meanwhile, back in the lab (part II)

When Shelley & Co. were about halfway done preparing Zed the Mammoth's thoracic vertebrae, they decided to open another plaster jacket: jacket #4, Zed's mandible! Their reasons were thus:

1) mammoth jaw means mammoth teeth. And mammoth teeth are excellent at revealing age. We already knew that Zed was fairly old when he died -- he's huge, for one thing, and there's evidence of arthritis on a number of his ribs, for another -- but we didn't know how old. Elephant tooth replacement occurs in very specific patterns, at very specific ages. They go through a total of 6 sets of molars in their lifetime, each molar slowly wearing down and getting pushed out by the one behind it. By comparing Zed's tooth wear to that of an African elephant, we can make a fairly accurate estimation of his age at death.
2) we have two extremely delicate mammoth tusks awaiting preparation. Working on Zed's similar-but-sturdier molars first may allow us to prepare for the tusks' preparation.
3) a very nice field producer from a very entertaining television show asked Shelley very politely to pretty please let them film the opening of the mammoth jaw jacket -- Shelley acquiesced. More on this when the time is right... [editor's note: oops, looks like I'm wrong. It was the thoracic vertebrae jacket that was opened on camera -- not the mandible jacket. Guess the field producer wasn't quite nice enough...]

Long story short: jacket number 4, containing mammoth mandible, was opened. And it looked like this:

Yuck! We were saddened to discover that a) the jaw is upside-down (no visible teeth means we must wait to learn Zed's true age!) and b) a tractor shaved off the bottom-most edges of the jaw, leaving what we in the business euphemistically call "discovery marks."

As you can see, Zed's matrix (the dirt surrounding the fossil)is primarily dusty brown clay -- not the dark, sticky asphaltic sand we find in Pit 91. This is good and bad -- good: it's easy to dig through; bad: it's dusty and dry. Dry means there's less asphalt in Zed's skeleton over-all; his bones may be a bit more fragile than many others found at Rancho La Brea. Shelley therefore decided to repair the bottom of Zed's jaw, giving it a solid base to rest on and preventing further damage. After the bottom half was cleaned and ready to flip, the jaw was built up with gray putty:

And a wooden base was constructed around it:

That pink stuff is cellophane. That wooden box is about to be filled with expanding foam, which will create a perfectly customized cradle for the jaw to rest it. The cellophane -- in addition to being quite fetching -- will keep the foam from sticking to bone.

Trevor assisting on the left, Shelley pouring on the right. The foam is created by mixing two separate fluids together, and waiting:

Look! It's Herb, waiting patiently! Herb is awesome; he volunteers here, and at the LA Zoo, and with the Dinosaur Institute at the LA Natural History Museum. He's basically enmeshed with every natural history organization in the greater Los Angeles area. I think he's trying to take over.

Anyway: the foam! It rises, like bread, but far less tasty:

Trevor shaved the few errant remnants, and then:

Yay! It's done! What a beautiful mandible base! The jaw itself was then very carefully turned, and placed into the base. Trevor removed another layer of plaster, and soon enough, Zed's molars finally revealed themselves.

Zed's on his last set of molars -- a pair of M3's. Mammoth teeth are similar to elephants in that they're made up of a series of undulating plates. These teeth erupt one after another, almost continuously throughout their lifetimes, and plates are worn down from front to back. Based on the amount of wear on Zed's teeth, Shelley estimates Zed's age at 47 years (+/- 2). Zed wasn't ancient, but he definitely would have qualified for AARP membership.

If mammoths lived as long as African elephants live now -- up to 60 years -- then Zed could have had another decade in him, had an asphalt seep not caused his tragic end. However, Zed's jaw contains a rather unexpected hint at what kind of life Zed would have lived. Look at the front of the jaw, between his molars, where his tongue would have rested:

That weird, drippy growth is pathological -- that is, it's not normal. While mammoths typically do have a kind of "spout" in that area -- sometimes it angles down, sometimes it points straight out -- they don't have the weird, bumpy, lopsided growth that Zed shows here. But here's the thing -- yeah, we know that growth is pathological. But just because it's weird doesn't mean it's necessarily uncommon. We have far fewer mammoths in our collection than we spoiled Rancho La Breans are used to dealing with -- 30-32, compared to thousands of dire wolves. And we have even fewer pieces of mammoth jaw. There are approximately five mammoth mandibles in our collection in which that particular feature (the mandibular symphysis) is more or less intact -- and certainly none anywhere as complete as Zed's. So it's hard to say if this growth is unusual or not. Who knows -- many mammoth mouths could have been lopsided and bumpy like Zed's. We won't know until we find more mammoths. All the more reason to keep digging.

But here's the other thing: several of Zed's other bones have pathological elements to them -- arthritic joints, broken and re-healed ribs. It's looking more and more as if Zed lived a pretty rough life. In fact, the latest jacket Shelley and Trevor opened -- just last week! -- contains another hint at Zed's life. But more on that next week. Or rather, next year. Whatever -- Happy new year!

meanwhile, back in the lab (part I)...

As temperatures turn colder, it's time for The Excavatrix to turn attention to warmer, more indoor activities -- such as the preparation of mammoth fossils in the lab (not that we excavators aren't still stuck outside... come rain, sleet, snow and hail, excavation marches on...). Lab Supervisor Shelley, her assistant Trevor, and our wonderfully dedicated volunteers have been hard at work on two of the plaster jackets from Zed, our semi-articulated Columbian mammoth.

The first jacket they cracked open: Jacket #91, labeled "mid-vert column." This jacket contains seven of Zed's thoracic vertebra -- a portion of his spine that connects with his ribs. In fact, you can see part of one of the ribs in the photo below, immediately above our scale/quarter.



The proximal ends (the portions closest to the spinal column) of two ribs were encased in this jacket along with Zed's vertebra. And niftily enough, we were able to reunite both ribs with their missing halves:



We're always thrilled when we can actually put these paleontological puzzles back together with a minimum of sturm und drang. There are millions of specimens in our collection, and that's not including the bones that have been cleaned but not yet catalogued. The longer we wait to reunite fossils with their broken bits, the more likely it is that the reunion will never happen. In this case, both ribs were deliberately broken in order to make the jacket smaller and more stable, and thus allowing it to protect the vertebrae all the better -- a fairly common practice in paleontological salvage and recovery. However, in many cases, fossils are broken either by the act of deposition itself -- bones collide with other bones and break into bits -- or by accident, during excavation. Asphalt is hard, and mistakes are unfortunately made! These 23 fossil blocks are particularly difficult digging; Deposit 1 in particular is practically cement. So the sooner we can put the bone back together, the better.

Anyway, back to Zed's spine. This particular assemblage is a great example of what we mean when we say "semi-articulated." The photo below is a close-up of one of Zed's thoracic vertebra, and the rib that was found immediately next to it. These two bones would have been articulated, or jointed in life. However, their positions shifted slightly after Zed's tragic end. The two semi-circles would have been joined together in life, but now they're a bit misaligned. Hence, semi-articulated.




Eventually these ribs were removed to allow Shelley et al to finish cleaning the vertebrae. And finished product looks like this:





Lovely! This jacket is now on display in the museum, by the fishbowl laboratory! Please, drop by, say hello, check it out. More on lab activities next week, holiday schedules permitting.

weekly update: don't trust anything with more than four feet.

You guys, I had a near death experience yesterday. It looked like this:

This may appear to be an innocent pile of rubble, but LOOK CLOSER!

Those legs! Those eyes! Those weird little pincher things! It is a SPIDER, people, and I did not get into paleontology to get CRAWLED ON and BITTEN by sneaky arachnids -- and yet this little guy and his cricket friends decided to jump all over me JUST BECAUSE I chiseled through their home. Blech. This is why I, personally, prefer invertebrates that have been dead for 10-40,000 years. Like these:

Millipedes! Or centipedes! Or maybe decapedes! A-lot-of-pedes! Whatever -- something that USED to have a lot of feet, but doesn't anymore and therefore CANNOT CRAWL all over me when I'm digging. In the particular grid that I'm working in, (C-2/L2 for those keeping score), there's a thin layer of green clay in between two layers of asphaltic sand, which is filled with compressed plant parts -- complete leaves in some cases, as Ryan found a few weeks ago -- and tons of insect/arthropod/etc remains all around. It looks like this:

Well, it more or less looks like this. Pretend that our digital camera doesn't get all washed out when it tries to photograph anything remotely black.

Per our boss, Collections Manager Christopher A. Shaw, this seam of green clay may be a layer of oak leaf litter -- thus, Deposit 1 was once surrounded by a grove of oak trees.

Meanwhile, on Deposit 10A, excavation marches on! We had another near-death experience last week, when we found what looked suspiciously like naturally occurring asbestos. Fortunately, we were totally wrong -- it's nothing but Epsom salt, and we are panicky excavators. So, here's to not getting mesothelioma!

yay! not dying!

We're only about 20cm below the original surface of Deposit 10A. But so far we've found several pieces of tortoise shell -- almost unheard of at Rancho La Brea until now -- and a near complete pond turtle shell.

update, of the weekly variety

it's Photo Collage Madness 2008! Click through to our flickr.com page for highlights and more photos.

Gallivanting in Mexico aside, paleontology marches on here at Rancho La Brea. The grid that had been giving us so much trouble two weeks ago has met its match, and its demise:

l to r: Saber-toothed cat humerus, giant ground sloth vertebra, dire wolf skull.

The dire wolf skull had been upside-down in the grid; once we got it out and flipped it over, we discovered that it was heavily grooved and pitted as a result of pit wear. Or, in other words: there's a hole in his head! Observe:

On the left: a dire wolf skull with a gaping hole in his forehead. On the right, our fair leader Kristen (who will hopefully be joining this blog in the near future), forehead still intact. Click through to our flickr site for more close ups (of the dire wolf skull, not Kristen)...

In other news:
-we've measured out approximately 34 bones since Oct 31st.
-we just opened a new deposit: number 10A. Photos forthcoming.
-we've made a great deal of progress in our mapping -- the entire surface of deposit 1 has been sketched and stitched together. Again, photos forthcoming.

Note from the Lone Male Excavator

Hi all. I'm still here, treading in a sea of tar and estrogen.

In an attempt to be more like Andie, I've decided to put up another post and to start reading occasional comic graphic novels instead of just paleomammalogy and Harry Potter books, as has become the habit. I found this graphic novel of the first 10 comics of "Y, The Last Man" about this guy who ends up being the last man on Earth after all the rest die from something (don't know yet what, but I think it must be something to do with an attack on some phenotype from the Y chromosome, eh?).

Anyway, this guy is left alone in a world full of women, so I thought the series highly appropriate for me. We'll see.

Anyway, pulled this juvenile Smilodon vertebra out the other day (see pic). It is a very confused vertebra; it does not know whether it's an individual vertebra or part of the sacrum. This is a sort of developmental disorder likely caused by genetic problems and not uncommon in Smilodon. You can see (compared to the adult normal vertebra in the pic) that one side of the bone thinks it is a normal vertebra and the other thinks it is part of the sacrum. Furthermore, the neural spine is both off-center and angled wierd. I thought this one was pretty neato, but Michelle is the excavator, excuse me, excavatrix, who is really into pathologies.

This is one of the sweet perks to having such a large collection/set of deposits like Rancho La Brea: not only do we get a clear picture of the complete skeletal morphology of members of our fauna, but we get a very good knowledge of the pathologies which affected them.

Also see below the complete leaf I uncovered yesterday!

the-past-two-weeksly update: no news is good news

No weekly update last week because we were in beautiful El Golfo de Santa Clara in Sonora, Mexico collecting fossils! We camped in the desert for five days; collected numerous ice age (but older than RLB) fossils; watched many beautiful sunsets; and returned home to the rather sobering realization that excavating at the La Brea Tar Pits for one day leaves one even grimier than camping in the desert (without showering!) for five. Gross, right? Anyway...

This is El Golfo:

View Larger Map

And this is us:

From left to right, standing: Laura Tewksbury, Trevor Valle, Robert Predmore, Melody Weaver, Chris Shaw, Michael Wilson, Andie Thomer. Kneeling: Fred Croxen, Aisling Farrell, Ryan Long

El Golfo de Santa Clara is a magical land, where cars glide along the ocean:

And boats wind up on the street:


And fossils are NOT in tar pits! Oh no! They are lying on the ground, for everyone to see! See all the little rocks in the picture below?


A good number of those are actually very small fossils. Geologist Fred Croxen (in the center, with the jaunty hat) is bagging up rocks and dirt from the surface, which will then be sifted through in mesh screens:

and eventually sorted through under a microscope for the same kinds of microfossils that we find here at Rancho La Brea. The fossils from El Golfo are considerably older than those here -- 1 to 1.5 million years old, compared to our measly 10 to 40 thousand -- but nevertheless contain many similar species as our tar pits.

More soon!

view from the top

Over the weekend, I put together a faux-panorama of the top of Deposit 1. Standing in the northwestern corner of the deposit, I did my very best David Hockney impression and photographed everything I could see from there, and then overlaid the images in Photoshop. Though its not nearly as helpful as a wide-angle photograph would have been, I think this still gives a good idea of what the overall deposit looks like. The fossiliferous grids are (so far) all in the eastern portion of the box; most other grids are sterile (no fossils). If you click on the image above, you'll be taken to our page on flickr.com (where we store all the photos featured on this blog, as well as many others), where you can mouse-over different parts of the photo to read descriptive notes.

weekly update: happy halloween!

We here at Rancho La Brea pride ourselves on our holiday spirit.

Michelle. Devilish excavatrix extraordinaire.

Unfortunately, Michelle took her Halloween persona a little too seriously today, and placed a hex on grid B-1.

The face (and index fingers) of evil.

Because ever since SHE worked in B-1 yesterday, we've come to a near standstill in fossil extraction. All of the bones are intertwined with one another, and completely STUCK in place. The big dire wolf skull is stuck on top of the lion skull, and the sloth vertebra is stuck next to the dire wolf skull, and the saber-toothed cat humerus is pinning the vertebra in place, etc etc etc. It is a veritable portrait of frustration. Observe:

VERITABLE, I say!

Curse you, devilish Michelle! And curse you B-1!

This week's tally:
-33 bones extracted, including that juvenile saber-toothed cat skull fragment:

Shelley's Halloween costume: hand model!

At first, we thought we'd broken the saber during excavation, but after closer inspection, it looks like the hole in the center of the tooth is the natural result of pit wear -- the erosion of bones caused by other bones as they all jostle around in the tar pit.

- We also got the second-to-last dire wolf skull out:

Photo by Michelle.

Happy Halloween!

weekly update: dogs and cats, living together, mass hysteria!

Yeah, it's messy, but does your office have lightsabers and power tools on the same shelf?

We're gonna try to make this weekly update thing happen, like, every week. On Fridays. But not this past Friday, because Blogger ate my last update before it posted properly (curse you, Google...). Thus, we're a little behind, so this is more of a The-Past-Two-or-Three-Weeks update.

So, The Past-Two-or-Three-Weeksly tally:
- 120 bones measured out between Oct 10 - 24

notable finds:
- the coracoid of a Teratornis merriami (Merriam's teratorn). Teratorn's were huge birds of prey; their name means "monster bird" in Greek; they had a 13' wingspan; and they looked kind of like gigantic condor-vulture hybrids.
- the radius of a Capromeryx (dwarf pronghorn)
- again, a whole grip of ribs from a whole bunch of animals, all laying on top of each other. Excavating them has been like playing pick-up sticks in a graveyard, but we finally got at least a dozen out of the way, including three complete vertebral (as opposed to sternal) ribs.
- several Giant Ground Sloth caudal (tail) vertebrae and haemal arches (mini-psuedo-vertebrae that articulate with the underside of caudal verterbae)
- the semi-complete underside of a turtle shell. This was found in a section of the deposit that we previously thought was sterile, which is very, very good news -- more bones means less boring fossil-less dirt to dig through.
- Dogs and cats are peacefully co-habitating in grid B-1; we've found 3 dire wolf skulls so far (2 are pictured below), various bones from at least 2 coyotes, various bones from at least 2 saber-toothed cats, and as Ryan previously posted, the skull of a North American lion has been uncovered, but not yet excavated.

Grid B-1, Level 2, as of October 24, 2008

One of the dire wolf skulls (from a particularly old individual -- his teeth are worn down almost to the root) is directly on top of the lion skull.

highlight of the north american lion skull. mouse-over for the highlight of the dire wolf (if the image doesn't immediately shift, wait a few moments for it to load, and try again).

- as I previously posted, the saber of a saber-toothed kitten has been exposed.

look!

As you can see, saber-toothed cats were born with little sabers, which makes one particularly pity the saber-toothed mothers...

notable events:
- After months of excavation, Kristen got the giant ground sloth scapulas out!!




and grid B-2 has gone from this:





to this:





That's a giant ground sloth ulna in the center. Eventually, I hope to plot the location of all sloth bones in Deposit 1 to get a better idea of how, exactly, the animal's skeleton fell apart.

Once again: progress!

today...

we found two saber-toothed KITTEN sabers! completely amazing. pictures forthcoming. wait, with bated breath, you shall....

Note from the Lone Male Excavator:

I have often been asked what it is like to work as the lone man among four women. I usually reply in one of two ways. On a good day I say, "It is awesome to work with four talented, intelligent, beautiful, tough women." On a day when I am forced to watch The View and/or Oprah during break times I say, "There are good days and bad days." In essence each of my responses is true, but overall, I work with four people that know, as I do, that we have one of the coolest jobs on Earth. Though our tight-knit group is a socially intense and complex small band of hominins, it is this author's opinion that intragroup cooperation is facilitated quite readily by the composition of individuals and the male to female ratio.

Now, I'm sure you've heard enough on that matter for this post, and even if you have not, too bad, because I have something far more interesting to discuss:
We have partially uncovered the skull of a North American "Lion" (Panthera atrox). I'm sure that pictures will be posted of this find as we make more progress in removing the bones still above it and, finaly the skull itself. From what we have seen so far it is at least fairly well preserved. As was noted in an earlier post, we have also found a P. atrox pelvis. The skull was found in the same grid only a few inches below. We are curious as to how many of the many ribs and vertebrae and other bones found in this grid might also be attributable to P. atrox. Many of the bones in this grid have been of Smilodon [including a complete saber (upper canine)] and it is not always easy to determine an identification of the more general bones until they have been cleaned in the lab.

Well (2!), until next time...

measure for measure

Earlier this week, we measured out the left half of an American Lion pelvis (or, more anatomically correctly, an innominate). Whilst typing this into yesterday's entry, I realized I've never actually explained what "measuring" a fossil entails, let alone why we do it.

"Measuring out" a fossil means recording the location of two to three of the bone's anatomical points (usually three) within the context of a 1m x 1m x 25cm grid. For instance, take our most recent innominate:



The three dots and abbreviations above represent the three different anatomical points: IC stands for Illiac Crest; PT means Pubic Tubercle, and DP means Dorsal Posterior (which isn't actually a point -- it's a general orientation. This portion of the bone is broken off, so there isn't an actual feature to measure. Instead, we measure an arbitrary point, and name it after the point's location in the body: Dorsal, or toward the spine, and Posterior, or toward the rear end).

Each of these three points gets three pieces of data of their very own: measurements of the fossil's location below the original surface of the deposit (abbreviated as "BD" for "Below Datum"), north of the southern most line of the grid (N), and west of the easternmost line of the grid (W). These measurements are written into our field notes, and carbon copied (literally, with little blue pieces of carbon paper) onto 3" x 5" cards. Confused yet? Fear not, it sounds much more complicated than it actually is. But here's an enhanced version of the final product:

Remember Algebra class waaaay back in 9th grade? Wait, let me rephrase that -- remember any of the math from Algebra class waaaay back in 9th grade? Yeah, me neither. However, had you paid closer attention to the graphing portion of your text (and less attention to Spitball Trajectory 101), you would recognize those three columns of numbers as coordinates within a 3-dimensional graph. For example, for the IC, x = 43, y = 42, z = 32.5, etc. By recording all of these coordinates, we're able to later reconstruct the fossil's position within the deposit. And in doing that, we can learn all sorts of nifty things about how skeletons fall apart within a tar pit, or which animal got trapped first, or how asphaltic sand shifts underground over time, and so on and so forth.

A better photo narrative of a fossil's journey from grubby, dirt-covered groundling to a finished, fully prepared specimen is forthcoming, but until then, I hope this has been helpful. Or, at the very least, has inspired you all to pay closer attention in Algebra II.

this week in urban paleontology

Busy, busy excavators we have been!


The photo above shows the 50+ fossils we've measured out over the last two weeks. Extremely note-worthy finds include:
- a metacarpal (hand bone) of a Capromeryx (an extinct and fairly rare species of dwarf pronghorn)
- numerous saber-toothed cat and dire wolf ribs
- at least 6 sub-adult thoracic vertebrae (vertebrae from the rib cage) of a saber-toothed cat. We think they're all from the same individual animal! They were all found in the same 50cm X 50cm x 25cm area of the fossil deposit, and all appear to be about the same age. This is the sort of semi-articulation or association that we've been so excited about finding, because we very rarely (if ever) find it in Pit 91.
- part of a dire wolf skull
- at least four coyote jaw pieces
- a sloth sternal rib (a rib from the front of the ribcage, rather than the back. If you can't find one in your own torso, don't worry -- humans do not have sternal ribs. If you do find one in your own ribcage, please let us know! We'd be extremely interested in studying you...)
- the astragalus (an ankle bone, AKA the talus in humans), scapula, and pelvis (pictured below) of an American Lion

the measured pelvis, in it's natural environment: a metal bucket and a plastic bag. more on this tomorrow

What does this mean? Well, we've found not just one, but TWO of Rancho La Brea's rarer species (the American Lion and the Dwarf Pronghorn) in our first month of digging, not to mention another unique instance of fossil association! This first deposit is already adding to our knowledge base, and these discoveries bode well for the rest our excavation.

And remember this?

(l to r: sloth left scapula, sloth right scapula, ryan)

it now looks like this:

(l to r: dustpan, sloth left scapula, yet another tibia, sloth rib, sloth right scapula, michelle)

Progress!