La Grotte d'Andrafiabe, one of the most accessible caves in the reserve, extends for at least eight kilometers of horizontal passages - and it is just one entrance to the underground network. Around 100 kilometers of cave passages have been mapped within the massif, and expeditions continue to find more. Where the calcific upper layers of limestone have been completely eroded away, the harder base rock beneath emerges as the tsingy - etched and sharpened by millennia of tropical rain falling at an average of 2,000 millimeters per year. Basalt, both as scattered boulders on the surface and as deep flows filling the canyons, adds geological complexity to a landscape already unlike anything else on the island. The caves themselves shelter species found nowhere else: blind fish, cave-adapted shrimp, and invertebrates that had never been described by science before the 1980s expeditions brought them to light.

When British expeditions first began cataloguing Ankarana's wildlife in the 1980s, the discoveries were striking enough to inspire a book title. Dr. Jane Wilson-Howarth's travel narrative Lemurs of the Lost World chronicled what the teams found: subfossil remains of giant extinct lemurs alongside living species that had never been formally described. Today, the reserve protects at least eleven lemur species. Crowned lemurs and Sanford's brown lemurs are the most visible, often spotted moving through the dry deciduous forest canopy. The aye-aye, Madagascar's strangest primate - nocturnal, with elongated skeletal fingers for extracting grubs from bark - also inhabits these forests. So does Perrier's sifaka, one of the most endangered of all lemurs, its population fragmented across the far north of the island.

During the 1986 expedition, ornithologists Phil Chapman and Jean-Elie Randriamasy documented 65 bird species from 32 families at Ankarana - nearly a third of all bird species that breed in Madagascar. What caught their attention was not just the diversity but the behavior. Small insect-eating songbirds across multiple species had formed mixed foraging bands, traveling together through the forest in coordinated groups. Paradise flycatchers hunted alongside common jerys and greenbuls. Sunbirds flew with vangas. Within each band, different species specialized in where they searched: some on tree trunks and branches, some along slender boughs, others beneath leaves. The arrangement benefited everyone. Each species caught insects that escaped the others, and the larger group was far more likely to spot approaching predators than any single bird foraging alone.

The subfossil record at Ankarana reads like a catalogue of what Madagascar has lost. Bones of the sloth lemur Babakotia radofilai, an animal that hung from branches like its namesake, were first described from specimens found here. The massive Megaladapis - sometimes called the koala lemur for its size and likely mode of clinging to trees - left its remains in these caves, as did the baboon lemur Archaeolemur and the giant Palaeopropithecus. These were not small creatures; some weighed as much as a human adult. Their disappearance, likely within the last two thousand years, tracks with human arrival on Madagascar. What survives at Ankarana is remarkable precisely because of what has already vanished. The reserve is not just a refuge for living species but a geological archive of the island's recent evolutionary past, preserved in limestone that was ancient when dinosaurs still walked.