Spiny mice have armadillo-like armor in their tails

The spiny mouse is an unassuming rodent, however it’s armed with a really particular tail.

CT scans present the tail is sheathed in a secret blanket of bony plates. Earlier than the scans, just one different group of recent mammals was recognized to wield this sort of armor: armadillos. The invention, reported Could 24 in iScience, might imply that the pores and skin bones are extra widespread in mammals than beforehand thought and will make clear their evolution. 

The rodent’s secret was revealed when evolutionary biologist Edward Stanley of the Florida Museum of Pure Historical past in Gainesville put a museum specimen of a spiny mouse (Acomys spp.) in an X-ray machine as a part of a multi-institutional undertaking to develop 3-D digital fashions of all vertebrate life.

It was a “nondescript wanting” mouse with barely spiky fur, Stanley says. However within the preliminary X-ray, its tail regarded uncommon. “It regarded form of darkish and peculiar,” he says.

A extra detailed CT scan confirmed the mouse’s complete tail was coated in overlapping bony plates throughout the pores and skin, below the floor layers.

To grasp how the bony plates develop, Stanley and his colleagues teamed with Malcolm Maden, a developmental biologist on the College of Florida. The workforce scanned the tails of new child spiny mice up to those who have been 6 weeks outdated. Bony plates kind first close to the bottom of the tail after which because the mouse ages, develop down the tail to its tip. CT scans revealed that three different species in the identical subfamily because the spiny mouse even have armor-studded tails. 

These bony plates, known as osteoderms, might assist hold spiny mice and their kin alive. The rodents’ pores and skin is particularly fragile and simply tears off, notably on the tail. It’s hypothesized that the tearaway pores and skin is a macabre protection, the place attacking predators are left with a mouthful or paw filled with shed pores and skin. The plates might stop predators from piercing too deep.

“In case you can cease the tooth or the claws of your predator on the tearaway boundary, then it’s a lot simpler to get away,” Stanley explains. The mice regenerate the misplaced pores and skin later.

However the tail’s pores and skin bones would possibly defend in opposition to extra than simply predators. For some cause, spiny mice routinely chunk one another’s tails, says Ashley Seifert, a developmental biologist on the College of Kentucky in Lexington. “So perhaps they’ve developed osteoderms as armament, however to defend their tails from one another as an alternative of predators.”

To higher perceive the organic underpinnings of the bony pores and skin, the researchers took pores and skin samples from the tails of new child spiny mice in locations with and with out osteoderms and analyzed gene exercise. 

In pores and skin samples with osteoderms, the exercise of a collection of genes related to bone cell improvement was boosted in contrast with samples with out osteoderms. However the exercise of genes that make keratin, a key constructing block for pores and skin, was ramped down. The subsequent step, Maden says, is to see how all these genes really develop the osteoderms.

The analysis may assist present insights into osteoderm evolution. Bony pores and skin is present in a wide range of reptile teams, having developed independently in crocodilians, many various lizard teams and a few dinosaurs (however no birds) (SN: 12/6/22). Madagascar’s fish-scaled geckos have osteoderms and shed pores and skin like spiny mice. Other than the rodents within the new research and armadillos, the one different recognized mammals with bony pores and skin are all extinct: an historical hedgehog-like animal known as Pholidocercus, floor sloths and armadillo kin known as glyptodonts (SN: 2/22/16).

Delving into gene exercise patterns isn’t finished in osteoderm analysis, says Chris Broeckhoven, an evolutionary biologist on the College of Antwerp in Belgium. Having this comparative information from mice accessible may yield key evolutionary insights.

One key perception, Maden says, may very well be “why [osteoderms] hold showing in evolution after which disappear.”

It’s additionally doable osteoderms are extra frequent amongst vertebrates than beforehand thought. No snakes have been recognized to have the bony pores and skin after which in April researchers reported discovering them in sand boas.

These discoveries are “an excellent instance of how it’s best to take a look at the world round you,” Maden says. “Who is aware of what you’ll uncover.”