At least hundreds of previously unidentified mammal species are hiding in plain sight around the world, Ohio State University researchers conclude in a new study published in the journal Proceedings of the National Academy of Sciences (PNAS). The authors found that most of these hidden mammals are small-bodied, many of them bats, rodents, shrews, and moles.
The authors explain that these unknown mammals are hidden from the naked eye in part because most are small and look so much like known animals that biologists have been unable to recognize that they are actually a different species.
“Small, subtle differences in appearance are harder to notice when you’re looking at a tiny animal that weighs 10 grams than when you’re looking at something the size of a human,” says Bryan Carstens, professor of evolution, ecology, and organismal biology at the University Ohio State (USA).
“You can’t tell they’re different species unless you do genetic analysis.”
The team used a supercomputer and machine learning techniques to analyze millions of publicly available gene sequences from 4,310 mammalian species, as well as data on where the animals live, their environment, life history, and other relevant information.
This allowed them to build a predictive model to identify mammalian taxa likely to contain hidden species. “Based on our analysis, a conservative estimate would be that there are hundreds of mammal species around the world that have yet to be identified,” Carstens says. In his opinion, that finding, in itself, would not surprise biologists. Researchers have only formally described between 1 and 10% of Earth’s species. “What we did that was new was predict where these new species are most likely to be found,” he continues.
The results showed that unidentified species are more likely to be found in families of small-bodied animals, such as bats and rodents.
The researchers’ model also predicted that the hidden species would likely be found in species that have broader geographic ranges with greater variability in temperature and precipitation.
It was not one, but five
Many of the hidden species are likely to be found in tropical rainforests as well, which is not surprising because that’s where most mammal species are found. But it is just as likely that many unidentified species live in a place as inhabited by humans as the United States. Carstens’ lab has identified some of them. For example, in 2018, they published an article showing that a little brown bat found across much of North America is actually five different species.
That study also showed a key reason why it is important to identify new species. One of the newly identified bats had a very narrow home range, just around the Great Basin in Nevada, making its protection especially critical.
“That knowledge is important for people who are doing conservation work. We cannot protect a species if we do not know it exists. As soon as we name something as a species, that matters in a lot of legal and other ways,” Carstens muses.
According to the results of this study, the researcher estimates that about 80% of the mammal species in the world have been identified. “The shocking thing is that mammals are very well described compared to beetles or ants or other kinds of animals,” he says. “We know a lot more about mammals than we do about many other animals because they tend to be larger and more closely related to humans, which makes them more interesting to us,” he says.
