Monday, February 8, 2010

Kissing the lipless

“Holly, it’s fossil time!”

My doctoral adviser, let’s call him Sid, made an appointment with a man from Philipsburg—which is about a 30-minute drive northwest over the ridges from Penn State—to see some fossils he had collected. Over the phone he claimed to have an Australopithecus skull.

Naturally I wanted to be involved even though I was 99% sure this guy had nothing and was even surer that he had nothing even remotely close to an australopith.

Lucy (source)
Australopithecus (which includes dear old “Lucy”) lived between about 4-2.5 million years ago and the only known fossil representatives come from Africa. That’s a long way from Happy Valley. Not that they couldn’t be found outside of Africa, but it’s incredibly unlikely they’d be found in Pennsylvania since the fossiliferous rocks in PA are hundreds of millions of years older than any primate, let alone any hominin. It was a solid bet that he had nothing, but there was no way I could have anticipated the extent of the nothing that he was so proudly about to show us.

The man came up to our lab and introduced himself, then took us down to the loading dock where he parked his car. He was about six-foot-five and built like a small power forward, but dressed like a Nascar mechanic. As we rode the elevator to go down to his car he described how he’s been out of work, on disability, for quite a while with nothing to do but search for fossils. He boasted, “As soon as I started looking there were fossils everywhere!”

His red American car was decorated with Nascar stickers to match his clothing. Inside the car a woman was sitting shotgun, but she never looked back at us, never came out, never made a sound. He popped open the trunk.

I could see lots of rocks but no fossils. I was expecting to see fish, brachiopods, trilobites, plants. You could tell Sid shared my waning hope that we’d be able to discern something fossilized.

While we picked over the rocks, the man muscled a boulder out of the trunk and onto the ground. “Here’s a skull,” he proclaimed.

“No it ain’t,” Sid deadpanned.

“See, here’s the septum.” He pointed to a deep impression in the middle of the oblong rock. “And here’s the nostril and here’s the lip,” he continued.

“I’m afraid you’ve just got a big curiously shaped rock there,” Sid said graciously. Never mind that it was the size of King Kong’s cranium.

Undeterred, the man moved onto the smaller bits that we were scouring. If we could find even the tiniest fossil, we could show him what real fossils from PA look like.

“Here’s an arrowhead. Here’s a spearhead. Here’s a tool. These are all tools,” he sorted through every last one of the box full of flat rocks, none of which had been flaked into tools.

“They all could be used for tools, sure,” said Sid.

I tried to help, “There’d be flake marks on the edges if these were arrowheads or spearheads. They’re also not the kind of rocks that Indians from around here liked to use to make tools. These are sandstone and Indians in this area preferred jasper. I can show you some tools in the museum upstairs.”

Sid wanted to teach this man about fossils so he said, “Holly why don’t you go get some of your stuff.”

I dashed into the building and up the stairs because I didn’t want Sid to suffer all alone in what was becoming a pathetically awkward situation. When I returned, the man was showing Sid a human footprint on the underside of the skull boulder.

“You can see the big toe. One. And then the rest of the toes here. Two. Three. Four. Five.”

“So it’s a human you think?” I asked to clarify things.

“Of course!” he grumbled, exasperated with me.

We tried to tell him that it was just an illusion due to the weathering of the rock. Sid even explained, “How old are these deposits, Holly? Something like 350 million years? Listen, back then the creatures that could have left footprints had 8 toes!”

I added, “The first land-fish, but even those are rare in these parts.”

This didn’t’ stop him from pulling out, from the same huge box full of stone tools, some thin, flat, foot-shaped rocks. Human footprints. Baby footprints. Matching sets, lefts and rights, fanned out like poker cards and dealt one-by-one into our hands.

This was about all we could take. We didn’t have any fossil human footprints to show him, but we did have all that other stuff I’d carted down to illustrate how bone looks when it’s fossilized. We showed him an oreodont skull. Then some Green River fishes that I got at a garage sale. Then a gorgeous brachiopod that I found by Tussey Mountain. It’s just like the Shell logo and all white in a black rock. Then we showed him some bits of placoderm fishes that I found to the north. Although broken up, they’re so obviously fossilized animal parts. We explained that fossils will look symmetrical like animals and plants do during life. Even if they’re flattened or crushed, there are patterns.

Then we showed him that he did have some fossils—tiny bits and smashed up pieces of invertebrates, like brachiopods and the like, were preserved in some of his cobbles. These were dead organisms, we said.

source
We thought we’d open his eyes the way most people need help the first time they prospect for fossils. To most newcomers any old interestingly shaped rock looks like a fossil because they imagine they’re hard to spot. Searching for fossils, to some amateurs, is like spotting bunnies and bears in the clouds.

Once rookies see how conspicuous fossils can be, they realize that they’re easy to spot, but that they’re just hard to come by because they’re rare or they’re buried for so long until erosion exposes them or a road cuts through. It doesn’t take imagination to see fossils. It takes prior knowledge about where to look and then patience and focus to find them. And, of course, luck.

This guy never had a eureka moment. He barely acknowledged the fossils that we showed him and he wouldn’t even touch them. He just lurched toward his boulder and ran through its facial features all over again. “But see, here’s the lip, and there’s an eye, and then …” We just shook our heads and pursed our lips as friendly as we could.

“Well folks I’ll have to say I disagree with you.” Then we shook hands and he drove off towards the geology department for another opinion.

*****

If you laughed at the lip part of the story... if you think it’s funny that someone would expect a hominin fossil to have a preserved lip, nostril, eyeball, well, trust me, you weren’t alone. That part gets people every time. But try to imagine if you knew next to nothing about fossils. From a newcomer’s perspective, it’s actually not that crazy to think that Lucy would come with lips.

I mean, think about your last trip through a museum or your last perusal of a book on evolution. Colorful reconstructions of the earliest of Earth's creatures look just like spruced-up versions of the fossils they left behind! It's as if trilobites are just little Han Solos waiting for Leia to push the button to unfreeze them and then they'll be right back to swimming around in the ancient sea.

But as time goes on, as you make your way toward the present, through the exhibit or page-by-page toward the end of the book, reconstructions of lumbering wooly rhinoceroses and spear-toting Neanderthals don’t look anything like their fossil remains!

We fully expect our hominin ancestors to be reduced to bones and teeth and that's okay.
-->It's unfortunate, but we're totally over the fact that we will probably never uncover Lucy's skin and hair, lips and nose, snot and earwax, muscle and ligaments, blood and bile, mouth and gut microbes, mucous membranes and epithelial linings, fat and eggs, and etc. But it's okay because her bones and teeth tell us quite a lot. Not as much as we'd like, but they reflect her growth patterns, dietary behavior, locomotor behavior, etc. - all of which form a combination of traits not only unlike other apes alive today, but also unlike other fossil groups in our family tree. The absence of soft tissue in our fossil record - traits which would be informative and just plain cool to have - has thus far not prevented paleoanthropologists from performing quality phylogenetic analyses of our fossil record.
But the decomposition of soft tissues can really screw up interpretations of other realms of the fossil record. For instance, the earliest chordates (a group of animals with notochords that includes vertebrates and, of course, humans) from Cambrian rocks all over the world aren't preserved like Lucy at all. They're also so tiny and delicate and they can get buried so quickly in sediments at the bottoms of large bodies of water, that they get sealed in rocks in such a way that impressions of their entire bodies, lips and all are preserved beautifully.

Or so we thought until this recent innovative paper in Nature showed that early chordates may not be preserved so beautifully after all. Sure paleontologists never take decay and decomposition for granted (or they shouldn't), but there's something potentially worse going on, as the authors explain.

They took living anatomical proxies of early chordates, choosing ones from very different branches of the tree, killed them, and then watched them decay.

Starred in (a), their subjects (b) were larval Lampetra (ammocoetes; Vertebrata; TOP) and Branchiostoma (amphioxus; Cephalochordata; BOTTOM).


As the creatures rotted, the researchers noted which traits disappeared first in the process.



And guess what?

In general, the most phylogenetically informative traits - the ones that are best at finely discriminating which branch of the tree each creature fits on - were the first to go! The least informative were the traits that stuck around, that held up to the most decay. Traits that point to more advanced vertebrates are gone, but traits that point to general chordate remain.

(FYI, the lips which don't say much at all (heheh), go almost immediately.)


So by the end of the experiment, distantly related creatures looked basically, at least phylogenetically, the same!



Say you found one of these rotten creatures that these researchers were observing... say you found it fossilized and, because this is what you do as a paleontologist, you must discern where it belongs on the chordate phylogeny.

You'd only have the parts present to diagnose its place in chordate evolution. And according to this study in experimental taphonomy, you might not have very many, or any, of the parts that can help you say much more than "stem" chordate. The authors called this "stem-ward slippage", meaning that, thanks to decay prior to fossilization, many fossil chordates are put deeper on the tree than they belong. In life they weren't as primitive as they are in death. The most significant result from "stem-ward slippage" could be placing a fossil organism at the base of a lineage, claiming it as a possible ancestor to the rest of the creatures on that lineage, when in reality it was just a side branch with no living descendants.

If you are a paleontologist and you work on creatures that lived near the base of major splitting events, like I do, then you, like me, need to keep your eyes and ears wide open to this notion of "stem-ward slippage" - no matter that we don't expect Proconsul or Ardi or Lucy to come with lips.

References
1. "Non-random decay of chordate characters causes bias in fossil interpretation" by Sansom, Gabbott and Purnell

2. "Kissing the Lipless" by The Shins

9 comments:

Ken Weiss said...

Another great, thoughtful and interesting post, Holly!

I had a nearly identical experience when I was a graduate student at Michigan years ago. Loring Brace was approached by someone with a fossil of a dinosaur shoulder blade that he'd found in his backyard and Loring and a couple of us students went downstairs from the Michigan Museum to see it.

It turned out that the shoulder blade was a hunk of concrete the construction crew had left in his backyard when his house was built. The discoverer's crushed look was sad to see.

A while back we posted a picture of a 150 million year old squid (at least I think we did that!), that showed all of its soft parts, ink sack included. And there are ancient insects preserved in amber so well that they seem still to be alive.

So preservation oddities are strange and diverse. One has to be skeptical! (Though I'm sure that yesterday I saw Cookie Monster in the clouds).

Holly Dunsworth said...

I saw Cookie Monster in the clouds once!

Ken Weiss said...

Yes, but MY Cookie Monster had lips! And he (she? it?) was eating an Oreo.

Holly Dunsworth said...

A black cloud with white filling?

Ken Weiss said...

Well, yes. As a former meteorologist, I can just say that the angle of the sun relative to cloud density and height can create the dark and light shades.

But I'll admit that my Cloud Cookie Monster was colorless (though a colorful experience, so to speak).

Holly Dunsworth said...

via PALEOBLOG ... a video of lamprey decay: http://www.youtube.com/watch?v=zKk1OFYDPEU

Anne Buchanan said...

Now, that's what YouTube's for!

"the Dude" said...

Actually soft tissues can be inferred. The Australopithecus afarensis 3 yr old Dik-1 (Selam) had a hyoid bone indicating presence of a soft tissue laryngeal air sac (which all extant hominoids retain except humans and small gibbons), revealing a probable part-time diet of swamp/wetland vegetation, with sac inflation during partial immersion.

Anonymous said...

nice post