and some species could rear into an upright position. Oren argued that those characteristics offered possible parallels with reports of a hairy, strongly built creature capable of standing on its hind legs and breaking vegetation. He also considered the structure of ground-sloth feet and aspects of their anatomy when interpreting reports of strangely oriented tracks and apparently armored skin.

The hypothesis nevertheless requires a major chronological leap. Ground sloths are considered extinct, and no accepted modern fossil, carcass or living specimen demonstrates survival into contemporary Amazonia. Features such as a single eye, belly-mouth and supernatural resistance to weapons also cannot be explained simply by identifying the traditional being with a ground sloth. Oren's hypothesis is therefore better understood as proposing that some animal-like encounters underlying part of the tradition might represent a remnant sloth rather than demonstrating that the folkloric Mapinguari as a whole is zoological.

Oren did not leave the idea entirely at the level of speculation. He interviewed Amazonian residents who claimed direct encounters, including people who said they had actually killed such animals, and mounted expeditions intended to obtain physical evidence. His work was controversial among other scientists, but it represented a genuine attempt to convert testimony into a falsifiable biological question: if a remnant ground sloth population existed, eventually it should produce diagnostic hair, dung, tissue, tracks, remains, photographs or a specimen.

A particularly useful record of those investigations appeared in 1999 when journalist Marguerite Holloway accompanied Oren's work for Discover. The report documented interviews with residents around Barra do São Manuel on the Tapajós River. Manuel Vitorino Pinheiro dos Santos described hearing an extraordinarily powerful human-like scream after hunting white-lipped peccaries and said he retreated toward the river rather than confront the source. The encounter illustrates both the strength and limitation of the Mapinguari dossier: a named person provided a detailed account in the landscape where the tradition exists, but the reported animal itself was not observed or collected by the investigating team.

Potential physical evidence gathered during searches did not resolve the case. Oren and his collaborators collected material including hair and dung attributed or suspected to be connected with the reported animal, but no sample established a previously unknown large mammal or surviving ground sloth. Later summaries of the investigation report that at least one dung sample instead produced evidence consistent with giant anteater, demonstrating why physical samples require a documented chain of custody and laboratory identification rather than visual resemblance or witness attribution.

In 2001 Oren returned to the hypothesis in Edentata, a publication of the IUCN specialist community concerned with anteaters, sloths and armadillos. He openly described the proposal as controversial but argued that even a small possibility of a surviving ground sloth warranted consideration because discovering such an animal would have major conservation implications. He cited multiple claimed face-to-face encounters and seven informants who said they had killed specimens, while still lacking the specimen needed to demonstrate the animal's existence scientifically.

Known Amazonian animals provide another avenue for interpretation. Large mammals observed briefly in dense forest can appear unfamiliar, and the giant anteater is particularly relevant because it possesses large claws, can rear onto its hind limbs and can be dangerous when threatened. Misidentification cannot account automatically for every Mapinguari report, particularly supernatural or culturally specific versions, but the identification of suspected Mapinguari material with a known species demonstrates the importance of testing mundane zoological candidates before proposing survival of an extinct lineage.

The modern ground-sloth interpretation has itself subsequently become part of Mapinguari culture. English-language cryptozoological accounts frequently introduce Mapinguari primarily as an Amazonian "living giant sloth," effectively reversing the historical sequence: an older and more diverse collection of traditions is explained through a zoological hypothesis proposed much later. That framing can obscure the fact that Oren deliberately selected particular physical characteristics from the broader tradition because those were the features relevant to his hypothesis. The features that do not resemble a ground sloth remain part of the folklore but are not evidence for the zoological proposal.

The most defensible conclusion is therefore deliberately open. Amazonian traditions concerning beings called Mapinguari or related names are well established, and twentieth-century researchers recorded testimony from named residents who interpreted their experiences as encounters with a physical animal. Oren's work elevated part of that testimony into a legitimate if highly speculative zoological hypothesis and subjected it to field investigation. Those searches failed to produce diagnostic evidence of a surviving ground sloth. The unresolved historical question is how much of the modern cryptid profile derives from older independent Amazonian traditions, how much reflects reports of known animals or ambiguous forest experiences, and how much was reshaped after the ground-sloth hypothesis became internationally popular.