I cling to a chain-link fence, the strap of the radio receiver clenched between my teeth as I climb sideways over an open ditch. It is clear from the smell that the local neighborhood has not gotten on board with the whole septic system plan.
“After we get around the sewage pipe, make a jump for the mud bank. You have boots, right? I think it’s only about ankle-deep,” Sarah tells me as she maneuvers around the chest-height pipe. “But watch out for the live electrical wire. And the bees.”
I grunt acknowledgment, trying not to breathe through my nose, and failing. I am well aware that if I drop this radio reviver, I have to go into the ditch after it, and I am also well aware that it is more valuable than I am.
I am not getting paid enough for this.
This is an easy calculation to make, as I am not getting paid at all.
The word “volunteer” first enters the English language around the year 1330; at the time it translated more like “puppet” or “mind-slave”. I muse on the appropriateness of that—surely you have to be a bit funny in the head to do this job.
The job today is to find a sloth by the name of Baguette, who is neighbor to the elusive Croissant. She’s a big, beautiful three-fingered Bradypus variegatus with a preference for large trees and advanced stealth technology, vs. our knee-high rubber boots, two large radio receivers, and the most advanced prefrontal cortexes in the mammal kingdom.
So far Baguette is winning.
Winning what, though, is hard to say. She isn’t getting paid for this either. We use words for sloths like “economy of motion” or “energy budget” because we humans are obsessed with the cost of things. There is an unceasing cash register in the back of our heads, always running, always tallying up the bill: How much for this? How much for that? Will I make rent this month, can I afford cheese? Hurry, hurry, hurry, time is money!
There is something counter-intuitive about the serenity of sloths; the way they sail through the canopy as if they have all the time in the world as if the forest is full of abundance. As if these scurrying, stressing humans below them are really being very silly.
It’s a helpful perspective to contemplate as I lift my eyes from the mud underfoot and look up into the ancient behemoth that is Baguette’s current home: emerald leaves and little yellow flowers, jeweled hummingbirds, crimson and black tanagers, draping lianas and velvet mosses. There is a majesty to trees that connects the earth below to the heavens above. Baguette’s home is a view worth the hike, and a good reminder that the most valuable things in the world don’t come with a price tag.
“Volunteer” from the Latin “voluntas”, meaning will, desire, choice, or wish. It’s a very appropriate word after all because there’s nowhere else I’d rather be.
“Oh my gosh,” says my boss, holding the binoculars to her face. “I think Croissant is a boy.”
I take my eyes off the beeping box attached to our portable radio antenna and peer into the trees, trying to find the small, tan colored sloth amongst the palm fronts and tree bark. Boy or girl, I personally think Croissant might actually be a coconut, but I defer to Amelia’s experience.
I also sympathize; it took me 27 years to figure out that I, too, was mislabeled as a girl, and longer than that to correct it. Luckily for the alleged sloth, or possibly coconut, SloCo is a very friendly and open organization and we can easily update our records. We also do not discriminate: both people and sloths of all sexes, genders, colors and species are welcome here.
Croissant is one of our Urban Sloths; sloths who have been volunteered to wear temporary radio collars and be studied so that we can better understand sloth behavior and how it is affected by humans in their environment. To this end we go out every day and track down each sloth, trekking through dirt roads, abandoned lots, overgrown jungle and occasionally backyards to find our Urban Sloths and gather data. I pull out a device for triangulating the height of trees and begin taking measurements of Croissant’s height, the tree that she (or maybe he) is in, and any observed differences since they were last spotted. As I do so, the radio antenna on my back shifts, pointing away, and begins beeping louder.
“Amelia?” I ask. “Are we sure that’s even Croissant?”
“It must be! How many tiny, 3-fingered sloths sleep in exactly this position, in exactly this Sangrillo tree, and also look exactly like Croissant?”
“Only, according to the radio, the sloth we’re tracking is over there.” I point in the opposite direction of where we are looking. “Do we have a confirmation of the collar?”
Amelia puts the binoculars up to her face again. “Not yet,” she grumbles, and soon we are climbing over the truck, standing in mud puddles (this would be me), craning our necks and using cell phones as zoom lenses to see if the alleged Croissant is wearing a radio collar. After a while, exhausted, hot, and covered in mud (mostly me), we have to admit that we cannot confirm this is our sloth. If sloths were people, we could just ask: Excuse me, what is your name? What are your pronouns? Do you like this tree? By the way, do you mind wearing a radio collar for a few months?
We spent the rest of the afternoon looking for the real Croissant, who, according to our instruments, is either 30 meters in the canopy pretending to be a termite nest, has buried her collar in the ditch, or has invented a new form of teleportation as a defense mechanism against being tracked.
Eventually, it begins to rain.
I run the equipment back to the truck while Amelia updates our records for the last several days with our new uncertainties. We don’t always like uncertainty, but this is science: just because something is easy doesn’t mean it is right, and making assumptions is not how you learn the truth.
Tomorrow we’ll be back again, looking not for the truths we want to impose upon others, but for the ones they have to teach us, if we are willing to listen.
If you are a fan of sloths, you might think that there are two main types:
Two-fingered sloths with their blonde fur and quintessential pig-like noses. There are two different species within the Choloepus genus.
Three-fingered sloths with their mottled grey fur and iconic black ‘masks’ around the eyes. There are currently four different species of three-fingered sloth all grouped together within the Bradypus genus.
But scientists are starting to realize that there is actually a third type of sloth. One that has the size, strength, and ferocity of a two-fingered sloth, but the physical appearance of a three-fingered sloth.
It is a species that no one really knows anything about, and one that scientists think is so unique that it might belong in a completely separate genus (called Scaeopus).
These are the maned sloths of Brazil, and they are the most endangered species among the continental sloths.
Maned sloths (Bradypus torquatus) are technically a species of three-fingered sloth, but they look and behave very differently to the three-fingered sloths that you might be used to.
Current research suggests that they separated off from the other sloth species approximately 19 million years ago and have been evolving independently ever since.
Unlike the other species of three-fingered sloths, the maned sloths are much larger with brown, fuzzy fur, and dark, hairless pads on their hands and feet (similar to the hands of two-fingered sloths).
They lack the iconic black mask around the eyes and male maned sloths do not develop a speculum.
Instead, both males and females of this species have spectacular long black manes of hair that tumble down around their necks and shoulders.
Working together to save sloths
While our SloCo headquarters are based in Costa Rica, we are committed to conserving and protecting all 6 extant species of sloth that are found throughout South and Central America.
Last month we were delighted to form an exciting new collaboration with Professor Gaston Giné and the Instituto Tamandua in Brazil to carry out important new research into maned sloth ecology.
Professor Gaston Giné has been researching maned sloths for over 10 years and much of what we know today about these sloths stems from the results of his work. He is a professor and researcher at the Applied Ecology and Conservation Lab of the Santa Cruz State University’s Biological Sciences department, and a research collaborator of the Instituto Tamandua.
Instituto Tamandua is a Non-Governmental Organization that works directly in the research and conservation of all Xenarthra species in Brazil (sloths, anteaters, and armadillos). Flavia Miranda, the founder and director of Instituto Tamandua, is the deputy chair of the IUCN Anteater, Sloth, and Armadillo Specialist Group.
Together with Professor Gaston Giné, Instituto Tamandua coordinates research into the maned sloths.
Due to the ongoing impacts of the COVID-19 pandemic, funding for wildlife research and conservation has become scarce as government resources are directed elsewhere. This crisis has left maned sloth research and conservation projects in Brazil vulnerable and in danger of running out of resources.
Thanks to the generous support of our donors, we are happy to have been able to provide funding for 10 new state-of-the-art GPS sloth backpacks that will be used by Gaston Giné and the Instituto Tamandua to continue their important work and better understand the ecological requirements, habitat preference, and movement patterns of this vulnerable species.
Team Sloth travels to Brazil
In March 2021, SloCo founder Dr. Rebecca Cliffe travelled to Brazil with two other members of Team Sloth (Cecilia Pamich and Patricio Silfeni), to deliver the new GPS backpacks and learn more about the maned sloths.
They travelled to the Reserva de Sapiranga, near Praia do Forte, where they met up with Gaston, his son Caian, and professional tree climber (and expert sloth spotter) Cosme Guimarães a.k.a. Coy.
For 7 days the team spent from sunrise until sunset hiking through the reserve searching for the elusive maned sloths. Some sloths were already being monitored by Gaston and needed to have their old backpacks replaced, but a lot of the sloths were new additions to the project.
Every time a sloth was found, Coy would quickly scale the tree and carry the sloth safely down to the ground where important body measurement data would be collected by the team. The new backpack would be fitted, and a brightly colored ribbon would be attached to the back to act as a visual marker for identification.
The sloths didn’t need to be anesthetized for the procedure as it was quick and simple, but it was necessary to use special Velcro mittens to cover the fingers and toes to prevent injury to the team.
During the course of the week, they managed to put GPS backpacks on 8 maned sloths (and mistakenly tried to capture a lot of termite nests that looked suspiciously like sloths)!
During their time in Brazil, the team were eager to learn more about the conservation problems being faced by maned sloths and to see how they could provide more help in the future.
Having come from Costa Rica (where sloths are literally falling from the trees and climbing through people’s houses), they were shocked to discover how few maned sloths there were inhabiting the Brazilian forest reserves.
The maned sloths they found were also all very shy, hiding at the tops of the tallest trees and moving higher when they heard the sound of approaching humans. This is in stark contrast to the sloths in Costa Rica that tend to ignore people completely and often wander unfearfully into urban areas (and therefore get themselves into trouble).
Finally, and perhaps most shockingly, the team were spooked by the eerie silence that followed them through the rainforest reserve where they were working. Upon entering a Costa Rican forest, you will reliably be greeted by the deafening hum of insects, screeching of parrots, and howling of monkeys. The rainforest feels and sounds alive. In the Reserva de Sapiranga of Brazil, the rainforest felt and sounded empty.
At first, they thought this difference was perhaps normal: the Atlantic forests are drier than the wet, humid rainforests of Costa Rica and so biodiversity is understandably different. But as the week progressed, it became apparent that poaching and human disturbances are big problems in this region. The team stumbled across several different poaching traps, and they noticed platforms that had been erected in trees where poachers would hide.
Why are maned sloths endangered?
While it is unlikely that people go out specifically to hunt sloths, it is known that sloths are opportunistically poached for food in some areas (on a recent trip to Guyana we discovered that sloth meat is regularly sold in illegal markets there).
Over time, it seems likely that opportunistic poaching may have contributed to the shy nature and low numbers of maned sloths remaining in the wild. However, this is certainly not the only problem.
Maned sloths have a very restricted range – they can only be found in a small strip of forest on the Atlantic coast of Brazil.Over 93% of these Atlantic forests have been lost in recent years due to deforestation for cattle pastures and plantations of sugar cane, cocoa, coffee, and eucalyptus.
As a result, maned sloths are severely affected by habitat loss, and the remaining forest reserves where they live are extremely fragmented and isolated.
How to help the maned sloths
In order to safeguard a future for the remaining maned sloth populations, a multifaceted conservation approach that engages and empowers local communities is required.
An important first step in the development of any conservation strategy is to properly understand the biological and ecological requirements of the species that you are trying to conserve. Without this knowledge, any attempt to mitigate the problems will likely be ineffective and short-lived.
We are hopeful that the GPS technology that we have provided will help to increase current knowledge about maned sloths, and we look forward to developing further conservation strategies with our partners in Brazil to help maned sloths in the future.
We would like to say a special thank you to Professor Gastón Giné, Instituto Tamandua, Applied Ecology and Conservation Lab of the Santa Cruz State University’s Biological Sciences department, Prefeitura de Mata de São João, the rangers of Sapiranga Reserve, and all the lovely people that shared their knowledge and experiences with us throughout our trip!
In an ideal situation sloths would live in primary rainforests, where the multi-story canopy interlocks and trees are shrouded in extensive epiphyte growth. In this environment, sloths are perfectly camouflaged and become practically invisible, hiding in the dense foliage at the top of gigantic trees.
Unfortunately, the remaining primary rainforests are dwindling as defirestation escalates, and sloths no longer have access to their preferred habitats. They are being forced to exist in increasingly urbanized environments, and here they cannot hide!
Sloths are slow-moving, habitual animals and are therefore very sensitive to changes in the environment. They are unable to run or jump to traverse gaps between trees, and so habitat fragmentation creates a lot of problems. While trying to navigate an increasingly urbanized world, sloths are being electrocuted on powerlines, attacked by dogs, hit by cars, and exploited by humans.
Sloths in Costa Rica are now considered to be of conservation concern due to habitat loss from agriculture, livestock production, and the increasing urbanization of the rainforest. In line with this, sloths are the most frequently admitted species to rescue centers in Costa Rica.
A massive lack of information on wild sloth behavior
Such a lack of knowledge makes it very challenging for us to develop effective methods to conserve sloths – it is very difficult to protect something that you don’t know anything about!
For two-fingered sloths in particular, even basic data on the natural history and ecological requirements of the species is lacking. For example, information on the habitat preference, ranging patterns, population densities, diet, and reproductive behavior of this genus is incredibly scarce, and for some sloth species, is completely absent.
With current extinction rates indicating that we are in the midst of a sixth mass extinction, a lack of knowledge covering the basic ecological requirements of a species is of concern due to the profound implications for the development of future conservation strategies.
The Urban Sloth Project aims to compare the behavior and activity budgets of sloths living in highly urbanized areas with those sloths living in healthier environments (protected primary rainforests).
Over the next 5 years, we will be tracking and monitoring 32 sloths (16 three-fingered sloths, and 16 two-fingered sloths) using VHF radio collars and compact data loggers. The results will be used to develop effective conservation strategies that will help humans and sloths to peacefully coexist.
Amount of time spent engaging in different behaviors.
Home range size.
Distance traveled per day.
Amount of time spent traveling in the canopy vs traveling on the ground.
Circadian rhythm of activity – How sloth activity is impacted by the environmental conditions (temperature, humidity, wind speed, rainfall, moon phase).
To protect sloths, we must first understand them
The knowledge we gain from this project will enable SloCo to make meaningful changes to the lives of sloths living in rapidly changing environments. For example, we will be able to identify which tree species are most important for sloths living in urban areas, and we can make sure that these species are protected and replenished.
We will also be able to identify areas where canopy connectivity needs to be improved to aid sloth dispersal via the installation of wildlife bridges and through targeted reforestation efforts.
You can follow The Urban Sloth Project through our social media platforms (Facebook, Instagram, or Youtube), and also by adopting Sharon, Croissant, and Cacao, where you will receive quarterly updates from our research team!
This project is only possible due to the generosity and kindness of our supporters – thank you for being a part of Team Sloth!
Paleontologists recently found compelling evidence of this predator-prey relationship, when they revealed an incredible specimen: the tibia of the giant ground sloth (Pseudoprepotherium) covered with 46 large teeth marks. Given the shape and size of the punctures, which were much too large for the other crocodilian species living in the area, scientists concluded that the attacker was a juvenile or sub-adult giant caiman (Purussaurus). Even as a juvenile, the giant caiman was estimated to be a whopping 4 meters (13 feet) long!
The pattern of bite marks suggests that the caiman attacked the sloth’s hind limb from below – much like their modern-day descendants do today.
The importance of wetlands to modern-day sloths
Although modern-day sloths have taken to the trees, wetlands still play an important role in their lives. From swamps to mangrove forests, these watery ecosystems are rich habitats for sloths. Low-lying marshy areas in Costa Rica are often filled with sangrillo trees – one of the sloth’s favorite trees that we grow in our forest nursery. The name “sangrillo” comes from the Spanish word “sangre” which means blood, because the sap of the tree is a dark red color.
Ancient ground sloths had the ability to stand on their hind feet, towering at an impressive 12 feet tall. Lacking this ability, how do modern tree-dwelling sloths navigate wetlands? Well, as it turns out, sloths are remarkably good swimmers, moving 3x as fast in water than on land.
Moreover, since these soggy areas are difficult to develop and prone to flooding, they are often the last refuges left for sloths and other types of vulnerable wildlife.
Swamps, marshes, mangroves, mudflats, lagoons, peatlands, bogs are all ecosystems that fall under the umbrella of what constitutes a wetland. A wetland is any area of land where water covers the ground, temporarily or at all times of the year. Many wetlands have the undeserved reputation of being smelly, inaccessible places that provide little to humanity.
Given how underappreciated wetlands are for all the gifts they bestow, it is understandable why many people find it so tempting to fill them. However, the ecological functions that wetlands provide disappear with the rising land. And inevitably the water will return, flooding the buildings and towns that were built upon the muddy ground.
Three-fingered sloth ‘adopts’ a two-fingered sloth baby!
These two sloths are not only different species, but they belong to two completely different families, separated by over 30 million years of evolution. Cross-species adoptions like this are incredibly rare in the wild, with only 3 other documented observations of this happening.
On the 20th December 2020, Gerald Pereira and Oscar Solano Rojas were guiding a group of tourists in Costa Rica. Sloths are a common sight on these tours, but that day they saw something that they had never seen before – nestled quietly amongst the rainforest canopy they spotted an adult three-fingered female tending to a two-fingered baby sloth.
Gerald and Oscar, both with over 11 years of experience working as ecotourism guides, knew they had witnessed something important.
The curious pair were observed in a fragmented strip of rainforest, sandwiched between a river, a pineapple plantation and a busy road. According to Oscar, “in that area, local people take great care of the sloths, so we always go to look there because there is a very large population”.
“Yesterday we started the tour, which we call the ‘Sloth Tour’, as usual. To see them active in the early hours of the day, we started the tour at 6am. Around 8am we arrived at a place where my partner Gerald and I saw a sloth hanging from a Cecropia tree. At first, it did not attract much attention, we saw that she was a female and a baby, but that morning we had already seen 3 baby sloths, and we did not think it was anything special or different from what we had seen. When we paid more attention to them, however, we discovered that it was a three-fingered female and a two-fingered baby.”
“I had already seen the two species in the same tree many times, and at first we thought it was just a coincidence that they were there together. When we found them it seemed like they were waking up. They both started scratching, and then the baby separated from the female, fed on cecropia leaves a little, and I thought that was the end of the interaction.”
“But then you see how the baby returns to the female, and she receives it with total naturalness, that is what surprised us the most. None of us who were there could believe it, neither Gerald nor I, because we had never seen it before. It left me astonished. In rescue centres, I had seen a certain attachment between the two species, but never in their natural habitat, as happened to us yesterday.”
As can be seen in the video footage captured by Gerald and Oscar, it does indeed appear that the two sloths interact with the gentle tenderness of a mother-baby relationship. When they returned to the area the next day, they once again found the pair snuggling together in a shady spot in the canopy. It certainly looks like the bond between these two sloths is much more than just a fleeting interaction. It appears as though the female has formally adopted this baby as her own.
Adult animals adopting unrelated young is nothing new to science, but in most cases these are intraspecies interactions – meaning that they occur between two unrelated individuals of the same species. This has most commonly been observed within sociable species, often herd or pack animals.
Interspecies adoptions – where a female adopts a baby of a different species – is an altogether much rarer occurrence in the wild. In fact, there have only ever been 3 other documented instances of this happening, and it has never before been observed in sloths.
In 2004, a group of capuchin monkeys were documented caring for a baby marmoset, and in 2014 a bottlenose dolphin adopted a baby melon-headed whale and nurtured it for it for 3 years. More recently, a lioness in India was found to have adopted an orphaned leopard cub in 2018 and she raised it alongside her own offspring.
Why do cross-species adoptions occur?
In evolutionary terms, caring for another animal’s offspring like this doesn’t make much sense. Raising a baby demands a lot of time and energy (something which a sloth has a limited supply of), and it is usually done with the purpose of propagating an individual’s own genes. So why do cross-species adoptions like this sometimes happen?
The truth is, scientists are still trying to understand it. Because these events are so rare, there isn’t much information available and each observed case appears to be very different. There are two popular theories:
Instinct: A lot of adult female animals are biologically hardwired through evolution to care for helpless infants. A cross-species adoption might occur accidentally after a female has recently given birth herself, when high levels of the hormone oxytocin encourage her to bond with the orphaned baby (even if it isn’t hers!).
Mutual benefit: If the benefits of the raising an unrelated baby outweigh the costs, this could explain why some interspecies adoptions take place. For example, it could be beneficial for a group of animals to add a new individual that would help to secure more food, or provide added protection. In some social species the simple benefit of companionship may be a driving force! This is unlikely to be an important factor for our solitary sloths though.
How did this happen?
The circumstances surrounding this adoption are not entirely clear, but SloCo founder and sloth expert Dr. Rebecca Cliffe has some ideas about what might have led to this unusual event.
“This is the first time that anything like this has ever been seen before in wild sloths, and it is certainly very interesting. I am used to sloths surprising us, but this has to be one of the most unusual things I have heard about. I suspect there are three possible scenarios which may have led to this happening:
1) Accidental human interference. Maybe someone found the baby sloth alone and tried to ‘reunite’ it with its mother, but accidentally paired it with the wrong sloth. Reuniting baby sloths with their mothers is a surprisingly common requirement for people in Costa Rica as babies are often found alone on the ground after falling from the tree.
A lot of people don’t realise that there are two very different types of sloth, and so they might not have realised what they were doing. In this situation, however, I would expect the adult sloth to reject the baby and so this feels like an unlikely scenario
2) The baby sloth lost it’s own mother, and instinctively clung onto the fur of another sloth. Baby sloths are born with a strong instinct to cling onto mom’s fur, and if they are separated, they tend to cling onto the next best thing. It isn’t impossible to think that this baby may have climbed onto the three-fingered sloth after becoming orphaned. However, in this situation I would also expect to see the adult sloth looking agitated and stressed out by her new uninvited companion – and I doubt the relationship would last more than a few hours.
3) The baby sloth lost its own mother, and the adult sloth recently lost a baby of her own. This unusual combination of events would provide a feasible opportunity for the pair to bond naturally due to a mixture of instincts and hormones. Although extremely rare, I think this is probably the most likely scenario!”
What happens next?
This unprecedented behavior leaves all of us with many questions – particularly regarding the welfare of both sloths! Will the baby survive? It’s certainly possible. While they are different species, they do share a broadly similar ecology.
The diets of both sloths overlap heavily, with both being predominantly folivorous (eating only leaves). Two-fingered sloths tend to be more flexible and adaptive with their choices, while three-fingered sloths are more selective about what types of leaf they will eat. With both species, babies maternally inherit knowledge about which trees are safe to feed from – and this arrangement may work in the baby’s favor!
Furthermore, it appears as though the baby sloth is approximately 7 months old. At this age, the baby would not be as reliant upon a steady source of milk from the mother as the natural weaning process would be taking place. Although the adult female could be producing milk, we don’t think this is essential for the survival of the baby at this stage.
Two-fingered sloths are also much larger than their three-fingered counterparts when fully grown, which means that the adoptive mother may have a challenge on her hands when lugging around her overgrown offspring.
But what happened to the baby’s biological mother? This remains a mystery. Considering the location in which the pair were observed is highly disturbed, it may be that she got into trouble with the busy road or nearby pineapple plantation. Or perhaps there was an accidental baby mix-up, and somewhere in the rainforest, a mother two-fingered sloth is tenderly nurturing a baby three-fingered sloth. It’s doubtful we will ever know for sure.
While there are certainly a lot of challenges for this pair to overcome, here at SloCo we have high hopes for their survival. After the unprecedented global difficulties that 2020 has brought, we are happy to embrace this heart-warming story (which has all the makings of a future Disney movie!).
We will be working closely with both Gerald and Oscar to monitor the two sloths as time goes on – we will keep you updated on their progress! For now, we are keeping our fingers and toes crossed for a happy ending.
It’s with a heavy heart that we must inform our supporters that the wild three-fingered sloth mom that was found to be caring for a two-fingered baby has passed away.
Local guides who were tracking the pair witnessed the mom and baby fall from their tree. Unfortunately, mom did not survive the fall. The baby was uninjured and climbed back up into the tree.
The guides continued to watch over the baby for the rest of the evening, and returned to the spot every day to check on him – but after three days he had ventured off on his own into the rainforest.
We estimate that the baby was around 8 months old, at which point he would naturally begin to distance himself from his mom. Team Sloth is optimistic that his two brilliant sloth moms taught him everything that he needs to know in order to survive in the wild!
The ‘mummified’ skin of a giant sloth proves that they coexisted with the first humans of South America
Although it was on display for a long time at the Museum of La Plata, Argentina, its age was uncertain. A new study indicates that giant ground sloths lived 13,000 years ago and coexisted with the first humans of South America.
The mummified skin of the mylodon was found on a scientific expedition organized in 1899 by the Museo de La Plata (UNLP). Mylodons were an extinct genus of animals that lived during the Pleistocene, a period that ranged from approximately 2.5 million to 10 thousand years ago.
Since it was first discovered in 1899, it has remained on exhibit. The artifact is a true treasure considering its surprising degree of preservation: it still has hairs and soft parts. After extensive discussions about its age, this remarkably preserved skin lost the interest of paleontologists until recently when a group of experts resumed studying it and dated it again. This time they used sophisticated techniques that left no room for doubt: the owner of that tissue lived about 13,200 years ago. This discovery has just been published in the journal Quaternary Science Reviews.
The skin of the giant sloth
The giant sloth – the common name for this genus – was one of the largest land animals in South America, weighing more than 1 ton and measuring 3 meters (almost 10 feet) in length. It had huge claws and walked on all fours, although it is thought that it could also stand on its hind feet (bipedal). With its herbivorous habits, it was part of the South American megafauna, the large mammals that dominated the planet during the Pleistocene.
The skin was found in the Cueva del Milodon (Milodon’s cave), a natural formation located in southern Chile that was explored in the late 19th century. The cave contains countless paleontological remains, and even evidence of early human activity. At that time the geographic limits of Argentina were still being established, which allowed for expeditions of many different origins to go and collect materials. As the story goes, when Argentinian naturalist Florentino Ameghino first saw the remains, he assumed that they belonged to a living species. This led him on an impassioned quest to find a living specimen, which of course did not happen.
“The skin is really striking: it is a centimeter and a half thick with long reddish-yellow hairs and it is hard like wood. In what would be the interior, it is covered by a ton of small bones, similar to a suit of armor, which is typical of some species of fossilized sloths,” explains Néstor Toledo, CONICET (National Council for Scientific and Technical Research) researcher on the Faculty of Natural Sciences and Museum of the National University of La Plata (FCNyM, UNLP) and one of the authors of the work.
First dated in 1974 with questionable results, the team of scientists sent a sample back to the same radiocarbon laboratory in the United States that had done the original analysis. They used a method to determine the age of carbon-containing materials and this time it was clear that that the sample was over 13,000 years old. The authors of the study also sent a fragment of skull bone from the same cave to an Argentinian laboratory which turned out to be 11,300 years old. This was the same age of two bone tools carved by ancient humans that were found next to the sloth hide, according to the original reports of the find.
The specialists also examined two sloth shoulder blades, one belonging to the local collection and the other belonging to the Zurich Museum of Natural Sciences. These bone pieces, which were dated between 12 and 13 thousand years old, have cut marks on made by tools and evidence of them being dragged across the ground. “This constitutes indirect evidence of human presence, that of course must continue to be studied, but it is an indisputable proof of coexistence with human beings and, if verified, it would be one of the oldest records in South America,” says Leandro M. Pérez, CONICET researcher at the FCNyM and leading author of the publication. This question takes on a special interest considering the debate on whether or not this giant fauna coexisted with these first settlers.
In addition to the new ages obtained, the investigation includes an exhaustive review of the dating methods of all the mylodon remains found in that same cave which appear in the scientific literature. Starting with the first of them, carried out in 1951 by Williard Libby, the winner of the Nobel Prize in Chemistry in 1960 and creator of the radiocarbon method, they verified a total of 36 records, discarding those that were unsuccessful or uncertain.
“We have taken on the monumental job of searching for each published piece of information, tracking the sample it refers to, and calling the laboratory in charge of dating it to trace a match between these references. We found some errors and we left only those reliable historical values,” Pérez explains, and adds:” It is not that before they worked badly, but that the protocols that we use today did not exist at the time. For example, they didn’t understand the importance of including a photo or a drawing of a material or assigning it a catalog number in the collection.
As a final reflection, the researchers highlighted two important values of their work. “On the one hand, there is interest on the climatological level, since it was a time of intermittent glaciations. Despite the very harsh conditions due to the cold and the amount of ice, this cave was inhabited continuously for at least a thousand years, according to our bibliographic review. For this reason, it raises countless questions about how this fauna could have evolved, which in the case of the ancient sloths were gigantic and woolly, while their current relatives are small and live hanging from the trees in tropical jungles,” argues Toledo.
Pérez alluded to a second relevant question, related to “the importance of valuing the heritage we have and the way the naturalists worked at that time, people who traveled to distant and hostile places without even knowing if they would return alive. Many museums in the world have pieces from this site because they were bought from collectors. But on the other hand, very few, like ours, have materials recovered in scientific expeditions organized and led by researchers from the institution.”
Although there is talk of “mummified” skin, in reality it is unclear if the term exactly applies to the way the famous “sloth leather” was preserved. “It is not how one might imagine an Inca or Egyptian mummy, subjected to a series of deliberate treatments to preserve it in this way. There was no dehydration here because the cave was terribly cold and humid, and it wasn’t from freezing either.
What took place was a more complex process. Right now we are carrying out a chemical analysis on some of the microcrystal sheaths that cover each hair, that we saw through electron microscopy,” described the authors, who speak of a kind of “natural tanning.” The material was buried under a meter-thick layer of manure that was compacted, and therefore lacked oxygen. “We think that the excrement produced the release of tannins, chemical compounds that are used to tan leather, and that spontaneously triggered the process,” concluded the experts.
-By Mercedes Benialgo, CONICET La Plata
Leandro M.Pérez, Néstor Toledo, Florencia Mari, Ignacio Echeverría, Eduardo P. Tonni, Marcelo J.Toledo. Quaternary Science Reviews. Radiocarbon dates of fossil record assigned to mylodontids (Xenarthra – Folivora) found in Cueva del Milodón, Chile. DOI: https://doi.org/10.1016/j.quascirev.2020.106695.
But what does this mean? And how does maintaining universal access to information have anything to do with sloths? In our quest to better understand these unique and enigmatic creatures, all information about them is valuable. Moreover, the success of the scientific method relies on open and equal access to information.
One of the key drivers behind the success of the scientific method has been the sharing of information. Studies are repeated in different contexts to see if the same results emerge and the knowledge gained from these experiments serve as the inspiration for new studies. Together we begin to chip away at the mysteries of the universe. However, despite its power, knowledge has not always been shared equally.
Today, many of our libraries have entered the virtual realm and yet they continue to provide free access to a great assortment of educational materials. However, despite the importance of open access to information, many scientific journals still act as the gatekeepers.
If you are a scientist who has just completed a study, your next step is often deciding whether you would like to publish your article in a traditional journal or an open-access journal. Historically, journals were only available in print form. Now in the age of the internet, many journals have opted to virtually publish their studies online.
Like public libraries, open-access journals are free and can be read by anyone with an internet connection. Seems like the best choice, right? Although publishing in an open-access journal can often lead to more visibility (since the study is readily available) there are hidden drawbacks.
Scientists pay to publish, and readers pay to view
Unlike most other trades, scientists do not get paid to publish their work – it is actually the exact opposite. First, scientists have to find funding for their research (through grant applications, fundraising or self-funding) and do the hard work of actually completing the investigation. If the project goes well and they end up with a publishable paper, they then have to pay a scientific journal to publish it.
The publication fees are typically thousands of dollars (with the cost to publish in the highest ranking journals often exceeding $10,000 per article).
The majority of scientific journals then charge an additional fee to anyone who wants to read the paper after publication. Many universities will pay the subscription fees, making a variety of journals and publications accessible for “free” to their students. However, for an individual who is not studying at a university, a single article can cost $30+. A price that for many is prohibitively expensive.
For this reason, publishing in an open-access journal is significantly more expensive than publishing in a more traditional pay-to-view journal. Unless the scientist hoping to publish the study has these kinds of funds available, they may have to choose a more restricted access journal, or not publish the important findings from their work at all!
Paying to access scientific information is not an option for the majority of people living and working in regions that are of critical conservation importance.
There is an important overlap between areas of poverty and key areas of global biodiversity. If the people working on the ground to protect and conserve wildlife cannot access the latest scientific information due to the financial constraints (or language barriers, with the majority of scientific journals only publishing in English) then the information isn’t reaching the people who need access to it the most.
SloCo’s commitment to open-access
Here at SloCo we believe that knowledge should be shared. Therefore all of the research that we have conducted on sloths is published in open-access journals. Our hope is that by enabling everyone access to this information, we can harness the power of collaborative science in order to more effectively understand sloths and how we can help them.
Five-ton giant sloth lived in Costa Rica seven million years ago!
A giant sloth weighing five tons and whose height could exceed twice that of a human being was part of prehistoric Costa Rica seven million years ago.
A group of paleontologists is working hard to determine the characteristics of this giant sloth to see if it corresponds with previously described species – or whether it is completely new to science!
This is part of a project that started in 2003 in San Gerardo de Limoncito, Coto Brus, about 11 kilometers from San Vito. In this area, the researchers searched for bones and fossils of different species.
For more than a decade, Ana Lucía Valerio, coordinator of Geology at the National Museum, and César Laurito from the National Institute of Learning (INA) searched and analyzed more than 2,600 samples of bones from dozens of different species that appeared throughout the expeditions.
“When I decided to go for paleontology, no one cared for something to appear here. Venturing out to find mammals was unthinkable. They told us ‘you are looking for little bones, it is not important, but the finding makes the world look again and say ‘something is happening here, something we did not expect and that is changing the vision of biological exchange'” Laurito explained.
This region is important because it provides further proof that Central America served as a bridge for animals to cross from South America to North America and vice versa.
“We are talking about something very old. The Isthmus only closed about 3.5 million years ago, but these sloths lived seven million years ago. So how did these giant animals from South America get to southern Costa Rica if they had no adaptations for swimming? It is possible that for a time there was a pass, a land bridge, for these animals to cross. This passage could exist for a short period of time, but for paleontology, a short period of time could be a million years ”
“In other words, species from South America are appearing much earlier than expected – by about four million years” he clarified.
In recent years, Valerio and Laurito have described many different species of prehistoric horses, camels, armadillos, and other types of mammals on Costa Rican soil.
However, they had a problem with the sloths’ material as they had no way to compare it. This type of research in paleontology is very new in Costa Rica, and so they formed a collaboration with Ascanio Rincón, head of Paleontology at the Venezuelan Institute of Scientific Research, who has been studying these prehistoric giants for many years.
Rincón helped to complete the next part of the analysis: determining what kind of sloths they are. All of the bones were found at the same site, but they accumulated during different years of searching.
“There is no record of these animals in North America until much later. What prevented them from crossing? Or what did they find here that made them stay longer without moving?” Rincón wonders.
For this new analysis, all bones must be photographed, measured, analyzed, described and compared with the bones of other giant sloths. After all of this, important aspects of these populations can be determined.
“Now we have to do the hard work, which is to compare it with the rest of the 14 or 15 genera that exist and determine who it resembles the most and who it resembles the least and see if we are dealing with a new species,” said Rincón. This is not easy. It is very difficult to find complete bones and so they only have small samples from which to draw conclusions.
“This is not how it looks in the movies. Not that it was just brushed off a bit and there it all appeared. We had to chop very hard rocks to be able to remove this. It took a lot of strength, a lot of searching, and sometimes bones of some species appeared, while sometimes other bones of other species. What we have today was put together and gathered over several years ”, Laurito indicated.
Rincón added: “It is hard to be able to know what is happening with only 15% of the body; how to put this puzzle together? In this case, we do have material from various types of bone that help us to better understand the panorama”.
The researchers reported that at least three individual sloths have been found as they discovered three bones of the same type but different sizes (ages). This indicates that these giant sloths may have traveled in a herd or as a family.
What do we know about this animal?
Although it is difficult to properly visualize what these extinct sloths looked like, scientists do have some ideas!
For example, it is known that they walked on the soles of their back feet and on the knuckles of their hands. The front claws were very strong and were probably used for digging. Furthermore, due to their massive size and weight, these sloths probably did not climb trees!
Their teeth were so strong they could feed on wood and other hard materials. These teeth had a remarkable ability to regenerate from the wear and tear that was incurred when chewing. In fact, chewing was essential to prevent the teeth from overgrowing and causing problems!
Giant sloths are known to have been social animals, possibly living in large herds or family groups.
The importance of the discovery
Within these discoveries, there could be now-extinct species that are new to science.
“The fossil hunter does not kill his prey, he resurrects it. We resuscitate that dam that we are looking for in order to get to know it and for people to know it” said Rincón.
Why is this important? Rincón was emphatic: “This type of knowledge helps us to understand who we are, where we came from, and it gives identity to the Isthmus. We cannot judge a book by its last page, we must see what comes before, and that is why it is necessary to study paleontology ”.
Six years ago, SloCo Founder Dr. Rebecca Cliffe launched a major research project into sloth genetics in Costa Rica. She started this project because she was concerned with the number of wild sloths in the South Caribbean region that are being born with debilitating birth-defects (missing fingers/toes, malformed ears, and misshapen limbs), and she wanted to know what was happening.
The results of this project have now been published and they reveal an unexpected situation with far-reaching implications for future sloth conservation and rescue efforts.
We collected hair samples from 98 two-fingered sloths (Choloepus hoffmanni) that originated from different regions throughout Costa Rica and used microsatellite analysis to look at the population genetics.
We made 3 important discoveries regarding sloth genetics:
We were able to identify 4 genetic groups of two-fingered sloths in Costa Rica (this is similar to having 4 genetic origins). If you are familiar with Costa Rican geography, these are the groups that we identified:
The West – sloths from the San Jose region
The North – includes sloths from areas surrounding Guápiles and further North
The East – sloths from within Limón city and surrounding areas
The South East – the South Caribbean region ranging from Bananito down to Manzanillo and BriBri.
It is important to note that there are probably many more groups than the four that we identified, but for logistical reasons we could not collect samples from sloths spanning the whole country. Our results only reflect the areas where we were able to focus our sampling efforts.
1) Sloths in the North are genetically distinct.
Sloths in the ‘North’ group were found to be genetically very distinct when compared to the other populations. This means that sloths in this region are substantially different from sloths in other areas of Costa Rica that we sampled. We suggest that it may be important to recognize this sub-population as a separate unit for management and conservation purposes.
2) Sloths in highly urbanized areas are inbreeding.
Sloths in the ‘West’ group have higher levels of inbreeding, (when individuals who are closely related reproduce). This may not be surprising when we consider that sloths here are restricted to living in severely fragmented forest pockets within the highly urbanized San Jose region.
This suggests that we need to focus more conservation and research efforts in this region to better understand the long‐term effects of habitat fragmentation.
3) Sloths have been moved around by humans.
Finally (and perhaps most importantly), we discovered that sloths in the West, East and South East groups were all surprisingly similar. This close relatedness between sloths living on opposite sides of Costa Rica is an unexpected and potentially concerning result. Particularly when we consider the vast geographical distance between these populations and the inability of sloths to travel long distances.
Interestingly, sloth populations in the South Caribbean were found to be more genetically diverse and had high levels of admixture (which means lots of sloths from lots of different origins have been reproducing with one another).
All of this points towards the translocation of sloths by humans in Costa Rica, where individuals have been removed from their areas of origin and released somewhere else.
How could this happen?
When we consider that approximately 3 – 4 sloths are admitted into rescue centers every single day in the South Caribbean, it is not surprising that some of these animals may have originated from further away.
The translocation of wildlife was particularly prevalent in earlier years when there were not as many rescue centers who knew how to properly care for sloths. The government of Costa Rica (and in one case a national airline) would regularly deliver inured sloths from all over the country to the Sloth Sanctuary on the Caribbean Coast as they were considered to be the only experts in sloth rehabilitation at the time.
This has since changed. In the last decade there has been an explosion of new rescue centers. Costa Rica now has more rescue centers per square mile than any other country, with over 250 registered facilities currently rescuing and rehabilitating wildlife! The current abundance of rescue centers means that the cross-country translocation of sloths may be less of a problem, but the regulation of release protocols is more difficult.
Is this mix-up of sloth genetics a bad thing?
We do not know, but it could be.
You may think that high levels of genetic diversity are considered to be a good thing in wildlife conservation – and this is true. Increased genetic diversity means less inbreeding has occurred and gives populations a stronger ability to adapt when faced with change.
However, as with most things, it is rarely that simple. Mixing individuals from different genetic backgrounds can also have a dangerous effect on the health and viability of populations through a process called ‘outbreeding depression’.
Animals often have unique genetic adaptations that help them to survive in the particular environment in which they live. For example, sloths that live in cold montane regions have adaptations to cope with a colder climate, including longer, thicker, and darker hair compared to their lowland counterparts. By moving individuals around, these adaptations can be lost and the inter-breeding that occurs can negatively impact the health of these populations.
A similar situation was recently discovered in orangutans that were reintroduced to the wild from rescue facilities in Borneo without knowledge on the genetic background and subspecies status of the individuals.
What does all of this mean for sloth conservation?
The genetic diversity between separate sloth populations have emerged over the course of millions of years. By mixing together populations that perhaps haven’t been in contact for millennia, we are potentially causing irreparable changes.
It may be that inter-breeding sloths from different genetic origins has no negative effects at all. But what if it does? Suddenly, we will have inadvertently compromised the viability of wild sloth populations and no amount of conservation work can ever reverse that damage.
Is it worth the risk?
This discovery means that rescue facilities in Costa Rica should consider the genetic background of rehabilitated sloths when planning future reintroductions. Sloths should be released in the areas where they originated from whenever possible.
This will undoubtedly present a challenge for overburdened and underfunded rescue centers. Combined with increasing pressure for post-release monitoring, it may seem impossible for animals to be returned to the place of origin and simultaneously tracked to ensure survival.
Furthermore, it may not be possible to always return an animal to the place that it came from. There may be a lack of suitable habitat in that area, or the rescue center may not have accurate records on where the animal was originally found (rescued animals often pass through several pairs of hands before arriving at a rescue facility, and tracking down the origin can sometimes be difficult).
What can we do moving forward?
There will be no convenient solution, but we must work together to find one.
Ultimately it is going to require increased government assistance, funding and collaboration between different rescue centers and release sites throughout Costa Rica. It will require increased transparency and improved record keeping in order to ensure that rescued sloths are returned to where they were found.
Furthermore, it will require the preservation of habitat where these distinct sloth populations are living (since they cannot be brought elsewhere).
When sloths were first being transported around the country, we didn’t know better. Now we do. Equipped with this new knowledge, we can now ensure that our actions to help them will truly lead to a long and healthy future for sloth populations in Costa Rica.
~ Dr. Rebecca Cliffe
Founder and Executive Director