For the last lecture - kitties!!
I am a cat person and could say lots about these animals, but here, we concentrate on a biomechanical issue that cats, above all other creatures, exemplify: The sabretooth morphotype. Everyone knows the image of the sabretooth cat. Theirs was a modestly diverse radiation of the Neogene, during which they were roughly as diverse as other large cats. Humans shared their world with them for most of our history, however they were extinguished at the end of the Pleistocene Epoch about 11,000 years ago. And yet sabretooth cats were only the last of a series of synapsids to develop the sabretooth morph. Others include:
Because other aspects of their biology are so mysterious (Were they warm-blooded? Did any of them use venom to subdue prey?) there is little we can say but note that they had long, laterally flattened canine teeth.
This is a better starting point. Like other therian sabretooths, Thylacosmilus was an ambush predator with long, flattened canines, flanges of the lower jaw that protected them from mediolateral bending when the moouth was closed, and very muscular forelimbs capable of a wide range of movement.
Creodonts (Paleogene - Neogene) are an extinct group of carnivorous placental mammals that was widespread and diverse during the Paleogene. (Interestingly they hung on in Africa into the Neogene.) Phylogenetically, they are the sister taxon to Carnivora, the monophyletic group containing most placental land macropredators. (Note: A "carnivore" is an animal that primarily eats meat. A "carnivoran" is a member of the clade "Carnivora." Not all carnivores are carnivorans and not all carnivorans are carnivores.
Though not as extravagantly sabretoothed as Thylacosmilus, Machaeroides resembles it in several ways, notably in the long canines and surprisingly muscular forelimbs.
Carnivoran phylogeny (Paleogene - Recent) is very intuitively clear:
A significant synapomorphy: Upper premolar 4 and lower molar 1 are transformed into carnassials blade-like teeth that cut meat with a scissor-like action. (Note, creodonts also had carnassials but they were not formed by homologous teeth!)
Nimravidae (Paleogene - Neogene) - One group of feliforms are worth noting. The nimravids are the first branch off the feliform tree, however their members convergently evolved cat-like features. Among them were sabretooth forms that are very similar to sabretooth cats, such as Barbourofelis pictured below. Remarkable considering that proper cats are more closely related to hyenas, mongooses, and civets.
Like Thylacosmilus and Machaeroides Barbourofelis had long thin canines and muscular forelimbs.
Felidae (Paleogene - Recent) - True cats appear near the Paleogene - Neogene boundary. The first well known fossil felid is Proailurus from the latest Paleogene of Eurasia.
Proailurus was about the size of a bobcat or lynx, but its proportions were very different. With short limbs and a flexible vertebral column, it is thought to have been arboreal, climbing in the manner of the living Malagasy fossa (a viverrid, not a cat). Proailurus and other early cats didn't have specialized canine teeth. By the early Neogene, however, a split had occurred between:
Biting cats: Diagnostic characters include:
A biting cat
Sabretooth cats: Diagnostic characters include:
A sabretooth cat
This contrast is, if anything, more apparent in anterior view: Panthera leo, the African lion. A biting cat.
The muzzle is short and the zygomatic arches (cheek bones) are wide. The skull accomodates lots of jaw musculature.
Machairodus giganteus, a lion-sized sabretooth cat.
The muzzle is long and the zygomatic arches (cheek bones) are narrow, constraining the mass of jaw musculature.
The postcrania of sabretooth cats are distinctive as well. Contrast the general limb proportions of a leopard:
and the Pleistocene Holarctic sabretooth cat Homotherium (with hyena for fun). (Note: During the last glaciation, Homotherium ranged across northern Eurasia and North America. In North America, its range overlapped with the American sabretooth Smilodon.
Thus, it seems that whereas sabretooth cats were weak in their bites, they (like other sabretooth mammals) were very strong in their forelimbs and necks. How did their feeding strategies contrast with those of biting cats?
Large biting cats are known for using a suffocating bite in which they clamp their jaws around the preys muzzle, holding its mouth shut. This allows them to kill large prey, but requires them to bite strongly, holding onto struggling prey with their jaws.
A sabretooth cat was clearly not up to this, as the action of struggling prey would risk breaking the canine teeth. Possible strategies might include:
Recent work indicates that the key to the sabretooth strategy lies in the powerful forelimbs:
Perhaps certain prey animals were more vulnerable to this kind of attack. Sabrecats would have depended upon them. Perhaps the North American extinction of creatures like horses and camels with exposed necks spelled the end for our native sabrecats, also. Sad that we can't see other aspects of their biology havign nothing to do with prey capture.