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/ / at its human admirer and revert to the wild. This is just what wolf-dog hybrids do quite frequently.

Further proof of why the shape and workings of the essential cat are so apt for its job of surviving as a prey-catching, meat-eating mammal (called an obligate carnivore: no veggies or fruits) is that this anatomical pattern has essentially come into being at least two other times—in the deep past and in Australia. Australia is, of course, a very strange place with an odd accent and where virtually no placental mammals ever evolved. Some arrived later, brought along by people. But before that there were effectively only marsupials, mammals that kept their infant offspring (in essence, fetuses) in a pouch, the most familiar of which are the kangaroo and the koala. A handful of egg-laying mammals, called monotremes, exist as well, the most familiar of which is the duck-billed platypus. In Australia there were a great variety of ecological niches, most of them comparable to niches in the rest of the world. Large kangaroos, for example, provided a niche for a good-sized carnivore to chase down, and evolution provided a very catlike array of big marsupial predators including a marsupial “lion” and also a marsupial dead ringer (well, almost) for a saber-tooth cat. The marsupial lion is of special interest to scientists. Called Thylacoleo carnifex, which translates to “marsupial executioner,” it was surely the most ferocious animal ever to grace the shores of Australia. Hugely powerful, with forelegs twice the thickness of a leopard’s, this 250-pound predator had an Australian version of the shearing cheek teeth called carnassials that most carnivores possess, except that these were especially large. Its canines were just stubs, but its front (incisor) teeth were exceedingly sharp. Its jaws andteeth have been described as “bolt cutters,” and it killed its prey—thought to include three-ton wombats—with a sudden devastating scissorlike bite that inflicted instant death. Related to the wombats, as are koalas and kangaroos, it seems to have gone extinct sometime about 30,000 years ago (thank heavens, one might say). Australia saw the rise, as well, of marsupial versions of practically all the families of placental mammals, a process called convergent evolution in which, at different times and/or places, similar niches or jobs call for similar actors. Second, and largely contemporaneous with the rise of the earliest cats, was another family of predators called nimravids that looked like cats and acted like cats but weren’t cats. Some speculate that the nimravids may have sprung from some doglike ancestor and evolved into a highly catlike form. The fossil record is just too sparse to be sure of any of this. The nimravids too developed long legs with claws on the feet, a shortening of the face, slicing cheek teeth, and big sharp canines. Some of them grew long, flat, and curved canines like the saber-tooths. But a tiny difference that only a paleontologist would see as important distinguished the nimravids from the true cats. The difference lay in a tiny organ called the auditory bulla, which is a capsule that houses the little bones that connect the eardrum to the inner ear. In cats this capsule still is mostly bone, while it was only cartilaginous in the nimravids. It couldn’t have been this feature alone that actually kept the two families separate while plying much the same niche for millions of years, but
Nimravid such is all the evidence the paleontologist often has. Over time the nimravid lineage produced more than six genera, and they died out some five million years ago, causes unknown, after a successful run of about thirty million years on the planetary stage. What is clear from all this reverting to a type is that the earth has long cried out for catlike predators. How long, in fact? The last of the dinosaurs left the earthly plane about sixtythree million years ago, and scientists have long thought that their demise allowed the mammals—tiny creatures that lived in the shadow of the reptilian lords of the earth, surviving on insects—to grow in number, kind, and size and, with hot-blooded alacrity, take over. In fact, some dog-sized mammals shared the planet in the last few dinosaurian eras, but most were smaller than dogs and most of the surviving mammals stayed pretty small for some twenty million post-dinosaurian years. At this point—about forty million years ago—there appears to have been a great change in the earth’s atmosphere, in particular a huge growth in the amount of available oxygen. The percentage of oxygen rose from 10 percent in dinosaurian times to 23 percent forty million years ago (that’s a bit more oxygen than we live on). Some speculate that it was this huge increase in available oxygen that permitted some mammals to grow larger, eventually providing the planet with the likes of twelve-foot tall sloths, enormous cave bears, a rhinoceros approximately the size of a two-story garage, and huge saber-tooth cats. In any event, by forty million years ago it was noticeably the mammals’ world and various sorts inhabited all the old dinosaur niches. Among these were the miacids—arboreal animals something like weasels. One branch of miacids gave rise to the

at its human admirer and revert to the wild. This is just what wolf-dog hybrids do quite frequently.


Further proof of why the shape and workings of the essential cat are so apt for its job of surviving as a prey-catching, meat-eating mammal (called an obligate carnivore: no veggies or fruits) is that this anatomical pattern has essentially come into being at least two other times—in the deep past and in Australia. Australia is, of course, a very strange place with an odd accent and where virtually no placental mammals ever evolved. Some arrived later, brought along by people. But before that there were effectively only marsupials, mammals that kept their infant offspring (in essence, fetuses) in a pouch, the most familiar of which are the kangaroo and the koala. A handful of egg-laying mammals, called monotremes, exist as well, the most familiar of which is the duck-billed platypus. In Australia there were a great variety of ecological niches, most of them comparable to niches in the rest of the world. Large kangaroos, for example, provided a niche for a good-sized carnivore to chase down, and evolution provided a very catlike array of big marsupial predators including a marsupial “lion” and also a marsupial dead ringer (well, almost) for a saber-tooth cat. The marsupial lion is of special interest to scientists. Called Thylacoleo carnifex, which translates to “marsupial executioner,” it was surely the most ferocious animal ever to grace the shores of Australia. Hugely powerful, with forelegs twice the thickness of a leopard’s, this 250-pound predator had an Australian version of the shearing cheek teeth called carnassials that most carnivores possess, except that these were especially large. Its canines were just stubs, but its front (incisor) teeth were exceedingly sharp. Its jaws andteeth have been described as “bolt cutters,” and it killed its prey—thought to include three-ton wombats—with a sudden devastating scissorlike bite that inflicted instant death. Related to the wombats, as are koalas and kangaroos, it seems to have gone extinct sometime about 30,000 years ago (thank heavens, one might say). Australia saw the rise, as well, of marsupial versions of practically all the families of placental mammals, a process called convergent evolution in which, at different times and/or places, similar niches or jobs call for similar actors. Second, and largely contemporaneous with the rise of the earliest cats, was another family of predators called nimravids that looked like cats and acted like cats but weren’t cats. Some speculate that the nimravids may have sprung from some doglike ancestor and evolved into a highly catlike form. The fossil record is just too sparse to be sure of any of this. The nimravids too developed long legs with claws on the feet, a shortening of the face, slicing cheek teeth, and big sharp canines. Some of them grew long, flat, and curved canines like the saber-tooths. But a tiny difference that only a paleontologist would see as important distinguished the nimravids from the true cats. The difference lay in a tiny organ called the auditory bulla, which is a capsule that houses the little bones that connect the eardrum to the inner ear. In cats this capsule still is mostly bone, while it was only cartilaginous in the nimravids. It couldn’t have been this feature alone that actually kept the two families separate while plying much the same niche for millions of years, but
Nimravid such is all the evidence the paleontologist often has. Over time the nimravid lineage produced more than six genera, and they died out some five million years ago, causes unknown, after a successful run of about thirty million years on the planetary stage. What is clear from all this reverting to a type is that the earth has long cried out for catlike predators. How long, in fact? The last of the dinosaurs left the earthly plane about sixtythree million years ago, and scientists have long thought that their demise allowed the mammals—tiny creatures that lived in the shadow of the reptilian lords of the earth, surviving on insects—to grow in number, kind, and size and, with hot-blooded alacrity, take over. In fact, some dog-sized mammals shared the planet in the last few dinosaurian eras, but most were smaller than dogs and most of the surviving mammals stayed pretty small for some twenty million post-dinosaurian years. At this point—about forty million years ago—there appears to have been a great change in the earth’s atmosphere, in particular a huge growth in the amount of available oxygen. The percentage of oxygen rose from 10 percent in dinosaurian times to 23 percent forty million years ago (that’s a bit more oxygen than we live on). Some speculate that it was this huge increase in available oxygen that permitted some mammals to grow larger, eventually providing the planet with the likes of twelve-foot tall sloths, enormous cave bears, a rhinoceros approximately the size of a two-story garage, and huge saber-tooth cats. In any event, by forty million years ago it was noticeably the mammals’ world and various sorts inhabited all the old dinosaur niches. Among these were the miacids—arboreal animals something like weasels. One branch of miacids gave rise to the
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