Walk Like a Sloth–lesson 11: the toes

Introduction to Walk Like a Sloth: lessons in ground sloth locomotion

compassGetting Oriented

Like you, and unlike tree sloths and most other ground sloths, Megalonyx had five (5) toes on each foot.  Your toes, like your fingers, have three (3) phalanges (segments) each, except your big toe and thumb which each have just two (2) phalanges. Megalonyx is the same, only the middle toe is the big toe, and has two (2) bones.  In Megalonyx the proximal phalanx (the bone closer to the body) and medial phalanx (middle bone) of the 3rd toe are fused, so completely that all traces that they started out as two separate bones have vanished. What looks like the proximal phalanx is actually the third metatarsal.

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Photos from OSL sampling trip

Holmes and I made a quick trip to the sloth site friday with Dr. Art Bettis, Department of Geoscience, University of Iowa.  Our goal was to collect a sand sample for optically stimulated luminescence (OSL) dating.  The radiocarbon data from the cores we collected last fall were inconclusive and hint that the sloths may be a lot older than we thought. OSL will give us the answer.   Sloth veteran Will Mott drove over from Council Bluffs to operate the bobcat and offer his usual extraordinary assistance.

Quartz sand particles  have tiny cracks and imperfections in their crystal structure that trap electrons emitted by radioactive elements in the surrounding sediment.  The longer they are buried the more electrons they trap.  Sunlight resets the “clock” so keeping the sample dark is essential.  Accuracy is about plus or minus 10-15%.  Expect a date in a couple of months. . . . Dave

 fossil hunters til end1sm Art recording GPS coord sm admiring tools 309sm Art Bettis close up 340sm capping tube 328sm Will closeup 312sm Holmes watching 326sm Will Mott 310sm mud flying 303sm Will extracting tube 320sm Art checking depth 294sm Art and Will 297sm Will digging 299sm thanks Evans Rentalsm two more sampling tubes sm site Dec 2011 283sm fossil hunters til end2sm   

 extracting tube 321sm beaver dam 282sm capping tube 358sm Art pounding  tubesm Art driving in tube 315sm Art capping tube 337sm extracting tubes 351sm

Fossil show report

DSCN0048sm  Our sloth bone prototypes were a big hit at the  Gem, Mineral and Fossil Show  this passed weekend. Total attendance was  4,500.  Hundreds  stopped by the table to learn about the sloth  project and  60-70 stayed for the powerpoint talk.

Many thanks to the  Cedar Valley Rocks & Minerals Society for sponsoring the event, Steve Struckman, UI College of Engineering Prototyping Center for expediting fabrication of the prototypes, Tony Smith at the Hobby Corner for his skillful paint-job, and graduate assistant Youbing Yin, Iowa Comprehensive Lung Imaging Center for fixing the last-minute kinks in the STL files.  

The radius and ulna prototypes provoked no little amazement.  Stop by the museum for a lesson on how sloths moved their arms and to examine the other prototypes.  Sloth on! 

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Sloth programs this weekend

We’ll be at the Cedar Valley Rocks & Minerals Society Gem, Mineral and Fossil Show this Saturday and Sunday, March 19-20, at the Hawkeye Downs Expo Center in Cedar Rapids.  The theme of the show this year is Treasures From Iowa’s Ice Age.  We’ll be showing off our traveling trunk of sloth bone-prototypes from the UI Engineering Design and Prototyping Center, and speaking at 10:00 AM  Saturday and 2:30 PM  Sunday.   For more details

Mutant Ninja sloths

Our adult had a problem–its tail was wounded in some kind of incident and

Two fused caudal vertebrae (left) with normal vertebra (right)

Two fused caudal vertebrae (left) with normal vertebra (right)

two adjacent vertebrae fused as the wound healed making movement in the joint impossible.   Did  another animal step on it accidentally? Was it wounded by a predator?  Injured in a fight with another sloth?  There’s no way of knowing.   If sloths used their tails like the third leg of a stool, i.e. to lean back on when they stood up, as some scientists suggest, our sloth was probably in pain every time she did.  Ground sloths used their tails in different ways–in Peru they flapped them while they swam grazing on seaweed on the bottom of the ocean. (Muizon and McDonald, 1995)

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Missouri sloth program photos

 DSCN0233smA terrific turnout for our sloth program at the University of Central Missouri in Warrensburg,  MO November 16th. Many thanks to Dr. Adel Haj, Department of Biology and Earth Science, for sponsoring the event. We estimated attendance at 260– including some outstanding geology students and a very charming bunch of excited pre-schoolers.  Sadly, university administrators announced in November that they are eliminating the geoscience program.  Hard to believe they would rob their students of the opportunity to experience this kind of joy. . . . dave

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radiocarbon results

The radiocarbon test on the humic acid Tom Stafford, Stafford Research, Inc.,   extracted from inside the Paramylodon bone came back this week: 5434 to 5305 years before present.  We had assumed the humic acid entered the bone canal system after death but clearly there is recent contamination. We planned to do the same test on the Megalonyx astragalus but given this result have decided the money can be better spent.  Any hope of linking the Paramylodon, which was found in a gravel deposit a short distance downstream from Megalonyx site, to our trio now rests on an analysis of rare earth elements deposited immediately post mortem , or finding more bones in situ.

Tests on the Megalonyx are more hopeful– Robert Feranec, Curator of Vertebrate Paleontology, New York State Museum,  managed  to extract a small amount of collagen from a molar  while he was assisting Alex Bryk, Penn State,  with a stable isotope analysis.  Bob had to do 7 separate extractions, but he got plenty.  To his eye, the collagen “looks fine. ” It weighed about 2.5mg. That’s not a lot, but enough. An AMS radiocarbon date should be available from Woods Hole  next month. . . . Dave

Dreamers and other peatland visitors


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.

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Sloth Program in Cedar Rapids Feb. 13

The Tarkio Valley Sloth  roadshow visits the Indian Creek Nature Center in Cedar Rapids Saturday, February 13 with a program entitled: Echos of Iowa’s Sloths. Starting time is 2 PM.

Ground sloths may be extinct but they aren’t dead. The footsteps of these recently departed elephant-sized Ice Age giants continue to echo through Iowa’s woodlands with important implications for today and the future. David Brenzel, former curator at the University of Iowa Museum of Natural History and co-principle investigator on the Tarkio Valley Sloth Project will discuss the excavation to recover the only Jefferson’s sloth family ever discovered, including the most complete adult and second-most complete juvenile of the species ever found, and research to-date. MEMBER:$3-NONMEMBER:$4 FOR MORE INFORMATION CALL 362-0664 .

Driving Directions

The road to an emerald city

I’ve been ruminating again about how our sloths might have died.  Looking for fresh inspiration, I hiked down the Grant Wood trail here on the edge of Marion, IA to the Hughes peat bed, a site not unlike the ancient Tarkio Valley, where I recently learned a pair of bison–adult and juvenile– met their untimely ends 5,000 years ago.

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the test of truth and time

No amount of logic or evidence can erase the image of unmatched ineptitude sloths have in the minds of the public and biologists alike. . . they are simply too different. Weirdness at this level prompted titters and contempt from the moment tree sloths were discovered. Buffon, naturalist to King Louis XV of France, suggested sloths were an experiment by The Creator to test the limits of life by piling one flaw upon another. . . one more and sloths could not exist at all (Martin et al., 1961). So it was with some surprise and no little delight that I read a recent paper by Vizcaíno (2009) that takes sloths’ greatest flaw–their lack of tooth enamel, and suggests it might in fact be their great evolutionary innovation.

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a halloween costume idea

Dress up as your favorite Ice Age ghost or orphan.

Thanks to Jan Ailes and the Cedar Rapids Indian Creek Nature Center for  sponsoring the Things that go Bump in the Night program again this year and the opportunity to tell guests more about ground sloths and their food.

Much fun had by one and all.

Watch the ICNC schedule for a  program about the Sloth Project this winter.

More  about Honeylocusts and other Ice age orphans. . . . Dave