Conservation implications of a new fossil species of hopping-mouse, Notomys magnus sp. nov. (Rodentia: Muridae), from the Broken River Region, northeastern Queensland

By: Vakil, V., Cramb, J., Price, G. J., Webb, G. E., and Louys, J. 

Summarized by: Mena Coles-Carruthers is a senior biological science major and environmental studies minor at Binghamton University. Mena is interested in ecology and evolution and enjoys learning new things about science every day. She loves to cook, bake, sing in choir, and hike in upstate New York. She can’t wait to pursue a career in biology and hopes to contribute to our collective knowledge of organisms and how they interact with their environment.

What data were used? Scientists have discovered new Australian hopping-mouse fossils from the genus Notomys. Five jaw and molar samples were found in the Tripot and Beehive Caves in the Broken River Provence of northern Australia. Researchers compared their data from these specimens with descriptions of other hopping-mouse species and museum specimens (from the Australian Museum, the Melbourne Museum, and the Queensland Museum), primarily examining the differences in the teeth, jaws, and body size between the specimens. 

What was the hypothesis being tested (if no hypothesis, what was the question or point of the paper)? The main point of this paper was to determine whether the new fossils were a novel species of Notomys, and to assess what this meant for the conservation of other hopping-mice and mammals all across Australia.

Methods: Rock samples were collected from the cave, then acid-digested in dilute acetic acid and wet-sieved through mesh to recover vertebrate fossils and separate them from the surrounding rock. Researchers extensively described the morphology of the jaw and molars and compared their fossils with museum specimens and descriptions of other species of Notomys available in published scientific research. They also used a regression equation to estimate organisms’ body mass based on their mean upper molar row length (the combined length of three molars), using published data on six Notomys species, along with measurements of the N. magnus samples.

Results: The researchers have determined that the discovered fossils are, in fact, a new species of the Australian hopping-mouse Notomys called Notomys magnus. This novel extinct species likely had a temporal range spanning the mid-Pleistocene to the early Holocene (~781,000–ad10,000 years ago). At an estimated mass of 83.2 g, N. magnus is considered to be a larger-bodied Notomys and is more massive than four of the six species with estimated body masses in this study. N. magnus falls into the critical weight range for mammals, meaning it is particularly susceptible to extinction. Since N. magnus was discovered alongside arid (desert)-adapted taxa, and most Notomys live in dry or desert-like climates, the new species is thought to be arid-adapted or open-habitat adapted. This means it likely had the ability to hyper-concentrate its urine so that it required less water, along with other helpful adaptations.

Why is this study important? Of the ten discovered species of Australian hopping-mouse, eight are considered extinct, vulnerable, near-threatened, or endangered. The newly discovered fossil mouse provides additional evidence that modern Notomys species may be at risk of extinction. The specific reason for the decline of many species of Notomys in the late Holocene (i.e. modern times) is not yet completely understood. This gap in information could be a hindrance on conservation efforts for modern hopping-mouse populations, as well as other mid-size mammals. Scientists are trying to gain as much knowledge as they can using the data they have available, and they are constantly using new information they learn about the past to inform our understanding of the present and future state of mammal conservation. The discovery of this new extinct species has further narrowed the organisms of concern to be larger bodied Critical Weight Range mammals, so researchers can use this to direct funding and research where it may be more needed. Additionally, the finding of this new species has highlighted a gap in knowledge about arid-adapted mammals in northern Australia.

Broader implications beyond this study: Critical Weight Range (35-3500g) mammals of Australia, especially those that are ground-dwelling, are thought to have declined the most rapidly in the last few hundred years. These critters are of mid-range body weight and are especially abundant during the late Quaternary Period. They are thought to be at higher risk of extinction due to the prey preferences of some introduced invasive predators. Some recently found extinct species in this category include organisms such as the Christmas Island Pipistrelle and the Bramble Cay melomyses. This newly discovered species (N. magmus) further validates the idea that Critical Weight Range species are most susceptible to extinction and may broaden the range of previously thought at-risk populations to the tropical north of Australia. 

Scientists think many extinct species of Notomys may have gone extinct due to European colonization of Australia as a response to pressures such as the introduction of non-native predators (like cats and red fox), loss of habitat, and a changing climate. This knowledge, when combined with ecological and genetic studies, could aid in conservation efforts on Australian mammals. However, if conservation efforts are not put in place for Australia’s other mid-sized mammals and rodents, they could also go extinct when they face similar pressures due to recent changes in environments, habitat, and climate. 

Citation: Vakil, V., Cramb, J., Price, G. J., Webb, G. E., & Louys, J. (2023). Conservation implications of a new fossil species of hopping-mouse, Notomys magnus sp. nov. (Rodentia: Muridae), from the Broken River Region, northeastern Queensland. Alcheringa: An Australasian Journal of Palaeontology, 47(4), 590–601. https://doi.org/10.1080/03115518.2023.2210192