The Sabertooth’s Terrible Hook: the case of Lothagam’s cat
Sabertooth cats are justly famous for their namesake upper canine teeth, but they had another remarkable weapon of trade: an enormous dewclaw which was quite appropriate for the tasks of catching prey and keeping it motionless while the cat applied its surgically precise killing bite.
There is plenty of evidence from the fossil record about the widespread presence of this feature in different species of sabertooth cats, but perhaps the most beautiful example is the holotype skeleton of Lokotunjailurus from the fossil site of Lothagam in Kenya. This sabertooth cat was an elegant, lightly built animal, about as tall at the shoulder as a lioness but with more slender bones and a much smaller body weight. The preservation of this specimen was so exquisite that it included a complete articulated forepaw with all the bones in place, down to the claw phalanges.
Back in 1999 I visited the National Museums of Kenya in Nairobi in order to prepare reconstructions of several species of fossil verterates from Lothagam, which would illustrate a monograph about the site and its fauna. During my visit to the museum I worked with paleontologists Lars Werdelin and Meave Leakey in the study of the fossils.
One of the advantages of working in a place like the National Museums of Kenya is that you have access to the skeletons of modern animals from their anatomy collections in order to compare and put the anatomy of fossils in perspective. A most interesting exercise was to put on the same table the bones of the forepaw of the sabertooth Lokotunjailurus, a modern lion, and a modern leopard. Of course the most striking feature of Lokotunjailurus was its dewclaw, which was larger than that of the lion, although the latter was clearly a larger and heavier animal. But the claws of the remaining digits of Lokotunjailurus were smaller than those of the lion, and in fact they were smaller than those of the leopard, although the latter animal was much smaller than either the lion or Lokotunjailurus.
What is the meaning of such distinctive claw proportions in the sabertooth? One interesting fact to consider is that among modern cats, the cheetah resembles the sabertooths in having a proportionally large dewclaw and small claws in the other digits. Another meaningful similarity is that in both the cheetah and the Lothagam sabertooth, the claws other than the dewclaw are less retractable than they are in more typical cats like lions and leopards. Does this mean that Lokotunjailurus was a sprint hunter like the cheetah? not likely, because its body porportions were not those of a sprinter, but it could certainly run at moderate speeds with more endurance than a modern lion.
It seems that in sabertooths, as in the cheetah, the dewclaw was especially important in catching and restraining prey, while the remaining claws had a greater role in locomotion, giving the cat a better traction on the terrain. This makes sense because sabertooths had a longer history as ground dwelling cats -they “came down from the trees” far earlier than their feline cousins did. A less advantageous aspect of the sabertooth’s claw anatomy was that the animals, especially the close relatives of Lokotunjailurus (including Homotherium and Amphimachairodus) were less than competent climbers, a price they had to pay for their efficient terrestrial locomotion. After all, evolution and adaptation are all about compromise.
You can see a discussion of the early evolution of the sabertooths’ dewclaw in this post about Promegantereon:
And now a drawing of the skeleton of the forepaw in Lokotunjailurus (with some bones slightly rearranged to fit their anatomical life positions), together with a reconstruction (bottom) of the appearance of the same paw in life . I have shown the paw with all claws protracted, in the position they would be while handling live prey. Claw sheaths are not bone and thus were not preserved in the fossil, but I have shown their hook-like outlines at the end of each claw phalanx.
And now a reconstruction of the life appearance of Lokotunjailurus based on the Lothagam skeleton. Here the claws are in a relaxed position as they would be during the normal walk, but even so their tips are visible. When the cat was running, the claws would protrude further and contact the ground, as they do in the cheetah.
To learn more about Lokotunjailurus and its adaptations look for the book “Sabertooth” in October!