Hello, everyone! I hope you’ve been enjoying Creature Feature so far. My name is Ms. Hackett. In the past, I taught here as the Muggle Studies professor and served, for a time, as your Dean of Students. Currently, I work as an arachnologist, studying spiders. I do, however, have a passion for many more creatures than just our eight-legged friends, as you will see I guide you through this lesson.
I’ve been excited for weeks now, knowing that I would be able to step back into the classroom for just a little while longer. I was even more excited knowing that I would be participating in this particular lesson - it, quite literally, hits close to home, due to where I grew up. Without further babbling, let’s begin.
Let’s face it, everyone loves sloths. Recently, they’ve become quite the sensation in the Muggle world. You can barely step foot into a shop or even walk past a jewelry vendor without seeing something sloth-related. They’re cute and make the most adorable noises ever. I mean, just look at this face. What’s not to love? It’s no wonder that people have been going crazy over them!
But, like all things in the natural world, this adorable little creature evolved from something else. Something much, much bigger.
In the world’s current pool of living sloth species, the biggest is the brown-throated sloth. These sloths grow to about 35 inches (just under three feet) in height and can weigh up to 14 pounds. That’s roughly the same weight of a small full-grown terrier and the same height as a one-year-old child. Knowing these statistics, you would think that these darling little animals would have come from something of similar, or maybe slightly bigger, size. Well… It’s certainly bigger, but I wouldn’t say ‘slightly.’
The bigger ancestor to these little cuties would be the giant ground sloth, as seen here. This gargantuan animal was larger than an African elephant bull and was only dwarfed in its time by the wooly mammoth and the hornless rhino.
The biggest of these species was Megatherium americanum, which could reach up to 20 feet in length (from the head to the tip of its tail) and could exceed weights of 8,000 lbs. Their downright huge size has given them the title of being one of the largest land mammals to ever exist. As a result, this fantastically interesting beast is the main focus of today’s lesson.
Starting at the head, you will first notice that they have a very large jaw structure. Because of its size, Muggle scientists speculate that they may have had a very long and powerful tongue, much like that of giraffes today, which would have been used to snap twigs and collect leaves. Megatherium had very narrow lateral cranial structures, leading scientists to believe that they had the ability to be selective in which twigs and leaves they pulled down and consumed.
Their bodies were very sturdy, hard, and muscular, coated in thick fur, and had thick skin as well. They had a very wide pelvic girdle, offering great stability when moving bipedally instead of quadrupedally. Speaking of their legs, they had strong back legs that were longer than their forelimbs, and a hefty tail that worked as a third limb for balance, much like we see in modern-day anteaters.
Also similar to our anteater friends was the fact that they could not walk with their feet flat. Because of their monstrous claws, they were forced to walk on the sides of their feet. This was discovered through fossilized tracks of the different species, all of which had to walk in this same way.
The various species of giant ground sloth differed in size and coloration, naturally, mostly coming in varying greys and reddish-browns. What set the many species apart were more minor things, such as regional differences, certain bone structures, and even the number of claws that they had.
For example, the genus Eremotherium (which I will go into further detail about into in a few minutes) was set apart from the other members of its family because it had an extra claw. While its relative species had a normal four fingers, two or three of which had claws, Eremotherium had five fingers and four claws.
So what, you may ask, did creatures of this size eat? For the most part, the answer to this is leaves and grasses. The majority of the species of ground sloths have been proven to be herbivorous. Fossilized dung samples found in caves have been the basis for this finding, and it seems like there was a very wide variety of plants that they would consume - one sample contained 72 different genera of extinct plants! It was not unheard of for them to dig for their food, either - digging up roots and tubers, as the Paramylodon (yet another genus of ground sloth) did, was actually very common for several species. Some even enjoyed eating flowers, as researchers have found heavy concentrations of pollen in several dung samples.
That’s all very interesting, right? But what about Megatherium itself? Extensive research done on the jaws and joints of this ground sloth have come to find that there is a very high probability that Megatherium was an omnivore. They have not come up with how, exactly, it would have hunted for its partial protein diet, but many believe that it was a scavenger.
REPRODUCTION AND FAMILY GROUPS
Let's discuss life on the family front. To the knowledge of scientists, ground sloths could only safely birth one offspring per pregnancy. They do not doubt that there were cases of twins, but they were probably rare, as the delivery of such large babies would be taxing. In fact, the survival rate of mother and multiple offspring likely would have been near zero. Solid information has yet to be found on how long the gestation period would have been. Given their size, however, most would say around the same term length as an elephant - 22 months.
An interesting thing to note about these creatures is that, thanks to information from fossils and DNA testing, we know they were long-term parents. Fossils were found in Iowa in the U.S. of a mother and two juvenile ground sloths - they were both hers, and both were of different ages. This shows rather plainly that their offspring stuck around for several years before going off on their own. This becomes even more interesting when you combine it with the fact that these were herd animals. In other words, they stuck together in herds that were essentially large families that cohabitated and traveled together. It is still uncertain whether this family consisted of one or multiple males, but most believe that just one male per herd may have been the case.
The Megatherium lived in the Middle Pliocene epoch (about 5.333 million years ago), and primarily inhabited the continent we now know as South America. The first full skeleton of Megatherium, discovered in Argentina in 1788, was found on the banks of the Luján River. This find was thanks to a man named Manuel Torres. The fossils that Torres found were shipped to Madrid and still reside there in the Museo Nacional de Ciencias Naturales.
Other species of ground sloth, on the other hand, have had fossils pop up all over North and South America and as far south as Seymour Island, near Antarctica. They even span out into Cuba and the Caribbean Islands.
The newest species of documented ground sloths, Eremotherium eomigrans, was only just discovered on June 26th of 2000. Almost two dozen of the species were discovered in an old limestone quarry in Haile, Florida by a University of Florida research team. They believe it was the earliest species to have traveled from South America, having come across the Panamanian land bridge. The skeleton that they found now sits in the Florida Museum of Natural History in Gainesville, Florida. It is the largest species of ground sloth to have been found in North America, weighing more than five tons and standing over 17 feet tall on its hindquarters.
I’ve been to the Florida Museum of Natural History quite recently, in fact, as I went there on a family trip over the winter break. Standing next to this skeleton is a tremendous experience. I stand at five feet, six inches, and this creature’s pelvic girdle is still taller than I am!
This is why I said that this lesson hits so close to home - Haile and Gainesville are only a couple of hours away from where I was born and raised. I remember visiting this museum many times over the summer breaks when I was a child, and I was always in awe of this animal, as I am of many of the world’s creatures.
The areas in which these creatures lived depended entirely upon the species. The Megatherium roamed the grasslands and lightly wooded areas in South America. They enjoyed arid, or semiarid, areas with sparse woodland for shade and food. While this is the case for several species of ground sloth, there were others that enjoyed different habitats.
As previously mentioned, the Eremotherium migrated as far as Florida. This would point to them preferring tropical, humid environments. Other genera lived in dry desert lands, such as Nothrotheriops, which lived in the area now known as Arizona. Apparently, back then, that area was even hotter than it is now! The differences in preference don’t stop there, either, as some species preferred dense woodlands, while others enjoyed more foothill-type regions, and even others stuck so close to the water that they spent a good chunk of their lives in it.
As for primary dwellings, a great deal of fossils have been found in anything from open plains to woodlands. Primarily, though, they seem to have been cave dwellers. Many, many fossils have been found in large caves that could have easily accommodated a family group of ground sloths.
EVOLUTION AND MORTALITY
The ground sloth is part of the superorder Xenarthra, which includes modern sloths, anteaters, and armadillos. With that information in mind, you would likely think that this means Megatherium and other species of extinct ground sloth would be direct ancestors of the sloths we know today. That is not the case, however. The evolution that led up to our present-day sloths cannot be determined, nor can our modern furry friends be linked to any known species of extinct ground sloth. There were, in fact, over 80 different known genera of ground and marine sloths that have long since gone extinct, and not a single one can be directly linked to the sloths we know and love today.
Some scientists speculate that the modern two-toed sloth, as seen here, is actually a type of ground sloth, but has evolved from a branch of ground-dwellers that may have come from arboreal-dwellers. This could explain their affinity for primarily remaining in the treetops. There has been no evidence found to fully validate this - such is the case with all current sloth species - as they have yet to find the in-between links that would complete the evolutionary chain.
The only possible link that has been found is that of the noticeable beginnings of their digits fusing together. There is much debate on this, as some believe that this was caused by the onset of what we now know as arthritis. Along with this possible cause of deterioration, there have been documented findings of several ground sloth species having various cancers and nutritional stresses and plenty of fractured bones. Spores of disease have been found in numerous remains.
There has been plenty of debate about the cause of extinction of these animals, and many argue that it was due to humans invading their living spaces. However, research has found that, ultimately, the end of the ground sloths, including Megatherium, more than likely had to do with climate change, rather than over hunting by humans.
Well, I hope you all enjoyed learning about this fascinating, gorgeous beast! I know I certainly had a wonderful time telling you about them. Following this lesson will be a quick quiz and a fun, completely optional, field trip of sorts. With that, I leave you with this amazingly adorable video.
Thank you all for coming in for this lesson, and enjoy the rest of our Prehistoric Creature Feature!
All pictures are found using the Google Images search engine, and belong to their owners. View of sloth skeleton from ground photograph taken by Ms. Hackett.