Although it got a brief treatment in the book Horns and Beaks, many people have been waiting for more information on the exceptionally-preserved Brachylophosaurus skeleton named "Leonardo." Due to be unveiled next week at the Houston Museum of Natural Science (the date was pushed back due to Hurricane Ike; the museum and Leonardo were unharmed), the fossil provides a unique look at the soft tissues of this particular dinosaur.
Dinosaur "mummies" have been found before, dating back to the 19th century, but in many cases little more than skin impressions were preserved. Leonardo, by contrast, is so well preserved that paleontologists are getting a look at the internal anatomy of the dinosaur, and the new paper (out in Palaios) focuses on gut contents.
Within the body cavity of Leonardo there is a large amount of plant material. The question is, however, whether those plants represent gut contents or found their way into the specimen by some other route. If the body cavity was preserved intact (i.e. there were no gaping holes in it) then there could be little doubt that the plant material represents gut contents, but if the cavity was punctured other possibilities open up. The gut contents might have stayed in the body and been reworked, they could have been mixed with outside plant material, or the original contents could have been removed and then replaced. The actual soft tissue of the digestive tract would have decomposed fairly quickly after death and so the contents would not have been in their original position even if they were preserved, but the first task of the researchers was to determine whether they were dealing with gut contents or washed-in plants (or both).
The paleontologists were not looking at whole leaves, stems, or other plant parts, though. The preserved plant material was very fragmentary, best described as "fragile, black crumbs." These little bits were substantially different from the woody material found in some hardosaur coprolites (or fossil poo), meaning that (if the fragments were true gut contents) shortly before death Leonardo had a lunch of leaves. The fragments were consistent with what would be expected for partially-digested hadrosaur meals, of course, but it did not make identification of the plants especially easy. This became even more vexing when the researchers realized that the high amount of clay inside the body cavity most probably meant that the body cavity was breached. There was a possibility that some of this material came in from the outside.
[As is pointed out in the paper, many animals have clay or soil inside their digestive tract as a result of purposefully eating it or the material coming in with the food. In Leonardo's case, though, the sheer amount of clay showed that it was probably not intentionally swallowed. If the hadrosaur did so then it would have eaten more clay than plants!]
If there was a mix of gut contents and material from outside, however, it would be expected that there would be different characteristics between the partially digested food and the washed-in plants. Being that the material was generally uniform, the alternatives became narrowed down to either preserved gut contents or outside material. While both options were plausible, the retention of gut contents seems more likely.
Exceptional preservation is typically a result of rapid burial; the longer a carcass is left out to rot the more it will be picked apart or otherwise broken down before preservation. Given that Leonardo is perhaps the most exceptionally-preserved large dinosaur yet found, the skeleton was probably buried very quickly after death. This means that if the plant material in the body cavity came from the outside it would have had to find a way in after the body wall was breached, something that is unlikely. Indeed, the type of plant material inside the body was not found outside the body in the surrounding sediment; it is more probable that the crumbly plant fossils were actual gut contents.
About 75 million years ago, in what is now Montana, a subadult Brachylophosaurus died. While it was not killed or consumed by a predator, the exact cause of death is still a mystery. Either in death or shortly afterward the body of the dinosaur was quickly covered by sediment, perhaps by a flooded river. Piled beneath the mud and clay the dinosaur was beyond the reach of the large predators (except, perhaps, its tail, which may have been tugged on by some scavenger), and its body slowly started to decompose. The internal organs went first, with a breach in the body wall letting enough water and sediment in to wash the gut contents around inside the body cavity. This process preserved some aspects of the anatomy but obscured others, but tens of millions of years later the descendants of the tiny mammals that lived in the corners of the Mesozoic world would unearth Leonardo's remains. Paleontologists have only just begun to understand what the skeleton can teach us about dinosaurs, and I'm sure we will be talking about Leonardo for many years to come.
J. S. Tweet, K. Chin, D. R. Braman, N. L. Murphy (2008). Probable Gut Contents Within A Specimen Of Brachylophosaurus Canadensis (Dinosauria: Hadrosauridae) From the Upper Cretaceous Judith River Formation Of Montana PALAIOS, 23 (9), 624-635 DOI: 10.2110/palo.2007.p07-044r
OK, two questions... why the tail stripes in the illustrations, and why do they end so abruptly just behind the hips?
Is this based on the fossil evidence or artistic license?
Wazza; I haven't seen anything yet about there being a preserved alternating color pattern in this fossil, so it is most likely artistic license. I know that the researchers working on another hadrosaur mummy, "Dakota," think it had a similar color pattern on the tail because the size of the tubercles on the skin changes on the tail, but as far as I am aware the color pattern choices here are entirely speculative.
I recently saw a Discovery (Canada) channel program about Leonardo. It was, unfortunately, one of those shows which is made tedious by excessive repetition of already presented information, manufactured drama (oh noes! X-ray machine not work! Okay, now works.), and a failure to deliver lots of information that should have been immediately available, like, say, a really close look at those interesting forelimbs and feet.
In spite of that, it was interesting enough (after all: mummified dinosaur!), although I don't know how accurate. But wrt to the body being breached or not, they had determined (or hazarded a guess) that Leonardo had been bitten before or soon after dying - I just can't recall if they said in what part of the body.
Hi wazza and Brian,
I was really interested by your question - I thought I had heard Dr. Bakker talk about this issue specifically, and it touches on something that a lot of our museum visitors are interested in - how do you come up with a fleshed out model from looking at a bunch of bones?
So, I asked him to send an answer to your question; here's what Dr. Bakker had to say about the coloration in the photos:
That's the giraffe-like thing in wet woodlands today.
Dinos had bird-style eyes, so camouflage had to match habitat colors. Dull browns and greys were not good enough to fool an eagle-eyed gorgosaur.
Early Judithian environs had wet forests with big conifer trees and, in the rainy season, thick underbrush. Dry season would bring browns & rust colors.
So........Mike Berglund has made a testable theory with his partially banded Brachy. Breaking the profile by having the tail a different color would help flummox predators, who would have a more difficult time seeing the whole body + tail shape. The thick verticals would help the beast blend in among the tree trunks.
How can we test color ideas? More paleo-environmental research. More thinking about fossil pollen, turtles, crocs & salamanders....all witnesses to rainfall, groundwater, and floral geometry."
So, his answer seems to second what you said, Brian - speculative, but speculations based on research, such as the research you have written about here.
Also - I meant to mention that Micheal Berglund (the artist Dr. Bakker mentioned in his response) is the paleo-artist that created the last image in this post (you can see his credit in the bottom right of the photo). The other image was created by Julius Csotonyi, who created the mural that will be on display in the Leonardo exhibit.
Thanks for the nice write-up!
On the potential breach and other interesting things raised in the documentary: The paper was essentially complete before the end of 2006, and is based on about half of my master's thesis (worked on fall 2003-spring 2006). Unfortunately, I don't have much to say on the scanning and so forth, because I wasn't involved with that part of the project.-Justin