The prevailing view of mammalian evolution is that with the extinction of the dinosaurs, the doors were opened for mammals to greatly diversify and fill a number of ecological niches. While this trend may hold true, new findings will likely reshape our thinking on some of the details. For example, recent finds of predatory mammals from the Cretaceous (just before dinosaurs went extinct) of small predatory mammals (one even has a dinosaur remains in it’s stomach) give evidence that mammals were diversifying before the extinction of the dinosaurs.

Castorocauda lutrasimilis

A new find from the Jurassic (which preceeds the Cretaceous) tells of an early aquatic mammal that was probably most similar to our modern platypus.

This mammal had a beaver-like tail, with webbed feet and seal like teeth, and it offers further evidence that mammals were diversifying earlier than we thought. It also provides the earliest evidence for fur in mammals.

This is what I find so exciting about evolution and biology. There’s always more to learn, and new evidence comes to light to challenge our understanding.

You can bet that two things will happen because of this new find. Young earth creationists will point to it as proof that the fossil record doesn’t show evolution, while intelligent design advocates will use the flawed logic of “if biologists can’t even get the evolution of beaver-like mammals right, how do we know they’re right about anything…” Both are regrettable and dishonest.

When Einstien realized there were problems with our theories of gravity, he worked to provide new understandings. He didn’t suggest the apple doesn’t fall from the tree. In the same way, Jurassic beaver like mammals don’t overthrow our theory of evolution, rather they overthrow our theory that mammals remained small and “undiverse” until the extinction of the dinosaurs. And while we evolutionary biologists can be a persnickety group, we also build our theories on the evidence around us. Sometimes that evidence causes us to change our understanding. This is a good and healthy thing, not to mention the very essence of science.

And not just any teeth. Crocodile teeth.

Here’s an interesting article on a mutation that scientists have uncovered, where a chicken embryo grows teeth. The mutations are fatal. The embryo dies in the egg, but some live as long as 18 days.

What’s most interesting about this is that the teeth are shaped like crocodile teeth. What the authors hypothesis is that during the evolution of birds, the genes for teeth weren’t thrown away, rather they were supressed so that they no longer expressed themselves.

Another thing that’s interesting to note is that we’ve believed birds evolved from the same group as crocodiles for a long time. While the general public may not know it, crocodiles have much more in common with birds than with your average lizard. They have crops and gizzards, three-chambered hearts, build nests, vocalize to their young.

Isn’t it just a little bit interesting that when chickens grow teeth, they end up looking just like those in a crocodile…

For a more in-depth discussion, see Pharyngula’s post on the subject.

In very broad, non taxonomic terms, can you name this animal?

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Now there’s a title that ought to catch people’s interest. Researchers have discovered an inverse relation between brain and testicle size among bat species.

In species where females mate promiscuously, male bats have proportionally larger testes and smaller brains. In species where females are monogamous, the reverse trend holds true.

The evolutionary hypothesis on why this exists is a good one. Since both brains and testes require lots of energy to maintain, there may only be energy for one or the other. In species where females are mating with multiple males, natural selection is strongly going to favor the male that can produce the most sperm. When that’s not an issue though, it makes sense that brain size and function is more useful than producing lots of extra sperm that aren’t needed.

I think other scientists should be quick to pick up on this work. I hypothesize that for any guy who’ll brag about his own, um, endowment, you’ll find the same inverse relationship holds true.

The Night Before Christmas? Or Transitional Species in Insect Evolution?

I came across the latter last night, and I found it fascinating. The author of this blog has summarized the discussion of cockroach and termite evolution taken from a new book, Evolution of the Insects by David Grimaldi and Michael S. Engel. (Hey, it’s never too late for a belated Christmas gift. Contact me if you need my address for where to mail the book.)

The article was really interesting. Basically, there’s a lot of evidence to suggest that termites evolved directly from cockroaches. In fact, it appears that termites are literally modified cockroaches.

I learned some pretty nifty things too. For example, there are wood eating cockroaches today (who knew!), which have the same (and closely related) gut flora (bacteria and protists) as termites. These little critters, essential for digesting wood, are passed down in the anal secretions which the young eat (pictures included at the link!). There are also termites which look very similar to roaches, sharing a number of their characteristics.

Kind of makes you rethink that whole phrase, “not a creature was stirring…”

MSNBC had a very interesting article today on a gene that has been identified that partially explains skin color in humans. They stumbled across this while looking for cancer genes in zebrafish, which come in a natural darker form and a human bred, lighter, golden form.

Then the scientists identified the human version of the gene, which has two main types — a version shared by Africans and East Asians, and a slightly different variant carried by nearly all Europeans. The researchers went on to show that this gene is partly responsible for light human skin in Europeans. This study appears in Friday’s issue of the journal Science, published by AAAS, the nonprofit science society.

What’s interesting is the conclusion that it was a very small change to our genetic code which led to humans having very pale pigmentation, such as Europeans have.

It also pointed out that we still have much to learn, and it wouldn’t surprise me a bit when science figures it out.

Why so many Europeans have one particular version of this gene is not yet clear. It is possible that the SLC24A5 version [of the gene] now seen in nearly all Europeans may have been useful for some specific reason and swept through a human population that gave rise to Europeans.

This new research does not conclusively explain why light skin might have been favored among Europeans, but the work is consistent with the longstanding but unproven hypothesis suggesting that light skin allows more absorption of the ultraviolet rays in sunshine that are necessary for making the essential vitamin D. Such a trait could have been favored at European latitudes.

The SLC24A5 gene, however, cannot explain all the differences in skin color in humanity. For example, Asians and Africans have the same version of the gene but quite different skin tones. More research will likely uncover other pieces of the genetic puzzle of human skin color.

While browsing this evening, I came across an article that both I, with my interest in biology, and my wife, interested in teaching and childhood development could both enjoy. Carl Zimmer of The Loom has an interesting article in the New York times titled Children Learn by Monkey See, Monkey Do. Chimps Don’t. (A quick hint… if you get prompted for a username / password and don’t want to register, pull up the article at Google News. Links from there seem to let people get through without signing in. I have no idea why).

Scientists were studying developing chimps (which for the record, are apes, not monkeys) and comparing their development with that of children. The author approved of his preschool daughter participating in the study, and, as Zimmer does, his prose of the results were both interesting and humerous.

Driving into New Haven for our meeting, I felt as if Charlotte had just taken some kind of interspecies SAT. It was silly, but I hoped that Charlotte would show the chimps that she could see cause and effect as well as they could. Score one for Homo sapiens.

Essentially, young chimps can see past unnecessary steps in accomplishing a task, while young children are completely committed to imitating. The evolutionary ramifications of this are quite interesting.

Mr. Lyons sees his results as evidence that humans are hard-wired to learn by imitation, even when that is clearly not the best way to learn. If he is right, this represents a big evolutionary change from our ape ancestors. Other primates are bad at imitation. When they watch another primate doing something, they seem to focus on what its goals are and ignore its actions.

As human ancestors began to make complicated tools, figuring out goals might not have been good enough anymore. Hominids needed a way to register automatically what other hominids did, even if they didn’t understand the intentions behind them. They needed to imitate.

That’s right. This one’s worth seeing, not just reading. I’ve come across a blog titled Olduvai George. It’s author is a 60 year old natural history illustrator, with a particular interest in the last 65 million years. Check out his first post for some examples of his work. With his illustrations, he can bring things to life in a very special way. Creatures that haven’t roamed the earth for some time can now stir the imagination.