Frozen mummy of a sabre-toothed juvenile gives clues about what the species looked like

Nature Scientific Reports has an open-access article reporting a rare find: a mummy of a kitten (“juvenile”) of a sabre-toothed cat, found frozen in the Russian Republic of Sakha, in Siberia. You can read the report by clicking below, or download the pdf here.

Mummies are rare because an animal has to die and then be permanently frozen in ice, and then later discovered. This is, as far as I know, the first mummy of a sabre-toothed cat, though skeletal remains are known. (These skeletal remains were used to identify the species of cat; see below)  It appears to be a young kitten, judging from comparison with a living relative, a three-week-old African lion (Panthera leo). The mummy’s remains were carbon dated to 31,808 ± 367 years ago, so it could have been contemporaneous with humans, who were probably in Siberia about that time.

Here’s a description of the specimen and then some photos:

The Badyarikha mummy (specimen DMF AS RS, no. Met-20-1) contains the head and the anterior part of the body preserved approximately to the caudal edge of the chest (Fig. 1). There are also incomplete pelvic bones articulated with the femur and shin bones. They were found encased in a piece of ice along with the front part of the cub corpse. The specimen is stored at DMF AS RS in Yakutsk.

Figure and caption from the paper (click figures to enlarge them):

And here’s a comparison of the heads of the specimen (top) with a preserved three-week old lion cub. The face of the sabre-tooth is flatter than that of the lion, but this is probably due to deformation of the specimen (see skulls below). But the mummified cats’ external ears (auricles) are not as prominent as those of the lion. (Smaller ears are a characteristic adaptation to cold climate, as protruding ears are a source of heat loss.) The mummy’s fur color was dark brown, with the paws and chin being lighter brown:

‘The authors make a big deal about the thickness of the neck, which shows that this was a muscular cat (compare with the lion cub below):

From the paper:

The mummy neck is longer and more than twice as thick as that of P. leo, ZMMU S-210286 (80.0 vs. 74.0, 52.0 vs. 32.0, respectively). The difference in thickness is explained by the large volume of muscles, which is visually observed at the site of separation of the skin from the mummified flesh.

Based on comparison of the skull with known fossil skeletons, they identified this cub tentatively as a juvenile Homotherium latidens.

Here’s an 8-minute movie about the genus Homotherium, showing a reconstruction of the animal and a lot of useful information:

And a photo of skulls of the sabre-tooth cub specimen (top row) and a 3-week old lion cub (bottom row).   The enlarged arches, where chewing muscles are attached, suggest that the species was adapted to inflict a strong bite (perhaps to use its serrated incisor teeth), though I’m not a paleontologist and am just guessing.

The authors say this:

One of the striking features of the morphology of Homotherium, both in adults and in the studied cub, is the presence of an enlarged premaxillary bone, containing a lateromedially expanded row of large cone-shaped incisors that form a convex arch. Among all the unerupted teeth of the Homotherium cub mummy, only the upper and lower deciduous incisors protrude with their tops from the alveoli.

Here’s where the premaxillary bone is: the orange one in front. You can see that this bone is larger in the mummy than in the lion cub.

 

Finally, the configuration of the paws, which are far more rounded in the mummy than in a lion cub, support the suggestions from the cub’s ears that this was a cat adapted to the cold. Forepaw photos, with A-C being the mummy and D being a lion cub. Rounded paws, also seen in lynxes and other cold-weather cats, are better for walking on snow, as they act as “snowshoes” that give a greater area of contact with the snow:

And the authors’ interpretation:

The front paw of the juvenile Homotherium latidens has a rounded shape. Its width is almost equal to its length, in contrast to lion cubs with their elongated and relatively narrow front paw (Fig. 7). The wide paw, the subsquare shape of its pads, and the absence of a carpal pad are adaptations to walking in snow and low temperatures. The small, low auricles and absence of the carpal pad in Badyarikha Homotherium contrast with the taller auricles and normally developed pads in the lion cub. All these features can be interpreted as adaptations to living in cold climate.

The carpal pad (“2” in the lion photo) is apparently missing in the sabre-tooth, and this is said to be an adaptation to walking in snow, though I’m not sure why.  But all the data indicate that this species of cat was muscular (the forepaws also suggest more muscles than the lion) and, as suggested from its Siberian habitat, adapted to a cold climate. You can learn more about the lifestyle of this genus of cat from the movie above.

h/t: Erik