Native Plants, Habitat Restoration, and Other Science Snippets from Athens, Georgia

Thursday: 19 January 2006

Cat Evolution  -  @ 04:06:17
There's a neat article, The Late Miocene Radiation of Modern Felidae: A Genetic Assessment in the Jan 6 issue of the journal Science (Science 311, 73-77 (2006)) by WE Johnson and quite a few other et al.'s on the evolution of the Felidae, the cat family.

I'm drawn to this, not *just* because it's cats, but also because systematics interests me and I really like the Miocene Epoch, that period of 18 million years starting about 25 million years ago. Lots of interesting things we see today started then: the formation of the Himalayas, Rockies, and Andes, the joining of North and South America, the separation of Antarctica from South America and Australia, the evolution of grasses and horses, and of the members of the cat family.

The authors of the work used DNA comparisons to build a phylogenetic tree of the 38 species of cat in 8 related lineages.

In a phylogenetic tree or cladogram, the species being examined "nest" in groups; here we have eight groups. You read the thing like a pedigree turned on its side. At the top right there's the Domestic Cat lineage, consisting of domestic cats and various European and African wild and desert cats being more related than to, say, African lions or bobcats. Also notice how recently the domestic cat lineage has appeared.

The Domestic Cat lineage is most related, in turn, to the nest under it: the Leopard Cat lineage (notice that leopard cats are not traditional leopards; those belong in the Panthera lineage, down at the bottom, most distantly related to domestic cats). A number of assumptions allow tentative dates of speciation to be placed, so the domestic cat lineage evolved 2-3 million years ago, about the same time as the emergence of the genus Homo. The cat family as a whole appeared only 11-12 million years ago, in the late Miocene Epoch.

At the very bottom of the above figure you find a group of species that are not in the cat family but are related. These are called outliers. The most closely related non-cat mammal is the banded linsang:

Other close relatives of the cat family include mongoose, spotted hyena, and civetcats, but these aren't as closely related to cats as the banded linsang is.

Another thing the authors were able to do, armed with present day knowledge of where these cats live and approximate times they evolved, was to trace out a pattern of migration throughout the world.

The colored geographical zones and colored lines are "zoogeographical regions". Cats as a family, then, evolved from the Panthera (lions and tigers and leopards, oh my!) lineage in the pink zone, the Palearctic region of Asia and Europe and radiated outward over the next 11 million years. The Domestic Cat lineage appeared in the Africa region only 2-3 million years ago.

On the far left, and aligned vertically, is a time plot of sea level. Even before the Miocene the continents generally looked like they do today but several noteworthy events occurred: India rammed into the Asian continent thrusting up the Himalayas in the mid-Miocene. The Andes and Rocky Mountains were forming. And Antarctica separate from Australia and South America. Prior to this the Miocene had been very warm, about 5 degC warmer than today on average, and sea levels were high. It's thought that, among other influences, this tectonic activity introduced a cooling effect into the earth's climate and from about 10 million years onward sea levels fluctuated as glaciations began to occur at irregular intervals. (Notice how in the last million years periodic glaciations have become much more frequent - seven such!)

It's these glaciations that expose shallow water ocean bottom, allowing migration from one continent to another and then cutting off migration as glaciations end and sea levels rise again. One of these routes was the well-known route across the Bering Strait between North America and Asia, and the Palearctic cats migrated back and forth and radiated into the North American Lynx (bobcats!) and Puma (cougars!) lineages, between 8.5 and 6.7 million years ago.

Finally, during the Pliocene about 3 million years ago the Caribbean Plate migrated eastward and joined North and South America. North American lineages were able to cross into South America and radiated into the Ocelot lineage, as well as jaguar (Panthera) and puma (Puma) lineages.

The work, extensive though it is, is not really seminal or anything, but it's a nice comprehensive story of the type that we see a lot of now. The documentation of relationships among species at the family level is extraordinarily enhanced by the marriage of traditional systematic characters, DNA analysis, and knowledge of plate tectonics and paleoclimate. And so there's the other aspect - the molecular one involving the various insertions and deletions and Y-chromosome aspects - that I haven't gotten into.

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