April 2023 – Uchneat RCL2 Blog

This week I am gonna look at what I think is one of the more well-known prehistoric mammals, the giant ground sloth Megatherium.

Megatherium Giant Sloth Facts and Figures — Megatherium

Megatherium lived between 5 million and 10 thousand years ago in South America. Though it may be difficult to see the resemblance, as mentioned above, Megatherium is in fact a species of ancient ground sloth. Ground sloths were once a very widespread and diverse family of animals, ranging in size from modern sloths to this species here, which reached 12 feet tall when on their hind legs and rivaled the size of modern bull elephants.

What was Megatherium? | Natural History Museum — Brotha starving

Like most animals that grew this large, size was probably an evolutionary defense against the many predators in South America at the time, such as giant crocodilians and big cats.

Despite its bearish appearance, megatherium was (most likely) a herbivore just like modern sloths, though there is weak evidence that it could have scavenged meat if necessary. Its size also probably came in handy for this herbivorous lifestyle, as it could stand on its hind legs to reach the taller vegetation that was untouched by other animals, similar to how elephants do today. As pictured above, you can see how the extremely thick and short hind legs, as well as a strong pelvis were able to support this behavior. It also appears to have used its muscular and thick tail as a tripod for further support. Although it was primarily quadrupedal, footprints have indicated that megatherium was not limited to just standing against a tree in this position and could actually walk fully bipedally.

Megatherium had large claws on all four limbs just as modern sloths do, and these actually prevented it from placing its feet flatly on the ground, forcing it to walk on the sides of its feet as pictured above. The claws on its forelimbs could be used to pick through vegetation and bring branches closer to itself while foraging. It also had a more narrow snout than any other sloth, and the long overhang on both the upper and lower jaw suggest that it had prehensile lips (meaning that they could grab stuff) to allow it to more carefully select what it ate.

Megatherium went extinct close to 10,000 years ago, which means it would have had plenty of overlap time with humans. As is the case with most large animal species of this time, unrelenting hunting was likely a significant cause of their extinction. This is further evidenced by cut marks in their bones which look to be made by stone tools. This time period also lines up with an extinction event (called the Quaternary Extinction Event) which brought the end to many species of megafauna, mostly due to climate and environmental changes that they could not adapt to quickly enough.

That’s pretty much all for this animal, it’s just another one that I think is interesting to visualize as something that was real given how different it looks from any of the animals we see nowadays. I hope you found at least something of interest in all of these blogs, I realize that it isn’t the most impressive passion but I think that looking at these unique animals is a thought-provoking topic that is worth sharing.

Sources:

https://www.nhm.ac.uk/discover/what-was-megatherium.html

https://www.britannica.com/animal/Megatherium

https://allthatsinteresting.com/megatherium

This post is going to focus on Thylacoleo, Australia’s marsupial predators.

Climate change the likely killer of Australian marsupial lion | UNSW Newsroom — Thylacoleo recreation

Thylacoleo lived in Australia between 2 million and 46 thousand years ago, and is roughly the size of a large dog. As the name “marsupial lion” suggests, thylacoleo was in fact a marsupial, meaning it carried its young in a pouch attached to its stomach. It was fairly unique among marsupials in that it was a carnivore. The only other case of

predatory marsupials I was able to find is Thylacines, which were coyote-like marsupials.

This animal’s habitat it believed to have been dry and open forests. It had an enlarged claw on its thumb as well as forelimbs that were more developed than its hind limbs. These traits suggest it may have been well adapted to climbing, and though they could run were probably not fast, possibly living a similar lifestyle to jaguars. It is also possible that this trait was necessary to remain safe from other predators of the time, such as the alligator-sized monitor lizard megalania.

Despite being commonly called a marsupial lion, thylacoleo has no relation to actual lions such as those in Africa, and the resemblance is a case of convergent evolution. Instead, the closest living relatives to this animal are koalas and wombats. Its ancestors were also herbivorous wombat-like animals, which places thylacoleo in a unique situation, as carnivores are rarely evolved from herbivores so closely as this.

Bones, Thylacoleo Carnifex Skull. — Thylacoleo skull showing dentition

Thylacoleo is also extremely eye-catching due to its strange arrangement of teeth. A pair of its upper and lower molars are enlarged and form flat, shearing blades, and other molars are either reduced or entirely absent. It also has adapted its front teeth to be long and sharp, serving the same purpose as canine teeth in most other mammal predators. This really serves to show how herbivores developed carnivorous traits, given its rabbit-like appearance and the development of grinding teeth into more of a cutting function.

The sources I have found state that Thylacoleo had the strongest bite force of any animal living or extinct, but pretty much every animal I have researched so far seems to, so I am pretty sure that that’s an exaggeration. Though maybe not the strongest ever, it would make sense for thylacoleo to have had an extremely strong bite force, as muscle connections in the jaw and the presence of incisors so far back in the mouth would indicate considerable jaw strength. This as well as the highly developed forelimbs and thumb claw described earlier suggest that thylacoleo was probably able to tackle and kill prey that was much larger than itself.

There isn’t much else about Thylacoleo, but I think it is a really interesting animal for a lot of reasons. Usually when I think of marsupials I think of kangaroos or koalas or whatever other herbivorous animals, so to think that there were once marsupial predators in Australia is cool to me. They also have such a unique dentition which is something that I feel tends to be pretty consistent in animals, so it really adds to the allure of this animalthat it has such a weirdly-designed mouth. Overall this is just another one of those animals that changes the way I look at the area where it used to live, because to know what used to live in Australia and how different it is from what is there today is something I find so cool to think about.

Sources:

https://australian.museum/learn/animals/mammals/thylacoleo-carnifex/

https://prehistoric-fauna.com/Thylacoleo-carnifex