They are scaled, covered in armor, and hide a secret identity. Nine-banded armadillos (Dasypus novemcinctus), the idiosyncratic mammal that ranges from southern Illinois to northern Argentina, are not in fact one species. Instead, the group of these unusual animals consists of four different species, according to A study published in June in the magazine Systematic biology.
Armadillos are part of Xenarthra, the mammal group native to the Americas that also includes anteaters and sloths. Although armadillos are a classic symbol of the American South, particularly Texas, where they have been a lovable mascot for everything from sports teams Unpleasant chain restaurantsthey actually arrived relatively recently. The armored animals first settled north of the Rio Grande late 1800safter they crossed the river on their own. Around the same time, the reptilian mammals were introduced to Florida by humans. They have continued to spread since then. In recent years, individual armadillos have been reported as far north as Illinois and Indiana and as far east as as Virginia. Why and how they manage to spread so widely remains a mystery, but now we are learning more about the different species of these remarkable creatures.
Through genetic and trait analysis, biologists say they’ve uncovered the secret variety lurking beneath the umbrella of the oversimplified armadillo clade. Previously, there were 21 recognized species of armadillo, so splitting one lineage into four represents a roughly 14 percent increase in dillo diversity. In addition to broadening the armadillo family tree, the new classifications could have significant conservation implications, as scientists view the four species in a new context.
Two of the newly defined species were proposed as subspecies in past research. One of the species sticks to the name and description of the classic nine-banded armadillo. The fourth represents a previously undescribed species (the first within the armadillos in 30 years).
The news means the state animal of Texas is getting a new name: it's now the Mexican long-nosed armadillo (Dasypus mexicanus), which covers the northernmost part of the nine-banded armadillo's former range – from Costa Rica to the US. And then there's Dasypus fenestratus living in the western Andes from Costa Rica through Ecuador, northern Columbia and northern Venezuela. Only the southernmost part of the former nine-banded range, which includes most of South America, is still the official home of the nine-banded armadillo.
Finally, there is the Guyanese long-nosed armadillo (Dasypus guianensis). This previously undescribed species inhabits the Guinea Shield, a 1.7-billion-year-old geological formation that encompasses several high-elevation areas underlying Guyana, Suriname, French Guiana and part of Venezuela.
“Each species now has a much more limited distribution,” says Anderson Feijóone of the study's co-authors and assistant curator of mammals at the Field Museum of Natural History in Chicago. “This finding changes the way we think [these animals’] ecological requirements,” he adds. What was previously considered a widely adaptable and widely distributed animal, with no risk of losing ground, will now have to be reconsidered four times over. It is possible that each species has different habitat needs or resources, and that – in some places – these are not being met.
“We will now have to reassess each of the four different entities,” Frederic DelsucDelsuc, the study’s senior author and an evolutionary biologist at France’s National Centre for Scientific Research, is also part of the specialist group at the International Union for Conservation of Nature (IUCN) responsible for classifying armadillo species on the IUCN Red List. He’d like to evaluate each of the four newly delineated species, though he’s not immediately concerned about any of them, given how often they’re smeared on roads, he says, indicating they’re likely “quite numerous.”
Although sad for armadillos, the mammals' tendency to get caught under the wheels of cars was actually a boon for the researchers. Just over half of their total 80 armadillo samples came from dried specimens, mainly museum specimens. But 34 samples were collected fresh in the field, “mainly from roadkill,” Delsuc says.
Using these armadillo pieces, taken from the entire former nine-banded range, the scientists extracted both mitochondrial and nuclear DNA. They conducted multiple analyzes to determine the exact relationships between their 80 study animals. In one type of analysis, they repeatedly grouped individuals by genetic similarity and found that four clusters emerged each time. In another type of analysis, they assessed gene flow between these clusters. Although they found some evidence of hybridization, these cases were rare and only observed at the edges of each group's range. “All this supports these four lineages as separate species,” says Mathilde Barthethe study's lead author who recently completed her PhD in molecular evolution at the University of Montpellier in France.
It's unclear how long ago the armadillo's different branches split off, but the presence of low levels of hybridization indicates that this was likely relatively recently, on the scale of evolutionary time, Delsuc notes.
In-depth genetic analysis was crucial to discovering and defining the species split, because all four species largely look similar visually. At first glance or in the field, “it’s very difficult to tell them apart,” Feijó says. But there are subtle differences in skull shape that allow experts to distinguish between skeletal specimens, Delsuc says. And the new Guianan species stands out the most from the others. It’s slightly larger, has a hairless carapace, one extra vertebrate and a domed, thick skull, according to Feijó’s formal description. Additional research could reveal that the species differ in other ways, such as behavior or diet.
The new findings were 25 years in the making and built on previous studies of armadillo diversity. There are still some limitations, however. The DNA in museum specimens is often contaminated and degraded. The scientists “took special care” to reduce the impact of that potential contamination and filter their data, Barthe says, but some oddities may have slipped through the cracks. Still, none of the researchers expect their proposal to cause much controversy. “The evidence has been piling up and has more or less led to this final conclusion,” Feijó says.
There is still so much to learn, even about mammal biology. “People usually assume that mammals are a very well-known group,” says Feijó. “But the reality is that we are just learning.” Today there are four newly defined species. Tomorrow he notes that there will probably be more to come.
