Homotherium: A saber-toothed cat of the North Sea

Dick Mol (Netherlands)and Wilrie van Logchem (Netherlands)

Somewhere around the Dutch coast, a mammoth herd, led by an experienced matriarch strolls along a trail on the cold, dry and treeless steppe – the mammoth steppe – typified by tall, tough grasses and Artemisia. The impressive herd numbers about thirty animals, reflecting several generations, young and old, trailing each other on their way to the river (the paleo-Meuse) for a drink. Meanwhile, far off in the background, we notice a stampeding herd of large steppe buffaloes, chased by a pack of lions.

Some hyenas are watching the scene with interest from their hideout in the tall, dry grass, eagerly hoping for some leftovers from the anticipated feast. Also hidden by the tall grass, another, strange and unknown predator observes the panorama – a saber-toothed cat. The head of the animal looks fierce. Incredibly long, flattened canines, sharp as daggers, are exposed when this Homotherium opens its mouth…

This drama is set in the Netherlands, some 28,000 years ago and it is quite plausible that such a scenario happened in the last part of the ice ages of the Pleistocene epoch.

The North Sea is being fished intensively today and Dutch fishermen not only collect flatfish like sole and plaice, living on the sea floor. They also retrieve the weirdest objects – fragments of shipwrecks from days gone by or bombs from World War II, jettisoned by the bombers in the dark days of the previous century. But, the most intriguing discoveries are fossil remains from animals that lived here, in the not-so-distant past, in a period when the world looked very different from today and when animals grazed on what is now the bottom of the North Sea.

A couple of months ago, we (together with Remie Bakker) published a book on a saber-toothed cat mandible, trawled from the seabed (The Saber-Toothed Cat of the North Sea published by Uitgeverij DrukWare). The book is about an ice age predator that is sure to capture the imagination – the saber-toothed cat. It is an extinct felid whose remains are very rarely found in Europe. Until recently, remains of the saber-toothed cat Homotherium in the region of the Netherlands were only known with dates of about one to two million years ago.

Fig. 1. Illustration of saber-toothed cats surrounding a woolly mammoth. © Remie Bakker.

Discovery of a saber-toothed cat

On 16 March 2000, the trawler UK33 from Urk in the Netherlands was fishing on the North Sea. The crew had selected a fishing area in the middle of the sea, half way between IJmuiden in the Netherlands and Lowestoft in East Anglia in the UK. When the nets were hauled on board, the trawler was in the southeast part of an area known as the “Brown Bank”. Included in the catch was a mandible and it was clear that it justified a closer investigation, and so a researcher acquaintance of ours was called in.

“A saber-toothed cat from the North Sea? From the Late Pleistocene? No, that can’t be!” is the prompt answer. It is known that two American saber-toothed cat species (Homotherium and Smilodon) were around until the late Pleistocene (10,000BC). However, the saber-toothed cat first became extinct in Africa and it is commonly assumed that these cats became extinct in Europe and Asia between 500,000 and 300,000 years ago, judging by the dating of the known fossils. So, it would seem that the idea of a very late Pleistocene saber-toothed cat in the North Sea could be rejected.

Fig. 2. The most recent jaw bone of *Homotherium latidens* in Eurasia with an age of 28,000 years, collected from the North Sea by the vessel UK33.

The researchers became convinced that this jaw was once part of a saber-toothed cat. But the question arose as to how this could be possible. Although the remains of a late Pleistocene saber-toothed cat had not been discovered before, this is not a compelling argument that it is not possible. Based on the morphology of the jaw, it has been convincingly demonstrated that the jaw exhibits all the characteristics of a saber-toothed cat, while all other forms of felids can be excluded based on the same morphology. Fossils of saber-toothed cats have always been rare anywhere in the world. The animal would usually be at the top of the food chain, which (by definition) makes them rare compared with herbivorous species in the same faunas. Therefore, the chance of finding fossils of top predators is much smaller than finding fossil herbivores.

Therefore, since the discovery and classification of the North Sea mandible to Homotherium latidens with a scientifically determined age of 28,000 years, we can conclude that this animal was also a member of the late Pleistocene mega fauna. The reason that this species has not been found before in the late Pleistocene could be its place at the top of the food chain, where the number of individuals is generally low. Alternately, due to the abundance of many different predator species and the pressure on the food chain, Homotherium may have been low in numbers because of competition among predator species, as there can be considerable differences in numbers of lions, panthers and cheetahs on the Serengeti savannah today.

Homotherium

Homotherium was a saber-toothed cat, the size of the modern lion. During the late Pliocene, about 3.5Ma, it showed up almost worldwide in Eurasia, Africa and North America. Its ancestor is the saber-toothed cat Machairodus that lived 15 to 2Ma.

The extinction of Homotherium started in Africa, where it disappeared in the early Pleistocene. Until recently it was assumed that it died out in Eurasia about 300,000 years ago in the middle Pleistocene. However, after radiocarbon dating the mandible collected by the Dutch trawler UK33 in the North Sea, we know that Homotherium continued on until at least 28,000 years ago in Western Europe. In America, this genus disappeared at the last glacial transition, some 11,500 calendar years ago.

Saber-toothed cats from Britain

Kessingland

In 1886, James Backhouse described the first Homotherium mandible found in the UK. It was a complete right mandible found in the Forest-bed Formation of Kessingland in Suffolk, dated to the early middle Pleistocene (780,000 to 450,000 years ago). This was a period of several complicated climate changes clearly affecting the faunas. However, in the 1800s, comparable mandibles were not yet available. This mandible had an overall length of 204mm and, based on the rate of wearing down of the cutting molar and the lack of crenulations, it can be concluded that the specimen belonged to an old individual.

Kent’s Cavern

In general, caves are very good places to find fossil mammal remains. Mammals use caves for shelter or as dens, and preservation conditions for bones and other hard remains are much better than in the open. Many extinct species have been found in caves first, hence cave bear (Ursus spelaea), cave hyena (Crocuta spelaea) and cave lion (Panthera spelaea). One of the most important caves in the UK is Kent’s Cavern, also known as Kent’s Hole, close to Torquay in Devon.

The likely age of the remains found here is 400,000 years. This is the type locality of Homotherium latidens, which means that the discoveries in this cave were used for its description and naming. Half a dozen curved and flattened upper canines with crenulations on the edges were found and these were already recognised as being important by the scientist William Buckland by the time Sir Richard Owen later used them for the first scientific name-giving of Homotherium latidens. In 1846, he proposed the name Machairodus latidens. Today, the species belongs to the genus Homotherium and the correct full name is Homotherium latidens.

Fig. 4. Kent’s Cavern in Devon is open to the public.

Robin Hood Cave

An interesting case is the find of the saber-toothed cat, Homotherium latidens, in the Robin Hood Cave in Cresswell Crags. The British palaeontologist, W. Boyd Dawkins, discovered a crown of the right upper canine in 1876. In his description, he suggests that this canine may have been brought into the cave by prehistoric hunters. At the root are scratch marks that may have been caused by human modifications. It clearly shows that attempts were made to thin the crown at the place where it had broken off. It also looks as if attempts had been made to drill a hole in it. It appears that the crown of the canine was being modified with the intention of using it for something like a necklace or amulet. This may have happened in the Late Palaeolithic, about 35,000 to 10,000 years ago. The particular shape and the sharp, saw-toothed cutting surface will certainly have fed the imagination of the hunters from that time.

A solitary or social predator?

The majority of palaeontologists agree that the species of the saber-toothed cat, Homotherium, would have been a solitary predator. This is based on comparisons to the lifestyles of modern big cats. With the exception of the modern lion (Panthera leo), all bigger and smaller cats tend to lead a solitary life. However, some specialists have argued that Homotherium may have been a social predator as well, hunting in small groups.

The logic of social hunting is based on the adaptations to its body for sustaining higher speeds, seen especially in the youngest species of the genus, Homotherium. Like the cheetah, these adaptations came at the expense of strength, compared with its contemporaries, the cave lion and cave hyena. The longer, more slender and less muscled front legs could generate an enormous speed, but at the expense of the capability to overpower a prey, especially the larger members of the fauna. To compensate for its lack of power, the animal may have lived in a social order and hunted in packs, like a pride of lions. If this were the case, it is very hard to estimate the number of individuals in such a pack.

Homotherium’s approach to a prey would probably have involved a typical stealthy, cat-like stalking to get close, concealed by the tall grasses. Alternately, an approach more in the open could have been possible like cheetahs and hyenas today. Like them, after the pursuit, Homotherium may have tripped the prey up using its large dew claw, causing it to fall to the ground as the cheetah is known to do. On the other hand, it may have used its incisors and long upper canines for an initial injury to the prey, slowing it down, a technique that is observed in dog-like predators and hyenas. It is conjectured that one or more saber-toothed cats may have pinned the prey to the ground, the cat’s back tightly stretched under tension, its hind legs firmly planted on the ground to resist the wrestling prey. At the same time, others may have gone for the deadly neck bite or a bite to the abdomen, killing the prey through loss of blood.

Fig. 5. Front view and side view of the first-ever-found lower jaw of *Homotherium latidens* from the UK. It was first described in 1886 by James Backhouse. This jaw dates from the early Middle Pleistocene and was found at Kessingland in Suffolk. It has a lenght of 204mm. Source: Backhouse, 1886.

Another reason for hunting in packs may have been brought about by climate change during the transition of the Pliocene to the Pleistocene, when the densely forested landscapes gave way to a more open vegetation with fewer tall trees. This change had a major impact on both the prey and the predators. The prey had to adapt to changes in diet while the predators faced a more complex situation. Hunting techniques in dense forest were not suitable for a more open landscape. Prey animals could see predators approaching due to the loss of vegetative cover. This also implies an increasing competitive pressure amongst the predators. To continue a successful existence, it may have become beneficial for Homotherium to hunt in packs.

Fig. 7. Illustration of saber-toothed cats giving a deadly throat bite. © Remie Bakker.

A currently popular hypothesis about the hunting strategy of a saber-toothed cat as a lone hunter is the hit and run hypothesis. It is thought that this predator could attack and issue some lethal wounds to the abdomen of a large prey animal. Then it would retreat, avoiding the counter-attack of the victim, which would eventually die from its injuries. However, this method may not be very effective in reality. In the open steppe landscape, the victim would attract the attention of the plentiful scavengers and predators, and the likelihood that its prey would be lost to rival carnivores such as cave lions, giant hyenas, or even other saber-toothed cats, would be significant.

Life-sized model

The North Sea mandible has inspired the Dutch sculptor Remie Bakker of Rotterdam. He has been collaborating with palaeontologists for many years and has created outstanding, life-sized ice age animals such as the woolly rhino and woolly mammoth, based on the fossil record. For him, the challenge was to build a life-sized model of Homotherium latidens using all the data available. In a couple of months, after consulting experts in the field of extinct and extant cats and Pleistocene vertebrates, he successfully brought the 28.000 years old Homotherium back to life.

Storage of fossil bones, collected by dredging the North Sea floor. The supply of new fossils from fishing nets is continuous. Collection Klaas Post, Urk.

Homotherium: A saber-toothed cat of the North Sea

Discovery of a saber-toothed cat

Homotherium