Happy Halloween — Attack of the Taxiderpy!

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Sometimes, it really isn’t your fault. You start off looking fabulous, but then time takes its inexorable toll.  Rust never sleeps and you seriously need a nose job.  Pangolin (Manis spp.) Image credit: Yale Peabody Museum / Curious Sengi.

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Other times, the best intentions of your preparator just goes a bit awry. . . .  Virginia opossum (Didelphis virginiana).  Image credit: Yale Peabody Museum / Curious Sengi.

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Then there are instances of– HOLY CRAP WHAT HAPPENED HERE?!?  Malayan or Sunda Colugo (Cynocephalus variegatus).  Image credit: Yale Peabody Museum / Curious Sengi.

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The Mole Hunter, Gillian Godfrey

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This mole (Talpa spp.) is delighted you are here!  Image credit:  Cani Animali e Natura.

In celebration of Mole Day, we honor the life and research of Dr. Gillian Godfrey, who is largely remembered for her work on the life history of moles (the furry, digging kind) and writing popular books on the subject.

Gillian was described as “an extremely shy but fiercely dedicated zoologist”, who was drawn to ecology despite the “abominable lectures” given at Oxford University by Professor Charles S. Elton (1900 – 1991).  After the term ended, she contacted Elton about joining his Bureau of Animal Population, but she did so with little expectation that she could have any hand in the scientific work going on there:

Her interview with Elton was awkward.  He told her he didn’t care to have women in the Bureau just yet. She offered to work as a bottle washer and that did the trick.  There wasn’t much future in bottle washing he retorted, so she had better come and do research (Crowcroft 1991).

Attitudes towards women in science in the 1950s was, at best, greeted with amusement or skepticism, but Gillian joined a group investigating vole (Microtus spp.) biology and pursued an ambitious research project on the “factors affecting the survival, movements, and intraspecific relations during early life” in vole populations (do not worry, the moles will come later).

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Vole (Microtus spp.)  Image credit: David Chapman via Saga Magazine.

The first step in this project was to induce the voles to nest so she could reliably return to her study subjects and trace their life histories.

With great single-mindedness, and almost no experience with hand tools, she set about mass producing nest boxes in D.K.’s [technician Denys Kempson’s] workshop.  After his initial consternation, not because of the possibility of her injuring herself, but because he feared she might damage his tools, he diplomatically suggested that she work undisturbed in the field store.  For many days the corridor echoed with the sounds of saw and hammer, and Gillian emerged with large numbers of wooden nest boxes with removable lids (Crowcroft 1991).

For all the work and enthusiasm poured into building nest boxes of all kinds of design, the voles were unappreciative of the effort and continued to built their own nests in clandestine locations (Crowcroft 1991).  So Gillian proceeded to comb every square inch of her study site, crawling about on her hands and knees, parting the long tussock grass, finding plenty of old nests, and learning more about the private life of voles than this frustrating exercise initially promised (Crowcroft 1991; Chitty 1996).  But this was no way to gather data for her project.

Then, in an inspired change of tactics brought about by the failure of the voles to use her nest boxes, she set out to trace their movements and find their nests by putting radioactive rings on their legs and finding them with a Geiger-Müller counter.  She was greatly assisted on the technical side by a physicist with amorous ambitions which were fruitless and ill-conceived.  Cobalt 60 wire was obtained. . . . before the Boss got wind of the project.  He was pretty upset by her initiative, but saw that the technique had such great possibilities that she got away with it.  This was the first time small mammals had been tracked in this fashion. . . . I [Crowcroft] still have some mental discomfort when I recall cutting up the wire for Gillian with two pairs of pliers, and rescuing bits that flew off by using the screaming Geiger counter (Crowcroft 1991).

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The portable Geiger-counter-on-a-stick used to trace the location of voles through the thick grass.  Image credit: Godfrey 1954.

It was a brilliant innovation, one Gillian claimed was inspired by the use of radioactive materials to track the movements of click beetles (Agriotes spp.) (Godfrey 1954).  By mounting a Geiger counter on the end of a pole, it was possible to sweep large areas of habitat and locate an individual animal (Mellanby 1971).  In writing up her novel methodology, Gillian acknowledged the advantage of this relatively non-invasive technique, since:  “Nearly all available information about small wild animals has been obtained by indirect methods. . . .and it is usually impossible to assess the errors introduced.  Trapping is frequently used in studies on movements but probably affects normal behaviour (Godfrey 1954).”

There were other breakthroughs to be had.  Crowcroft (1991) writes:

I can recall finding Gillian in the vole room, hands streaming with blood and face streaked with tears, bravely pressing on with vole examinations, and explaining with great embarrassment, “Oh, but they bite so hard!”  A few weeks later she was deftly holding them by the loose skin of the back with one hand, palpating the abdomen with the other.

One imagines that this determination and persistence carried Gillian through the tough years doing her doctorate.  While composing her thesis, she was caught in the cross-currents of opposing views held by her examiners.  Forced to write and re-write sections to appease these men who considered each other heretics, Gillian still navigated the conflicting torrents, and emerged triumphant.  She was granted a doctorate by Oxford University in 1953 and was the first woman to complete such a degree in the Bureau of Animal Population (Crowcroft 1991; Chitty 1996).

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What the radioactive tracking data look like for a single vole.  For this given research project, Gillian collected 709 recordings of 23 animals.  These maps showed the average distance between farthest points of capture was 29.04 yards (26.6 m), encompassing an area of 235.17 square yards (215.04 square meters).  Data like these provide important information on the life history and distribution of these small mammals.  Image credit: Godfrey 1954.

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Moles are incredibly adapted to life digging underground:  reduced, almost useless eyes, ears lacking any external pinnae, and powerful digging forelimbs.  Since moles spend nearly all their lives underground, it had been almost impossible to reliably track their daily movements.  Image credit: Mellanby 1971.

Gillian applied the same radioactive tagging technique to study the movement of moles (Talpa spp.), which are true insectivorans and not rodents like voles.  This method was ideal for tracking these secretive animals.  Instead of ringing the leg, a metal band with a soldered capsule containing radioactive Cobalt 60 was fixed to the mole’s conveniently club-shaped tail, which did not permit the ring to slip off when secured at the base.  The ring could be detected up to 30 cm (1 ft) underground using the Geiger counter.

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This drawing demonstrates the mole’s club-shaped tail:  constricted at the base and widening towards the end.  The black rectangle represents the position of the radioactive tracking ring.  The shape of the tail prevented the ring from slipping off.  Image credit: Mellanby 1971.

Even though Gillian’s tracking method became more sophisticated over the years, it was still a hazardous business to work with radioactive materials.  Though she only tracked one animal at a time, she still had to be careful that the animals did not escape from the study site and leave radioactive rings strewn all over the English countryside.  Of course, there was concern that prolonged exposure to Cobalt 60 would have a deleterious effect on the moles.  Despite all these dangers, Gillian discovered a lot about these animals, including their reproductive habits, home range, and propensity towards three bouts of periodic activity over a 24 hour period (Mellanby 1971).  In 1960, Gillian and her husband, Peter Crowcroft, a Tasmanian zoologist and zoo director (Chitty 1996), published The Life of the Mole, which received both academic and popular praise (Kettlewell 1961).

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Image credit:  Oxfam.

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Image credit: Amazon.co.uk.

Unfortunately, Gillian Godfrey’s own trail quickly goes cold.  Like many women of her time, Gillian was largely defined by her husband.  She married Peter Crowcroft in 1952, while they were still students together at Oxford (Lidicker & Pucek 1997).  We learn from an article in the Chicago Tribune that Peter was hired to be director of the Brookfield Zoo in 1968.  At the time, Gillian was researching marsupials at the University of Adelaide, but would soon leave to join Peter in Chicago.  Upon Peter’s death in 1996 at the age of 73, we read in his obituary that Gillian was, in fact, his second wife.  But at the time of publication, she had disappeared from the picture and Peter was survived by another wife, Lisette.

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Gillian seems to have retained her maiden name throughout her scientific career, but sometimes it was necessary to remind people to whom she was married.  Image credit: Godfrey 1954.

What happened to Gillian?  The answers are harder to find.  Radioactive tagging is no longer used to track animal movements in the field, so it is quite likely this contributed to her work fading from scientific consciousness.  But it was an ingenious solution to the problem of following shy, elusive animals in way that was least disruptive to their habits.  Were there more ingenious solutions to address new questions that sparked her interest?  I wish that I were able to find more information about Gillian’s later life and career, and that I could provide some kind of conclusion to this story.

So, Gillian, if you are out there, I hope you know that we think you are amazing!

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Gillian out the field, listening for radioactive small mammals.  Image credit: Godfrey 1954.

References

Australian New Zoo Head at Brookfield.”  Chicago Tribune.  7 February 1968:  4.  Chicago Tribune.  Web. Accessed 20 October 2016.

Chitty, Dennis.  1996.  “Do Lemmings Commit Suicide?  Beautiful Hypotheses and Ugly Facts.”  New York, NY:  Oxford University Press.

Crowcroft, Peter. 1991.  Elton’s Ecologists:  A History of the Bureau of Animal Population.  Chicago, IL:  The University of Chicago Press.

Kettlewell, H.B.D.  1961.  “All about the mole.”  New Scientist 9 (217):  107.

Lidicker, W.Z. & Z. Pucek.  1997.  “William Peter Crowcroft (1922 – 1996).”  Acta Theriologica 42 (3):  343 – 349.

Mellanby, Kenneth.  1971.  The Mole.  New York, NY:  Taplinger Publishing Company.  

Behind the Glass — Brontotheres

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Mondays are quiet here in the public galleries since the museum is closed to visitors.  So we took the opportunity to squeeze through some tight wall spaces and clamber into an exhibit case for an official photo shoot for YPM VP 12048, the type specimen for Brontops robustus.  The pebble-strewn ground is a lie.  It is actually a perilous game of walking on thin ice:  keep your weight on the bouncing planks of plywood, avoid falling through the chicken wire!  Of course, all those darned loose rocks covering everything make it impossible to see the difference. . . . . . Image credit: Yale Peabody Museum / Curious Sengi.

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Up close and personal.  This animal belongs to the Family Brontotheriidae.  Brontotheres are odd-toed ungulates (perissodactyls) and greatly resemble rhinos; however, modern analysis shows that this extinct lineage of mammals are most closely related to horses (Benton 2005).  Image credit: Yale Peabody Museum / Curious Sengi.

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Though a few areas of this skeleton may be reconstructed, what you see on display here is the real fossil!  This well-preserved and largely complete specimen was discovered in 1875 near Chadron in the northwest corner of Nebraska in Oligocene aged deposits (Osborn 1929).  Image credit: Yale Peabody Museum / Curious Sengi.

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Brontotheres (sometimes called by their older name, titanotheres) are the subject of a richly illustrated, two-volume masterwork by American Museum paleontologist Henry Fairfield Osborn (1857 – 1935).  The exact specimen on display today is reconstructed here in an illustration originally published by O.C. Marsh in 1889.  Image credit: Osborn 1929.

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The skeleton was actually mounted for display in 1916 under the direction of Richard Swann Lull (1867 – 1957), who studied under Osborn.  Unlike the static standing pose in the Marsh illustration, Lull opted to capture the moment of a charging run, with the pert little tail in the air with rhino-like indignation.  This exact same pose can be seen on display.  When Lull measured the skeleton after it was mounted, he reported the height at the shoulder to be 8 feet, 2 1/2 inches (2.5 meters).  Image credit: Osborn 1929.

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Fanciful reconstruction of life in a brontothere herd.  There used to be very different grazers out there on the Great Plains!  Image credit: Restoration by Erwin Christman & Charles R. Knight, reproduced in Osborn 1929.

References

Benton, Michael.  2005.  Vertebrate Paleontology, third edition.  Oxford:  Blackwell Publishing.

Osborn, Henry Fairfield.  1929.  Titanotheres of Ancient Wyoming, Dakota, and Nebraska, Vol. 1.  Washington, D.C.:  United States Government Printing Of

Colugos, or Snapshot of Life in a Snuggie

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What on earth is a colugo?!?  Sloth in a snuggie?  The potoo of mammals?  Despite the erroneous common name, “flying lemur”, colugos are gliders belonging to their very own distinctive group, the Order Dermoptera.  The share a common branch of the phylogenetic tree with treeshrews (Scandentia) and primates (Primates).  Malayan colugo (Galeopterus variegatus).  Image credit: David Yeo via gettyimages.

While researching last week’s post on specialized comb-like grooming structures in a variety of mammals and searching online for images of colugos, I noticed an astonishing number of photographs taken of this animal caught in the middle of, well, taking a poop.

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What is going on here?  Image credit: Crystal and Byran in Singapore.

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OK, I’m getting the picture here.  Image credit: My Blog.

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Image credit: Ecology Asia.

The pose is striking.  Colugos are enveloped in a snuggie-like wingsuit that extends around the body to form a gliding membrane called the patagium.  The rather long tail is also entrapped within this fabric of loose skin, looking like the pointed end of a diamond-shaped kite.  In order to keep this delicate membrane clean and in good order, defecation and urination happens in a vertical “standing” posture — usually the animal clinging on the trunk of a tree — and flipping up the tail, inverting the patagium over the back and exposing the nearly naked skin of the underside (Dzulhelmi & Abdullah 2009).  Wharton (1950) makes further observations on colugos captured from the wild.  Note that colugos are misleadingly termed “lemurs” here:

Captive lemurs can be stroked without much offense to the animals.  A sweet agreeable odor surrounds them.  They are clean.  When wet or dirty they can not rest until they have groomed themselves thoroughly.  To avoid solid excrement, which is a goat-like pill, or to urinate, they hang by the front legs from a branch, drop the hind legs and curl the tail over the back.  A pocket-like space just exterior to the anus is opened by this action.

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Step 1.

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Step 2.

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Image credit:  Step 3. Terrific series of a colugo doing its business. A vegetarian diet of leaves, flowers, fruits, buds, sap, and nectar keeps you regular (Dzulhelmi & Abdullah 2009). Image credit: tHE tiDE cHAsER.

Being caught at the toilet is a vulnerable moment for all of us, but perhaps even more so for the shy, elusive colugo continuously spotted by wildlife photographers.   And colugos seem to radiate an aura of adorable haplessness.  Specialized for living up in the trees, a colugo on the ground is practically useless until it can flop over to the nearest vertical surface and hop-climb up to safety (Wharton 1950; Dzulhelmi & Abdullah 2009).  Its chief defense against threat is camouflage and if that fails, quietly sidling around to the other side of the tree trunk in an “unnoticed escape” maneuver (Dzulhelmi & Abdullah 2009).

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“Please don’t look at me.”  Image credit: Gehan de Silva Wijeyeratne via Wildlife and Travel.

Colugos can also potentially glide away from danger.  Gliding has evolved independently many multiple times within mammals, but colugos are probably amongst the most impressive.  One animal was recorded to have traveled 136 meters (446 feet) with only a 10.5 to 12 meter (34 to 39 foot) loss of elevation (Nowak 1999).  Many glides have been measured to be over 100 meters (328 feet) (Nowak 1999; Vaughan, Ryan, & Czaplewski 2015).

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The gliding membrane, or patagium, extends from the neck to forelimbs, between the fingers and toes, between the limbs, and from hindlimbs to tail.  The membrane is supposedly so thin that it is almost possible to read through it (Wharton 1950).  This particular colugo is a mother, with a single youngster clinging across the belly like a belt.  Females usually give birth to one offspring after 8 weeks gestation and keep the baby enclosed within the patagium like a hammock for 6 months.  As the youngster grows, gliding decreases (Dzulhelmi & Abdullah 2009).  Image credit: Cede Prudente Blog “Wildlife Photography in Borneo.”

Gliding most likely evolved as a foraging strategy to move quickly from one food-bearing tree to another (Vaughan, Ryan, & Czaplewski 2015).  Colugos travel predictably from their tree hole dens in a daily nocturnal commute through the forest.  While this routine is convenient for photographers and the few intrepid scientists studying colugos, this behavior pattern has also been utilized by the native peoples of tropical southeast Asia who hunt these animals for their scant meat and soft, luxurious fur (Wharton 1950; Dzulhelmi & Abdullah 2009).  Wharton (1950) published a natural history of a colugo (Cynocephalus volans) species found on the Philippine island of Mindanao, which included this account (again, he uses the erroneous term “lemur”):

My Manobo companions indicated the path taken by the lemurs in leaving this particular tree, and told me that several weeks previously several natives had shot at the lemurs with bow and arrow.  Indeed, an arrow was still sticking in the side of a nearby mamacoa tree. . . . From a cavity 45 feet above the ground a head appeared and a lemur shuttled out and around the trunk.  It hesitated a moment and, with a twisting, outward leap, spread its membranes.  It dropped very steeply for perhaps twelve feet, then swooped across to land on the mamacoa tree, practically on top of the arrow which was impaled there.  Shooting the animal seemed to be a simple problem with the natives, once the exact landing place was determined, for experience showed that the animal would land on that spot the next time.

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Image credit: BBC Earth via YouTube.

Perhaps spurred by this curious observation in the forest, Wharton engaged in a rather unkind test of the single-minded flight path of the colugo:

Once, as an experiment, I repeated tossed a lemur from a tree about thirty feet high.  It always chose to sail towards a group of palm trees that stood near the beach.  Since the animal was obviously not in top shape and the direction it chose was down wind, it would invariably land heavily on the ground about forty feet from the tree with no obvious attempt to break its fall with its legs.  Lemurs are known to be of a low order of intelligence.

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Image credit: ImgKid via ZME Science.

Dodging the occasional human hunter and inquisitive zoologists of the “hands-on” variety are probably now the least of the colugo’s worries.  Utterly dependent upon forests, colugos are facing the consequences of massive deforestation in southeast Asia.  While it appears that their populations are either holding steady or only declining at a slow rate, thanks to an ability to tolerate disturbed habitat and adapt to secondary forests or plantations, there is still enough of a mystery surrounding the biology of colugos to prevent any confident declaration of their long-term future.

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What’s not to love?  Image credit”  Hendy Mp via Tumblr.

References

Boaeadi & Steinmetz.  2008.  “Galeopterus variegatus.”  The IUCN Red List of Threatened Species 2008.  Accessed 10 October 2016.

Dzulhelmi, M.N. & M.T. Abdullah.  2009.  “An ethogram construction for the Malayan Flying Lemur (Galeopterus variegatus) in Bako National Park, Sarawak, Malaysia.”  Journal of Tropical Biology and Conservation 5:  31 – 42.

Gonzalez, J.C. et al.  2008.  “Cynocephalus variegatus.”  The IUCN Red List of Threatened Species 2008.  Accessed 10 October 2015.

Nowak, Ronald M.  1999.  Walker’s Mammals of the World, Volume 1, 6th edition.  Baltimore, MD:  The Johns Hopkins University Press.

Vaughan, Terry A., J.A. Ryan, & N.J. Czaplewski.  2015.  Mammalogy, 6th edition.  Burlington, MA:  Jones & Bartlett Learning.

Wharton, Charles H.  1950.  “Notes on the Life History of the Flying Lemur.”  Journal of Mammalogy 31 (3):  269 – 273.

 

Looking Good, Part II — Toe Combs, Tooth Combs, & Pectinate Teeth (Mammal Edition)

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It’s not easy putting this all together, ya know?  Ctenodactylus gundi, or Common Gundi, is a soft-furred rodent that uses specialized bristles on their hindfeet for grooming.  Image credit: vetchyKocour via DeviantArt.

Last week on Curious Sengi, we explored pectinate claws in birds, a structure that looks like an obvious comb-like grooming tool.  However, as we have seen, the whole story is a bit more nuanced.

Our furry relatives have evolved a number of different strategies to clean and maintain their pelage, but here we are going to take a closer look at examples of mammalian comb-like structures, i.e., toe combs, tooth combs, and pectinate teeth.

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Eastern Barred Bandicoot, Perameles gunnii.  Image credit: Dave Watts via Arkive.

Some groups of marsupials are characterized by a curious fusion of toes in what is called a syndactylous digit, where the second and third digits of the hindfoot are reduced in size and bound together in the same sheath of tissue.  Each digit remains distinct skeletally, but appear like a toe with two claws.  Bandicoots, koalas, kangaroos, wombats, and the Australian possums have this syndactylous condition (Martin, Pine, & DeBlase 2001).  Based on early observations of living marsupials, it was clear that the syndactylous digits were not rudimentary structures, but specialized grooming claws (Wood Jones 1925).

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A stripey backside this magnificent deserves a proper grooming tool.  Eastern Barred Bandicoot, Perameles gunnii.  Image credit: Yale Peabody Museum / Curious Sengi.

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Detail of the second and third digit fused into a single syndactylous claw.  Wood Jones (1925) declared that these are “. . . .definite hair combs, put to no other use whatever.”  Image credit: Yale Peabody Museum / Curious Sengi.

Gundis (Ctenodactylus spp.) are highly social rodents found in the rocky desert areas of North Africa.  They are appealingly plump and covered in soft, dense fur that provides both protective coloration and insulation from cold, high winds, and heat (Honig & Greven 2003).  The two middle toes of the hindfoot — the second and third digits — are equipped with tufts of bristly hairs arranged in multiple rows.  The lower combs, just above the claw, are short, strong, and curved.  The upper combs, which are layered above the lower combs and merge into the fur of the leg, consist of longer and finer hairs (George 1978; Honig & Greven 2003).

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Skeleton of the left hindfoot with the second and third digits isolated to show the rigid hairs above the claws.  The genus name, Ctenodactylus, aptly means “comb toe” (George 1978).  Image credit: Honig and Greven 2003.

Given the importance of maintaining clean, ectoparasite-free fur in all mammals, why do gundis have a specialized grooming structure?  George (1978) hypothesized that gundis have very sharp, curved claws necessary for scrambling about on rocks, but ill-suited for grooming soft, dense fur.  Gundi fur also has a tendency to pull out easily, possibly as a defensive mechanism where quick shedding can facilitate slipping out of a predator’s grip.  George filmed these animals grooming and saw that when scratching themselves, the claws were always turned under.  This exposed the fur only to the toe combs and avoided contact with the sharp claws that could shred away hairs.  Other very soft-furred rodents, such as chinchillas, also have toe combs.

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Gundis love scratching their rumps!  George (1978) observed wild animals rump scratching six times an hour.  This video sequence shows characteristic three-legged acrobatics involved in reaching the backside with the toe combs.  Image credit: Honig and Greven 2003.

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After each grooming session, the toe combs are carefully cleaned (Honig & Greven 2003).  The bristles of the upper comb are clearly seen in this photograph. Image credit: cocoparisienne via Pixabay.

Moving from the foot end to the mouth end, many mammal lineages have independently evolved teeth in the lower jaw to act as combing structures.  The most important example of this occurs in lemurs and lorises.  The lower incisors and canines in these primates have each become slender, elongate, procumbent tines and then tightly packed together to form a combing array (Rose, Walker, & Jacobs 1981; Martin, Pine & DeBlase 2001).

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Skull and lower jaw of the Diademed Sifaka, Propithecus diadema.  The tooth comb appears as a tight grouping of procumbent incisors and canines at the very front of the mandible.  Image credit: Yale Peabody Museum / Curious Sengi.

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Unlike other lemurs, the sifaka’s tooth comb consists of only four teeth:  two incisors and two canines (Martin, Pine, & DeBlase 2001).  The sharp, canine-like fangs on either side of the tooth comb are actually premolars.  Image credit: Yale Peabody Museum / Curious Sengi.

Tooth combs in primates has been a long part of their evolutionary history, with loris-like fossils from the Early Miocene (approximately 23 to 15 million years ago) showing tooth root positioning similar to the modern tooth comb array.  The oldest definitive evidence comes from 7 to 8 million year old remains of Nycticeboides simpsoni from the Siwalik Group of Pakistan (Rose, Walker, & Jacobs 1981).

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Skull of the Pygmy Slow Loris, Nycticebus pygmaeus.  Note the upper incisors and canines are not tightly arranged into a combing structure.  Tooth combs are limited to the lower jaws.  Image credit: Yale Peabody Museum / Curious Sengi.

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Loris tooth comb consisting of four incisors in the middle and two canines flanking the outside.  Image credit: Yale Peabody Museum / Curious Sengi.

Another intriguing example of tooth combs in the fossil record emerges from the Early Eocene, approximately 56 to 41 million years ago.  This comes from an enigmatic group of possibly carnivorous extinct mammals known as arctocyonid condylarths.  With even their taxonomic affinity a big question mark, how was it possible to extrapolate grooming behavior from bones and teeth?  Rose, Walker, and Jacobs (1981) used scanning electron microscopy to show distinctive microscopic wear patterns in known modern tooth comb groomers and compared them with the condylarths.  A lifetime of combing through fur generates minute striations along the side edges of the teeth, where the hairs pulled through and left “whip marks.”  The condylarths Chriacus sp. and cf. Thryptacodon sp from Wyoming both showed signs of these striations, indicating they were using their teeth as grooming tools.

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Scanning electron microscope (SEM) images of modern tooth combers on the left and condylarth fossils on the right.  Both show signs of microstriations indicative of grooming.  Image credit: Rose and Walker 1981.

Behavioral observations show primate and non-primate (e.g., colugos, tree shrews) tooth combs used in grooming, but also for collecting food, especially for gouging bark, scooping out fruit pulp, and scraping tree sap or gum.  This draws up the question of whether tooth combs evolved first for grooming or for procuring food (Szalay & Seligsohn 1977; Rose, Walker, & Jacobs 1981).  In 1972, Martin posits that food scraping is primary to grooming.  Szalay and Seligsohn (1977) address this hypothesis, ultimately rejecting it upon functional grounds.  Scraping bark or sap requires a strong, cutting edge.  In generating this edge, it does not make functional sense to make the teeth longer and thinner, breaking up the cutting edge and making each tooth more susceptible to bending stress and potential breakage.  In addition, in the wild forests bereft of dentists going on about flossing, long interdental spaces would become a nightmare of food impaction and rot.  While the discussion continues about what tooth combs were originally adaptive for, there is little question that based on observations of live animals, the tooth comb is a multi-purpose tool.

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Colugos, gliding mammals closely related to primates and tree shrews, possess pectinate teeth.  In this tooth comb array, each incisor is divided into as many as 20 elongate tines (Aimi & Inagaki 1988). Lower jaw of the Phillipine “Flying Lemur”, Cynocephalus volans.  Image credit: Yale Peabody Museum / Curious Sengi.

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The pectinate teeth occlude against a toothless pad on the upper jaw.  Colugos are noctural herbivores that forage on leaves, buds, fruits, and flowers.  They have been observed using their pectinate incisors to scrape off the soft-tissue of tough leaves (Rose, Walker, & Jacobs 1981; Aimi & Inagaki 1988).  Image credit: Yale Peabody Museum / Curious Sengi.

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Mother colugo grooming her youngster. Image credit: Tumblr.

References

George, Wilma.  1978.  “Combs, fur and coat care related to habitat in the Ctenodactylidae (Rodentia).”  Zeitschrift für Säugetierkunde 43:  143 – 155.

Honigs, Sandra & Hartmut Greven.  2003.  “Biology of the gundi, Ctenodactylus gundi (Rodentia:  Ctenodactylidae), and its occurrence in Tunisia.”  Kaupia 12:  43 -55.

Martin, Robert E., R.H. Pine, & A.F. DeBlase.  2001.  A Manual of Mammalogy with Keys to Families of the World, 3rd ed.  Long Grove, IL:  Waveland Press, Inc.

Rose, Kenneth D. & Alan Walker.  1981.  “Function of the mandibular tooth comb in living and extinct mammals.”  Nature 289:  583 – 585.

Szalay, Frederick S. & Daniel Seligsohn.  1977.  “Why Did the Strepsirhine Tooth Comb Evolve?”  Folia primatologica 27:  75 – 82.

Wood Jones, Frederic.  1925.  “The R.M. Johnston Memorial Lecture, 1925.  The Mammalian Toilet and Some Considerations Arising From It.”  Papers and Proceedings of the Royal Society of Tasmania:  14 – 62.