Warning – potential book spoilers ahead

I like to keep a lot of visual references and trinkets of inspiration around me when I write. Dotted around my workspace are various Schleich dinosaurs – Carnotaurus and T. Rex have prominent places (what can I say, I like predators!); and a selection of plush toys including a sabretooth, Nessie, and a black jaguar cub. Then, there are black jaguar and black leopard models, slightly overshadowed by the huge ‘stray cat’ Smilodon from Rebor.

On my desk is a selection of teeth and claws. Some are real, whilst others are museum replicas. I have megalodon, great white, and mako teeth that are all the genuine article, as well as two other fossil shark teeth I’ve never been able to identify 100% (found on a beach on the Isle of Sheppey). Incidentally, the great white tooth was found on a beach in La Jolla, California.

Among the replicas is the tooth you see in the picture below. It’s a cast of a canine from Homotherium. Also known as the scimitar-toothed cat, this was one of the most widely distributed sabre-toothed predators to have existed, having roamed North and South America, Eurasia, and Africa. 

Sabretooths are featured in my books, and I’m often asked why I didn’t choose Homotherium as the species that ultimately plays a major role in the ongoing storyline. There’s a couple of reasons, but first, did you know how many different sabretooths there are to (hypothetically) choose from?

Homotherium belonged to the Machairodontinae (meaning daggertooth) sub-family within the Felidae (true cat) family of mammalian carnivores. Like all in this sub-family, they are most known for their enlarged maxillary canines. In almost all cases, these protruded from the mouth on either side of the jaw and were visible even when the mouth was closed. But, in the case of Homotherium, it’s likely that despite having relatively large canines, they would have been hidden by the upper lips and lower gum tissues, just like in modern big cats. This was just one reason Homotherium didn’t make the cut. I needed a sabretooth that could be recognised for what it is – despite Homotherium’s convenient European fossil record.

Don’t be fooled into thinking Homotherium didn’t pack a punch though. They were about the size of a male African lion. And not only were its teeth designed for slashing, but also a powerful gripping bite capable of delivering deep puncture wounds.

Joining Homotherium in the Machairodontinae is also Amphimachairodus (thought to be some of the earliest sabretooths to inhabit Europe); Lokotunjailurus (think a long-legged, more gracile lioness) was known from the Miocene epoch across Kenya and Chad; Nimravides – a tiger-sized sabretooth that appeared in the late Miocene and has been found exclusively in North America; and Xenosmilus. 

If you’ve read my books, you’ll know why I’ve paused there. Xenosmilus was big, even for a sabretooth. In fact, only Smilodon (who’ll we’ll come to later) was noticeably larger in terms of mass. Yet it stands out among others in the sub-family for other reasons.

Before Xenosmilus was discovered, sabretooths fell relatively neatly into two categories. Scimitar-toothed cats, like Homotherium, had mildly elongated canines and long legs. Dirk toothed cats, like Smilodon, had long upper canines and stout legs. Xenosmilus broke the mould. It had short, muscular legs and a robust body – yet its canines weren’t as pronounced. And those teeth were different in other ways too. All of Xenosmilus’ teeth were serrated, and its top teeth aligned with the bottom in a way that enabled it to concentrate its bite force on two teeth at a time. This is where Xenosmilus gets its name – which means ‘strange smile’. The unique way that its canines and incisors operated together in biting, also led to the moniker, ‘the cookie-cutter cat’. 

The skull of Xenosmilus also features a pronounced and significant sagittal crest compared to others in the family. This meant it had phenomenal jaw strength and bite force, thanks to the muscles that would have been attached here. Together, these features have led to the theory that Xenosmilus adopted a bite and retreat hunting strategy. It would use its formidable teeth to inflict a deep wound, then wait until the prey was incapacitated. The peccary bones found close to the two type specimens indicate not only a liking for pork, but also that the species may have hunted collaboratively. 

It was these unique features that led to Xenosmilus playing the role it does in my stories. But we’re only halfway through the very top layers of the sabretooth family tree.

A smaller, sub-group are the Machairodontini, made up of; Machairodus – meaning ‘knife tooth’ and who gives this little clan their name; Hemimachairodus – known from finds in Java and Indonesia; and Miomachairodus, known from finds in China and Turkey. They were large cats, similar in size to the smaller subspecies of modern-day tigers.

The Metailurini include Metailurus – a cat we know from only partial remains, but its elongated rear legs mean that it was probably an accomplished jumper. Others in the group include Adelphailurus, Stenailurus, and Yoshi – a species proposed to be quite cheetah like in behaviour. Because these species have only been identified from small finds, what we know about them is limited, but new details are being published regularly with study. 

The exception in this group is one of my favourites – Dinofelis, whose name means ‘terrible cat’. There’s some argument that Dinofelis belongs to the Smilodon sub-family, but for now, they lie here. These jaguar-sized cats were powerfully built with prominent sabres and extremely robust front limbs. They were also widespread, with fossils found across the North America, Europe, Asia, and Africa, from between 5 and 1.2 million years ago. It has also been proposed that Dinofelis preferred forest habitat and may have had a spotted or striped coat – like the modern day clouded leopard and ocelot. 

Finally, we come to the best known of the sabretooths – the Smilodontini. These include the three sub-species of Smilodon, but also the family groups of Rhizosmilodon, Promegantereon, Paramachairodus, and another favourite – Megantereon. The latter may have been a direct ancestor of Smilodon and was jaguar-sized, but even heavier set with lion-like forelimbs. Despite this, they are thought to have been able to climb relatively well and take down prey as large as a horse. And unlike its relative Smilodon, who was limited to North America, Megantereon was found in Eurasia and Africa too.

Smilodon is not only one of the most well-known sabretooths, but also one of the most easily recognised prehistoric mammals ever discovered, thanks in part to hundreds of fossils retrieved from the La Brea tar pits. Its name means scalpel, or ‘two-edged knife tooth’. Its teeth are easily the most impressive of all sabres in terms of size and were tools used for precision kills. However, these formidable upper canines were relatively weak and fragile. They had stocky, bear-like bodies and are thought to have been ambush predators that preferred thick forest and vegetation as habitat. Again, we’re not sure if they were co-operative hunters – but it is thought likely that they lived in small family groups. 

All the above sabretooths are part of the Felidae family – making them true cats. But they weren’t the only sabretooths out there. There are others, most of which fall under what are known as false sabre-toothed cats – including the nimravidae and barbourfelidae. These animals are part of the Feliformia sub-order. Again, if you’ve read my books, you’ll be familiar with that name in terms of hyenas and their fossil relatives. But it also includes animals like the Madagascan fossa, the binturong of Asia, as well as civets, mongoose, and meerkats. Cats too are part of this sub-order, and the false sabre-toothed cats are obviously more closely related than these others – but are still different from true cats.

As for sabretooths and their modern-day cat relatives, it’s thought that they shared a common ancestor from about 18 million years ago. But the family ties between the sabretooths themselves are quite strained too. For instance, Homotherium and Smilodon are probably more distantly related from each other than your typical house cat is to a tiger. But genetically, we can still forge that connection to modern day big cats like lions and tigers from studies carried out on fossil mitochondrial DNA. It’s more direct in species related to Homotherium, which is another reason Xenosmilus was a good fit on paper. It had the strength and size of Smilodon but benefited from being part of the larger sabretooth family, with more of a genetic tie (however slight) to modern big cats.

As for would a modern-day big cat, like a jaguar, be able to breed with a sabretooth like Xenosmilus… we obviously don’t know. My conjecture is that as true cats, it’s technically possible and viable. There would no doubt be many unknown evolutionary and biological barriers to overcome, but, as a favourite fictional character facing similar concerns famously once said… “life finds a way”. 

And whereas we’ll never be able to bring back a dinosaur from its DNA to find out what it might conveniently splice with, don’t be so sure when it comes to prehistoric cats. Their DNA – from cave lions to Smilodon, has been found and identified, and in some cases, even mapped. Maybe in the near future, just like in my books, we’ll be able to visit something akin to a Pleistocene Park!

If you can’t wait until then, you can discover how these cats and others play a role in my books here.