Big Cats Everywhere:
Fast Cats, Climbing Cats, Saber-Cats, Semi-Saber Cats, even Fast Saber Cats.
I love Lucy. Anatomically, that is. Her skeleton is a marvelous combo. She has our human joints – knee, ankle, wrist, backbone – for upright posture. And she has some chimp/gorilla-style components – short legs, slightly splayed big toe, long forearm, upper arms that could swing high above her head, and small brain. Plus some unique features we don’t see in any modern species – the ball on the thigh bone is set on a long neck that comes off the main shaft.
Modern australopith specialists seem to agree that Lucy was a triple-threat. She could run as we do, bipedal, on flat level ground. Short legs meant that she wasn’t super speedy. She could swim, with kicks and arm swings. And she could climb far better than we, since her shoulder was more ape-like, her big toe was a bit divergent and her shin was shorter.
Lucy and her kind needed three-dimensions to move because she was surrounded by a spectacular array of predators, all of whom loved Lucy in a culinary sense. The australopith age (5.8 to 1.8 million years ago) produced the richest and scariest variety of big feline meat-eaters the world has ever seen:
1) Leopards. Modern-style leopards were common in forested habitats. Just like their modern day survivors, the fossil leopards have short, wide, flexible legs and body, a build excellent for sudden ambush, great leaps, and agile climbing. Body weights went from 50 lbs to 200 lbs.
2) Lions & Tigers. The lion-like cats are rare but present with australopiths at a few sites. Lion-like cats are huge, up to 500 lbs, with a build designed for open-habitat hunting in groups. Legs are longer, straighter than a leopard’s. Speed over level ground is higher. Because of the great weight, climbing is less agile.
3) Cheetahs. Turbo-cats – these speedsters have greyhound-like limbs, very long and tipped with nails not claws. Living cheetahs are leopard size – 120 lbs average. But fossil cheetahs got as big as lions and are common in australopith sites all over Africa. Cheetahs sacrifice climbing ability for acceleration and velocity on the ground.
4) Semi-Saber Tooths – Dinofelis. These felids have the bodies of leopards with an enlarged upper fang. The saber isn’t as long and sharp as a true saber tooth’s but is far more formidable than in any modern cat.
5) Dagger-Tooth Saber Cats – Homotheres. The faster of the two kinds of true saber-tooths, homotheres grew to lion size but had longer forearms and often longer paws, with nail-style claws. Climbing would be slow but speed on the ground higher than a lion’s. The jaws are frightening – the mouth could open very wide, baring huge upper teeth shaped like daggers. The tooth crown was flat side to side, wide front-to-back, and exceptionally sharp front and rear. Like a meat-eating dinosaur fang, the homothere killing tooth was saw-edged.
6) Sword-Tooth Saber Cats – Smilodonts. Shorter in the limb with more jaguar-like paws, the smilodonts were, on average, far slower than their homothere cousins but much better at climbing. Sizes ranged from leopard to tiger, 50 lbs to 500 lbs. The killing fangs were longer but thicker and stronger – better for stabbing deeply.
Ok – imagine that you are Lucy, 3.4 million years ago. Can you outrun any of these five cat varieties? Nope. Even the thickest-limbed leopard or smilodont could catch you in a hundred yards. The cheetahs and homotheres would get to you even more quickly. What do you do? Go up. Leopards and Dinofelis and small smilodonts could climb well, so you better go even higher in the trees, holding on to branches too thin for the cats.
Remember – australopiths didn’t make stone tools. Their best defense would be to escape to a cat-free micro-environment. The threat from cats probably explains the combination of design features we see in australopiths – with an emphasis on superior climbing ability. The ape-like shoulder was a key joint – it let Lucy grasp small branches above her head as her toes held on to a lower branch.
Texas Connection. And yes, the Lone Star State had every one of the five types of big cats. The Bering Land Bridge let new cat species spread from Old World to New World and vice versa as soon as they evolved.