More on the Chubut Monster

Posted by Nima On Tuesday, June 3, 2014 4 comments

A few more pieces of information have been trickling out about the new giant titanosaur found in Chubut province, Argentina. While it may be anyone's guess when the paper will be out (and I would rather they take their time and get it right, instead of rush the process and end up with wrong measurements or figures) there are some important things we can already tell from the existing pictures.

First of all, the pictures are not comprehensive of the whole find. The news reports mentioned the discovery of up to 8 individuals at the site. The pictures that have so far appeared show at most the remains of two or three. However there is more of the site that was excavated, a portion that barely shows in any of the pictures.

But first, a few new looks.

This appears similar in many aspects (the position of the cracks mainly) to the huge femur that Pablo Puerta posed (or planked) next to on those pallets in the last post. But it just looks too small to be the same one. Nobody here looks unusually tall, yet the bone looks a bit more modest than the one with Puerta in the picture. That said, this thing is still definitely "family sized". *Lucky kids. I never got to be that close to a dinosaur at their age.*

But there's more to decipher at the site.

Look at that high, pointy lateral bulge (foreground).  If anyone had doubts about lognkosaurian affinity, this should squash them like the creature itself. Only two lineages of sauropods have such high and angular lateral bulges on the femur - lognkosaurian titanosars, and some euhelopodids and acrofornicans. This odd placement may have evolved other times, but so far we don't know of any more. (Also note the top of the pubis with its deep base and pinched foramen... that's about as close to Futalognkosaurus in shape as these parts ever get.)

The same femur and pubis from a different angle. Most of the other remains here were plastered and ready for removal by this point.

The field at its densest point. Shoulder, hip, rib, femur and spinal material is all present here.

Another view of the bone bed. Notice the scapula, femur, and one of the thickest ribs are easily visible.

But then of course someone has to make a map. A field map of the site may yield further clues, but for now we have to settle for color-coding what's there. Color coded maps are probably the most convenient for easily identifying parts of the same individual, as in this one of Bonitasaura:

So based on the photos of the Chubut finds, we come up with this (forgive the psychadelic craziness of the neon colors, there aren't that many other ways to get bones to stand out in heavy shaded angles and similar-colored rock):

Red = ribs, blue = scapula, turquoise = coracoid, orange = vertebrae, yellow = probable vertebrae , light green = femora, deep green = humerus, magenta = pubes, purple = ilia (?)

The most complete view of the site - note the large eroded femur at front, a bigger individual that that of the two other more complete femurs, and the large area at back, with plaster casings. There is far more to the site than just these few bones in the foreground, there's a whole pile of bones further back which were barely photographed aside from here.

One of the two smaller femurs at this location, the left femur. The disarticulated pubes and the shoulder material are probably from this same individual, note that the coracoid is not fused to the scapula so clearly this animal was immature at death. The femur flipped over during burial, pointing head-down. It's possible the pelvic area was scavenged.

The same femur, in that angle that shows off the sharp lateral bulge. The same bones (here largely plastered in a later dig phase) are colored in. There appears to be the centrum of a vertebra jammed in the matrix between the two pubes. also there appear to be two broken theropod teeth on the pubis, right below the foramen. It's looking more likely this carcass was scavenged. But the scavenger apparently didn't get a chance to cause much damage to the skeleton.

The same femur and pubes. Note the humerus (green) in the background.

The dense cluster from downhill view. Note the huge scapula and its squared-off proportions, typical of lognkosaurs and other titanosaurs. Here you see the femur from its bottom end (and the pubes from their top ends). At far left is part of the humerus, and some thin cervical ribs are also visible closer up. The un-colorized rusty patch jutting out from under the scapula may be a bone or an artifact of preservation.

Keep in mind this is just what I could identify from the photos. There may be other bones in some of the jagged lumps of rock around the site, which I have not marked. It's tempting to see bones everywhere you look, but until you know for sure what you are looking at, it's better NOT to interpret everything as an organic structure let alone part of the animal.

In any case this may make it a bit easier for artists. I wonder if they found any skull material or osteoderms at the site...