On the Track of Unknown Animals is a cryptozoological book by the Belgian-French zoologist Bernard Heuvelmans that was first published in 1955 under the title Sur la Piste des Bêtes Ignorées.

The English translation by Richard Garnett was published in 1958 with some updating by the author and with a foreword by Gerald Durrell.

"[4] On the Track of Unknown Animals cites animals that had only been discovered relatively recently, such as the pygmy chimpanzee, coelacanth, Komodo dragon and giant panda; and those that are believed to have become extinct relatively recently, such as the moa and Tasmanian tiger.

A major theme is that these animals were generally known to local peoples, but their stories were dismissed by visiting zoologists, particularly the okapi.

[5] The author then discusses evidence for mystery animals from all over the world including the Mokele-mbembe, sea serpents and the Yeti, with an extensive bibliography.

Reviewers praised the breadth of study, careful citation and the author's knowledge[4][5] but it was criticized for being somewhat shallow and "overly long and rambling.

Sea serpents and their ilk are no longer the stars – Why we no longer believe in fantastic beasts – Our planet still has many unknowns – The white deserts of the Poles – Africa has not revealed all its mysteries – Light does not necessarily come from the East – The lost worlds of the Green Continent – The terra incognita of zoologists – The Alpine legged worm – The lesson of the Tatzelwurm Chap.

The imprudent assertion of Baron Cuvier and the inopportune tapir – The giant ape with a dog’s snout and the relict chevrotain – The dwarf hippopotamus, buried by the unbelievers – The aptly named takin and Schomburgk’s invisible deer – Last-minute rescue of the mi-lou – The monkey with the Parisienne nose and Père David’s black and white bear – And the series continues!

– President Grevy’s Funny Zebra and Colonel Przewalski’s Horse – Small Fry with a Sensational Character – Three Discreet Giants: the Kodiak Bear, the White Rhino, and the Mountain Gorilla – The Incredible Okapi – The Giant Forest Boar – Resurrection of the Pygmy Hippopotamus – The Third Elephant – The Pygmy Swamp Elephant – The Pygmy Elephant is Not an Invention of Ivory Traffickers – The Komodo Dragon and the White Flag of Lake Toung-Ting – Great Apes Have Their Pygmies Too – A Tale of Enigmatic Feathers – The Animal with No Name, the Leopard-Hyena, and the Flying Jackal – The Romantic Adventure of the Lady and the Giant Panda – The Thorny Case of the Cambodian Gray Ox – Our Latest Acquisition: An Andean Wolf Fur Chapter 3: Survivors from the Past.

– The Tailed Men of Indochina – The Sign of the Beast – Demons with Sharp Forearms – Tyrants Follow One Another and Often Look Alike – Are Hairy Gnomes Dwarf Pithecanthropus?

– The Moustachioed Ape-Men of Perak Chapter 5: Orang Pendek, the Incongruous Ape-Man of Sumatra.

Badak Tanggiling, a Very Unusual Rhinoceros – The Identity of the Scaly Rhinoceros – A Puzzle for Zoologists – Invention and Discovery of the Ape-Man – There is Orang and Orang – Portrait of the Little Gibbon – Could It Be an Old, Hairy and Mangy Gibbon?

Snakes in the sky and snakes in the waters – The gauarge, image of an extinct dinosaur – Yarama-yha-who, the child-eating gnomes – The Philippine wood demon – Australian animals look faked – Impossible egg-laying mammals – The bunyip, omnipresent bogeyman – The bunyip’s description is becoming clearer – Is it an ordinary seal or an aquatic marsupial?

– Captain Eberhardt’s Incredible Trophy – The Skin Has Been Preserved Intact Since Time Immemorial – Suspicious Irruption of the Fearsome Iemisch – Were Mylodonts Domestic Animals?

10 – On the difficulty of assessing the size of a living snake – The giant anacondas of the Marquis de Wavrin – The giant boa, rival of the anaconda – The “sucury gigante” of Father Heinz – Lorenz Hagenbeck wants to film the monster – Would a 40-meter snake weigh five tons?

Quadrumane incubi and succubi – Terror in the Matto Grosso – The great tailless ape of Mr. de Loys – Baptism of the ameranthropoid – Is it an American pithecanthropus?

The Disturbing Science of the Eskimos – The One Who Lives Under the Earth – From the Impossible Northern Elephant to Baron Kagg’s Super-Cow – Inopportune Intervention of the Behemoth and the Woolly Rhinoceros – Of the Canned Mammoth – Portrait of the Hairy Colossus – The Extinction of the Mammoth Has the Character of a Dogma – The Retreat of the Hairy Hordes – The Presumed End of the Giant – Has the Mammoth Really Disappeared?

– The Colossus Struck Down by Light – The Mammoth is a Forest Animal – The Monster Seen Alive – The Hairy Elephants of Yermak the Conqueror

The Hot Nights of the Black Continent – Africans Are Subtle Observers Who Interpret the World in Their Own Way – Do Gorillas Abduct Women?

– Africa is a conservative continent – The mountain dwarf rhinoceros and the aquatic elephant – The little spotted lion of Mount Kenya – There is Simba and there is Marozi – A bundle of concordant testimonies – Unconvincing objections – It could well be a new species – What if the lion-leopard were a hybrid?

Trader Horn’s Giant Diver – The Lukwata of Lake Victoria-Nyanza – The Lau, the Tentacled Serpent of the Sources of the Nile – Half Elephant, Half Dragon: The Monster of Lake Bangweolo – The Chipekwe of the Sources of the Congo – The Report of Lewanika, King of the Barotse – There Is a Photo of the Dilolo Dragon – Charged by a Dinosaur, or the Misdeeds of Belgian Humor – The Coje Ya Menia of Upper Cuanza – The Mokélé-Mbembé of Baron Von Stein zu Lausnitz – Is There One or More Amphibious Monsters in Africa?