“This is one of the best examples of a spring marsh I have yet seen. . . ” wrote State Geologist Charles White about this Marion, Iowa fen in the course of his critical statewide survey of Iowa’s wetlands in the fall of 1867 (White, 1867). However, White didn’t come to admire the flora.  The future of the State rested upon what he could learn here about turning this peatland into an urgently needed fuel source.

Coming largely from the forested eastern U.S., Iowa’s early settlers were the first to encounter vast expanses of prairie, and face the bleak prospect of developing an economy without a ready supply of wood.  The soil was incomparable and opportunities boundless–limited only the fuel shortage.  Timber was in desperately short supply, especially in the north and west, and disappearing rapidly everywhere.   Once it became evident Iowa’s coal deposits were limited to the southern counties, hopes coalesced around peat as a source of energy. . . at least as a stopgap until new forests could be grown.  White wrote (1868):

Our peat “. . .  will soon become invaluable. . . for (it) lies wholly beyond the limits of the coal-field, and the timber, although enough for the present inhabitants, can not supply a tithe of the fuel which the prospective population of a region so fertile and inviting, will soon demand. Peat has there a local value which can not be questioned.”

Mention peat today, and potting soil or fertilizer probably springs to mind—not so for earlier generations. Dwindling timber supplies had stirred some limited commercial fuel ventures in New England early in the century (Hawes, 1912), but few native-born Americans had any direct experience with burning peat.  Cultural roots and memories run deep though, and many Iowa families were of northern European stock, with a long tradition of burning peat.  Some British and Irish immigrants, coming here to farm or build railroads, found themselves overseeing peat operations instead (Cedar Falls Gazette, 1867).

Half the peat harvested in the world today is used for fuel (Turetsky and St. Louis, 2006).  The European Union has 125 peat-fired power plants, mostly in Finland and Estonia, with more being announced every year (International Peat Society, 2010).  Some of the new plants are 100% peat-fired, but many older coal-fired plants are converting to co-burn peat, reducing their average mercury and sulfur emissions and significantly extending their service lives.

Good dry peat is a light clean fuel.  It is easily kindled and burns with a hot red flame leaving little smoke, soot or ash.  Unlike coal, though, there is no clinker or slag; low sulfur means no acid rain either.  There’s a pungent odor to burning peat that some people find objectionable, but others liken to Scotch whisky.   Pound for pound, plain dry peat has about the same heating value as pine (Savage, 1905), but owing to its lower density, needs twice the storage space—8-18X more than coal (Davis, 1907).

 Peat is the partially decayed remains of plants.  It is the permanent saturation by water keeping dissolved oxygen low that retards decomposition and distinguishes a peat-bog or fen from a marsh (which dries out occasionally, speeding decomposition).  The types of plants, the degree of decay and chemical composition of peat vary widely.  It may be a light and fibrous sponge, or a dense black muck with no visible structure–changing by depth and location in the bed.  The usual sequence of a deposit is a tough fibrous mat overlaying a progressively denser and darker muck, but depending on the hydrology of the site, this sequence can be reversed, or repeated, with sediment inter-layered.   Given enough time, heat and pressure, a deposit of peat will be transformed into a more uniform bed of coal, but at this stage it’s a highly variable natural living raw material.

Peat is more than just a sodden compost heap of leaves and stems. The aerated top layer of a peat bed is interwoven with the roots and rhizomes of living plants.  Most store their food and overwinter here.  Nutriments like this made wetlands an attractive destination for hunter-gatherers, especially in the spring after a hungry winter, before the uplands had much to offer. Native Americans had the tools needed to access this underground bounty–few animals do, however, except for moose maybe. . .  and ground sloths.   More than a few of the Megalonyx skeletons found in situ, including our Tarkio trio, have been recovered from bottomlands—three of the more complete specifically from peat bogs like this one (McDonald, 1998).

Still, peatlands are relatively barren of wildlife compared to other ecosystems.  The living conditions that make life hard for plants, affect animals too (e.g. high water, low oxygen (for the burrowers), etc. ). Small mammals stick to the hummocks and the trails left by deer and other visitors.  Travel is difficult, unless you’re a bird, and dangerous besides, judging from the many bison bines uncovered here and elsewhere (Toennies, 2003).  Generally, visitors find what they need, and leave.  It may not be food or water drawing sloths and bison here though–some of these plants may offer trace elements the animals need.   Caribou retreat to boreal bogs for calving to avoid wolves (Rettie and Messier, 2000) . . . our “baby” is older than that though.

Sphagnum and Hypnum mosses make up the bulk of boreal peat-bog deposits but sedges predominate in Iowa’s beds (Pammel, 1909).  Trees and shrubs are an important component of some northern bogs but they were less common here–only likely to invade after drainage and intense grazing or other disturbance (Middleton, 2002).  From an energy perspective, the specific plants that make up peat are less important than the impurities.  Contamination like loess, silt and sand, the shells of mollusks, and the bones of the occasional mammal that falls in, are unburnable and leave ash—too much (>25%) and the peat is worthless as a fuel.

In Europe, peat was traditionally harvested by hand—cut into blocks or turves with special peat-spades (“slanes” in Ireland) and then air-dried. Working together, an average family could cut enough peat in one week to heat a cottage all winter (Rotherham, 1999).  Cutting and lifting the heavy wet sod was work grown-ups; children usually saw to drying the blocks—carefully turning and restacking them several times over four to six weeks to expose fresh surfaces to the sun and wind.  The blocks are highly friable and break apart easily with rough handling. Drying had to be finished by winter—ice crystals destroy the structure, and frozen wet blocks collapse upon thawing.  An average household needed 5-8,000 turves per year—a stack that could be as large as the house itself (ibid.). 

Preparing peat for fuel was a demanding process–one traditional peoples in Europe had managed for at least two thousand years (Rotherham, 2009), but in the U.S., where labor costs were high, exploiting peat for a mass market faced some daunting challenges.   Nonetheless, a far-thinking group of Quakers came here to Marion, Iowa in 1866 to tackle the challenge, and put the State, and perhaps the Nation, on the path to energy independence.  Next time: The Marion peat enterprise. . . . Dave

References

Cedar Falls Gazette, February 8, 1867.

Davis, C. A. 1907. Peat: essays on its origin, uses and distribution in Michigan. State Board of Geological Survey.  Lansing, MI.

Hawes, J. W. 1912. An Historical Address:  Celebration of the 200^th anniversary of the incorporation of Chatham, Mass. C. W. Swift, Publ.  Where?

Huels, F. W. 1915.  The peat resources of Wisconsin.  Wisconsin Geological and Natural History Survey.

International Peat Society

McDonald, H. G. 1998.  The sloth, the president, and the airport.  Washington Geology 26: 40-42.

Middleton, B. 2002. Nonequilibrium dynamics of sedge meadows grazed by cattle in southern Wisconsin.  Plant Ecology 161  89-110.

Pammel,  L. H.  1909.  Flora of northern Iowa peat bogs. Iowa Geological Survey 19: 739-784.Rettie, W. J. and Messier F. 2000. Hierarchical habitat selection by woodland caribou: its relationship to limiting factors. Ecography 23:466–478.

Rotherham, I. D. 1999.  Peat cutters and their landscapes:  fundamental change in a fragile environment.  Landscape Archaeology and Ecology 4: 28-51

Rotherham, I. D. 2009.  Peat and Peat Cutting.  Shire Publications, Oxford, England

Savage, T. E. 1905. 2  A Preliminary Report of the Peat Resources of Iowa.  Iowa Geological Survey Bulletin No 2. Des Moines, IA

Toennies, J. L. 2003.  Dows Holocene fossil bison assemblage, Franklin County, Iowa:  Its application to conservation, interpretation, and outreach.  University of Iowa, Department of Geoscience, M. Science thesis.

Turetsky, M. and St. Louis, V. L. 2006. Disturbance in boreal peatlands.  In Ecological Studies, Vol. 188,  Boreal Peatland Ecosystems.  R. K. Wieder and D. H. Vitt (Eds.), Springer-Verlag, Heidelberg.

White, C. A.  1867. Marion Register, December 11, 1867.

White, C. A.  1868.  First and Second Annual Report of the State Geologist.  F. W. Palmer, State Printer.  Des Moines, Iowa.

  Photos of the  new “baby” scapula and ribs, plus pics of the site prep.

Link to newspaper story

Sloth Volunteers,

There will be a special program featuring the Tarkio Valley sloths kicking off the 150^th anniversary of the Museum of Natural History, University of Iowa during the afternoon and evening of Thursday, May 7.

First, there will be an open house in the Paleontological Repository, where the University’s paleontological collection is housed, from 3:00-5:00 PM. This is informal and you can visit as you wish. Staff will be present to answer questions. This will be held in Trowbridge Hall which is one building north of the Pentacrest (Old Capitol area) and next to the Union parking ramp.

At 5:00, our featured speaker- Greg McDonald will spend most of this time in the Museum Lab (Room 12) on the ground floor of Macbride. This show-and-tell will be for sloth volunteers, their families and their special guests only. RSVP if you plan to  attend. Sarah will have name tags for you and these will get you into the Museum lab for a personal visit with Greg and to view of the bones that you have collected.

At 6:00 PM, there will be an public open house in Iowa Hall the entrance gallery (first floor) of the Museum of Natural History in Macbride Hall. Macbride is on the north east corner of the Pentacrest. Enjoy refreshments, exhibits (including a temporary exhibit on the Tarkio Valley sloths) and visit with friends. At 7:00, Greg will present ‘The Museum and the Megalonyx: A History of Great Aspirations and Sloths in Iowa’ in the auditorium of Macbride Hall. This is on the second floor. Greg has devoted his research life to Ice-Age ground sloths and associated, large, extinct mammals. He will tie this into the Tarkio Valley project. It will be exciting. You can find more about Greg and the program  at http://www.news-releases.uiowa.edu/2009/April/042409sloth_talk.html

We recommend that you park in either the Iowa Memorial Union Ramp or the one just south of the Old Capitol Mall. You can find a map for the former at: http://www.uiowa.edu/~maps/m/mh1.htm. There are lots of restaurants in the block across the street from the Museum. 

Pam, Sarah, Dave and Holmes especially hope that you can attend.

Sloth on!

Holmes

Mark your calendars for Thursday, May 7. Dr. Greg McDonald, Senior Curator of Paleontology for the National Park Service, renowned giant ground sloth expert, and consultant on the Tarkio Valley Sloth Project, will offer a lecture: The Museum and the Megalonyx: A History of Great Aspirations and Sloths in Iowa, at 7:00 PM in the Macbride Hall Auditorium on the University of Iowa campus.  Meet Greg at a public reception before the lecture, from 6:00-7:00 PM, in the Iowa Hall gallery of the Museum of Natural History, Macbride Hall.  Greg is an excellent speaker and a real sloth enthusiast.  It will be an interesting and entertaining evening.

McDonald’s lecture kicks off a year-long celebration of the 150^th anniversary of the Museum of Natural History, the oldest museum in Iowa.  Check  the museum’s web site http://www.uiowa.edu/~nathist/  for details of other upcoming events.   

 McDonald (1977) was the first to note the similarity of Megalonyx teeth to those of  VAMPIRE BATS.  Like sloths, but unlike other bats and most other mammals, the common vampire bat, Desmodus rotundus, has teeth that are comprised entirely of dentin, with a jacket of cementum.   SEM analysis shows the thin layer of enamel that vampire bats have at birth wears away quickly (Freeman, 1998).  As in Megalonyx, the bats’ teeth are ever-growing.  They compensate for the rapid wear of the soft material by grinding upper teeth against lower in a systematic way to keep them sharp (Phillips and Steinberg, 1976). Ever-growing teeth are common in rodents but the biting surface in this case is a combination of dentin and enamel.  As the softer dentin erodes and the enamel precipice chips, the animals are left with a long-lasting but jagged edge.  A nice tool for cutting and slicing plants and seeds, but vampire bats depend on stealth to secure their meals. A  smooth razor blade works better than a serrated edge for shaving hair or feathers off a patch of skin and making a clean painless incision.  The cementum jacket of the bats’ teeth is about as hard as the dentin, eliminating the chipping problem where they meet. But the ugly rumors about sloths and vampire bats didn’t get started simply because of tooth morphology. The scandal-mongers cite several other lines of evidence for making this unsavory connection.

Some of the ground sloths, including Megalonyx, show a marked affinity for caves. McDonald (2003) reports that 34 out of the 152 sites from which M. jeffersonii remains have been found are caves (including sinkholes, rock shelters and fissure fills).  Nothrotheriops shastensis shows an even stronger association with caves—39 out of 52 known localities.    In contrast, of the 168 late Pleistocene sites known for Paramylodon harlani, only 4 are true caves.  The largest North American sloth, Eremotherium laurillardi, is known from just 10 late Pleistocene localities and none is a true cave.   Clearly caves figure in the natural history of some sloths—whether to provide protection from predators, or shelter while sleeping or giving birth, or to help control body temperature in extremes of hot and cold, conserve water, or another reason is still TBD.  (image borrowed from)

Obviously Megalonyx survived in locales without caves or natural rock shelters of any kind.  In that case they may have simply dug burrows or settled into hollow trees (like bats).  Remarkably, several apparent sloth burrows have survived to the present day in Argentina, measuring 1.8 meters in width and up to 40 meters long (Vizcaino et al. 2001). The claw marks inside are too large to have been left by the ice age armadillos, but match up well with the morphology of both the Glossotherium and Scelidotherium ground sloths. Frenguelli (1928) recovered the skeleton of a Scelidotherium within such a burrow.

Modern tree sloths are also nocturnal like bats, but that’s an aversion to predators not daylight.  McDonald (2003) suggests Nothrotheriops may have retreated to caves more often than other ground sloths to avoid the daytime heat of its desert habitat, waiting for the cool of the night to feed. However, the continent-wide distribution of Megalonyx suggests they had no such metabolic limitations. And an adult Megalonyx likely lost little sleep worrying about predators either, and so probably stayed in bed until the sun was up like the rest of us. (image borrowed from)

The scurrilous rumors have probably been reinforced by the lurid accounts of the giant vampire bats that lived here in the Ice Ages.  The Pleistocene mammals included a diverse assortment of bats including vampires.  Many accompanied their hosts into extinction.  The fabulously named Desmodes draculae, is estimated to have been about 25-30% larger than the common vampire bat of today (Freeman, 1998).   Much still needs to be learned about the natural history of this mammal, especially its range. Blood is almost all protein, and without fat reserves vampire bats are highly sensitive to cold, raising questions about the ability of D. draculae to survive in northern climates.  Uncertainty about the diet of Megalonyx, its renowned adaptability, the blood-sucking food-niche that was probably open in the North, and the aforementioned unsettling similarity of its teeth to Desmodes spp. are presumably responsible for the irresponsible speculation that Megalonyx may have been an opportunistic sanguivore. (image borrowed from)

Megalonyx is generally believed to be a browser, of course (McDonald and Anderson, 1983), but how they ever managed to survive north of the Arctic Circle (Stock, 1942) is a wonder.   Guthrie (1980) has proposed grasses flourished there in lieu of the moss and lichens that eke out their existence there today, supporting a broad range of grazers—the so-called mammoth steppe.   It has been suggested that perhaps Megalonyx was supplementing its diet with something besides plants. Those nightmarish claws have been an enigma from the moment they were first discovered and then there are those teeth. . . and let’s be honest, this isn’t the first ground sloth cast as a possible psycho (Farino and Blanco, 1996).  One might contemplate the thought that what was nipping at the toes of mammoths wasn’t Jack Frost, but blood-sucking sloths. . . .

Everyone has heard the stories of course–Dracula, the Undead, etc. . . .  Myths about supernatural creatures that consume the blood of the living have come from nearly every culture on Earth since the beginning of recorded history (McNally, 1994).   Could they originate in paleolithic folklore?  Vampires in European mythology are usually described as bloated, ruddy in color and with long fingernails, as first depicted in cinema in the 1922 German silent film Nosferatu. Is the resemblance merely a coincidence or an unconscious connection to primal and well-founded fears? (image borrowed from)  

Then there is the little matter of elephant garlic, Allium ameloprasum. Garlic has been a part of folk medicine for thousands of years.  Over 800 therapeutic formulas are listed in the Codex Ebers, the Egyptian medical papyrus dating to 1550 BC (Nguansangiam et al., 2003).  Data on elephant garlic, a leek actually, is less complete but it has been shown to have some of the same effects as true garlic (Morita et al., 1988), including presumably its legendary ability to ward off vampires. Personally, I don’t think I’m going to lose any sleep worrying about vampire sloths walking at night with the Undead.  But I still have one nagging question. . . so if there weren’t any vampires, what were the elephants doing with the garlic?  (image borrowed from)     Happy Halloween. . . Dave

References

Farina, RA and Blanco, RE. 1996. Megatherium the stabber.  Proceedings: Biological Sciences 263 (1477): 1725-1729. 

Freeman, PW. 1998.  Form, function, and evolution in skulls and teeth of bats.  Bat Biology and Conservation. TH Kunz and PA Racey (eds.).  Smithsonian Institution Press.  Washington, D.C., pp. 140-156. 

Frenguelli, J. 1928.  Observaciones geologicas en la region costanera sur de la Provincia de Buenos Aires. Universdad Nacional del Litoral, Facultad de Ciencias de la Educacion, Anales 3: 101-130.

Guthrie, RD. 1990. Frozen Fauna of the Mammoth Steppe:  The story of Blue Babe. The University of Chicago Press.

McDonald, HG. 1977. Description of the osteology of the extinxt gravigrade Edentate Megalonyx with observations on its ontongeny, phylogeny and functional anatomy. Masters thesis, University of Florida.

McDonald, HG and Anderson, DC. 1983.  A well-preserved ground sloth (Megalonyx) cranium from Turin, Monona County, Iowa.  Proceedings of the Iowa Academy of Science 90: 134-140.

McDonald, HG. 2003. Sloth remains from North American caves and associated karst features. Ice Age Cave Faunas of North America. B.W. Schubert, J.I. Mead and R.W. Graham (eds.), Denver Museum of Nature and Science, Denver, CO.

McNally, RT and Florescu, R. 1994. In search of Dracula: the history of Dracula and vampires. Houghton Mifflin Company. New York, NY.

Morita T, Ushiroguchi T, Hayashi N, Itakura Y, Fuwa T. 1988. Steroidal saponins from elephant garlic, Bulbs of Allium ampeloprasum L. Chemical and Pharmaceutical Bulletin 36: 3840-3846.

Nguansangiam, S, Angsubhakorn, S, Bhamarapravati, S and Suksamrarn, A. 2003.  Effects of elephant garlic volatile oil (Allium ampeloprasum) and T-2 toxin on Murine skin. Southeast Asian Journal of Tropical Medicine Public Health 34: 899-905.

Phillips, CJ and Steinberg, B. 1976. Histological and scanning electron microscope studies of tooth structure and thegosis in the common vampire bat, Desmodus rotundus.  Occasional Papers of the Museum of Texas Tech University 42:  1-12.

Stock, C. 1942.  A ground sloth in Alaska. Science 95 (2474): 552-553.

Vizcaino, S.F., Zarate, M.,  Bargo,  M.S.,  and Dondas, A.  2001. Pleistocene burrows in the Mar del Plarta area. Acta Palaeontologica Polonica 46: 289-301.

 It doesn’t sparkle like the Hope diamond or King Tut’s gold, but the most amazing artifact in the museum is an oblong softball-sized coprolite from a ground sloth.  It came to us from a donor who in the early 1970’s helped her father, a National Park Service ranger, collect samples from a cave near the west end of the Grand Canyon.   Kids being kids, a couple of the giant horse apples were ”forgotten” on the bottom of a knapsack—puny wages for a day of packing sloth poop down to an NPS boat 500 feet below, on a path scuffed out by very different feet 30,000 years earlier.   The donor lives in Iowa now and read about the sloth project. . . the rest you know.  

Like the ruins of a medieval cathedral,   Rampart Cave today only hints of its former glory. It once held the largest deposit of ground sloth dung known.  But in 1976 a careless hiker left a campfire smoldering inside the cave and the deposit was almost entirely consumed—a tragedy Paul Martin has likened to loss of the ancient library at Alexandria, Egypt (Martin, 2005).   Bones from the cave indicate the dung belongs to the Shasta sloth, Nothrotheriops shastensis, the smallest of the four North American late-Pleistocene ground sloths.  Like Megalonyx they became extinct at the end of the ice ages 12,000-odd years ago.  The identification was recently confirmed in a major breakthrough in DNA sequencing  (Poinar et al., 1998).  Some researchers from that same team are trying to repeat their accomplishment with our bones now.  (images below borrowed from http://www.geocities.com/shioshya/paleo/index.htm)

The dung ball smells sweet, like incense, with no lingering odor of ammonia or feces.  I had the notion of getting a scratch-and-sniff souvenir made for the museum gift shop and pursued getting the smell reproduced.   I contacted a couple of companies that offered an impressive selection of synthetic scents.  They promised to get back to me, but never did.  Too bad, they could have been a big hit with the kids.

Experts have found over 70 different species of plants in the Rampart deposits.  Many occur in just trace amounts—probably ingested accidentally while the animals browsed.  The bulk of the Shasta diet apparently consisted of desert globe mallow (Sphaeralcea laca), Mormon tea (Ephedra navadensis), saltbush (Atriplex), reed grass (Phragmites), acacia (Acacia  greggii), yucca and agave.  A UI botany student looked at that list and explained the problem reproducing the smell—the plants aren’t especially aromatic. Scratch-and-sniff works best with sharp distinctive scents, not the subtle bouquet of French wine.    

People and sloths apparently like to eat the same kinds of things, especially around a salad bar. Admittedly, Megalonyx may have had an entirely different diet than Shasta–no one has ever found a deposit of their dung to know for sure.  But we do have a preliminary report on the pollen from the site, which allows us to describe a sloth forest generally and make some judgments about the food that would have available. It’s the kind of forest Native Americans preferred too, and long labored to maintain–and that may not be a coincidence.  One might speculate about the role sloths and other ice age megafauna had in creating this forest before people, and the degree to which they eased the way for humans to replace them and spread across the continent.   (image borrowed from http://www.artlex.com/ArtLex/Reh.html) 

Details about the pollen and the Iowa sloth forests in 2 weeks.. . . Dave 

Martin, P.S. 2005. Twilight of the Mammoths:  Ice Age extinctions and the rewilding of America.  University of California Press.  Berkley, CA. 

Poinar, H.N., Hofreiter, M., Spaulding, W.G., Martin, P.S., Stankiewicz, B.A., Bland, H., Evershed, R.P., Possnert, G., Paabo, S. 1998. Molecular coproscopy:  dung and diet of the extinct ground sloth.  Science 281: 402-407.

Species evolve in the most astonishing ways! That idea was reinforced for me recently when I was rereading Greg McDonald’s thesis and stumbled across a note about Megalonyx teeth that I hadn’t caught previously. I’ve written before about sloth teeth and the error of assuming differences between sloths and other mammals are evidence they were inept or stupid and maladapted.  Some remarkable mammals owe much of their success to abandoning the “normal” patterns of the so-called “higher” mammals and following the path of ground sloths. Greg cites an amazing example . . . as my generation would say, the implications are mind-blowing!  (image borrowed from)

So here’s the challenge:  There’s a living mammal with teeth that bear a remarkable functional resemblance to those of Megalonyx (excluding other Xenarthrans). That is, its teeth are made up entirely of dentin wrapped in a layer of cementum, and as in sloths they are self-sharpening and ever-growing. What animal is it and what special advantage does this adaptation give it to survive in its unique niche?  

No fair running out and getting Greg’s thesis.  Think about it and send in your guesses–remember to include your rationale. . . you are in for a surprise.  The answer in two weeks. . .  . Dave 

These photos came in recently from Pete Eyheralde, the Naturalist at the Mahaska County (IA) Conservation Board.   He presented a couple of fossil programs this year which highlighted the sloths. Pictured:  First graders at Moravia Elementary School.

Pete is a long-time member of our Sloth Rapid Response Team, a veteran of several digs and has also assisted with fossil prep. in the lab here.   (The sloth fossils in the photos are cast replicas we made here at the University just for this purpose.) 

This photo is from his Nature Center and a day this summer when a group of children came out to go fossil hunting in the old limestone quarry they have  there at the Russell Wildlife Area. 

Visit his web site at http://www.mahaskaconservation.com/naturecenter/index.php.  Thanks Pete. 

How big is our adult sloth? Greg McDonald says the average adult Megalonyx weighed 2,400 pounds (McDonald, 2005).  That’s based on a standard formula used to approximate the weight of mammals based on measurements of their femurs, and engineering principles relating the strength of a column to its cross-sectional area.  I’m a little dubious about applying the formula to sloths though. There’s nothing normal about the shape of most of their bones.  Even a simple measurement like the femur’s diameter isn’t straightforward. Add a lingering uncertainty about sloth locomotion and lifestyle (bipedal vs. quadrupedal), and any weight estimate has to taken with a grain of salt.   But, as Greg once told me, you have to start somewhere, and why not with the bone used in all the other mammals, and a bone that’s been recovered often enough to provide a reasonably-sized sample.  If you stick to femurs, at least you can compare sloth weights in relative terms. We’ve recovered an adult femur and you’ll see a weight estimate when Meghann, our resident anatomy expert, is sure we’re measuring it from the right anatomical points.

Caniniform teeth, because they are found in fair frequency, offer another way to compare Megalonyx sizes in relative terms.  Caniniforms are the front teeth, or tusks, in Megalonyx and some other sloths.  Why not just call it a canine? Sloths seem to have evolved them independently from the other mammals in a nice example of convergent evolution, so paleontologists call them a form of canine rather than a canine proper.  In the same way, they refer to sloth molars as “molariforms.”  

The figure at the right, taken from McDonald (1998) compares Megalonyx lower caniniforms from 25 different individuals. We added a point showing the approximate measurements of the Tarkio Valley adult. Ground sloths were evolving to grow larger over time, so the size of the tooth suggests we have a late Pleistocene specimen that weighed well over 2,400 pounds–in fact, it may be the second-largest Megalonyx ever found.  That will have to do until we get Meghann’s analysis.   The point off on the far right is the giant specimen from Darke County, OH that Greg once called the “Arnold Schwarzenegger” of Megalonyxes.   Arnold looks to be slightly bigger but we’re not through measuring.  All I can say is,  “Hasta la vista, baby. . . .” Dave

References

 McDonald, H.G. 1998.  The Massacre Rocks local fauna from the Pleistocene of southeastern Idaho. WA Akersten, HG McDonald, DJ Meldrum and MET Flints (eds.), In And Whereas. . . Papers on the Vertebrate Paleontology of Idaho Honoring John A. White, Vol. 1, Idaho Museum of Natural History Occasional Paper 36: 156-172.

McDonald, HG. 2005. Paleoecology of extinct Xenarthrans and the great American biotic interchange. Bulletin of the Florida Museum of Natural History 45: 313-333.

Excavation in the West Tarkio Valley of southwest Iowa has revealed the second most complete skeleton of an adult Megalonyx jeffersonii ever recovered, lying in situ, and partially intermingled, with the remains of two juveniles.  The specimens are buried in primary deposits, offering unprecedented opportunities for research into paleoenvironments during the Pleistocene/Holocene transition and insights into the behavior, habitat, resource partitioning and family associations of this keystone species.  See the Project Summary for more information.