It's a Cat!
Cat fanciers won't want to miss the July 2007 issue of Scientific American! This month's Genetics feature, "The Evolution of Cats 1," traces the history of the family Felidae from a common ancestor some 11 million years ago, back and forth across four continents, to the 37 cat species living today. I've been looking for precisely this information for years now-and without the least fanfare, along comes a Scientific American article (not even mentioned on the cover, if you can believe it) so perfectly attuned to my needs that I was tempted to hunt around in the same issue for a description of the early stages of red-giant formation, which is my other long-unanswered scientific curiosity.
Before the advent of efficient DNA sequencing techniques, the relationships among the world's felids were poorly understood, to put it kindly. One problem was that fossils of closely related cat species are difficult to tell apart: take away the tiger's stripes and the lion's mane, and what's left underneath looks pretty similar. Compounding this was the natural resistance of cats to situations that might get them fossilized. (Anyone who has visited the La Brea Tar Pits will undoubtedly object. From the fossils recovered, it would seem that saber-toothed cats of the genus Smilodon were lined up for miles, eagerly awaiting a chance to enjoy pitchy oblivion. I'll wiggle out of an answer by noting that I'm only interested in the ancestors of modern cats, whereas Smilodon has no living descendants.) Thus, even us youngsters may recall reading books about cats in which, for instance, lions were lumped in with domestic cats in the genus Felis. (As it happens, any grouping that includes lions and domestic cats has to include the entire cat family-please see below.)
DNA samples from all modern cats, collected in cases with great difficulty owing to the scarcity of living individuals, provided a wealth of new information from which the authors constructed a phylogeny (family tree) of unprecedented resolution. The authors identified eight important lineages that give rise to all extant cat species, which they grouped into eleven genera. Plate 1 (click here for large version) is a simplified version of the tree presented in the article, displaying at the present only the genera without the added complexity of the splits among the species within every genus. (I do list at least one representative species for each genus, and more if they're well known.) Note that Panthera split off first from the lineage culminating in the domestic cat (Felis catus 2): the King of the Animals and the queen of your living room chair diverged nearly eleven million years ago. Consequently, any taxon (group of related organisms) that included both Panthera and Felis species must also encompass all Felidae, because the point of divergence between the two genera is ancestral to the entire family.
Though the information from the DNA greatly refined the phylogeny, the fossil evidence was still needed to help fix the ages of the intermediate ancestors. After all, the DNA sequences represent the leaves on the outermost twigs of the feline family tree, and you can imagine how difficult it can be to guess the major branching points from the trunk just from the positions of the very tips of the longest branches.
A remarkable feature of feline natural history is the rapidity with which feline populations migrated throughout Eurasia and the Americas. All living cats are likely descended from an Asian ancestor of the now extinct genus Pseudaelurus. However, the eleven million years of evolution since the founding of modern Felidae were speckled with intercontinental journeys, during periods when the sea level was low enough to expose land bridges across the Bering Strait and at both end of the Red Sea. Territorial imperatives force cats to spread out with a quickness, and abundant, untapped prey populations may also have motivated their dispersal when avenues were open. No fewer than four migrations between Asia and North America, and four more from Asia to Africa, have punctuated the history of the Felidae. Remarkably, extant species of the genus Panthera are spread as far as Africa, Asia, and the Americas. Lions and tigers and pumas, oh my!
Panthera is also distinctive in that it encompasses all cats that can roar. This ability derives from a modification of the hyoid bone, which helps support the tongue and which is necessary for human speech. Our hyoid is all of a piece; but the bone in Panthera is split in two, with the two halves connected by a strip of cartilage. This bifurcation gives the hyoid the flexibility needed to get a really good roar on. Roaring comes at a price, however: cats who can roar cannot purr, and vice versa. (I, for one, am thankful that Yuki wakes me up in the early morning with a nice, cozy, rattly purr. My blood pressure would not withstand middle-of-the-night roaring on any kind of recurring basis.)
Our historical tale of the cat ends on a sad note. Of the baker's three dozen cat species, Felis catus, with a global population of some 600 million, is nearly unique in that it is not teetering on the brink of extinction. As cute and cuddly as "our" cats may be, the world would become significantly poorer if destruction of habitats and simple, pig-headed human selfishness pruned the cat family tree all the way down to one branch.
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1O'Brien, S. J., and Johnson, W. E. (2007). The evolution of cats. Sci. Am. 297 (1), 68-75.
2The domestic cat is so closely related to the wildcat Felis silvestris that some taxonomists merge them into one species. In this classification system, Fluffy and Toonces are assigned the subspecies name Felis sylvestris catus.
Before the advent of efficient DNA sequencing techniques, the relationships among the world's felids were poorly understood, to put it kindly. One problem was that fossils of closely related cat species are difficult to tell apart: take away the tiger's stripes and the lion's mane, and what's left underneath looks pretty similar. Compounding this was the natural resistance of cats to situations that might get them fossilized. (Anyone who has visited the La Brea Tar Pits will undoubtedly object. From the fossils recovered, it would seem that saber-toothed cats of the genus Smilodon were lined up for miles, eagerly awaiting a chance to enjoy pitchy oblivion. I'll wiggle out of an answer by noting that I'm only interested in the ancestors of modern cats, whereas Smilodon has no living descendants.) Thus, even us youngsters may recall reading books about cats in which, for instance, lions were lumped in with domestic cats in the genus Felis. (As it happens, any grouping that includes lions and domestic cats has to include the entire cat family-please see below.)
DNA samples from all modern cats, collected in cases with great difficulty owing to the scarcity of living individuals, provided a wealth of new information from which the authors constructed a phylogeny (family tree) of unprecedented resolution. The authors identified eight important lineages that give rise to all extant cat species, which they grouped into eleven genera. Plate 1 (click here for large version) is a simplified version of the tree presented in the article, displaying at the present only the genera without the added complexity of the splits among the species within every genus. (I do list at least one representative species for each genus, and more if they're well known.) Note that Panthera split off first from the lineage culminating in the domestic cat (Felis catus 2): the King of the Animals and the queen of your living room chair diverged nearly eleven million years ago. Consequently, any taxon (group of related organisms) that included both Panthera and Felis species must also encompass all Felidae, because the point of divergence between the two genera is ancestral to the entire family.
Though the information from the DNA greatly refined the phylogeny, the fossil evidence was still needed to help fix the ages of the intermediate ancestors. After all, the DNA sequences represent the leaves on the outermost twigs of the feline family tree, and you can imagine how difficult it can be to guess the major branching points from the trunk just from the positions of the very tips of the longest branches.
A remarkable feature of feline natural history is the rapidity with which feline populations migrated throughout Eurasia and the Americas. All living cats are likely descended from an Asian ancestor of the now extinct genus Pseudaelurus. However, the eleven million years of evolution since the founding of modern Felidae were speckled with intercontinental journeys, during periods when the sea level was low enough to expose land bridges across the Bering Strait and at both end of the Red Sea. Territorial imperatives force cats to spread out with a quickness, and abundant, untapped prey populations may also have motivated their dispersal when avenues were open. No fewer than four migrations between Asia and North America, and four more from Asia to Africa, have punctuated the history of the Felidae. Remarkably, extant species of the genus Panthera are spread as far as Africa, Asia, and the Americas. Lions and tigers and pumas, oh my!
Panthera is also distinctive in that it encompasses all cats that can roar. This ability derives from a modification of the hyoid bone, which helps support the tongue and which is necessary for human speech. Our hyoid is all of a piece; but the bone in Panthera is split in two, with the two halves connected by a strip of cartilage. This bifurcation gives the hyoid the flexibility needed to get a really good roar on. Roaring comes at a price, however: cats who can roar cannot purr, and vice versa. (I, for one, am thankful that Yuki wakes me up in the early morning with a nice, cozy, rattly purr. My blood pressure would not withstand middle-of-the-night roaring on any kind of recurring basis.)
Our historical tale of the cat ends on a sad note. Of the baker's three dozen cat species, Felis catus, with a global population of some 600 million, is nearly unique in that it is not teetering on the brink of extinction. As cute and cuddly as "our" cats may be, the world would become significantly poorer if destruction of habitats and simple, pig-headed human selfishness pruned the cat family tree all the way down to one branch.
_______________________
1O'Brien, S. J., and Johnson, W. E. (2007). The evolution of cats. Sci. Am. 297 (1), 68-75.
2The domestic cat is so closely related to the wildcat Felis silvestris that some taxonomists merge them into one species. In this classification system, Fluffy and Toonces are assigned the subspecies name Felis sylvestris catus.