Zaglossus hacketti

Zaglossus hacketti, now usually placed in the genus Murrayglossus, is an extinct giant long-beaked echidna from the Pleistocene of Western Australia. Known mainly from fossils found in Mammoth Cave, it is thought to be the largest monotreme ever, around 1 m long and weighing 20 to 30 kg. Cut and burn marks on some bones suggest it was occasionally hunted by early humans.

Zaglossus hacketti, the giant echidna, is known exclusively from Pleistocene fossil remains discovered in the Mammoth Cave and Naracoorte Caves regions of Australia, so direct behavioral observations are impossible. However, based on skeletal morphology—particularly its robust limb bones, which suggest it was roughly the size of a small sheep (making it the largest monotreme ever known)—and comparisons with its living relatives, the long-beaked echidnas (genus Zaglossus) of New Guinea, paleontologists infer that this species was likely solitary and largely nocturnal or crepuscular, avoiding the heat of the Pleistocene Australian forests and woodlands it inhabited.

Like modern echidnas, Z. hacketti probably relied on a combination of powerful digging forelimbs and a keen sense of smell (via electroreceptors in its snout, a trait shared across monotremes) to locate prey and evade predators such as thylacines and marsupial lions. Communication in living echidnas is minimal, consisting mostly of low grunts and chemical scent cues, and it is reasonable to infer a similarly cryptic, low-vocalization lifestyle for this extinct giant. Home range size and territorial behavior remain speculative, though its large body size and inferred slow metabolism suggest expansive, resource-dependent foraging ranges within Pleistocene sclerophyll forest and woodland habitats.

As an insectivore, Zaglossus hacketti is presumed to have fed primarily on soil and litter-dwelling invertebrates, particularly earthworms, termites, and beetle larvae, following the dietary pattern observed in extant long-beaked echidnas, which specialize heavily on earthworms rather than ants or termites (unlike the short-beaked echidna). Its elongated, toothless snout and long, sticky tongue—inferred from cranial fossil remnants—would have been well suited to probing deep into leaf litter, rotting logs, and soft forest soils to extract subterranean prey.

Given its enormous size relative to other echidnas, Z. hacketti likely required substantial daily caloric intake, foraging across wide stretches of forest floor. Monotremes possess notably low metabolic rates for mammals, which may have allowed this giant species to survive on a modest, though steady, supply of invertebrate prey. Water dependency was likely low, with much of its hydration derived from prey items, consistent with the semi-arid to temperate Pleistocene climate fluctuations across its native range.

No direct fossil or genetic evidence documents reproduction in Zaglossus hacketti, but as a monotreme it almost certainly reproduced by laying a single soft-shelled egg, incubated in a temporary abdominal pouch, mirroring the reproductive strategy of all living echidnas and the platypus. Breeding was likely seasonal, timed to cooler months to align hatchling development with periods of higher invertebrate abundance, a pattern seen in modern Zaglossus and Tachyglossus species.

After hatching, the underdeveloped puggle would have remained in the mother’s pouch or a specially excavated nursery burrow, nursing on milk secreted through mammary patches (echidnas lack nipples) until it developed spines, at which point it would be relocated to a den. Sexual maturity in modern echidnas is reached between 4 and 7 years, and given the larger body size of Z. hacketti, a similarly extended juvenile period—or longer—is plausible, along with an extended maternal investment period.

Zaglossus hacketti is extinct, having died out during the Late Pleistocene extinction event that eliminated much of Australia’s megafauna approximately 40,000–50,000 years ago. Leading hypotheses for its extinction include a combination of climatic drying trends that reduced suitable forest habitat, and the arrival of humans in Australia, who may have hunted megafauna directly or altered ecosystems through fire-based land management practices, which reduced forest cover and invertebrate-rich habitats essential to its survival.

As a slow-moving, ground-dwelling species with limited defensive strategies beyond its spines, Z. hacketti would have been vulnerable to increased predation pressure and habitat fragmentation during a period of significant ecological upheaval. There are no active conservation initiatives, as the species is unambiguously extinct with no possibility of rediscovery; contemporary interest lies purely in paleontological research, with the IUCN classification of “Extinct” reflecting its permanent loss from the fossil record, alongside occasional taxonomic notes referencing its evolutionary relationship to extant, Vulnerable-listed Zaglossus species in New Guinea.

• Largest Monotreme Ever: Zaglossus hacketti is the largest monotreme known to science, estimated to have weighed up to 30 kilograms (66 lbs)—roughly the size of a large dog or small sheep, dwarfing its living echidna relatives.
• Named After a Pioneering Paleontologist: The species was named in honor of Winifred Hackett, an early 20th-century amateur naturalist and fossil collector who contributed significantly to excavations at Mammoth Cave, Western Australia.
• Known Only From Fragmentary Fossils: The entire species is described from a handful of limb bones (humerus, femur, and other postcranial elements) recovered from cave deposits, meaning much of its anatomy is reconstructed by scaling up from living echidnas.
• A Pleistocene Megafauna Survivor Turned Casualty: It coexisted with other iconic Australian megafauna such as Diprotodon and giant short-faced kangaroos, all of which vanished in the same broad extinction wave.
• Electroreception in a Giant Package: Like all monotremes, it likely possessed electroreceptors in its snout, allowing it to detect the faint electrical signals generated by muscle contractions of hidden invertebrate prey.
• Egg-Laying Giant: Despite its immense size compared to modern echidnas, Z. hacketti almost certainly retained the ancestral monotreme trait of laying eggs rather than giving live birth.
• Living Relatives Still Endangered: Its closest surviving relatives, the long-beaked echidnas of New Guinea (genus Zaglossus), are today listed as Critically Endangered or Vulnerable, making this extinct giant a haunting reminder of the fragility of the echidna lineage.