First Fossils of an Aquatic Sloth Found in Continental Environment in Argentina

First Fossils of an Aquatic Sloth Found in Continental Environment in Argentina

Researchers have discovered the remains of a specimen of Thalassocnus, a marine sloth found for the first time in a continental environment in Northern Argentina. This discovery significantly expands the geographic distribution of this lineage of fossil sloths.

A team of paleontologists from CONICET Argentina has discovered the remains of a specimen of Thalassocnus, a marine sloth, for the first time in a continental environment. The discovery occurred in the province of Jujuy, Northern Argentina. The team estimates the age of the fossils to be between 3 and 5 million years old, corresponding to the period between the latest Miocene and the Pliocene.

Thalassocnus is a type of giant sloth that could reach almost two meters in length and weigh more than 120 kilos. The remains found in Jujuy belong to an upper limb of the animal and include the radius, ulna, and part of the articulated left hand.



An aquatic sloth on the mainland?

The research team poses two hypotheses in the paper. The first one estimates that the progressive aridization that developed since the Miocene on the Pacific coast could have been a factor that stimulated the dispersion of Thalassocnus towards southern zones, such as Chile, and later to continental zones, such as the eastern Puna, in search of favorable conditions. }

The second hypothesis proposes that its original distribution could have been much broader, including Argentina, Peru, and Chile, and that later the most derived species adapted to marine environments. “This specimen was found very far from the coast, so this new evidence indicates that this specimen, like other sloths that have been studied in Peru, were less adapted to marine environments and that they had the possibility of having a frugivorous diet. and omnivorous”, adds Sofía Quiñones, CONICET postdoctoral and first author of the research.


Restoration of Thalassocnus natans. Proportions based on skeletal mount. Credits: Wikipedia / FunkMonk (Michael B. H.)

Why is this discovery important?

This discovery significantly expands the geographic distribution of this lineage of fossil sloths, and the importance of this record for Argentina and for the entire continent cannot be overstated. The research team continues to carry out annual campaigns in the region in search of new specimens that will allow for further expansion and elucidation of the history of this enigmatic animal.

The article “Unexpected record of the aquatic sloth Thalassocnus (Mammalia, Xenarthra, Folivora) in the upper Neogene of the Puna (Jujuy, Argentina)” was published in the Journal of Vertebrate Paleontology in 2022.

Source: CONICET Nordeste. Top Image: Pedro Cuaranta

Bibliographic reference:
Sofía I. Quiñones, Alfredo E. Zurita, Ángel R. Miño-Boilini, Adriana M. Candela & Carlos A. Luna (2022): Unexpected record of the aquatic sloth Thalassocnus (Mammalia, Xenarthra, Folivora) in the upper Neogene of the Puna (Jujuy, Argentina), Journal of Vertebrate Paleontology

Resurrecting giant ground sloths with Augmented Reality

Resurrecting giant ground sloths with Augmented Reality

For a chance to picture what the prehistoric Shasta ground sloth may have looked like, virtual and augmented reality may be our best bet.

Ice Age giants such as mammoths, mastodons, giant beavers, saber-toothed cats, and dire wolves once roamed the American continent with giant ground sloths. But around 10,000 years ago, after the end of the last Ice Age, America’s impressive megafauna went extinct.

It’s not known how exactly these species met their end, but some scientists now argue that it was a combination of both climate change and human hunting.

These prehistoric animals have long-captured the imaginations of scientists, artists, and the general public. They have been depicted at museums and in popular media for many decades — often with a bit of artistic license thrown in!


humans hunting giant sloth
A recreation of humans hunting giant sloths / Illustration: Alex Macclelland, Bournemouth University.

Paleoart and Augmented Reality as an educational tool

Understanding the importance of paleoart as an educational tool — and that much of the paleoart that exists in popular culture is not based on hard paleontological evidence — a team of scientists have sought to digitally recreate these long-departed Ice Age creatures in a scientifically accurate way.

In their paper, La Brea Tar Pits Paleoart published in Palaeontologia Electronica, the team laid out the design of 13 Ice Age animals, citing their scientific methods and encouraging their research to be discussed, peer reviewed, and referenced for future work — something not before seen in paleoart.


From the article: A. Low immersion conditions used a handheld smartphone. B. High immersion conditions used a smartphone inserted into an inexpensive headset. C. To provide binocular vision in the headset, the smartphone screen is split into two smaller images, greatly reducing available screen space and resolution. 


“We think paleoart is a crucial part of paleontological research,” said Dr. Matt Davis, the study’s lead author. “That’s why we decided to publish all the scientific research and artistic decisions that went into creating these models. This will make it easier for other scientists and paleoartists to critique and build off our team’s work.”

The team created reconstructions of Ice Age animals that were found in the La Brea Tar Pits in Downtown LA — an important site for paleontologists owing to the incredible level of preservation of the fossilized plants and animals found there. Almost as well known are the models and sculptures that have been created for the tar pits to convey to the public what it might have looked like during the Ice Age.
Yet these sculptures, argue the authors of the paper, are scientifically inaccurate. They point out that Harlan’s ground sloth has been reconstructed with a worryingly inconsistent number of toes! Such inaccuracies often seen in paleoart not based in grounded science can lead to, and perpetuate, misconceptions about Ice Age animals.


From the Article: Stages in the development of a low poly dire wolf model. A. Mesh showing the overall 3D shape of the model. B. Rigging showing the model’s skeleton. Colors represent the “weights” of different bones and joints on the overall model’s deformation while moving. C. The 2D texture file. D. The finished, rigged model with texture correctly wrapped around the mesh.

The Shasta’s sloth

In digitally recreating Ice Age animals found at La Brea Tar Pits, the team analyzed fossils of the extinct animals, and in some cases, the closest living relatives of the extinct species were used as a reference. The morphology and behavior of living animals such as the Przewalski’s horse, polar bear, and African lion were coded into the metaverse Ice Age animals.


Model of Shasta ground sloth (Nothrotheriops shastensis).
Model of Shasta ground sloth (Nothrotheriops shastensis). Check the 3D model animation here.


As there are no close living relatives of the Shasta ground sloth, the team based the AR version on a fossilized specimen that was found preserved in guano inside a fumarole in Aden Crater, New Mexico. The bones of this animal were held together by preserved ligaments and tendons, giving the team a very accurate view of the sloth’s morphology. Incredibly, the sloth was so well preserved that it still had patches of skin, which included 45mm-long pale yellow hair. The digital Shasta ground sloth’s face was given coloration common to the modern three-toed sloths.




The Harlan’s ground sloth


Model of Harlan ground sloth (Paramylodon harlani)
Model of Harlan ground sloth (Paramylodon harlani). Check the 3D model animation here. 


Harlan’s ground sloth was also brought to life in AR and VR. As there was no preserved soft tissue found for this animal, the scientists looked to the mylodon, a ground sloth of similar size and shape to the Harlan’s ground sloth. A mylodon specimen was found with patches of skin containing reddish-blond fur, which the team decided to give to their digital Harlan’s ground sloth.



Meet the Ice Age sloths with your phone!

If you want to meet the Ice Age ground sloths along with their prehistoric neighbors in AR, you can experience them via Snapchat by scanning the below codes; via Instagram by searching in the Effects gallery, or via the SketchFab app.

sanpachat codes to see ground sloths


You’ll meet the animals in deliberately low-definition so that they can run on phones. This also gives scientists the opportunity to refine features as fossil data continues to be unearthed.

William Swartout, CTO at California Institute for Creative Technologies and co-author of the study explains: “The innovation of this approach is that it allows us to create scientifically accurate artwork for the metaverse without overcommitting to details where we still lack good fossil evidence.”


-Samantha Stocks

SloCo Collaborator

Prehistoric Rock Art Might be Early Representations of Giant Ground Sloths 

Prehistoric Rock Art Might be Early Representations of Giant Ground Sloths

In the Amazon rainforests in the country of Colombia, there is a place called Serranía La Lindosa, with rock cliffs decorated in ancient drawings. There are thousands of paintings covering 12 kilometers (8 miles) of rock in an area that has been largely inaccessible. Some of the paintings depict animals easily recognizable to modern people, such as turtles, guanacos, or humans—and just possibly, giant sloths.


Juancho Torres/Anadolu Agency via Getty Images


A study by José Iriarte and his colleagues published in the journal Philosophical Transactions of the Royal Society proposes the following:

“We argue that they are Ice Age rock art based on the (i) naturalistic appearance and diagnostic morphological features of the animal images, (ii) late Pleistocene archaeological dates from La Lindosa confirming the contemporaneity of humans and megafauna, (iii) recovery of ochre pigments in late Pleistocene archaeological strata, (iv) the presence of most megafauna identified in the region during the late Pleistocene as attested by archaeological and palaeontological records, and (v) widespread depiction of extinct megafauna in rock art across the Americas.”

Daily life scenes

The paintings of the Serranía de la Lindosa are surprisingly well preserved. Some of the scenes seem to show the first contemporary humans in early Amazonia going about their daily life, while others seemingly depict ritual scenes, hunting, interacting with plants, and forest and savannah animals.


Photo: Wikipedia / Julianruizp


Pictures of birds, turtles, and other animal species that inhabit this large tropical forest require little interpretation; however, there is controversy among paleontologists and archaeologists about whether the other creatures represented are in fact giant sloths, elephants, and prehistoric horses.

A giant sloth with a baby?

One of the pictures is the silhouette of a large animal that might be a giant ground sloth, along with a miniature version of itself that it is probably safe to call its offspring. As any would-be artist of modern sloths can tell you, they are not creatures with particularly distinctive shapes.


Ice Age megafauna rock art in the Colombian Amazon? José Iriarte, Michael J. Ziegler, Alan K. Outram, Mark Robinson, Patrick Roberts, Francisco J. Aceituno, Gaspar Morcote-Ríos and T. Michael Keesey


Interpretation of the silhouette as a sloth relies heavily on the assumption that the ancient artists faithfully represented the proportions of the creature in question, which—given the depictions of the nearby human figures—they did not always do.


(a) Giant sloth painting at La Lindosa: 1. massive claws; 2. short rostrum; 3. large head; 4. robust thorax; 5. inverted pes; 6. offspring; 7. miniature men. (b) Artistic reconstruction of Eremotherium patterned after its closest living relative Bradypus. (c) Artistic reconstruction of Arctotherium patterned after its closest living relative, Tremarctos ornatus (Mike Keesey). Keesey’s reconstructions are figurative works of art, where he took the liberty of adding features that are not visible in the rock art like fur, ear canals and wrinkles, among other features. (Online version in color.).


“ Its overall morphology, large head, short rostrum, robust thorax, reduced number of digits on the pes, and prominent claws recall a giant ground sloth. Presented in a quadrupedal stance, the sizable forearms appear to be longer than the hindlimbs. The manus consists of three to four digits extended distally, whereas the pes appears to have five digits with varied orientations.

Notably, the depicted animal appears to exhibit pedolaterality, that is, the characteristic inverted pes, where the dorsal surface of the foot faces laterally and the planar surface of the foot faces medially. Three transversal lines compartmentalize the body in four parts and give the figure an appearance of surficial texture.

The white mark on its head seems to be representing an eye. Behind the head, there appear to be a few protuberances along the dorsal surface that might represent prominent scapula and shoulder musculature. The animal is accompanied by an offspring and surrounded by animated miniature men, some of whom extend their arms towards the painting.

The relationship of the animal with the men appears to be central to the artist’s message. The comparatively smaller illustrated humans that accompany the animal appear to provide a perspective on a scale that points to the sheer size of the specimen.”


The controversy

Interpreting ancient rock art is a much more difficult process than it initially seems. For example, how old is “ancient”? The art on the cliffs of Serranía La Lindosa is made with mineral pigments that are not suitable for carbon dating, so inferences must be drawn from organic materials in the area that CAN be carbon dated, such as bone tools that might have been paintbrushes, or food remains from the human settlements nearby.


Ice Age megafauna rock art in the Colombian Amazon?
José Iriarte, Michael J. Ziegler, Alan K. Outram, Mark Robinson, Patrick Roberts, Francisco J. Aceituno, Gaspar Morcote-Ríos and T. Michael Keesey

Jorge Peña and Fernando Urbina of the National University of Colombia believe that the paintings may be much more recent than the last ice age. In their 2016 publication “War dogs, horses, cattle and other themes in the rock art of the Serranía de la Lindosa (Guayabero River, Guaviare, Colombia): A conversation” they argue that many of the paintings in La Lindosa might be much newer, even post-European-contact. If the paintings are only a few hundred years old, it would explain their exceptional state of preservation, but would certainly rule out interpretations of pre-historic humans hunting ice-age megafauna.

Urbina says: “(The paint) shows a quadruped with an offspring, caught in a trap. Its size, in relation to the human figures facing it, could suggest that it is extinct megafauna. However, the exaggeration in size may depend on various symbolic reasons. Also, it could happen that the human figures correspond to children or dwarfs, or dwarf children. Federmann in his chronicle speaks of the encounter with members of an ethnic group of very short stature. Finally, it could be perspective management”

Until we have better estimates on the age of the paintings (which could happen as soon as late 2022), the question of the species remains unanswered. Do these mysterious cliffside drawings capture the brief moment of overlap between the last of the giant ground sloths and the first humans of South America? What did the drawings mean to the artists that created them? What animals did they see, what stories went along with the pictures, and what would they have to say to us about the splendor of the world as it was?

-Cecilia Pamich & Ames Reeder

Mylodon Giant Sloth, opportunistic omnivore?

Mylodon Giant Sloth, Opportunistic Omnivore?

Sloths these days are small, tree-dwelling animals that live high up in the rainforest canopy and do a good imitation of the plants they eat. They’re slow, they’re green, and they can’t jump—but a new study published in the journal Scientific Reports suggests their ancestors weren’t the strict vegetarians their reputation would have us believe.

There are six living species of sloths: four species of three-fingered and two species of two-fingered sloths. The slower, smaller three-fingered sloths are obligate folivores (they eat only leaves), and the two-fingered sloths eat a greater variety of leaves and occasionally supplement with fruit.

giant sloth
Illustration: Franklin Rodríguez

Once upon a time

In the ancient Pleistocene sloths made up a large part of the South American ecosystem. Sometimes literally large: the giant ground sloth Mylodon darwinii was three to four meters (over 10 feet) long and weighed up to two tonnes (about 4,400 lbs).

Based on fossil records of its teeth and current sloth dietary habits, Mylodon was assumed to be an herbivore—although scientists often wondered how the gut-to-body weight ratio of this giant ground sloth supported a strictly vegetarian diet.

Paleoecology is a difficult field to study. Scientists have to use indirect evidence of bones and fossils to extrapolate things like diet and behavior, and the giant ground sloths lack the sharp teeth and claws that most modern carnivores use to capture and kill prey.


giant sloth mylodon
Illustration of a Mylodon darwinii by Néstor Toledo


This is where a relatively new technique called “amino acid compound-specific isotope analysis” comes in: this is a measurement of certain nitrogen isotopes found in hair, nails, and some parts of the bones and teeth, and can tell us where the animal in question got its dietary amino-acids from. This analysis can differentiate between amino acids based in plants or animals, and even tell if the diet was primarily seafood or land-based meat.

Comparing samples from modern animals, including sloths, anteaters (which are related to sloths), and a range of omnivores, researchers from the American Museum of Natural History have determined that Mylodon was in fact also an omnivore.


Mylodon giant sloth omnivorous
Mylodon Reconstruction by Jorge Blanco

How to be an omnivore giant sloth

This immediately begs the question of: how? After all, the number of animals that can out-run a modern sloth are basically all of them, and ancient ground sloths do not show signs of being speedy creatures. The speculation is that the giant Mylodon might have foraged for bird eggs or scavenged meat from animals killed by other predators—after all, it doesn’t take an impressive turn of speed to hunt down a corpse.

Not all giant ground sloths turned their teeth to meat-eating; like all modern sloths, Mylodon’s North American cousin Nothrotheriops shastensis was purely herbivorous.

Humanity’s ancient ancestors certainly fed upon the giant ground sloths, and it is interesting to think that some of them might have occasionally returned the favor. Luckily for modern humans, we are safe from the small two- and three-fingered sloths of today, and they would surely be happy to be kept safe from us as well.


humans hunting giant sloth
A recreation of humans hunting giant sloths / Illustration: Alex Macclelland, Bournemouth University



Journal Reference:

Julia V. Tejada, John J. Flynn, Ross MacPhee, Tamsin C. O’Connell, Thure E. Cerling, Lizette Bermudez, Carmen Capuñay, Natalie Wallsgrove, Brian N. Popp. Isotope data from amino acids indicate Darwin’s ground sloth was not an herbivore. Scientific Reports, 2021; 11 (1) DOI: 10.1038/s41598-021-97996-9


-Ames Reeder

Did humans cause the extinction of the giant ground sloths?

Did humans cause the extinction of the giant ground sloths?

“We believe that human beings are mainly responsible for the extinction of megafauna in South America,” said Luciano Prates and Ivan Perez, CONICET researchers at the Faculty of Natural Sciences and Museum of the National University of La Plata, Argentina, and authors of a scientific study on the matter, which is published in the journal Nature communications.

Based on a vast amount of data collected via fossil and archaeological records ranging across the entire subcontinent, their work associates the hunting activity of the first groups of people with the demographic decline, and subsequent disappearance, of all large mammal species, occurring at the end of the Pleistocene Epoch (also known as the Ice Age), between 13 and 11 thousand years ago.


Recreación de cómo era la cacería del perezoso gigante
A recreation of humans hunting giant sloths / Illustration: Alex Macclelland, Bournemouth University

The fish tails

This study contradicts the widely accepted hypothesis in South American archeology: that large animals disappeared as a result of environmental changes. It was thought that the increasing temperatures and changes to vegetation resulting from the previous ice age (about 18 thousand years ago) was the catalyst which led to a mass extinction.

Instead, the new research focuses on where temporal and geographical evidence coincides, specifically where megafauna and ‘fish tail’ spearheads overlap. This very specific type of spearhead is similar to the ‘Clovis’ spearhead, which existed only in North America and is closely associated with hunting mammoths.


The “Fishtail” spearheads defining feature is that they are “bifacial” (having two faces). They tended to be symmetrical and made of many different types of stone such as chalcedony, opal, or jasper, which are ideal for carving due to their high silica content./ Photo: Museo Colonia


Clovis point | pleistoscenery
Preserved ‘Clovis’ points, like this one, were the first clear evidence of human activity in North America. These spearheads were used by the Clovis people to hunt large animals, and it’s existence coincides with the extinction of mammoths, giant sloths, and giant bison in North America./ Photo: pleistoscenery


“In both cases, they are large, broad tools with a very sophisticated technology,” Prates describes,  “Their existence is very short-lived: they only appear between 13 and 11 thousand years ago and they are not found any earlier on.” Adding to this evidence, scientists observed that the demographic curve of human beings began to decrease over the same period megafauna entered the last stage of extinction.

More evidence for an old hypothesis

This new evidence emerged after comparing 51 temporal records of the ‘Fishtail’ tip with 269 fossils of ten megafauna species – including the American horse and the Megatherium or giant ground sloth– all dated using radiocarbon techniques, which determines the age of carbon-containing materials.

“What we found first is that populations of megafauna kept increasing until at one point – 12,900 years ago – they began to decline sharply. This coincides exactly with the moment of appearance of the fishtail tips, so we suppose that when humans obtained this new technology they began to hunt these mammals, and hence led to the decline of these populations,” explains Perez.


Fig. 2
The temporal change in the density of large mammals (a), Fishtail projectile points (b), and all archeological sites (c) described using SCPD curves. Different regions are indicated in shading colors: Andes (light blues), Pampa (light red), Patagonia (light green). X-axis represents Calibrated years BP and Y-axis the standardized summed probability. / Image: Luciano Prates e Ivan Perez


“This situation lasts for 2,000 years and ends with the simultaneous disappearance of the animals and the spearheads, which shows us that they were intimately linked,” adds Prates. In this scenario, the drop in the human demographic curve is a result the overhunting of the fauna – human populations began to reduce due to the disappearance of one of their main subsistence resources.

  • Read More: The hidden “armor” found in the skin of a giant ground sloth


The published research also includes a geographic analysis comprising of 156 spatial records of ‘fishtail’ tips and another 204 spearheads which correspond with specimens of megafauna. These specimens came from 1660 archaeological sites between 7-15 thousand years old throughout South America.

The results also support the authors’ hypothesis that the majority of the megafauna were found in the same places as the weapons. “This means that the people who hunted with this technology were located in the regions where these animals lived, which were mainly the open steppes of the pampas of Uruguay, southern Brazil and Argentina, and Patagonia,” says Prates.


This figure shows the density of megafauna in South America (left), and the density of ‘Fishtail’ points (right) / Image: Researchers courtesy


“Using all this information as a base, a product of combined paleontological and archaeological evidence, our work postulates that human beings were primarily responsible for the extinction of the megafauna.”

“However, early humans did not compulsively attack all the species present, as suggested by the North American paleontologist Paul Martin 40 years ago,” says Perez, “We suspect that people dedicated themselves to hunting only a few species, however this caused such a deep imbalance within the ecosystem that eventually, given the added climatic changes, triggered a general collapse of the entire community of large mammals.”


Mercedes Benialgo


Prates L., Perez I., Late Pleistocene South American megafaunal extinctions associated with rise of Fishtail points and human population. Nature communications. DOI:

Original article in Spanish:

The hidden “armor” found in the skin of a giant ground sloth

The hidden “armor” found in the skin of a giant ground sloth

Argentinian scientists used X-rays on a 13,000-year-old sloth skin and discovered thousands of tiny bones on the inside.

After having managed to determine the precise age of the famous mummified skin of a Mylodon (an extinct species of giant ground sloth) the same scientists continue their quest to further understand this ancient animal.  This well-preserved skin was found on a scientific expedition, led by the Museo de La Plata (UNLP) at the end of the 19th century and continues to shed some fascinating results.

The scientists applied a rare diagnostic technique in the study of paleontological remains: X-rays. The results of the analysis, which have just been published in the Journal of Morphology, allow us to infer previously unknown aspects of the biology and evolution of the huge sloth Mylodons.


giant sloth mylodon
Weighing between 1,000-2,000 kilograms (2204-4409 lbs), the mighty Mylodon reached lengths of about three meters long (10 feet). / Illustration: Nestor Toledo

The skin is 13,200 years old and is only a portion of an animal whose largest specimens reached more than one ton in weight and three meters in length. It is believed that the ideal conditions of the cave in which it was found led to its excellent degree of preservation (which includes mummified hair and other soft parts).


mummified giant sloth
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. / Photo: Nestor Toledo

The pattern of the bones

Embedded in the skin is a layer of thousands of small bones ranging from the size of a lentil to 2 centimeters in diameter. These well-ordered structures caught the attention of the study authors, who decided to X-ray it using portable equipment for veterinary use. “This feature of the skin of the giant sloths was already known about, but it was thought that these bone pieces were scattered at random, but we discovered that they are arranged according to a pattern,” says Néstor Toledo, CONICET researcher at the Faculty of Natural Sciences Museum of the National University of La Plata (FCNyM, UNLP) in Argentina.


giant sloth armor skin
This Image shows the disposition of the ossicles of the Mylodon and comparison in size with a human. | Image: CONICET


Thus, in the four radiographs taken, these tiny bones (called ossicles) – were shown to form rows or bands in some areas, and rosettes or stars in others. When looking for bibliographic references that could complement these observations, they found that, without knowing it, they applied the same technique that Wilhelm von Branco had used over a century before.

Wilhem von Branco was a German scientist who published a report on X-ray analysis in 1906.  X-ray technology had just been discovered a decade before, and he applied this new technology to different paleontological pieces, among which, coincidentally, was another Mylodon skin preserved in the Natural History Museum in Berlin.

To the great surprise of Toledo and his colleagues, von Branco had also noted the same patterns in the skin bones of the Mylodon that they were now seeing.

“By superimposing von Branco’s radiographs with ours, we came to understand that the rosette structures would be located in the area of ​​the spine and its surroundings, while the row ones would be located on the sides and near the legs.”

“With this information, we began to discuss the probable functional reasons for these positions, thinking of those bones as a kind of armor that would still enable movement,” describes Toledo.

Therefore, the skin over the parts of the body that needed greater flexibility (such as the armpits or the belly) could fold or wrinkle, while other parts benefitted from a more rigid structure. All these conjectures raised a new question: Why did these animals have such thick skin that was reinforced with these small bones?


armor skin

An actual armor?

“The strongest hypothesis regarding the function of this dermal skeleton is related to defense against other organisms: firstly, possible predators, but also individuals of the same species during combat (such as competing males) based on the behavior of some current mammals,” explains Alberto Boscaini, CONICET researcher at the Institute of Ecology, Genetics, and Evolution of Buenos Aires (IEGEBA, CONICET-UBA).

Although the first option casts some doubts as to which species would attack animals of this size, the main argument would be evolutionary in nature: the oldest records of ossicles in the skin date back to other Mylodonts of the Mylodontini group, which lived about 10 million ago and were quite a bit smaller.

“They could have been eaten by carnivorous marsupials and large birds, so having an internal shell would be a great advantage. It may be that this structure was inherited by subsequent generations, even as they increased in size,” says the expert.


ancient sloth
Artist’s rendition of a giant caiman (Purussaurus) attacking a giant ground sloth (Pseudoprepotherium)./Image by Jorge A. González


Related to the issue of evolution, another question appears, but this time it looks to the present. “In paleontology, resorting to current animals as a key to understanding those that no longer exist is very common and is known as the ‘principle of actualism’.

In this case, we can look to the only living mammal that still has bones in its skin: the armadillo, which has similar bone patterns as the sloths of the past, that is to say, the rosettes and rows of ossicles,” Boscaini describes.

Although for the researchers this could answer the purely functional questions related to the necessary rigidity and mobility in the different areas of the body, these similarities could also suggest a shared development pattern, “perhaps related to the expression of the same genes,” he points out.

Handling and cultural significance

The application of X-rays to the mummified skin was a delicate procedure that required the participation of specialized technicians to be able to use the equipment without moving it from the display case in which it is exhibited. More than a century prior, von Branco also used X-rays to examine a preserved skin but he went about it in a very different way.

To do so, he exposed the preserved “leather” to steam to soften it and then stretched it on a smooth surface on which he took X-rays. “The positive thing is that those plates have an extraordinary quality and were very useful for our study, but in truth, it is an unthinkable thing to do today: it is practically an attack on a piece that is unique and invaluable,” he explains. Leandro M. Pérez, also a CONICET researcher at the FCNyM and one of the authors of the work.


giant sloth skin armor
Leandro Pérez, one of the researchers, next to the showcase where the skin is exhibited. Photo: Courtesy of researchers.


According to Leandro, the enactment of the Argentinian Law for the Protection of Archaeological and Paleontological Heritage in 2003 was very important to prevent the manipulation of these types of remains or fossils. “The sloth skin that we have in the local museum is a real treasure: it is likely that nothing remotely similar will be found again.”

“The mummified skin has some very deep cuts and even some parts missing because in the ’70s samples were extracted for the first radiocarbon dating, a method that looks for the presence of isotopes of a certain chemical element within the sample. Nowadays, even though it is wrinkled and dehydrated, we know that it should not be modified (even though that is how we usually take X-rays) which is why in many areas the bones are superimposed on each other,” added Pérez.


-By Mercedes Benialgo, CONICET La Plata

Bibliographic references:

Nestor Toledo, Alberto Boscaini, Leandro Martín Pérez. The dermal armor of mylodontid sloths (Mammalia, Xenarthra) from Cueva del Milodon (Ultima Esperanza, Chile). Journal of Morphology. DOI:

Original text:

Being a giant sloth in an ancient wetland

Being a giant sloth in an ancient wetland

Thirteen million years ago, when giant ground sloths roamed the Earth, a vast wetland known as the Pebas Mega-Wetland System extended across northernwestern South America. This network of rivers and swamps was home to a variety of large fauna: caimans and crocodiles over 10m in length, turtles 3.5m in diameter, rodents the size of buffalos, and of course giant ground sloths!

Paleontologists believe that these giant crocodilians preyed upon the ground sloths. However, evidence of a stand-off between these ancient giants is extremely rare, making a recent discovery of the remains of ground sloth in the Peruvian Amazon even more remarkable!

The Peruvian Amazon/Photo: Wikimedia Commons by Martin St-Amant

Searching for clues from the past

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!

Artist’s rendition of an ancient giant caiman (Purussaurus), the top predator of Miocene swamps in South America (person added for scale) /Image: Wikimedia Commons – Nobu Tamura (


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.


ancient sloth
Artist’s rendition of a giant caiman (Purussaurus) attacking a giant ground sloth (Pseudoprepotherium)./Image by Jorge A. González

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.


pygmy sloth
Pygmy sloth in the mangrove forests of Isla Escudo de Veraguas, Panama/Photo: Suzi Eszterhas


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.


Three-fingered sloth (Bradypus variegatus) swimming across a river in Limon, Costa Rica/Photo: Suzi Eszterhas

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.

The importance of wetlands to humanity

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.


mangrooves sloth ancient
Mangroves of Australia at low tide/Photo: by hbieser on PixaBay


Wetlands provide food and shelter to a vast array of species, including us. They protect our coasts from the buffering of waves, reduce the severity of floods, absorb pollution, and purify our water resources. They are essential to the health of our fisheries, serving as “nurseries” for many types of fish that feed our coastal communities. In addition to fish, wetlands provide rice for 3.5 billion people globally.

Wetlands are also important allies in our fight against climate change, with mangroves and sea grasses absorbing 40-50x more carbon than other terrestrial forests.


mangroove wetland
Mangrove forest/Photo: By sippakorn at Pixabay

In addition to the life-giving resources they provide, wetlands sustain our economy. More than a billion people depend on wetlands for income. Moreover, the services they provide for free would cost US $47 trillion a year –  making them the most valuable type of ecosystem.

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.


Two-fingered sloth (Choloepus hoffmanni) in Cahuita, Costa Rica/Photo: Suzi Eszterhas


Appreciating wetlands means recognizing all the services that they provide for us and the many unique creatures that live there. Globally, 40% of Earth’s species live and reproduce in wetlands and 25% of all species live in coral reefs. Every year, 200 new species of fish are discovered in freshwater wetlands. Conserving wetlands means ensuring a healthy future for these species (and us) for many generations to come.


-Katra Laidlaw

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The ‘mummified’ skin of a giant sloth proves that they coexisted with the first humans of South America

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.

Secretos de una joya del Museo de La Plata: científicos del CONI
Leandro Pérez, one of the researchers, next to the showcase where the skin is exhibited. Photo: courtesy of researchers.

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.

giant sloth skin
Photo: Courtesy researchers

“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.

The scientific process

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.

giant sloth skin
Photo: Courtesy researchers

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.

Interesting questions

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.

Secretos de una joya del Museo de La Plata: científicos del CONI

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.”

carlos ameghino
Fiorentino Ameghino, considered the first Argentinian paleontologist, and team in one of their expeditions.

Mummification: yes or no?

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:


Love avocados? Thank the Giant ground sloths!

Love avocados? Thank the giant ground sloths!

Did you know that we can thank giant ground sloths for the avocados we have today? Giant ground sloths were one of the few ancient herbivores large enough to swallow avocados whole, thus serving as an important seed disperser for these delicious fruits that we know and love today!

Illustration of the giant ground sloths by Robert Bruce Horsfall/Source: Wikimedia Commons


Many plants, especially in tropical ecosystems, have evolved to rely upon animals to spread their seeds. Only extra-large herbivores such as the giant ground sloths had the ability to swallow avocado seeds whole, meaning that they could carry them around in their digestive tracts and eventually defecate them far away from the parent tree!

Evidence of these ancient symbiotic (mutualistic) relationships can still be seen today. For example, honey locust trees (Gleditsia triacanthos) have large sweet-smelling seed pods that were eaten by megafauna. They also have big, intimidating spikes on their trunks which likely served as an important defense against these giant herbivores. Now a popular city tree due to their ability to withstand poor conditions, modern versions of honey locust trees have been bred without spikes although their supersized seed pods still litter our bustling city streets.

Seed pods and thorns of the honey locust tree (Gleditsia triacanthos). Although seemingly powerless against modern tree-dwellers these spikes likely served as a vital protection against the large herbivores of the Pleistocene./Images:

How big were the giant ground sloths?

These ancient ancestors of modern-day sloths truly lived up their name. Like bears and anteaters, they had the ability to stand on their hind legs, making them the largest bipedal mammals to have existed. Over 100 species of giant ground sloths lived throughout North, Central, and South America, ranging in size from the formidable Megatherium americanum which towered 3.5 meters tall (12 feet), and weighed up to 4 tons, to the considerably smaller 90-kg (200-lb) Cuban Megalocnus. 


Skeleton of the giant ground sloth (Megatherium americanum)/Source: Wikimedia commons


The giant ground sloths of North America disappeared around 11,000 years ago and their South American cousins followed suit around 10,200 years ago. However, amazing fossil evidence from 2007 revealed that 200-lb Megalocnus were still lumbering around the islands of Cuba as little as 4,200 years ago!


Skeleton of the considerably smaller Cuban ground sloth (Megalocnus rodens)./Source: Wikimedia Commons

Why did the giant ground sloths disappear?

Like many of the memorable megafauna of the last ice age, the exact cause of their extinction remains somewhat murky. Megatherium fossils have been found with cut marks on them, suggesting that ancient humans did consume these giant beasts. However, humans and the giant ground sloths of Cuba coexisted for a period of about 1,000 years. It is likely that a combination of over-hunting and/or climate change led to their demise.


Artist’s interpretation of the giant ground sloth (Megatherium) of the Pleistocene and two Glyptodon./Source: Wikimedia commons


Although the last of the giant ground sloths disappeared around 4,200 years ago, modern sloths carry on their legacy. Scientists have hypothesized that modern-day two and three-fingered sloths evolved from two distinct lineages of extinct giant ground sloths. In other words, although not closely related, two and three-fingered sloths both evolved independently to live in trees, in a process called convergent evolution. However, recent genetic evidence suggests that the species of sloths alive today may have evolved from an ancestor that was comfortable on the ground as well as in the trees.


The future of avocados

Without their ancient seed dispersers, the future of avocados is now in our hands. Unfortunately, avocado trees are quite sensitive to changes in temperature and water. A single avocado requires 60 gallons of water to grow. Fluctuations in rainfall and temperature due to climate change are causing shortages of these lucrative crops. Moreover, the expansion of avocado farms in Mexico has led to the destruction of pine and fur forests thus affecting monarch butterflies. The high demand for avocados has even caused gang warfare to break out in areas such as the Michoacán state of Mexico, where almost 80% of the US’s avocados come from.

Also known as “alligator pears” avocados became popular due to the targeted marketing efforts of Californian farmers in the 1990s./Image:

A sustainable future for avocados means growing them in places where water is plentiful using agricultural methods (such as agroforestry) that make space for biodiversity.


-Katra Laidlaw



Five-ton giant sloth lived in Costa Rica seven million years ago!

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.

giant sloth
The bones found correspond to giant sloths similar to those in this image, whose height can easily exceed twice that of a person. Illustration: Franklin Rodríguez

“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.

Describing the sloths:

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.

giant sloth found in costa rica
The Venezuelan paleontologist Ascanio Rincón (left) is in the country to collaborate with the research of Ana Lucía Valerio Zamora and César Laurito Mora, who have spent years studying the paleontology of fossils found in Coto Brus. In the photograph, they present the ankle bone of a giant sloth. Photo: Rafael Pacheco

“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.


giant sloth
These are some of the giant sloth bones scientists are analyzing. Photo: Rafael Pacheco

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.


Giant Ground Sloths lived in North and South America and went ...

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 ”.

-Source: Diario La nación Costa Rica