The Tarkio Valley Sloth Project

Even in the frenzy of the blood and the pain, the snarling and dying at a kill site there is a choreography that has evolved to share the spoils and reduce conflict. The patterns that predators leave behind often provide clues pointing to their identity–even if the site is 12,000 years old and absent distinctive tooth marks.  Gary Hanes has spent years studying the kill sites of various predators and his research provides a general picture of their different patterns. 

 According to Haynes (1988) every wolf pack has its hierarchy and once the prey is dead, and often even before, the process of staking out claims on preferred cuts and dividing the carcass begins. The dominant wolf will take the choice position.  The blood and internal organs inside the abdomen are a favorite first pick.  Sternal elements and ribs are usually damaged in the process.  Other high ranking wolves will claim the rump and upper legs where there are large masses of flesh.  If there are more animals in the pack than can comfortably situate themselves around the carcass to eat without invading each other’s space, they’ll start disarticulating the limbs, causing distinctive damage on the proximal ends of the femora and humeri , and their anchoring points on the pelvis and scapulae.  The prizes will be carried a short distance away to be gnawed on in relative solitude. Lower ranking wolves will tear off smaller less desirable parts (e.g. ears, tail,  jaw/tongue) and carry them further away. These satellite consumption spots will be randomly distributed around the carcass and about 20 feet apart (Haynes, ibid.).   Tooth marks and distance will be correlated as wolves lower in the pecking order tend to invest more time gnawing on their meager rations instead of trying to muscle in and steal another portion.

The scatter of bones at a wolf kill site rarely exceeds 100 ft. from ground zero. Within this area one can expect to find the skull, ribs and vertebrae, but rarely the sternal elements, patelae (knee bones) and caudal (tail) vertebrae.   A few of the major limb bones are likely to be missing—more if scavenging has been heavy.   The lower legs of hoofed animals offer more tendons and ligaments than muscle so they are often discarded uneaten and the bones are often found in anatomical sequence.  If scavenging is heavy, the lower leg may represent a prized morsel and elements may be transported miles from the kill site (Haynes, 1985).  The scatter is normally lower at a non-kill/scavenging site, though that will increase over time with scavenging by a host of creatures and kicking.   Most, if not all of the major limb bones should be close by. Wolves will normally leave even a fresh-dead prey carcass relatively intact.  Unless they are particularly hungry, wolves simply prefer to do their own “shopping” (Haynes, 1982).

Wolves follow predictable sequences in disarticulating and consuming a kill. Their pattern of utilization varies with the prey species and its particular anatomical characteristics, its size, how hungry the wolves are, how many individuals are in the pack, and the season.    The chart below summarizes his findings for large prey over 300 kg (~660 lbs.–e.g. moose or bison size).  According to Haynes,  the patterns are so regular for a particular predator and prey species that out-of-sequence disarticulation or damage, or the absence of a normal step, are reliable indicators of scavenger activity instead of predation, or other disturbance processes such as trampling, etc. (Haynes, 1982).

adapted from Haynes1982 and 1999

It’s probably too soon to use scatter diagrams and limb bone tallies to test the predator theory with the sloths.  We still have the entire south bank of the creek to explore and map.  However, we do have a large sample of bones to appraise using Haynes’s rules of carcass utilization.  The ribs we have range from perfect to stage III. Our sole femur (R), the truest indicator of predation according Haynes (1982), shows signs of light scavenging by small mammals but none of the damage to the greater trochanter that he predicts from disarticulation by predators. The other femur (L) is missing entirely.  Both tibiae are missing as well.  Humeri heads are toothmarked and overall the bone shows Stage III damage, as do the vertebrae and the pelvis.  The one ulna that survived (R) looks untouched—no signs of the disarticulation damage at the olecranon process (elbow) that he predicts in the case of a kill.  One scapula (R) is almost pristine, but the other one is heavily damaged by trampling–no evidence of gnawing however.   The skull is stage II while the mandibles are stage III.  

Conclusion:  no traces of disarticulation by predators judging from the adult bones we’ve found so far.  However, most of the “baby’s” bones are still missing.  All of the “toddlers” major bones are AWOL too,  except for the distal half of one humerus.  If we assume the baby weighed about 90# and the toddler perhaps 300# (based on scapulae, the only common bone we have), that’s about 200# of flesh–a healthy dinner for a pack of wolves.  How much would a pack of wolves eat at one sitting?  Would they have turned their attention to the tender youngsters before eating a tough old adult?  Would they have abandoned the adult’s carcass only half eaten?  What accounts for the disparity in utilization stages of the carcass and why are the bones from the right side better preserved than those from the left?  Hayne’s rules would say even if predation is confirmed, the deviations from the expected pattern indicate there are other factors at work. . .  but he also warns that the rules may be entirely different for ground sloths.   As ever, we have more questions than answers, but Haynes’s research holds out the promise that with some more data maybe we can start to peel back the layers. . . .   Dave

References

Haynes, G. 1982. Utilization and skeletal disturbances of North America prey carcasses.  Arctic 35: 266-281.

Haynes, G. 1985.  On watering holes, mineral licks, death, and predation.  In Environments and Extinctions:  Man in late glacial North America,  Eds.  J Mead and D Mettzer.  Center for the Study of Early Man.

Haynes G. 1988. Prey bones and predators:  potential information from analysis of bone sites.  Ossa: 7: 75-97.

Haynes, G.  1999. The role of mammoths in rapid Clovis dispersal.  In Mammoth and mammoth fauna:  studies on an extinct ecosystem.  Proceedings of the first International Mammoth Conference, St. Petersburg, Russsia. P. 9-38.

If predators killed the sloths, and the site hasn’t been disturbed too much (e.g. by scavengers, trampling, weathering, transport, etc.), the killers’ fingerprints will still be present. The signs of predation versus mere scavenging, according to Haynes, are in the evidence left behind after the meal—the kind of damage to specific bones, the pattern of disarticulation, and the arrangement of the bones around the kill site (Haynes, 1980a).  Different predators have different MO’s.  Those vary with the specific prey species, the season, environmental conditions, how hungry the predators are, how much meat is available, and how many individuals there are in the pack or pride (Haynes, 1983).  The patterns are so regular that one can reliably look for causes other than predation when deviations from the norm are observed.

The Ice Ages offered a formidable cast of killers, but attacking a healthy adult Megalonyx, (a.k.a. “Giant Claw”) wasn’t a job for a solitary predator. Downing a giant sloth demanded teamwork. The giant short-faced bear (Arctodus simus) was once thought the greatest terror on four legs and maybe capable of going it alone, but modern studies suggest its size owed more to its herbivorous habits and bone-crushing/scavenging abilities, and at best it was only an opportunistic predator (Emslie and Czaplewski, 1985).  The number of sabertooth cats (Smilodon fatalis) found at La Brea with serious wounds suggests a social structure that made it possible for them to survive even crippling injuries, but whether that cooperation extended to hunting is TBD.  Evidence from Friesenhahn Cave in Texas indicates it was used as a den by the more lightly-built sabertooth, Homotherium serum, the scimitar cat.  All the living Felids that den are solitary, however (Rawn-Schatzinger, 1992).     The remains in the cave suggest H. serum specialized in racing in under the noses of momma mammoths and dispatching careless two year-olds with a strategic bite or two, and then dashing away apparently to wait for the youngster to bleed to death and the herd to depart, no doubt in frustrated fury.   Other Homotherium species in the Old World followed similar practices with juvenile mastodons and rhinos (Lange, 2002).  Bits of Harlan’s sloth (Paramylodon harlani) have been recovered from Friesenhahn Cave but there’s no evidence a cat brought it there, much less killed it (Graham, 2007).  The scimitar cat’s style of hunting makes it a solid candidate for causing the wound we’ve found on our toddler’s back, but it would not have tried the same trick on an adult sloth. American lions (Panthera leo atrox) probably hunted like their African cousins, by stealth and ambush around watering holes and other locations frequented by their prey (Grayson, 1991).  The absence of any fossils  from  eastern North America suggests, like their modern descendents, they preferred open habitat to the woodlands favored by Megalonyx (McDonald and Anderson, 1991).  The lifestyle of dire wolves (Canis dirus) is still debated, but their massive teeth suggest scavenging probably played the preeminent role in their diet. If predators killed our sloths, the prime suspect has to be a social hunter like the timber wolf (Canis lupus). That’s lucky, because Gary Haynes has spent a lifetime studying wolf kill sites.

Every predator has a unique approach to eating a specific prey species and even when they leave no distinctive tooth marks (which is the rule), they often leave a telling signature in the specific areas they damage bones, the elements they ignore and the arrangement of the carcass when they leave. When wolves prey on moose and bison the most reliable indicator is the damage to the femora (Haynes, 1980b).     Even with very light feeding, wolves destroy the greater trochanter.   Now the greater trochanter of any prey species is hardly a tasty tidbit–wolves that attack here have one purpose—cutting the muscles that hold the bone in the acetabulum or hip socket.  Predators are dangerous–to other animals and sometimes to each other.  Even social predators can turn decidedly asocial in the blood lust of a kill—they demand elbow room.  The first principle for recognizing the kill site of a social predator likethe timber wolf is looking for the evidence of the divvying up the spoils and creating the needed separation. 

Next week—a look at our sloth femur:  Dancing with wolves . . . . Dave

References

Did predators killed the sloths?  Last week Holmes and I were looking at a rib from the adult that’s currently  on display in the lobby when we noticed a large puncture and some adjacent gnaw marks. The wounds are partially obstructed by the case and easy to overlook.  They were obviously caused by  large sharp teeth and indicate a carnivore was present close to the time of death.  Carnivores don’t gnaw on bones to sharpen their teeth like rodents.  They may mouth an old dry bone they happen across, but nothing more.  If a carnivore bit into this bone, there was meat on it.

Identifying the forces that  can break and shape bones has been a concern of archaeologists for decades as intriguing assemblages of bones and bone fragments have surfaced at sites like Africa’s famous Olduvai Gorge.  The question was whether the remains indicated human hunting, and if the  bone splinters and spiral fractures were evidence of tool manufacturing.  Paleontologists like Voorhies (1969), Behrensmeyer (1975) and Hill (1976) broke many hearts showing stream transport, scavenging, weathering or trampling were responsible more often than humans. 

Predators don’t always leave obvious calling cards.  Haynes reports often finding  wolf kill sites with nary a scratch on the bones (Haynes, 1980).  Behrensmeyer (1975) and Voorhies (1969) showed a pattern of survival of the ends of the major limb bones was a strong indicator of carnivore activity. Predators and scavengers normally disarticulate limbs at their proximal or ball-joint ends first, damaging the bones at predictable points of muscle attachment.  The proximal ends of the humerus and femur also have very thin walls and offer an easily accessible and delectable center of marrow.   Few carnivores will pass it up unless they are overwhelmed with meat such as at the scene of a mass-drowning or other catastrophe.  Carnivores usually ignore the distal ends of humeri and femora (i.e.  elbows and knees).  Those joints are tightly wrapped in tendons and ligaments and offer little in return, so they are more likely to survive untouched and become fossilized.  Is it just a coincidence that we have three nearly identical distal ends of humeri (2-adult, 1-toddler)?

But fingerprints at the scene don’t prove their owner caused the deaths.  Carnivores are as likely gnaw off the end of a humerus or puncture a rib stripping the flesh from the steaming carcass of a fresh kill as cold carrion. How are we to determine if our sloths spent their last moments in a terrifying struggle against a pack  of predators, or simply died a “natural” death (e.g. from disease, malnutrition, drowning, etc.), and their remains were simply scavenged post-mortem?

Gary Haynes has spent a lifetime studying predator kill sites, and the patterns he has found could add an exciting new dimension to our understanding of the sloth site.   Resources, according to Haynes,  are distributed in predictable ways in the environment and to survive  animals learn the patterns all around them and across the seasons. Predators survive by mirroring that environment, especially the behavior of their prey,  and so their behavior becomes extremely patterned too, including at the site of a kill.  The location, distribution, condition, and type of bones or bone fragments  left at a kill site–sometimes even a single bone, can be distinctive enough to distinguish predator activity from scavenging and the presence  of a particular carnivore–no punctures or gnaw-marks required!  A wealth of information about an ecosystem may be revealed, such as how many wolves, for example,  were in a pack, the season of the year when they made the kill, how hungry they were, how vulnerable their prey was . . . even their favorite NFL player.  If Ice Age predators behaved like their modern-day cousins and followed the same general ecological rules–and Haynes believes  they did–relatively undisturbed bone assemblages such as ours can reveal much about predator-prey interactions, even involving extinct species (Haynes, 1982). . . . Dave  (to be continued)

References

Behrensmeyer, AK. 1975.  The Taphonomy and Paleoecology of Plio-Pleistocene Vertebrate Assemblages East of Lake Randolph, Kenya, Bulletin of the Museum of Comparative Zoology 146: 473-578.

Haynes G. 1980. Prey bones and predators:  potential information from analysis of bone sites.  Ossa: 7: 75-97.

Haynes, G. 1982. Utilization and skeletal disturbances of North America prey carcasses.  Arctic 35: 266-281.

Hill. AP. 1976. On carnivore and weathering damage to bone. Current Anthropology 17:335-336.

Voorhies, MR. 1969.  Taphonomy and population dynamic of an early Pliocene vertebrate fauna, Knox County, Nebraska, University of Wyoming, Contributions to Geology, Special Paper No. 1. 

This was the announcement the University released to the press this week.  We’re grateful to the NSF for their continuing support and to all the volunteers working on the project who make it possible.  Our sincere thanks.    Holmes and Dave

UI sloth excavation project awarded $20,000 NSF grant

The University of Iowa’s Tarkio Valley Sloth Project has been awarded a $20,000 grant from the National Science Foundation (NSF) to complete the excavation of the remains of three giant sloths and begin research of this unique discovery. The project is a joint effort of the UI Museum of Natural History, Department of Geoscience in the UI College of Liberal Arts and Sciences, and Office of the State Archaeologist, all teaming up with volunteers and students from across the Midwest.

A skeleton of a giant Ice Age sloth was discovered by Bob and Sonia Athen in 2001 behind their home near Shenandoah, Iowa, in the bed of the West Tarkio Creek. More bones were subsequently found on the property of the adjoining landowners, Dean and Loreta Tiemann, who, like the Athens, graciously agreed to allow the excavation and to donate the fossils to the University of Iowa.

The elephant-sized beast lived in Iowa for thousands of years before going extinct around 12,000 years ago. To date, more than 100 major elements have been recovered, making this individual the second-most-complete skeleton ever found of this rare species. In 2006, two juvenile sloths of the same species were discovered nearby.

According to project leader Holmes Semken, emeritus professor in the UI Department of Geoscience, only six semicomplete skeletons of this species have ever been found and this is the first time any juvenile, much less two, has been found directly associated with an adult. They also are buried in sediments that will provide valuable environmental data about the climate at the time.

“This could be our ‘Rosetta Stone’ for understanding the family life of these mysterious creatures,” Semken said. Over 40 bones of the older juvenile have been recovered, making it also the second most-complete juvenile of its kind ever found.

“The NSF is excited about the discovery and has indicated that we can count on their continuing support if we keep making progress like we have,” said Semken. “They see the potential here for a major contribution to our understanding of the Pleistocene extinction event in which almost 40 large mammals became extinct at the same time. They also realize they are getting a lot of bang for their buck through the tremendous support we’ve received from the university, the Page County community, the Iowa Archaeological Society, Mid-American Paleontological Society, the Boy Scouts, Iowa Academy of Science, and staff and students from educational institutions all across Iowa.”

The project has also received assistance from the U.S. Department of Agriculture, the U.S. Army Corps of Engineers, the U.S. Geological Survey and the National Park Service.

“It’s a breakthrough project for the university,” said sloth project co-leader David Brenzel of the UI Museum of Natural History. “The NSF recognized that our goal to educate people about the process of doing science is as important as the research itself. They are providing specific funding to expand our educational outreach efforts through public programs and the Web.”

Last month, a blog was started about the project at http://www.slothcentral.com, which can also be found by going to http://www.uiowa.edu/~nathist.

“The blog will allow anyone interested in the project to submit questions and contribute ideas. We hope it will be fun, educational, attract some professional interest, and also inspire young paleontologists,” Brenzel said. Photos of the dig and associated lab work are available at http://www.uiowa.edu/~nathist/Site/sloth/index.html.

For further information or to volunteer for the project contact Sarah Horgen at the UI Museum of Natural History, sarah-horgen@uiowa.edu, Semken at Holmes@slothcentral.com, or Brenzel at David@slothcentral.com.

STORY SOURCE: University of Iowa News Services, 300 Plaza Centre One, Suite 371, Iowa City, Iowa 52242-2500

MEDIA CONTACTS: Sarah Horgen, UI Museum of Natural History, sarah-horgen@uiowa.edu, 319-335-0606; George McCrory, University News Service, 319-384-0012, george-mccrory@uiowa.edu

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.

Popular opinion holds ground sloths are extinct because they were  too inept to survive.  Polite critics often point to sloth teeth as one example of their maladaptation, foregoing the customary jabs at their supposed beach bum lifestyle and grooming habits. This came to mind recently when we received some photos from Daniela Kalthoff, PhD, a researcher at the Swedish Museum of Natural History.  She’s studying the microstructure of sloth teeth and offered us some amazingly detailed images of a Megalonychid tooth to aid our research (left).

We sectioned a molar in the UI Department of Geoscience last year, and found possible growth lines.  A Micro-CT scan taken at the Iowa Institute for Biomedical Imaging showed some intriguing concentric circles that experts eventually determined were imaging artifacts and not real.  The teeth proved too dense for a scan to show much.  If we can prove the divisions are indeed annual growth lines, we might be able to measure Megalonyx growth rates and determine their ages.   Colleagues at Penn State are preparing to sample the layers for their isotopes which could indicate seasonal diet changes, some climate indicators, and possibly migration patterns.   Photo:Alex Bryk, student, Penn State (left), Jeff Dorale, Asst. Professor, UI Geoscience (right)

People have been looking at sloth teeth since the pioneering work of Retzius (1837) and Owen (1840, 1845) and pointing out their deficiencies. Sloth teeth lack the hard enamel of other mammals, and even people who should know better have concluded they are woefully primitive and another example of sloth ineptitude.  Not too long ago one authority hypothesized excessive tooth-wear might even be responsible for the ground sloths’ extinction (Ferigolo, 1985).  Diet changes forced upon the animals early in the Holocene presumably  tipped them into oblivion (too much arugula probably).

Instead of enamel, sloth teeth are made of dentine, the material inside your teeth.  It’s arranged in concentric layers of different kinds and degrees of hardness, surrounded by cementum.  Kalthoff is studying the microstructures of each variety.  Dentine is soft and erodes rapidly.  To compensate for this, sloth teeth grow continuously throughout their lives. The inner layer is softer than the outer layer so it wears down more rapidly as sloths chew, forming a cup in adults,  with a constantly renewing sharp crest—perfect for cutting vegetation into bite-sized pieces (Naples, 1995).

Enamel became the dental material of choice in mammals because we evolved the genes to adjust its structure to different directions of stress in different teeth, or areas of a tooth, by reorienting its crystals and changing its thickness.  Enamel has a very high mineral content–92% by volume compared to just 69% for dentine, and that makes it hard and durable–tooth cusps resist wear and stay sharp (Rensberger, 1995). 

The crystalline structure that gives enamel its strength, however, also makes it brittle when stressed in the wrong direction. Dentine is actually 20X stronger in its weakest direction (Ramussen et al., 1976).  Anyone who has ever bitten down on a wayward cherry pit or unpopped kernel of popcorn knows how quickly you can chip a tooth if you stress it in the wrong direction.  Sloths never had to slow down eating looking for old maids–maybe not so inept afterall.

Recommendation: If you take a sloth to the movies, make him buy his own box of popcorn. . . . Dave

References

Ferigolo, J. 1985. Evolutionary trends of the histological pattern in the teeth of Edentata (Xenarthra), Archives of Oral Biology: 30: 71-82.

Kalthoff, D.C. 2004. Dental microstructures in fossil and recent Xenarthra (Mammalia). Journal of Vertebrate Paleontology 24 (suppl. to 3): 77A.

Naples, VL. 1995. The artifical generation of wear patterns on tooth models as a means to infer mandibular movement during feeding in mammals.  In Functional Morphology in Vertebrate Paleontology. JJ Thomason (ed.) Cambridge UIniversity Press.

Owen, R. 1840, 1845. Odontography. London

Rasmussen, ST, Patchin, RE, Scott, and Heuer AH. 1976. Fracture properties of human enamel and dentin. Dental Research 55: 154-164.

Rensberger, JM.1995. Determination of stresses in mammalian dental enamel and their relevance to the interpretation of feeding behaiors in extinct taxa. Functional Morphology in Vertebrate Paleontology, J. Thomason (ed.) Cambridge University Press.

Retzius, A.A. 1837. Mikroskopiska undersökingar öfver Tändernes, sädeles, Tandbenets struktur.  Stockholm.

Ground sloths were first discovered by science in 1789 when a giant skeleton was found on the banks of the Rio Luyan near Buenos Aires. Their existence didn’t surprise the local natives who had long held the animals were living underground like giant moles occasionally venturing too close to the surface and dying because of exposure to sunlight (Heuvelmans, 1995).

That’s the same legend Siberian natives evolved to explain the appearance of mammoth carcasses in the river banks after spring floods (Tolmachoff, 1929). I was reminded of that this week as I slopped through the muck inside a local museum looking for salvageable artifacts. Our first sloth was uncovered by the big 1993 flood, hopefully we don’t lose it to the Flood of 2008.

A 500-year flood fifteen years after a 100-year flood–either that’s really bad luck or we’re doing something wrong. The underground has always been a place of dark mysteries and strange animals, but there’s no mystery in what happens when you tile, pave over or compact 56,276 square miles of land (Iowa’s area) to drain the water as quickly as possible into the nearest river. The agony for the thousands of displaced people is clear, but the soil that’s currently making its way downstream to the Gulf won’t be as easily replaced as their ruined possessions.

George Washington Carver offered one of the most hopeful predictions for Iowa ever conceived, “ I believe the Creator has put ores and oil on this earth to give us a breathing spell. As we exhaust them, we must be prepared to fall back on the farms, which are God’s true storehouse and can never be exhausted. For we can learn to synthesize materials for every human need from the things that grow” (Blouin, 2005). When things calm down a bit and people feel a little more secure, maybe we can take a hard look at the way we manage our soil and water. That’s Iowa’s fortune washing away. Our future is a lot darker as a result–there’s no mystery about that. . . . Dave

References

Blouin, MT. 2005. Iowa builds on agricultural strengths to advance a bioeconomy. Industrial Biotechnology 1:92.

Heuvelmans, B. 1995. On the Track of Unknown Animals. R. Garnett (transl.) Kegan Paul International.

Ides, EY. 1706 Three Years Travels from Moscow Overland to China. London.

Tolmachoff, I. 1929. The carcasses of the mammoth and rhinoceros found in the froze ground of Siberia. American Philosophical Society 23: I-74b.

I cited Swedish explorer Erland Nordenskiold in a post last week and forgot  to mention the role he played in one of the last great natural history adventures of the 19^th century. 

In 1895 a former merchant sea captain named Hermann Eberhardt, farming on the shores of a inlet called Ultima Esperanza (”Last Hope”) in southern Chile discovered a giant cave  on his property. Inside he found a large fresh-looking skin covered with long reddish-gray hair and embedded with bean-sized bones.  Scientists identified it as that of an extinct Mylodon ground sloth.  Further excavations uncovered bones with bits of dried tissue still attached, plus evidence  of human habitation.

Today we know the bones and skin were preserved by the climate inside the cave, but to Professor Florentino Ameghino of the Buenos Aires museum, the skin appeared fresh.  He remembered a story a friend had told him of seeing a strange animal while exploring in the area.  Ameghino linked the story and the skin to a legend of a large nocturnal beast local natives called iemisch, with giant claws it used to dig burrows where it slept during the day.  Ameghino concluded the iemisch  was a  living Mylodon ground sloth.  His announcement created a world-wide stir. (Ameghino, 1898)

Erland Nordenskiold was a voice of reason in the hullabaloo and conducted the first systematic excavation of the cave.  However, publication of his study only added fuel to the fire.  He determined the evidence of human habitation lay in a distinct horizon above and separate from the older lower horizon with its sloth bones, dung and dried grass.  (Nordenskiold, 1900). Modern radiocarbon dating of the dung indicates the cave was occupied by sloths from about 13,500 years B.P. to 10,500 B.P. (Markgraf, 1985). 

Others concluded from the large quantities of the dung and finely chopped “hay” that sloths had been kept captive inside the cave by natives fattening them for slaughter, behind the stone wall  Nordenskiold had reported.  Some even suggested the sloths had been domesticated (Allen, 1942). Today we know the sloth “corral” was merely fallen rock from the ceiling (Naish, 2005)

In 1900 the Daily Express sponsored an expedition to Patagonia to capture a living Mylodon. The venture was mismanaged however and the leader, HV Hesketh-Prichard, quit before reaching the cave.  He dismissed the idea as a hoax (Hesketh-Prichard, 1902).

Nordenskiold offers us a lesson on the sloth project–finding three sloths in close proximity doesn’t make them a family no matter how good it looks.   Only careful excavation, painstaking attention to stratigraphy  and detailed chemical analysis will do that. . . . Dave

References

Allen GM. 1942.  Extinct and Vanishing Mammals of the Western Hemisphere. Special Publication #11, American Committee for International Wild Life Protection.

Ameghino, F. 1898. An existing ground-sloth in Patagonia. Natural Science 13: 324-326.

Hesketh-Prichard, HV. 1902. Through the Heart of Patagonia.

Heuvelmans, B. 1995. On the Track of Unknown Animals.  R. Garnett (transl.) Kegan Paul International.

Markgraf,V. 1985.  Late Pleistocene faunal extinctions in southern Patagonia.  Science 228: 1110-1112.

Naish, D. 2005. Fossils explained 51: Sloths. Geology Today 21: 232-238.

Nordenskjold E. 1900.  La grotte de Glossotherium (Neomylodon) de Patagonia. Bulletin de la Societe Geologique de France: 29: 1216-1217.

Sloth Advisors, Volunteers and Friends,

Let’s start with the good news. The NSF has awarded the sloth project $20,000 to continue excavation, conduct a detailed osteological analysis of the remains, start exploratory DNA analysis of the adult and two juveniles and provide for an outreach intern to maintain the sloth website and  design teaching materials focused on the sloth analysis. NSF regards this award as preparatory for submittal of another proposal for comprehensive analyses of the sloths including a series of chemical analyses on the bone as well as detailed studies of associated seeds, pollen and depositional environments at the time the sloths died. We are pleased to continue our association with NSF.

The bad news is water. As you know the Shenandoah area has been declared a disaster area. I hesitate to hazard another guess about when we will be able to dig again. Bob tells me that water in the Tarkio was up to his picnic table, our staging and overlook area, last week. That’s 30 feet above the sloth. It has dropped to 8 feet but the current is too fast to construct new levees (we will use an excavator for this). It may be late summer or early fall before things dry up as predicted. The NSF grant runs for two years so we have time. Also, NSF tells me that a 6 month extension is easy to get. That gives us through summer 2010 to recover the critters. Hopefully, the sloth-bearing unit, which is resistant to erosion, has not been materially damaged.  Holmes

8.17 inches since last Wednesday.  Page County is officially a state disaster area.   The sandbagging we did in 2006 has saved us so far. . . keep your fingers crossed.  

It’s bad for sloth-digging but worse for farmers.  http://www.valleynewstoday.com/site/news.cfm?newsid=19760409&BRD=2703&PAG=461&dept_id=555139&rfi=6  

Dave