Mammals are some of the most well-studied animals on the planet, but hundreds of unidentified species could still be hiding in plain sight.
It is estimated that only one to ten percent of Earth's species have been formally described in the scientific literature. The phenomenon, called the Linnean Shortfall, means that there is a discrepancy between the number of species with taxonomic descriptions and the number of actual living species roaming Earth, which can introduce challenges for preserving biodiversity.
To help solve the issue, researchers used machine learning, genetic sequences of mammals, and data about their habitats to create a predictive modeling tool. The team found most of these unknown hidden species could be hundreds of small mammals like bats, rodents, moles, and shrews, reports Patrick Greenfield for the Guardian.
These mammals are often misclassified as other species because some can look similar, or their size alone makes it difficult to point out critical morphological differences. Some species that are in fact different from one another are often taxonomically lumped together, Science Alert's Carly Cassella reports.
"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 that is human-sized," study author Bryan Carstens, an evolutionary biologist at Ohio State University, said in a statement. "You can't tell they are different species unless you do a genetic analysis."
Previous models have predicted that 80 percent of mammals have already received a formal classification. However, with more than 6,400 mammal species described on record, it means that there may still be more than 1,000 unknown species, reports Science Alert.
Using the machine learning model, the team analyzed the geographic and biological data of over 4,000 mammals to identify which groups, or taxon, are likely to have unreported species. Bats, rodents, hedgehogs, and shrews are among the orders predicted to have the most undescribed mammals, per Science Alert. Further, the team also found that these orders are found in wide geographic ranges with high variation in temperatures and precipitation, reports the Guardian.
Many hidden species are most likely living in tropical rainforests, a statement explains. This finding isn't surprising since rainforests hold the most mammal diversity on the planet.
However, many unidentified species could be all around us. For example, in 2018, Carstens and Ariadna Morales, a graduate student, published a paper that found the little brown bat (Myotis lucifugus) is actually five different species, a statement explains.
The DNA-based analysis combined with traditional classification techniques developed by Swedish botanist Carl Linnaeus in the 1700s is helping scientists identify and reorganize life on Earth, per the Guardian. The team is calling for renewed funding in taxonomic research to close the gap between identified and unidentified mammal species.
"That knowledge is important to people who are doing conservation work. We can't protect a species if we don't know that it exists," Carstens explains in a statement. "As soon as we name something as a species, that matters in a lot of legal and other ways."