Our Cenozoic Mammalian Cousins (November 20)

We had our introduction to mammals back in the Triassic. They were ratty little critters then, but now that the non-avian dinosaurs are gone our mammals have become very serious and prolific.

So many mammal groups appeared in the early Cenozoic that we cannot cover them all in this course, or even mention many of them. That diversity dilemma is actually part of the story of the extraordinary adaptive radiation of the mammals, which has been made more complex by recent genetic findings that mammal diversification was not entirely due to the dinosaur extinctions. Note in that story that the three-part division of mammals we see today (monotremes, marsupials and placentals) began in the Cretaceous. You may also want to refer to the mammal evolution site on Wikipedia, which is very well updated.

Again, the webpages from Berkeley will be highlighted here because they are organized in the most useful ways for us. You will want to look at their short rodents page, and of course make a side visit to the Rat and Mouse Club of America (where one of their ethical principles is that they don’t sell their pets to the Snake and Tarantula Club). Now jump WAY up to the proboscidean (elephants, mammoths, mastodons) page just to delight in the wondrous variety in modern mammals. There are many sites devoted to mammoths, mastodons and other “Ice Age” mammals, including the Pleistocene exhibits at the Russian Paleontological Institute. Carnivores are always interesting, and are in themselves highly diverse. They include wolves, dogs, cats, raccoons, bears, weasels, hyenas, seals, and walruses. A hero to your cat is the ancient sabretooth, highlighted in special exhibits this year at Berkeley and the Illinois State Museum. (Watch an old school animation of a sabretooth from the BBC.) You can now make another mammal diversity leap to our unlikely cousins the cetaceans (whales and dolphins; here’s an Eocene whale found a few years ago in Egypt). The ungulates, or hoofed mammals, are an excellent group to use in a study of evolutionary patterns. The artiodactyls (cloven-hoofed mammals) include the prosaic sheep, goats, camels, pigs, cows, deer, giraffes, and antelopes (and now whales!). Their relatives the perissodactyls (“odd-hoofed” mammals) include rhinos, horses and tapirs today, but they were much more diverse in the past. The evolution of the horse is a classic story, told well at the “Fossil Horses in Cyberspace” site at the Florida Museum of Natural History.

Here is the Fall 2017 Final Exam description. (Test seating: Students with last names starting with A through H in Room 205; I-Z in Room 216.) Even though the final is about a month from now, you’ll want to start studying. Those superquizzes will be your encouragement!

Remember: Review sessions every Wednesday, 3:30 – 4:30 pm, in Scovel 205.

Mammoth tooth from the Pleistocene of Ohio.

Geology in the News –

There is a new and interesting argument that the Late Cretaceous asteroid hit just the right spot to cause the global extinctions. The hypothesis is that striking an area rich in petroleum injected massive amounts of soot into the atmosphere that further cooled climate. There will be debates soon over this.

The end-Cretaceous Chicxulub Crater is in the news as scientists publish the results of a drilling expedition into it. They have supporting evidence for why this crater has a peak ring that is unique on Earth but common elsewhere in the Solar System. There are cool images in the version of the story from The New York Times.

The BBC has a separate story on the drilling results that includes a cool animated model of how the Chicxulub Crater was formed. There were for a few minutes mountains as high as the Himalayas!

How long did it take for life to recover from the Cretaceous extinctions? New studies suggest about four million years, but up to nine million years in North America, which was hit hardest.

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