Wednesday, August 3, 2011

Return from Los Angeles

Deinonychus © John Conway


We just finished a very productive week of work at the Los Angeles County Museum of Natural History (e.g. the LACM). I am back in Pittsburgh, and working over the final details of a paper we have put together for a top peer-reviewed journal. We cannot disclose the details at this time, except to say that the paper involves feathered dinosaurs (such as the wonderful Deinonychus above by John Conway of Ontograph Studios). The realization that many theropod dinosaurs were feathered really started to solidify in the 1990's. The number of known specimens with feathers continues to grow steadily, and these extremely bird-like animals have greatly changed our understanding of bird origins and the systematics of dinosaurs. However, there has been relatively fewer rigorous biomechanical investigations. As you might expect, we have gone and done exactly that for one species of note. With any luck, we will be posting a followup about this research when it's accepted for print!


We also worked on our analysis of mosasaur swimming. Mosasaurs were marine reptiles of the Cretaceous, found to be closely related to modern snakes and monitor lizards. The group included some real aquatic giants, the sort of animals you probably would not want to go swimming with...

Mosasaurs were traditionally reconstructed with snake-like body plans (look at images on Google to see some traditional illustrations). However, in 2010, a team reported on the best mosasaur fossil in the world. This fossil greatly alters our knowledge of mosasaur body plan. In a nutshell: they were more "whale-shaped" than snake-shaped in many respects. Here is a photo of the fossil, and the simple reconstruction from the PLoS ONE manuscript showing the updated body plan:
The specimen is on display in the new Mesozoic Life/Dinosaur Hall at the LACM (go check it out West Coasters!) Note that it has a streamlined, tapering body shape (what we call "fusiform" in the technical literature) and a tail fluke. The fluke is vertical, as in a shark fin, rather than the horizontal fluke of dolphins and whales.

I have been consulting for Creative Differences on their upcoming show Dinosaur Revolution (for Discovery Channel). One item of note that came up recently in my discussions with the crew working on the show is mass estimations in mosasaurs. Some of the estimates out on the web treat the animals as if they their mass scaled similar to whales. You'll note, however, that while the streamlined body shape is similar, whales have huge heads. They also have comparatively short tails. What this means, overall, is that mosasaurs would have probably been rather less massive than a whale of similar length. However, the available power for propulsion may not have been terribly different. We will talk more about what this all means in future posts, but be ready for some rather fast mosasaurs (at least in short bursts).

Cheers,

--MBH

9 comments:

  1. I remember reading that Mosasaur paper when it first came out and being far from convinced by the putative kink indicative of a two-lobed tail. It seems to far forward, too gentle, and not indicated by any perceptible wedge-shaping of the caudals. (Even though the text of the paper says they are wedge-shaped, I don't see it in the figures.)

    Have you now seen this specimen yourself and verified that interpretation? Or are you working on a specimen that shows this feature better?

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  2. (BTW., if you publish comments only after moderation, you will never get a good discussion going in the comments section. At SV-POW!, the policy is to let through anything not auto-detected as spam so long is it's from someone who's had a comment approved in the past. It works really well, and lets the conversation develop when none of us are around to moderate.)

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  3. I'm having a hard time understanding how the Deinonycus's arms are posed. The claws on the hand are at the top front of the "wing." How does that work?

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  4. Mike T: I appreciate the feedback about comment moderation. I have disabled moderation (leaving spam filtering on) as you suggested. Thanks very much!

    As for the mosasaur: I have investigated the specimen myself in detail, and while the "wedging" is quite subtle, the downward turn seems to be real. I have also examined the Platecarpus here in Pittsburgh, and while it is not as fantastic overall (no soft tissue), the tail kink is considerably more obvious. In fact, they mounted the specimen with a straight tail (it was done prior to the PLoS paper) only by making the spinous processes overlap where the tail turns downward (i.e. at the peduncle).

    The downward turn is rather further forward than I would have originally expected, as well, but I've been working on a reconstruction of the body plan myself (it helps me to do my own and compare to the authors' version), and it actually produces a pretty reasonable fluke position for a mid-speed burst adapted predator, especially if one considers that the motion can begin in the trunk (just anterior to the pelvis).

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  5. Kurt: The structure of the hands in derived theropods (birds included) is indeed pretty weird. The hands/wings fold such that the fingers are pushed towards the forearm and the elbow is tightly flexed. To visualize, imagine moving your wrist such that your small finger was pressed towards your ulna. The turn at the top of the wing is actually the wrist, and the fingers are pointed downwards. The claws then curve forwards out of the wing.

    This skeletal diagram by Scott Hartman should help: http://skeletaldrawing.com/psgallery/gallery.htm

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  6. Thanks, Mike H. It's good to get independent witness to the asymmetrical mosasaur tail, and it will be better yet when someone publishes a convincing set of specimen photographs that document it.

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  7. I found a drawing that seems to show things pretty well (for birds).

    http://keaalu.deviantart.com/art/Folded-Bird-Wings-18570573?offset=20

    Number 7 seems closest to the Deinonychus pose.

    I've obviously never paid enough attention to how birds fold their wings!

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  8. We also worked on our analysis of mosasaur swimming. Mosasaurs were marine reptiles of the Cretaceous.

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  9. The specimen is on display in the new Mesozoic Life/Dinosaur.

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