MSGID: 1:317/3 646ee477   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Move over, armadillos: There's a new bone-plated mammal in town    
      
     Date:   
         May 24, 2023   
     Source:   
         Florida Museum of Natural History   
     Summary:   
         Armadillos have long been considered to be the only living   
         mammals that produce protective bony plates. But a new study   
         unexpectedly shows that African spiny mice produce the same   
         structures beneath the skin of their tails, which until now had   
         gone largely undetected.   
      
      
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   FULL STORY   
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   Mammals are a bit odd when it comes to bones. Rather than the bony   
   plates and scales of crocodiles, turtles, lizards, dinosaurs and fish,   
   mammals long ago traded in their ancestral suit of armor for a layer of   
   insulating hair.   
      
   Armadillos, with their protective and flexible shell of imbricated bone,   
   are considered the only living exception. But a new study, published in   
   the journal iScience, unexpectedly shows that African spiny mice produce   
   the same structures beneath the skin of their tails, which until now   
   had gone largely undetected.   
      
   The discovery was made during routine CT scanning of museum specimens   
   for the openVertebrate program, an initiative to provide 3D models of   
   vertebrate organisms for researchers, educators and artists.   
      
   "I was scanning a mouse specimen from the Yale Peabody Museum, and the   
   tails looked abnormally dark," said co-author Edward Stanley, director   
   of the Florida Museum of Natural History's digital imaging laboratory.   
      
   He initially assumed the discoloration was caused by an imperfection   
   introduced during the specimen's preservation. But when he analyzed the   
   X-Rays several days later, Stanley observed an unmistakable feature he   
   was intimately familiar with.   
      
   "My entire PhD was focused on osteoderm development in lizards. Once the   
   specimen scans had been processed, the tail was very clearly covered   
   in osteoderms."  Spiny mice osteoderms have been observed at least   
   once before and were noted by German biologist Jochen Niethammer,   
   who compared their architecture to medieval stonework in an article   
   published in 1975. Niethammer correctly interpreted the plates as being   
   a type of bone but never followed up on his initial observations, and   
   the group was largely overlooked for several decades -- until scientists   
   discovered another, seemingly unrelated peculiarity of spiny mice.   
      
   A study from 2012 demonstrated spiny mice can completely regenerate   
   injured tissue without scarring, an ability common in reptiles and   
   invertebrates but previously unknown in mammals. Their skin is also   
   particularly fragile, tearing at roughly one-fourth the amount of force   
   required to injure the skin of a common mouse. But spiny mice can heal   
   twice as fast as their relatives.   
      
   Researchers hoping to find a model for human tissue regeneration   
   have begun mapping the genetic pathways that give spiny mice their   
   extraordinary powers of healing. One such researcher, Malcolm Maden, just   
   so happened to have a lab in the building across from Stanley's office.   
      
   "Spiny mice can regenerate skin, muscle, nerves, spinal cord and perhaps   
   even cardiac tissue, so we maintain a colony of these rare creatures for   
   research," said Maden, a biology professor at the University of Florida   
   and lead author on the study.   
      
   Maden and his colleagues analyzed the development of spiny mice   
   osteoderms, confirming they were in fact similar to those of armadillos   
   but had most likely evolved independently. Osteoderms are also distinct   
   from the scales of pangolins or the quills of hedgehogs and porcupines,   
   which are composed of keratin, the same tissue that makes up hair,   
   skin and nails.   
      
   There are four genera of spiny mice, which all belong to the subfamily   
   Deomyinae. However, aside from similarities in their DNA and potentially   
   the shape of their teeth, scientists have been unable to find a single   
   feature shared among species of this group that distinguishes them from   
   other rodents.   
      
   Stanley, suspecting their differences might only be skin deep, scanned   
   additional museum specimens from all four genera. In each, he found spiny   
   mice tails were covered in the same sheath of bone. The closest relatives   
   of Deomyinae -- gerbils -- lacked osteoderms, meaning the trait had likely   
   evolved just once, in the ancestor of erstwhile disparate spiny mice.   
      
   The ubiquity of osteoderms in the group indicate they serve an important   
   protective function. Just what that function might be wasn't immediately   
   apparent, however, due to yet another peculiar attribute of spiny mice:   
   Their tails are uncharacteristically detachable. Tail loss is so common   
   in some spiny mouse species that nearly half the individuals of a given   
   population have been shown to lack them in the wild.   
      
   "This was a real head-scratcher," Stanley said. "Spiny mice are famously   
   able to deglove their tails, meaning the outer layer of skin comes off,   
   leaving behind the muscle and bone. Individuals will often chew off   
   the remainder of the tail when this happens."  Despite their powers of   
   regeneration, tail shedding is a trick that spiny mice can only perform   
   once. Unlike some lizards, they can't regrow their tails, and not every   
   part of the tail separates easily.   
      
   To find out why rodents that seem ambivalent about keeping their tails   
   would go through the trouble of covering them in armor, the authors   
   turned to a group of similarly odd fish-tale geckos from Madagascar. Most   
   geckos lack osteoderms, but as their name implies, fish-tale geckos are   
   covered in thin, overlapping plates, and just like spiny mice, they have   
   incredibly fragile skin that sheds at the slightest provocation.   
      
   According to Stanley, the osteoderms in fish-tale geckos and spiny mice   
   possibly function like a type of escape mechanism.   
      
   "If a predator bites down on the tail, the armor might keep the teeth   
   from sinking into the tissue beneath, which doesn't detach," he said. The   
   outer skin and its complement of bone plating pull away from the tail   
   when attacked, affording the mouse a quick escape.   
      
       * RELATED_TOPICS   
             o Plants_&_Animals   
                   # Mice # Rodents # Genetically_Modified # New_Species   
             o Earth_&_Climate   
                   # Ozone_Holes # Earth_Science   
       * RELATED_TERMS   
             o Adipose_tissue o Salamander o Oceanic_trench o Virus o   
             Lemming o Volcano o Plate_tectonics o Toxicodendron   
      
   ==========================================================================   
   Story Source: Materials provided by   
   Florida_Museum_of_Natural_History. Original written by Jerald   
   Pinson. Note: Content may be edited for style and length.   
      
      
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   Journal Reference:   
      1. Malcolm Maden, Trey Polvadore, Arod Polanco, W. Brad Barbazuk,   
      Edward   
         Stanley. Osteoderms in a mammal the spiny mouse Acomys and the   
         independent evolution of dermal armor. iScience, 2023; 106779 DOI:   
         10.1016/j.isci.2023.106779   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/05/230524181855.htm   
      
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