As a follow up on Cara's earlier post on our desert expedition, I'd like to talk a bit more about the nitty-gritty of the science!

Whales don't walk, silly!

Wadi al-Hitan (Valley of the Whales) is one of the major paleontological sites in the world for understanding the evolution of whales & their migration 40 million years ago from land into the ocean.

But Justin, I thought that life started in the oceans, then moved to land... why would whales go backward?

Well, yeah, life did start in the oceans, but mammals evolved on land, breathing air. First little rat-like things while the dinosaurs were around, which later evolved into the diversity of mammals we know today (and the ones that we knew earlier in the 20th century that are now extinct). But then there are all of the ocean mammals... whales, dolphins, manatees, seals... they must have evolved from land-based mammals.

Whales don't walk, silly! How could they do that with fins? -Lara

Ahh, because now they can't walk, but back then, they still had hind legs! And their predecessors could walk. Now, the whales we are talking about here did not actually use their legs for walking anymore. They were something like 40 feet long with 1.5 foot hind legs, so their legs were mostly useless (and the front "legs" had begun to fuse into the configuration that we now associate with front fins.

"Ideas are tested by experiment." That is the core of science. Everything else is just bookkeeping.

-Zombie Feynman, http://xkcd.com/397/

The theme for the day went like this: scientists used to think X, then a new scientist realized Y, now scientists know Z.

Exhibit A: Fossilized Mangrove Roots

Scientists used to think Wadi al-Hitan was an ancient, humoungous mangrove forest...

As any dirt loving Arizonan knows, a hike into the Grand Canyon takes you on a journey through millions of years of geological history, with different types of rock and soil marking boundaries between different geological ages. The same can be seen in Egypt, whether in the bluffs of the Muqattam Hills (site of the terrible landslide shortly after we arrived in Cairo) or in the cliff faces of the wadis of the desert.

Most such layers look (to my untrained eye) simply like different colors and patterns of rock, but in the region of Wadi al-Hitan, there is a layer about 3 meters thick whichlooks like tons of mostly-verticle ropes, weaving in and out of each other. The layer covers many square kilometers of desert. At approximately the same level, entire trunks of petrified wood can be found, leading geologists to hypothesize that the entire area was once a huge mangrove forest... that is, shallow water, covered with thick trees.

Then a new scientist realized that they are actually burrows...

But why would there be whales in a huge mangrove forest? An expert in invertebrae fossils took one look at the "mangrove roots" this past summer and said... "Um, actually, guys, these aren't roots.They are invertebrae burrows. You know, snails, worms, etc, living at the bottom of a really deep ocean."

Now scientists know that the area was a really deep sea...

So, things make a bit more sense now. It was actually a really deep sea, hence the whalebones. And the petrified trees? Sunken driftwood.

Example B: Giant snake

Scientists used to think that the bones they were findng were from a huge sea serpent...

Because all they found initially were vertebrae and ribs, whch were really long. So they named the beast Basilosaurus. Anyone who was as obsessed with dinsaurs and National Geographic as I was when I was a kid will notice the -saurus at the end bears a strinking resemblance to such creatures as Tyrannosaurus, Stegosaurus, and other reptiles as opposed to mammals like Mastadon, I'm also told that anyone with a decent knowledge of Latin will note the differences in the words, as well, as the -saurus indicates "lizard."

Then a new scientist realized that it is actually a mammal...

Once they found a specimen with a skull. Then, forelimbs. Then hindlimbs. All clearly mammalian.

Now scientists know that the species is a whale...

So, we have to get rid of that nasty lizard name, right? Name it something more fitting of a mammal, like Zeuglodon.

Well, they tried, but there is a standard in species naming that the first name sticks, even if its Latin meaning (King Lizard) was somewhat inaccurate.

End of story, right?

No. Not at all. Because scientific explanations ae continuously changing.

But there it was, the whole history of science, a clear story of continuously new and changing explanations of old facts. The time spans of permanence seemed completely random he could see no order in them. Some scientific truths seemed to last for centuries, others for less than a year. Scientific truth was not dogma, good for eternity, but a temporal quantitative entity that could be studied like anything else.

- Robert Pirsig, Zen and the Art of Motorcycle Maintenance

Each answer begets a multitude of interesting questions.

How did they swim? Did they have a fluke?

Thought the details of the physiology aren't very clear to me, one of the main pieces of evidence which paleontologists are looking at to try to figure out how they swam is the vetebrae. By measuring the sizes and shapes of the vertebrae, they can put together a picture of how the whales moved. For example, the neck vertebrae in modern whales are "squished" together, giving whales short, stocky necks without much articulation. But these whales had larger vertebrae, indicating that they had necks which could move. Also, they seemed to have particularly long vertebrae once past the ribs, likely to give them enogh leverage to move their relatively small flukes (the back fins). It is only recently that paleontologists found evidence of flukes.

These are just bones that have become rock! You can't actually find anything useful in them, can you?

Once of the cooler findings of the researchers working out at Wadi al-Hitan is the role of the recently dead whale in the ocean ecosystem. By looking at marks on the fossilized bones and shark teeth in the vicinity of the skeleton, they have begun to understand the food chain surrounding the whale carcass.

Marks on the fossils indicate that mollusks and such setup camp on the nutrients of the whale carcass, which were then eaten by smaller sharks, whose teeth are found concentrated very close to the whale skeleton. It is only farther from the skeleton that they find the larger teeth of larger, more aggressive hunting sharks, which likely fed on the smaller sharks eating the mollusks.

An entire oceanic ecosystem, captured in stone, and slowly eroding to reveal itself in the Egyptian Sahara.

Note: I didn't know any of this stuff before we went on this little trip. It was all beacuse of our awesome rock-loving guide, John Graf. It was obvious from his incredibly rich knowledge, unending patience with questions, and passion for teaching & sharing, that he is doing to be a damn good professor one of these days.