The marsupial mole, Notoryctes, an enigmatic creature inhabiting the sandy landscapes of Australia, has long puzzled scientists regarding its evolutionary lineage. Its highly specialized adaptations for a subterranean lifestyle, including a lack of external ears and functional eyes, a backward-facing pouch, and powerful digging forelimbs, made it challenging to determine its closest relatives. For decades, the true identity of this elusive mammal remained a subject of debate. Even within Australia, these small, hand-sized creatures are rarely seen, their existence unknown to many. Early European settlers were intrigued by reports of this "new Australian mammal" in the late 19th century, speculating on its classification as a marsupial or otherwise. However, the Indigenous peoples of central Australia, who lived near the now Uluṟu-Kata Tjuṯa National Park, were already familiar with the marsupial mole, incorporating it into their cultural stories and traditions.
Recent genetic analysis, using a frozen museum specimen, has finally shed light on the marsupial mole’s evolutionary history, confirming its place within the marsupial family. The backward-facing pouch, a unique adaptation, likely aids the female in navigating sandy terrain while carrying her young. Unlike other mole species, Notoryctes doesn’t construct permanent tunnels. Instead, it “swims” through loose sands and dunes, pushing its way through the substrate. The researchers also identified a supplementary hemoglobin gene, which may enhance the mole’s oxygen-carrying capacity, enabling it to survive in oxygen-poor underground environments. Further supporting their marsupial classification, genetic evidence revealed genes associated with abdominal testes, a characteristic shared by several other subterranean mammals. This adaptation eliminates the external scrotum, potentially reducing drag while moving through the soil.
The specific evolutionary branch from which Notoryctes originated presented a more complex puzzle. The extreme anatomical modifications associated with subterranean life often obscure evolutionary relationships. The two extant Notoryctes species exhibit streamlined, almost beanbag-like bodies, perfectly suited for navigating tight spaces. Their forelimbs have evolved into powerful digging tools, and their testes are retained within the abdomen, unlike surface-dwelling mammals. The lack of external ears and eyes, replaced by a fur-covered face with a prominent, fleshy "shield," further distinguishes them from their above-ground relatives.
The genetic analysis reveals a surprising kinship between the marsupial mole and two superficially dissimilar marsupials: bilbies and bandicoots. Bilbies, with their rabbit-like appearance, and bandicoots, resembling large shrews with pointed snouts, inhabit surface environments and possess functional eyes and ears. Despite their striking differences in appearance, this study, along with another recent genetic analysis, firmly places marsupial moles, bilbies, and bandicoots within a closely related group, highlighting the dramatic impact of subterranean adaptations on morphology. This evolutionary grouping presents a compelling example of adaptive radiation, where a common ancestor gives rise to diverse lineages, each specializing in a particular niche.
The marsupial mole, bilbies, and bandicoots form a sister group to Tasmanian devils and several other non-mole-like species, further emphasizing the evolutionary distance between Notoryctes and other animals commonly referred to as moles, such as true moles and mole-rats. This evolutionary placement demonstrates the profound anatomical transformations that can occur when a lineage transitions to an entirely subterranean existence. The marsupial mole’s unique adaptations underscore the power of natural selection to shape organisms for their specific environments, even to the point of dramatic divergence from their closest relatives.
The identification of Notoryctes as a true marsupial, closely related to bilbies and bandicoots, resolves a long-standing evolutionary mystery. This discovery emphasizes the importance of genetic analysis in uncovering hidden relationships and demonstrates the remarkable plasticity of the mammalian body plan in response to environmental pressures. The marsupial mole stands as a testament to the extraordinary diversity of life, particularly within the unique fauna of Australia. Its specialized adaptations, including the backward-facing pouch and extra hemoglobin gene, provide invaluable insights into the evolutionary processes that shape life underground. Further research on these elusive creatures will undoubtedly continue to unravel the intricacies of their biology and evolutionary history, contributing to our understanding of the remarkable adaptability of life on Earth.
