A hairy issue

If you happened to read my January blog on armadillos, you may recall these armored South American mammals and their kin are placed in the order Cingulata, which means “belted ones.” You may also recall that the closest relatives of these armored mammals are sloths and anteaters, which are grouped with cingulates in the supraordinal group Xenarthra.

One thing I did not mention in that blog is the name of the sloth-anteater group: Pilosa, which means “hairy ones.” Most mammals have hair, so this might not strike you as a particularly useful name. But among xenarthrans, sloths and anteaters are quite hairy compared to armadillos, most of which appear almost naked by comparison. Probably the most conspicuous exception to this generalization is an armadillo that bears the specific epithet pilosus in reference to its remarkably hairy body: the hairy long-nosed armadillo.

The hairy long-nosed armadillo was named more than 150 years ago by J.L. Fitzinger based on a skin he purchased from an animal dealer in London (Castro et al. 2015). He placed the species in its own genus, Cryptophractus, which essentially means “hidden shell,” because its long, thick fur almost completely covers its carapace, effectively hiding it from view.

Figure 1 Mounted Specimen.jpg
The holotype specimen (NMW 222) of the hairy long-nosed armadillo that was described by Fitzinger in 1856. The specimen is in the collections of the Naturhistorisches Museum Wien in Vienna, Austria. Photograph by F. Zachos, courtesy of M. Castro.

It turns out that the name the Cryptophractus was particularly appropriate for this animal for another reason: it is one of the least-known, if not THE least-known, xenarthran alive today. It is only found in the Andes of central Peru, and within that region, it is apparently restricted to areas at about 2,200-3,600 m elevation (7,000-12,000’) that receive at least 60 cm of rainfall annually (about 24”). Barely two dozen specimens of the hairy long-nosed armadillo have ever been collected, and virtually no information is available about its natural history (Feng et al. 2017). As of 2014, only three scientific papers had ever been published on the species (Superina et al. 2014). Your best chance to see one is by visiting the Museo de Historia Natural of the Universidad Nacional Mayor de San Marcos in Lima, which may be the only museum to have a mounted specimen on display. This is not an animal you can go see in a zoo.

Figure 2 Map New.jpg
Documented range of the hairy long-nosed armadillo based on specimens with known collection data (red dots) and its potentially suitable habitat based on its inferred ecological tolerances (blue shading). Note how little of the armadillo’s estimated range is within protected areas, which are outlined in orange. From Feng et al. (2017:fig. 4).

The hirsute nature of the hairy long-nosed armadillo is also clearly evident in the bones of its shell. These osteoderms have very large pits on their surface for housing hair follicles and their associated glands. The most likely explanation for this armadillo’s thick fur is that it insulates the animal in its relatively cool mountain habitat. Armadillos as a group tend to be limited by cold temperatures (this is why the nine-banded armadillo has not spread as far north as some other immigrants from South America), and long-nosed armadillos lack insulating fat in their osteoderms unlike some other cold-adapted armadillos (Krmpotic et al. 2015). The hairy long-nosed armadillo is about the same size as a nine-banded armadillo but has more moveable bands in its shell (up to 11), a longer snout, and a variety of other, more subtle distinguishing features.

Figure 3 Osteoderms.jpg
Osteoderms (shell bones) of the hairy long-nosed armadillo (Dasypus pilosus, left) compared to the nine-banded armadillo (D. novemcinctus, right). The illustration in the center depicts some of the hair and keratinous scales (gray shading) covering the osteoderms as well as the osteoderms themselves. Note the greater size and abundance of pits on the osteoderms of D. pilosus compared to D. novemcinctus, a reflection of the thick fur coat of the hairy long-nosed armadillo. Photograph courtesy of M. Castro. Illustrations from Castro et al. (2015:fig. 5).

But how different is this armadillo in an absolute sense? Like everything in taxonomy – the science of naming and grouping species – this is a matter of discussion. In 1928, one expert decided that the hairy long-nosed armadillo was not that different from the nine-banded armadillo and kin, so he shifted the species to the genus Dasypus. Its scientific name became Dasypus pilosus. Three decades later, researchers took a compromise position and made Cryptophractus a subgenus of Dasypus, creating the scientific name Dasypus (Cryptophractus) pilosus.

Never heard of a subgenus? You are not alone. The number of taxonomic ranks (categories) is almost endless thanks to various prefixes that exist for elevating and demoting commonly recognized ranks such as classes, orders, and families. A subgenus allows taxonomists to group species together within a genus to indicate which ones are more closely related to one another. Most long-nosed armadillos are in the subgenus Dasypus. (Yes, the genus and subgenus names can be exactly the same.)

In 2015, Mariela Castro and colleagues revisited the DasypusCryptophractus issue by conducting a thorough anatomical study of the hairy-long nosed armadillo and analyzing its evolutionary relationships based on characters of the skull, armor, and skeleton (Castro et al. 2015). Their analysis suggested that the hairy long-nosed armadillo diverged from other species of Dasypus relatively early. That observation, combined with the original concept of the genus Dasypus, led the authors to conclude that the hairy long-nosed armadillo should be placed in its own distinct genus, Cryptophractus, rather than just a subgenus of Dasypus.

Just last year, the first comprehensive molecular analysis of armadillo evolutionary relationships was published, and it painted a very different picture of long-nosed armadillo evolution (Gibb et al. 2016). Its authors found that the hairy long-nosed armadillo was among the last species of the group to evolve rather than the first; they estimated that its lineage diverged from that of the nine-banded armadillo less than 3 million years ago. As a result, they concluded that there is no reason to place it in a distinct genus. However, they did suggest that the greater long-nosed armadillo, Dasypus kappleri, a species that was placed in its own subgenus in the late 1970s, probably SHOULD be given distinct generic status as Hyperoambon kappleri. If accepted, this genus could include three species rather than just one, as a study published last year proposed that two subspecies of greater long-nosed armadillos should be recognized as species in their own right (Feijó and Cordeiro-Estrela 2016).

FIgure 4 Phylogeny.jpg
Evolutionary relationships of long-nosed armadillos (Dasypus spp.) based on skeletal characters (A) and mitochondrial DNA (B), with the position of the hairy long-nosed armadillo highlighted in green. Estimated times of divergence of the different lineages are indicated by white bars in B. A is modified from Castro et al. (2015:fig. 2) and B is modified from Gibb et al. (2016:fig. 2).

Got all that? If not, don’t worry; things will probably change over the next few years. That’s how things work with taxonomy and systematics. But here are a few important take-home messages.

First, whatever the proper scientific name of the hairy long-nosed armadillo may be, it is one pretty neat example of the morphological and ecological diversity of living armadillos! Do you think you would recognize it as an armadillo if you were to see one in the wild? Maybe, maybe not. But you would certainly be very lucky to have seen it.

Second, there is still an awful lot that we do not know about mammals alive today. As a paleomammalogist, I am constantly searching for the remains of species that we never knew existed and trying to determine how they fit into ancient ecosystems. But there are plenty of mammalogists doing the same thing for species that still exist today. I am certain there are several wonderful PhD dissertations just waiting to be written about the life and times of the hairy long-nosed armadillo.

Finally, taxonomy isn’t usually viewed as exciting or interesting, but since it reflects our current understanding of evolutionary relationships, it is as dynamic as evolution itself. The biggest challenge is that our taxonomic system was invented by humans to make sense of a natural world that often defies classification.

References cited:

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