A new armadillo species was hiding in plain sight

by milagroswan787
The newly described Guianan long-nosed armadillo.

The newly described Guianan long-nosed armadillo. Credit: © Quentin Martinez (https://quentinmartinez.fr/)

They’re scaly, covered in armor, and hiding a secret identity. Nine-banded armadillos (Dasypus novemcinctus), the idiosyncratic mammal that spans from southern Illinois to northern Argentina, are not actually one species after all. Instead, the group of these unusual animals is made up of four distinct species, according to a study published in June in the journal Systematic Biology

Armadillos are part of Xenarthra, the mammalian group native to the Americas that also includes anteaters and sloths. Though armadillos are a classic symbol of the southern U.S.–particularly Texas, where they’ve been a lovable mascot for everything from sports teams to chain restaurants, they’re actually relatively recent arrivals there. The armored animals first established themselves north of the Rio Grande in the late 1800s, after crossing the river of their own accord. Around the same time, the reptile-esque mammals were introduced by humans to Florida. Since then, they’ve continued to spread. In recent years, individual armadillos have been spotted as far north as Illinois and Indiana and as far east as Virginia. Why and how they’re managing to expand so widely remains a mystery, but now we’re learning more about the various species of these peculiar creatures.  

Through genetic and trait analysis, biologists say they’ve uncovered the covert variety hiding under the umbrella of the over-simplified armadillo clade. Previously, there’ve been 21 recognized species of armadillo, and so breaking one lineage into four represents about a 14% increase in ‘dillo diversity. In addition to broadening the armadillo family tree, the new divisions could have significant conservation implications as scientists consider the four species in a new context. 

Two of the newly defined species had been proposed as subspecies in past research. One of the species sticks with the name and description of the classic nine-banded armadillo. The fourth represents a previously undescribed species (the first within armadillos in 30 years). 

The news means that Texas’ state animal is getting re-named: It’s now the Mexican long-nosed armadillo (Dasypus mexicanus), which occupies the most northern part of the former Nine-banded armadillo’s range–from Costa Rica into the U.S. 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, encompassing most of South America, remains the official home of the nine-banded armadillo. 

Finally there’s the Guianan long-nosed armadillo (Dasypus guianensis). This never-before-described species inhabits the Guinean Shield, a 1.7 billion year old geological formation comprising multiple high-elevation regions underlying Guyana, Suriname, French Guiana, and part of Venezuela.  

A specimen of the new species, collected in 1961, in the Field Museum’s collections. Credit: Kate Golembiewski, Field Museum

“Each species now has a much more restricted distribution,” says Anderson Feijó, one of the study co-authors and assistant curator of mammals at the Field Museum of Natural History in Chicago. “This finding shifts the way we think about [these animals’] ecological requirements,” he adds. What was previously considered a broadly adaptable and wide-ranging animal, at no risk of losing ground, will now have to be re-considered four times over. It’s possible each species has different habitat needs or resources, and that–in some places–those aren’t being met.

“We’ll now have to reassess each of the four different entities,” Frédéric Delsuc, senior study author and an evolutionary biologist at the French National Center for Scientific Research. Delsuc is also part of the specialist group at the International Union for Conservation of Nature (IUCN) in charge of classifying where armadillo species should fall on the IUCN Red List. He is eager to evaluate each of the newly delimited four species, though he’s not immediately concerned about any of them, considering how frequently they’re splattered on roads, he says, indicating they’re probably “quite numerous.”

Though sad for armadillos, the mammals’ tendency to end up beneath the wheels of cars was actually a boon to the researchers. A little over half of their 80 total armadillo samples came from dried samples–mostly museum specimens. But 34 samples were collected fresh in the field, “mostly from roadkill,” says Delsuc. 

Using these armadillo bits taken from across the entire, former nine-banded range, the scientists extracted both mitochondrial and nuclear DNA. They conducted multiple analyses to parse out the exact relationships among their 80 study animals. In one type of analysis, they repeatedly grouped the individuals by genetic similarity, and found four clusters popping up over and over again. In another type of analysis, they assessed gene flow between these clusters. Although they found some evidence of hybridization, these instances were rare and only observed at the margins of each group’s range. “All of this supports these four lineages as distinct species,” says Mathilde Barthe, the lead study author who recently completed her PhD in molecular evolution at the University of Montpellier in France. 

It’s unclear how long ago each of the armadillo branches diverged, but the presence of low levels of hybridization indicates it was likely relatively recent, on the scale of evolutionary time, notes Delsuc.

Thorough genetic analysis was critical to discovering and defining the species split because, for the most part, all four species look visually similar to each other. On first glance or in the field, “it’s very hard to tell them apart,” says Feijó. However there are subtle differences in skull shape that make it possible for experts to distinguish skeletal specimens, says Delsuc. And the new Guianan species is most distinct from the others. It’s slightly larger, has a hairless shell, one additional vertebrate, and a domed, thick skull, according to Feijó’s formal description. Additional study could find that the species diverge in other ways, like behavior or diet. 

The new findings were 25 years in the making, and built on past studies of armadillo diversity. However, there are still some limitations. The DNA contained in museum samples is often contaminated and degraded. The scientists took “special care,” to reduce the impact of that potential contamination and filter their data, says Barthe–but some quirks may have fallen through the cracks. Still, none of the researchers expect their proposal to stir much controversy. “The evidence has been piling up, and kind of leading to this final conclusion,” says Feijó. 

There is still so much to learn, even about mammalian biology. “Usually, people assume mammals are a very well known group,” says Feijó. “But the reality is we are just learning.” Today, there’s four newly defined species. Tomorrow, he notes there’s probably even more to come.

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