Giganotosaurus: Giant Southern Hunter

The Giant Southern Hunter compared with a human. As you can see, it was truly a colossal predator!
Image Credit: Durbed, https://www.deviantart.com/durbed/art/Giganotosaurus-carolinii-290866454

In the issue of Empire magazine (released 9th of April 2022), Colin Trevorrow; director of the upcoming film “Jurassic World: Dominion”, talks about the appearance in the film of a Giganotosaurus. He describes Giganotosaurus as “like the Joker” in that “it just wants to watch the world burn”, referencing a quote from the Christopher Nolan film “The Dark Knight”. This didn’t fill me with high hopes for this dinosaur’s portrayal in the film, and instead symbolizes a problem the Jurassic franchise has had since Jurassic Park III; dinosaurs being portrayed as movie monsters, rather than as animals. If any dinosaur started acting like the Joker in behaviour, then it wouldn’t sit well with me because it is applying “human” traits (albeit those of a psychopathic clown!) onto an animal. The animal kingdom can be full of what we might consider dark, cruel and disturbing behaviour. However, there is a difference between giving an animal traits that are plausible based on how the natural world is, and traits that are just not realistic to what an animal would do. I bring this up not to be the stereotypical accuracy obsessed paleo nerd moaning about dinosaur portrayals in popular media (that deserves a blog article of its own). Instead, it is to show why it’s important for any media that communicates palaeontology to have animal behaviour, even speculative ones, that is plausible; people will watch it and believe that what they’re seeing on screen may have at least an element of truth. For example, AppleTV+’s Prehistoric Planet, while being a documentary series rather than a blockbuster film, also has speculative behaviour. But what it does well is that it is behaviour that has a basis in nature (and especially in the animals closest living relatives). Furthermore, it’s behaviour that stems from animals just trying to survive, rather than from more human like motivations. Since a lot of the mainstream publics exposure to dinosaurs is through the Jurassic Park/World series, any unrealistic behaviour that’s shown in these films going to be more embedded into the public consciousness. So, people may come away with thinking that Giganotosaurus was psychopathic. A monster, rather than animal.

So, to link this rant with this blog article, what would the real Giganotosaurus have been like?

Giganotosaurus carolinii (meaning “Carolini’s Giant Southern Lizard, named after it’s discover, the fossil hunter Ruben Dario Carolini), was a large theropod dinosaur that lived roughly 99-96 million years ago in the Patagonia region of Argentina, South America during the “Cenomanian” stage of Late Cretaceous. Its fossils were first found in 1993 and later described in 1995 by Coria & Salgado. These fossils showed that Giganotosaurus had a relatively low skull, robust hind limbs and vertebrae, a reduced shoulder girdle and slightly less forward-facing eyes compared to other large theropods. Furthermore Giganotosaurus and its close relatives (but unlike other large theropods such as Tyrannosaurs), possessed three fingers on each hand rather than two. Giganotosaurus’ skull was also proportionally large compared with its body and was truly massive even for a large theropod (with estimates of up to 1.95 metres long!). You might think such a large head would’ve been a burden, but it was supported by huge neck muscles and had openings in the skull bones, called “fenestrae”, that lightened the skull without sacrificing strength. Also, just like other dinosaurs Giganotosaurus would’ve had a system of air sacs spread throughout its skeleton. These lightened the bones further while also allowing for an extremely efficient, bird like respiratory system where air passed from the lungs into the air sacs during inhalation, then passed from them back through the lungs on expiration, ensuring that a higher proportion of oxygen can be extracted, therefore more is available for aerobic respiration and therefore more energy is available to fuel its metabolism.

A skeleton of Giganotosaurus carolinii on display at the Fernbank Museum of Natural History in Atlanta, Georgia.
Image Credit: Jonathan Chen, https://commons.wikimedia.org/wiki/File:Giganotosaurus_at_Fernbank.jpg

Giganotosaurus belonged to a group of theropod dinosaurs known as the Carcharadontosauridae. These medium-large theropods were generally among the largest land predators around during the early, mid and early stages of the Late Cretaceous, and have been found in most continents, including Africa, North America and Asia as well as South America. The group eventually went extinct sometime in the Late Cretaceous (roughly 80-85 million years ago), with climatic changes playing a role in their downfall. One other suggested theory for their extinction was that they were outcompeted by newer large theropods, with the Tyrannosaurs being one such group. This is not thought to have been the case anymore, with the incredibly short armed, blunt faced Abelisaurs and the long limbed, large clawed Megaraptorans in the south, and the famous Tyrannosaurs in the north instead growing larger and taking advantage of the open niches left vacant by the Carcharadontosaurs.

This Tyrannosaur connection goes further when it comes to Giganotosaurus. When it was revealed to the world via the Coria & Salgado paper in 1995, Giganotosaurus instantly made headlines as theropod dinosaur that was bigger than Tyrannosaurus rex! As a result (since Spinosaurus fossils other than the ones destroyed in World War Two had yet to be described) this made Giganotosaurus the largest known theropod dinosaur at the time. However, there are always caveats with grand statements like this. The chance that any animal will fossilise is incredibly small. Giganotosaurus itself is only known from two partial individuals out of a total population that likely numbered in the tens to hundreds of millions across the entire existence of the species. Therefore, we barely have a minute sample of the total population. So, whilst Giganotosaurus was colossal, with size estimates ranging from 12.5-13.2 metres long and weights between 6-8 tons, it’s hard to say whether this was an average size for this species or not. We may not have discovered the largest Giganotosaurus, just as we may have not found the largest T. rex. So it’s hard to say which animal was bigger based on our small sample sizes. But from what we DO have, on average Giganotosaurus may have been slightly longer, but T. rex was generally heavier. Since mass is often more important when it comes to judging who’s “bigger” (more mass = more muscle and power), T. rex might have been the bigger animal on more occasions. But, this can easily change as more fossils are discovered! This conclusion is further helped by the discover, after Giganotosaurus had been described, of “Scotty”; a Tyrannosaurus bigger than any previously known T. rex specimen. But not to worry Giganotosaurus fans, there would have been size variation within both species. So some Giga’s may have been bigger than some Rexes. This argument also applies to the largest sauropod dinosaurs. Argentinosaurus is considered by many to be the largest sauropod (and largest land animal) that we know of, but there is a lot of overlap with other large sauropods like Patagotitan and Maraapunisaurus. Also, as a quick side note, there’s a trope in media and with dinosaur fans (and I’m guilty of this too!) where any new supersized theropod is always compared to T. rex! There’s no doubt that T. rex is a superstar, but it’s a little annoying that it’s always this benchmark, and that any new theropod that’s even remotely close in size has to be compared to the Rex rather than known purely as its own thing.

A large body size was vital for Giganotosaurus as it allowed it to hunt the big Sauropod Dinosaurs that it lived with, such as the Titanosaur Andesaurus. However despite this, even one Giganotosaurus might not have been enough to take an adult on. So, like any large carnivore Giganotosaurus may have focused on sub-adults, or already weakened adults, or gone after smaller dinosaurs, and scavenged if the opportunity arose. If, that is, it was alone! Fossils of a very close relative of Giganotosaurus (also discovered in Patagonia from slightly older rocks) named Mapusaurus, have been known from multiple individuals of different ages that appear to have been buried together at the same time and place. This has led some to suggest that it, and potentially Giganotosaurus, hung around in groups. So if this giant carnivore wasn’t intimidating enough, imagine a whole group of them! The numbers would have helped to even the odds when hunting giant sauropods. Giganotosaurus was also equipped with sharp, slicing teeth that were like steak knives, perfect for slicing through chunks of flesh and causing, as some documentaries would say, “shock and blood loss”. Furthermore, it’s strong forearms and sharp claws would enable it to grip larger prey, supporting it as it bit and slashed at them. It wouldn’t have hunted just sauropods though, with South American iguanodontid dinosaurs also being on the menu. These could be sprightlier than a sauropod, but Giganotosaurus has been calculated (in Blanco & Mazzetta 2001) to have been capable of reaching speeds of up to 14 metres per second (roughly 31 mph), which is roughly the same as a Grizzly Bear. This would’ve been more than enough, combined with surprise (or at least, as much surprise as a near 13 metre, 6-8 ton giant could get!) to ambush and kept up with its prey. Furthermore, even if the initial attack didn’t finish the job those slicing teeth would inflict deep wounds. The resulting blood loss would weaken the prey considerably, so all a Giganotosaurus (or a group/mob/gang of Giga’s) would need to do is follow and wait.

A close up of Giganotosaurus‘ enormous head, from the same Fernbank Museum skeletal mount. Note the multiple blade like teeth.
Image Credit: James Emery, https://www.flickr.com/photos/emeryjl/3583031860

The idea that Giganotosaurus might have run around in groups raises interesting questions. What would interactions between Giga’s have been like? First off, if they did hunt in groups, it is unlikely that Giga’s would’ve been co-ordinated pack hunters, nor that they had a pride like social structure as Lions do. Just because large carnivores are found buried together doesn’t necessarily complex social groupings, neither does it indicate they had the co-operation to plan lion-like hunting strategies. Instead, it’s more likely they would’ve been more like congregations of Komodo Dragons, Crocodiles or certain Birds of Prey; opportunistic joining together to gang up on prey, but with no co-ordinated strategy. As such when it came to feeding there may have been a free for all! This is where large size would’ve helped. Larger individuals can throw their weight around and intimidate other Giga’s into backing off a juicy part of the carcass, or one that’s being scavenged by another Giga or other large predator. Larger size may also have been a factor in males warding off other males, or females intimidating other females, for the right to attract a mate, with a larger body size equaling a more fit, healthier and therefore more attractive partner. It must also be remembered that even huge carnivores like Giga’s would’ve started as smaller, less able youngsters. Parental care within large carnivorous dinosaurs is often somewhat speculative, as unless there’s a bonebed that preserves multiple individuals of different ages (as has been found with some Tyrannosaurs) or a trackway containing a mix of adults and juveniles together we can only make educated guesses for any animal. In the case of Carcharadontosaurs like Giganotosaurus, as an enthusiast, my own educated guess is that there possibly was some parental care initially (as seen in birds and crocodilians) but then the young would eventually have to fend for themselves. Adolescent Giga’s, being smaller than the adults, likely focused on smaller dinosaurs, the babies of larger dinosaurs, and smaller reptiles and mammals as they were too small to take on giant sauropods. In this way the adolescents would’ve filled a different ecological niche from the adults; the role of medium sized “mesopredator”. Alternatively they joined a gang of adult Giga’s on occasion, picking up the scraps initially inbetween the larger adults. Or maybe they did a mixture of both! These are just ideas I’m throwing around, but maybe in the future there will be an exceptionally preserved fossil or trackway that will give more insight into their behaviour.

Giganotosaurus isn’t the Joker, but an extinct animal whose size and predatorial abilities have made it well known among the paleontological community. Soon, as a result of “Jurassic World Dominion” and other future paleo media, it will be more well known among the general public too, for better or worse!

A scale comparison of some of the largest mega theropods. The Giganotosaurus used in this is on the larger scale compared to the T. rex, which based on the “Sue” specimen (though we now have the even larger “Scotty” specimen). However this T. rex may have been just as if not heavier and there is a lot of overlap between the two!
Image Credit: KoprX, https://commons.wikimedia.org/wiki/File:Longest_theropods.svg

References/Further Reading

• Coria & Salgado 1995, the paper that described the first known fossils of Giganotosaurus carolinii, which had been unearthed 2 years prior.

https://www.nature.com/articles/377224a0#citeas

Coria, R., Salgado, L. A new giant carnivorous dinosaur from the Cretaceous of Patagonia. Nature 377, 224–226 (1995). https://doi.org/10.1038/377224a0

• Calvo & Correa 1998, a follow up paper describing a second specimen of Giganotosaurus that was roughly 8% bigger than the holotype (i.e., the reference specimen that is used as the example of that species and is the specimen all new discoveries are compared to).

https://www.researchgate.net/publication/40662857_New_specimen_of_Giganotosaurus_carolinii_Coria_Salgado_1995_supports_it_as_the_largest_theropod_ever_found

Calvo, Jorge & Coria, Rodolfo. (1998). New specimen of Giganotosaurus carolinii (Coria & Salgado, 1995), supports it as the largest theropod ever found. Gaia. 15.

• Blanco & Mazzetta 2001 paper that evaluated the cursorial abilities of Giganotosaurus.

https://agro.icm.edu.pl/agro/element/bwmeta1.element.agro-article-78acb920-1953-4e1e-85e5-a2ae1686dc49

Blanco, R. E., & Mazzetta, G. V. (2001). A new approach to evaluate the cursorial ability of the giant theropod Giganotosaurus carolinii. Acta Palaeontologica Polonica, 46(2).

• A blog post on fossilera.com by Ashley Strack which gives a wonderful outline of Giganotosaurus, including its discovery, paleobiology, behaviour and more!

https://www.fossilera.com/pages/giganotosaurus-cretaceous-terror-of-argentina

Strack, Ashley, “Giganotosaurus: Cretaceous Terror Of Argentina”, FOSSILERA, www.fossilera.com, https://www.fossilera.com/pages/giganotosaurus-cretaceous-terror-of-argentina

• The Prehistoric Wildlife fact page on Carcharadontosauridae.

http://www.prehistoric-wildlife.com/articles/carcharodontosauridae.html

Prehistoric Wildlife, “Carcharodontosauridae”, Prehistoric Wildlife, www.prehistoric-wildlife.com, http://www.prehistoric-wildlife.com/articles/carcharodontosauridae.html

“All hail the Great Beast Megatherium!”

File:Megatherium NT small.jpg - Wikimedia Commons
A reconstruction of the Great Beast
Image Credit: Nobu Tamura, (© N. Tamura), http://spinops.blogspot.com/2015/02/megatherium-americanum.html

“Deluded! Madman! Fake Scientist!”

The Cryptozoologist had been called these a lot throughout his professional career, (as well as other, more mean things). Time after time after time he had failed to discover any of the amazing creatures’ people claimed to have seen, with the majority being proven to never have existed in the first place. Now, nearing his retirement, he was wandering the amazon rainforest looking for yet another cryptid; the “Mapinguari”. “Just turn around” the voice in his head said (not for the first time). “They’re just stories made up to attract tourists or hoaxers trying to make a name for themselves or misidentified animals. None of them are real!”. The Cryptozoologist sighed, and for the first time in his life he wondered “Maybe I am a crazy old man”. Then he heard it, a crash of vegetation coming from the trees just to the left of him. He turned round, straining to locate exactly where the noise had come from. Then he saw it, and his jaw dropped. What he was seeing was an animal believed to have gone extinct 8,000 years ago. It was a great beast taller than an elephant and just as bulky, which possessed huge claws that it was currently using to pull down branches from a nearby tree towards its mouth. As he took out his camera and frantically took pictures two more large adults shuffled out of the forest, one of which had a baby clinging onto to its back. “They wouldn’t believe me” the Cryptozoologist thought. “But just wait till they see you!”

This “Great Beast” is known scientifically as Megatherium Americanum (meaning “Great Beast from the Americas”). Megatherium is an animal that palaeontologists have known about for a very long time. The first fossils were discovered in 1787, four decades before the first dinosaurs would be found, in Argentina by a man named Manuel Torres. After their discovery these bones were shipped to the Museo Nacional de Ciencias in Madrid, Spain, where they still reside today (another reason to visit Spain!). It was from these bones that French naturalist Georges Cuvier first described and named Megatherium, noting its close relation to modern day tree sloths. After these first fossils more were discovered, including bones found by Charles Darwin from 1832-1833 during the first Beagle expedition. Even nowadays new discoveries are revealing more insights. For example a paper published in 2017 (by Bocherens et. al.) looked at preserved collagen proteins in Megatherium fossils to give insights into its diet. Some people have gone a step further and claimed that Megatherium is still alive somewhere in South America. Stories from Brazil tell of the “Mapinguari” or “sloth monster”; a shaman who was transformed by the gods into a giant sloth-like creature. Cryptozoologists (like the one in the story) think the Mapinguari is actually a late surviving species of Megatherium, however scientists (and yours truly) don’t take these stories seriously due to absence of any concrete evidence.

A mounted skeleton of Megatherium with a awe inspired human for scale!
Image Credit: Beatrice Murch, https://www.flickr.com/photos/blmurch/3495336846

Megatherium belonged to a large order (or “superorder”) of mammals known as the xenarthans. Modern xenarthans include Tree Sloths, Anteaters & Armadillos, but during the Cenozoic era this group was much more diverse. From their origins in South America they ended up colonising North America, grew to a range of shapes and sizes and occupied a wide variety of habitats ranging from the treetops (e.g. modern tree sloths) to even the ocean (e.g. the swimming ground sloth Thalassocnus). Megatherium itself belonged to a sub-order of xenarthans commonly known as the “Giant Ground Sloths”. These sloths were very different from their slow moving and tree dwelling modern counterparts. They were bulky, ground living herbivores with large and sharp claws. While Megatherium itself was confined to South America other species of Giant Ground Sloths migrated across the Isthmus of Panama into Central and North America. This was during the great American interchange; a time where multiple species from South America migrated into North America (and vice-versa). As a result Giant Ground Sloths established populations in places such as Costa Rica, Texas and California.

Because multiple fossils of the “Great Beast” have been known to palaeontologists for some time we have a pretty good idea of what it would have been like. Megatherium roamed the South American pampas, mostly in Argentina, Bolivia and Uruguay, from the Pleistocene (roughly 400,000 years ago) to Early Holocene (roughly 8,000 years ago) periods of the Cenozoic era (a timespan commonly known as the “Ice Age”). This beast stood over 3.5 metres tall when fully upright and weighed up to 4 tonnes, making it the largest animal in South America during the Ice Age and the largest xenarthan ever. Its potbellied frame was supported by column-like hind legs that would have given it a long reach. Furthermore preserved Megatherium track-ways and its skeletal anatomy indicate that it could have walked on two legs as well as on all fours. Its front limbs were tipped with large, non-retractable claws which were used for pulling branches closer to them to eat and for digging up roots and tubers. In fact the claws were a reason that Megatherium was initially thought to have been a burrower, living like giant mole! Big claws would have undoubtedly been very effective defensive weapons with Megatherium using them, alongside its large size, to protect itself from predators, such as the large Sabre-Tooth Cat Smilodon populator. Other distinctive features include a relatively narrow snout, a prehensile upper lip (like a black rhino) and a thick shaggy coat. This coat is found on most Megatherium reconstructions and is based on the discovery of exceptionally preserved hair and hide specimens of related Giant Ground Sloths. However a study from 2002 (Fariña 2002) has speculated that Megatherium might’ve been nearly hairless! This is based on the observation that modern large mammals, such as elephants and rhinos, are mostly hairless to prevent them from overheating in hot climates (large animals produce a lot more excess heat). Megatherium may seem very different to what we would think of a typical large herbivore today. However the overall body plan of a large, bulky, bipedal herbivore with large claws has actually appeared a few times throughout earth’s history. One example is the Therizinosaur dinosaurs; a group which lived a full 65 million years earlier than Megatherium but is thought to have lived a similar lifestyle. This is an example of convergent evolution; where two completely unrelated organisms, often separated by millions of years of evolution, evolve similar body plans to live in similar ways. It’s a very fascinating phenomenon that has resulted in a lot of symmetry between modern and extinct animals (e.g. Dolphins and Ichthyosaurs).

A Megatherium looking at the horizon as two glyptodonts waddle by!
Image Credit: D. Bogdanov (DiBgd), https://commons.m.wikimedia.org/wiki/File:Pleistocene_SA.jpg#mw-jump-to-license

Such a majestic animal is another example how diverse the megafauna were during the last Ice Age. However the majority of these animals are not around anymore. Megatherium’s story is similar to other megafauna. Climate change at the end of the last Ice Age played a part, resulting in a loss of habitat and decline in population. This was combined with the arrival of modern humans into South America roughly 14,500 years ago. Some Megatherium bones bear distinct marks on them that indicate that they were cut by human tools. Furthermore other bones have been unearthed alongside human made stone tools and weapons. Tools, high intelligence and co-operation made humans a terrifying predator for a Megatherium to try and defend itself against and humans were so efficient that Megatherium numbers dwindled further. Eventually the dynasty of the Great Beast would come to a close 8,000 years ago. This unfortunate end makes one wish that the Cryptozoologists were right, and that Megatherium was somehow still living in South America to this day. If this were the case then I’m sure many more people would see what a “Great Beast” it really was.

References/Further Reading

Bocherens et. al. 2017 paper reconstructing the diet of Megatherium from analysis of collagen in the fossils

Bocherens et. al. (2017), Isotopic insight on paleodiet of extinct Pleistocene megafaunal Xenarthrans from Argentina. Gondwana Research, 2017; 48: 7 DOI: 10.1016/j.gr.2017.04.003

Billet et. al. 1997 paper examining the inner ear anatomy of Megatherium and what it tells us about its body mass and agility

Billet, G et al. “The inner ear of Megatherium and the evolution of the vestibular system in sloths.” Journal of anatomy vol. 223,6 (2013): 557-67. doi:10.1111/joa.12114

Natural History Museum website article profiling Megatherium and detailing a project that was digitally scanning all the fossils Charles Darwin collected on the 1831-1836 Beagle voyage

Brewer, Pip, “What was Megatherium?”, Natural History Museum, https://www.nhm.ac.uk/discover/what-was-megatherium.html

Fariña 2002 paper suggesting that the largest Giant Ground Sloths, such as Megatherium, were mostly hairless

Fariña, Richard. (2002). Megatherium, the hairless: appearance of the great Quaternary sloths (Mammalia;Xenarthra). AMEGHINIANA. 39. 241-244.

Politis et. al. 2019 paper, published in Sciences Advances, on the discovery of Megatherium remains that show evidence of Human Hunting

Politis, Gustavo & Messineo, Pablo & Stafford Jr, Thomas & Lindsey, Emily. (2019). Campo Laborde: A Late Pleistocene giant ground sloth kill and butchering site in the Pampas. Science Advances. 5. eaau4546. 10.1126/sciadv.aau4546.

Smilodon: The Sabre-Tooth (not a) Tiger

Smilodon looking over his kingdom
Image Credit: Charles R Knight, http://www.charlesrknight.com/dinosaur-artist-charles-r-knight/Knight%20article.pdf

Right, I’m going to start off by clearing up a common misconception. Despite often being called it in popular media Smilodon was NOT a Sabre-Toothed Tiger, or related to tigers at all! It was a Sabre-Tooth Cat (or Machairodontinae if you want to get technical). Also, the term “Sabre-Tooth Cat” refers to the family that Smilodon is a part of rather than just Smilodon itself. Other examples of Sabre-Tooth Cats include; Dinofelis, which lived across Africa, Eurasia and North America during the Pliocene to the Early Pleistocene (5.5-1.5 million years ago) and has a reputation for being a hunter of Australopithecus and other early human ancestors (which it may or may not have done). Another example is Homotherium, a smaller Sabre-Tooth Cat species which lived around the same place and time as Smilodon.

With that out of the way, let’s find out more about this large and rather striking extinct kitty.

To start with, the first piece of anatomy that everyone notices when looking at Smilodon is its large sabres (which could measure up to 28cm long – almost as long as a school ruler!). Contrary to popular belief Sabre-Tooth Cats like Smilodon were not the first animals to evolve sabre teeth. That title instead goes to animals like the Gorgonopsids, a group of “mammal-like reptiles” that lived in the Late Permian period around 265-250 million years ago. They, and other “mammal-like reptiles” are a fascinating group of animals in their own right which I’m sure I’ll tackle in a later blog. While the sabres in Smilodon look very formidable they were actually surprisingly fragile, and could break easily if used for usual ripping and slashing attacks. Smilodon also had a relatively weak bite, and needed to open its mouth very wide in order to extend the sabres out fully. As a result it is thought that the sabres were used for careful, quick surgical bites to the prey’s neck in order to puncture the neck and ensure a quick end without too much struggle. The iconic positioning of these sabre-teeth is that they’re exposed on the outside. While this continues to be scientific consensus there have been suggestions that Smilodon and other sabre-tooth cats may have had fleshy lips covering them instead.

A reconstructed skeleton of Smilodon fatalis from the Sternberg Museum of Natural History in Hays, Kansas, USA. As you see the sabre-teeth are certainly eye-catching!
Image Credit: James St John, https://www.flickr.com/photos/jsjgeology/15420386216

There are other parts of Smilodons anatomy that also set it apart from modern day big cats. It was larger and more heavily built than a modern lion or tiger, measuring up to 1.5 metres long, a metre high and weighing up to 400 kilograms. Smilodon also possessed thick front leg bones with big muscle attachments. This suggests that Smilodon would not have been a pursuit hunter, but instead an ambush predator, stalking its prey, getting close and then leaping out and pinning them down using their powerful front legs, before then employing the sabres. In terms of behaviour it was a matter of debate as to whether Smilodon lived in prides (like lions) or were solitary like tigers, with reconstructions, paleoart and documentaries switching between the two. However some fossil Smilodon show previous serious injury and not only managed to recover but live to an old age. Also a joint study in 2008 by the Zoological Society of London and the University of California, assessed the large number of Smilodon remains found at Rancho La Brea Tar Pits who had turned up at the tar pits in response to prey distress calls. They compared these with the numbers of modern African predators that turned up to similar distress calls at similar traps. The results showed that the number of Smilodon found compared well to the numbers of pack hunting animals, such as lions and hyenas. Both of these observations indicate that these sabre-toothed cats lived in packs. (On a side note; Rancho La Brea is in my top 5 places to visit in the world!)

Smilodon fossils have been found across the Americas, having first evolved in North America before migrating to South America via the newly formed Isthmus of Panama land bridge. The first fossils, being of the South American species Smilodon populator, were discovered by Lund in Brazil in 1840. Further species discovered, all mostly based in North America, include; Smilodon fatalis (discovered by Leidy in 1869) and Smilodon gracilis (discovered in 1880 by the legendary Edward Drinker Cope of dinosaur fossil fame). Of these species Smilodon populator was both the youngest, evolving only 1 million years ago, and the largest.

A size comparison between 3 different Smilodon species and an average human. Smilodon populator of South America was the largest, followed by the North American Smilodon fatalis and Smilodon gracilis.
Image Credit: Aledgn, https://commons.m.wikimedia.org/wiki/File:Wiki_Smilodon_Size.png

Such a beautiful cat would be a sight to witness across the American plains. Sadly, like the rest of the megafauna that lived alongside them, they died out during the last Ice Age around 10,000 years ago. A few reasons have been suggested for this; competition with humans for prey being one of them. However it is likely that a changing climate, resulting in habitat reduction, and the loss of the large megafauna that Smilodon preyed on (which could have partly been a result of human hunting) were the main reasons. With large prey gone and with Smilodon not having the endurance to hunt the smaller, swifter mammal herbivores that remained, their numbers dwindled.

Still, Smilodon has gone down in history as one of the most striking extinct animals yet described. Its sabres have repeatedly captured the imagination of generations of people in museums and in popular media. Personally I’m sure of two things about Smilodon:

1. If I had to pick a fossil skull to own, it would be one of these sabre tooth cats, and

2. If one of them could speak it would have the voice of Denis Leary!

EDIT: A small addition to this blog. As well as being found in the USA Smilodon fatalis has also recently been discovered to live as far north as Canada, with the paper describing the new Canadian fossils (Reynolds, Seymour & Evans 2019) only published in January 2019.

References/Further Reading

Carbone et. al. 2008 paper on pack hunting behaviour in Smilodon

Carbone, Chris, Maddox, Tom, Funston, Paul J, et. al., (2008), Parallels between playbacks and Pleistocene tar seeps suggest sociality in an extinct sabretooth cat, Smilodon, Biol. Lett.5, 81–85, https://doi.org/10.1098/rsbl.2008.0526

An interesting blog by Mark Witton, published on his blog site, on exposed teeth in Paleontological reconstructions. Smilodon is one of the animals he talks about.

Witton, Mark, “Exposed teeth in dinosaurs, sabre-tooths and everything else: thoughts for artists”, markwitton.com/blog, Oct. 9, 2016, markwitton-com.blogspot.com/2016/10/exposed-teeth-in-dinosaurs-sabre-tooths.html

Christiansen & Harris 2005 paper, published in Journal of Morphology, on body size estimates of three Smilodon species

Christiansen, P. and Harris, J.M. (2005), Body size of Smilodon (Mammalia: Felidae). J. Morphol., 266: 369-384. doi:10.1002/jmor.10384

Reynolds, Seymour & Evans paper on the Canadian Smilodon fatalis fossils (For the EDIT).

Reynolds, A. R., et al. (2019). “Late Pleistocene records of felids from Medicine Hat, Alberta, including the first Canadian record of the sabre-toothed cat Smilodon fatalis.” Canadian Journal of Earth Sciences 56(10): 1052-1060.