28 July 2009

With Ryan gone, life is much daintier here at Rancho La Brea.

dainty dainty dainty
ping ping ping!

However, this does not mean that we are not still capable of great feats of strength:

meena angry, meena smash!
once, this was a chisel. now, it is rubble. such is life.

as is evidenced by the still-growing pile of broken tools left in our wake (volunteer Meena broke this one...)

Thus, over the last week our girlie muscles have brought Deposit 7B down almost a meter below its original grade. 7B is small, and not densely fossiliferous, but nevertheless productive enough to stay interesting:

7b as it was... and never shall be again.

The femur is the latest of several sabertoothed cat bones we've excavated from this area (including a skull!), and we're wondering if they're all from the same individual animal. We won't know for sure until they're cleaned and officially identified by the folks in the lab.

Less immediately exciting, but still important: there's a huge chunk of rock hard oxidized asphalt right in the middle of the deposit. There are bones around this asphalt, but not in it. We think this might be a vent -- the fissure in the ground that the asphalt originally oozed up from! We've seen this in Pit 91 before, but haven't been able to observe it as well as now. We only worked in Pit 91 for 12 weeks out of the year, and would only excavate a fraction of the exposed grids each season. This means that though interesting geological features were documented, it would sometimes take years to see if they continued another foot below the surface -- just because it took us that long to excavate the entire floor. Working year round with smaller deposits is allowing us to focus on unexpected geologic/taphonomic environments like this one.

I mentioned the lab earlier, and soon we'll have a proper Update From Indoors but until then:

here's a soundtrack-less time lapse of the preparation of Zed's right femur. Still a work in progress, but you get the general idea. Email subscribers: visit excavatrix.blogspot.com to see the video. Or scroll down:

zed's femur

to see Zed's femur in it's shiny, well polished glory.

That's it for now, more later!

21 July 2009

may the force be with ryan

ryan's favorite outfit

Sad but true: our Lone Male Excavator has left us for more exotic locales (grad school in plant and soil sciences on OAHU) and we miss him already. Ryan has been a careful and conscientious excavator, a funny dude, a good friend, and last but not least, an incredibly snazzy dresser (plaid + camo = AWESOME).

Yes, we will miss his hard work, his dedication to replacing shoring boards in the heat of summer, and his enviable ability to reach things on tall shelves, but we will also miss his encyclopedic knowledge of all things Star Wars, his willingness to talk in funny voices for our amusement, and perhaps most of all...

ryan's chair

his unparalleled ability to re-purpose old broken office furniture during his lunch break. The above photo may appear to be an ordinary office chair, but look closer! It is actually an office chair attached to another chair because it broke off its original base. The wooden legs of the base chair have been careful sawed at an angle for maximum comfort.

And what became of the base of the chair, you ask? BEHOLD:

ryan's sidetable

This is quite possibly my favorite piece of furniture ever. It's an end table! On WHEELS! This handcrafted beauty is made of another chair (with the back sawed off) screwed onto the base of the broken office chair, with a piece of laminate for a top. And it's the perfect height for chips and salsa!

Finally, Ryan's coup de grace:

ryan's desk

A genuinely well-made desk for volunteer Christina, made out of the side of box 10B (I think it's 10B).

In conclusion: Ryan is awesome! We totally miss him! He is funny and us taught about plants and how to sharpen tools and such! However, on the bright side: we now have a couch to sleep on when we go to Oahu...

Godspeed, Ryan

Godspeed, Ryan, and may the force be with you.

14 July 2009

Final Note From the Lone Male Excavator

Shore, -ing. (Verb):

the process of replacing old side-wall boards in large dug-out spaces (e.g., Pit 91).

This post will serve as both an introduction to some of the "other work" that excavators (and excavatrices) perform at Rancho La Brea and a documentation of the particular method of shoring board replacement that the Lone Male Excavator has developed.

So as the thick boards holding up the side walls of Pit 91 grow old, they often bow out, rot out, or both. Up above the pit, 14ft x 11 3/4" x 2 3/4" boards are stored ready to be cut to an average of about 75" long for use as a shoring board.

After a board is slated for replacement, of course it must be extracted. This is commonly far more difficult than it sounds. If the board is rotted to extremes on the ends locked in by the I-beams, then it is not too tough for a hatchet to cut through one end and pry the board out with a crowbar. If the board is not rotted away much at the ends, however, (as the boards pictured here) it can be quite difficult.

Initially, a cut with a circular saw is made through the board(s) being replaced. This is very dangerous and every safety precaution must be taken at this point (e.g., clean goggles, steady hands, hard hat). It is also messy and anything, including one self, which should not get covered in sawdust should be protected. If two parallel cuts, about 2" apart are made, extraction will be easier. Our cordless circular saw, however, does not cut deep enough to go through to the back of the boards.
So I have added to this method inspired by the wisdom of William A. Akersten's thought on sabertooth cat incisor (front teeth) functional morphology.

The points on large, cone-shaped incisors of Smilodon fatalis are separated to the extent that when they pinch together top to bottom and pierce into the skin of prey, they are thought to create a perforated line which allows for easy tearing off of chunks of flesh. When we are unable to pry/break out a board along the saw cuts, holes can be drilled along the cuts to create such perforated lines which can then be hacked trough easily or broken out through prying.Once a board is out, the wall of earth, often asphalt saturated, must be shaved a little with hand tools or, in dire need, a pneumatic chipper. Occasionally fossils are found in the side walls, so these must be watched for and documented when discovered.

Depending on the thickness of the new board and the bowing out of the old board shaving the walls may take up to a couple hours. Once this is done a measurement for the new board's length is taken, giving about an inch and a half behind the lip of each I-beam. (Often, when you think you've shaved enough and try to get the new board in, you find that a few spots need more shaving. The first of these two pictured here took me 3 attempts. I also found that I had cut it too long and had to take an inch off one end.)

After you've seen that the board will fit the space you've shaved out of the earth-wall, you must get it equally situated behind the lip of each I-beam... not so hard when you've got two-three boards out and you are doing the bottom board, but if you are trying to slide a single board over in a single space (like w/ the second board pictured) it can sometimes involve a long trial messing with crowbars. I have no solution, except putting in the lag screws early and trying to use them to slide the board. This does not often work.

If gaps are left, they are reduced by placing thin pieces of wood at the bottom of boards.

The boards are locked in between (and behind the lip of) I-beams which run about 40 ft under ground. As much of the board as possible is slid behind the inside of the I-beam before 5/16" holes are drilled beside the lip of the I-beam for 9/16" x 3 3/4" lag screws. The lag screws go through, what I'm gonna call, giant square washers which tighten the board flush to the I-beam. A thin, small piece of plywood is often needed between the shoring board and the giant square washer.

There you have it; Shoring 101. The final exam is getting a board replaced and not injuring yourself in the process.

So the Lone Male Excavator is off to grad school. This is my last day as an excavator at the Page Museum at Rancho La Brea, but I will still be around in spirit. (In fact don't be too surprised to see posts in the future by The Ghost of the Lone Male Excavator.)

08 July 2009

a small but big discovery

Hello! We found a very neat thing a few weeks ago:

Associated bird skeleton in situ at the La Brea Tar Pits

It's a bird! It's a plane! It's-- wait, nope, it's a bird. The many small bones in the upper left-hand corner (with the big arrow pointing at them labeled "bird") are all from a small passerine, (or "perching bird"). These bones likely represent an associated individual; they were found in a slightly separate layer of asphaltic sand than the rest of the deposit, and some bones even appear to be somewhat articulated. In other words: this is the almost complete skeleton of a small bird; this is extremely rare; I have named him Kevin.

Though most birds are passerines, they are nevertheless rare at Rancho La Brea; our collections are dominated by bigger birds of prey like teratorns and condors. It's hard to say what species Kevin is, exactly -- especially without cleaning and preparing the bones first -- but Lab Supervisor Shelley says he's about the size of a scrubjay.

Kevin the associated bird from Project 23 at the La Brea Tar Pits

The bones in the numbered in this photo are as follows:

  1. carpometacarpus
  2. scapula
  3. 2 limb bones -- not sure which exactly
  4. sternum
  5. tibiotarsus? I think?
  6. tarsometatarsus
  7. femur?
The photo above was taken after removing a number of other bones separately, such as ...

furculum of small bird (kevin)
the furculum...

scapula of small bird (kevin)
another scapula...

A passerine humerus, with finger for scale

...and a humerus (as well as an articulated synsacrum and femur, several vertebrae, and several phalanges that I don't currently have photos for). After removing these uppermost bones and discovering there were even more underneath we decided to remove the rest of the skeleton in one block...

Associated bird skeleton about to be removed

which was accomplished by gently prying the layer of asphaltic sand it was rested in with well-placed screwdrivers and chisels.

Though this skeleton is exciting in and of itself, its context may actually be more important. As regular blog readers may remember, up until now Deposit 1 has been more dirt than fossils. There's a dense cluster of bones in the southeast corner that has yielded at least 1000 specimens (and at least that many more to come), but about 3/4ths of the box has been largely sterile. Not anymore. As we dig deeper into the so-called "sterile" areas, we've found a new layer of fossils:

where kevin was found.

This is a different style of deposition than in the "main" bone cluster we've previously worked on:
  1. These fossils are spaced further apart, and spread out more evenly -- not all jumbled together like pick-up-sticks.
  2. These bones are broken, weathered, and worn. The bones in the other cluster are largely complete
  3. Many of the longer bones and bone fragments point in the same direction (scroll back up to the top of the page to get a closer look) -- perhaps implying stream movement? We don't know! But it's interesting...
Kevin was found in the northwest corner of this grid (near where the meter sticks cross) in a slightly separate layer of asphaltic sand -- perhaps implying that he flew in and got stuck after the rest of these unlucky beasts? Again -- we don't know! But also interesting! We will keep you posted as things and finds progress.