Tuesday, September 20, 2011

Dinosaur Revolution: Anhanguera

Those of you that watched episodes 3 and 4 of Dinosaur Revolution (which aired exactly one week ago) saw the sequence focusing on the large pterodactyloid pterosaur, Anhanguera.  This was one of the sequences I had the most input on, so I thought it might be fun to chat briefly about some scientific background that inspired the sequence.

Parental care in pterosaurs?
The sequence opens with a mother Anhanguera visiting her nest of offspring, whom she then kicks out of the test for their first flights (these end poorly for the first two babies, but the "hero" character survives to fly another day).  We have relatively little evidence regarding the specifics of parental care in pterosaurs.  What we do have is good evidence that pterosaur babies were able to fly very early in life, and that the eggs were of a soft-shelled structure, which implies that the eggs were buried in foliage rather than brooded in the manner of birds.  This manner of egg-laying alone does not tell us much about parental care - "leathery" eggs are laid by some taxa that do guard young (crocodilians) and many that do not (most squamates, though some of those guard nests and young, too).  However, the fact that baby pterosaurs were so well developed, and likely able to fly early in life, is at least suggestive that there was not an extended period of parental care.  Baby pterosaurs probably set off from the nest relatively early (possibly immediately).  Check out Darren Naish's blog post from February on pterosaur babies and eggs for more.

Pterosaur Locomotion
There are three major types of motion shown in the sequence: ground locomotion, launching, and flight.  As it turns out, the first two of these are really the same "mode" of movement.  After speaking with David Krentz, he and I thought it would be interesting to show the baby Anhanguera hopping in a saltatorial fashion.  There are no trackways that show this mode of locomotion in pterosaurs, but we also don't have any trackways that can reliably be mapped to ornithocheirids yet, and the limb proportions of ornithocheirds like Anhanguera are consistent with a saltatorial method of movement.  This observation is noted in the paper that Mark Witton and I published in 2010.  It is published in the highly acclaimed, open access journal PLoS ONE, and is freely available here.

The takeoff mechanism features the quadrupedal launch model that I proposed in 2008, and which was further used to make predictions about pterosaur ecology by Mark and I in the PLoS ONE paper.  Julia Molnar generated a wonderful animation of quadrupedal launch for Anhanguera, and it has appeared across multiple venues, including National Geographic.  She was subsequently kind enough to make it freely available on YouTube.  I have inserted the video below.  You can also pull it up by clicking here.

I have written about quadrupedal launch on other web resources previously, so I won't belabor the point here.  In short, takeoff acceleration in animals tends to be generated mostly by the walking limbs, rather than the wings.  As such, takeoff is really a form of running or leaping (usually the latter).  The strengths of the limb bones in bending and torsion, particularly with regards to the moments sustained for leaping, are therefore highly indicative of launch mode.  Pterosaurs turn out to be much more bat-like in this regard than bird-like: they had forelimbs which were much stronger than the hind limbs across a wide range of body sizes.  By contrast, large birds have stronger hind limb elements (particularly the femur) when compared with the forelimb elements.  Giant pterosaurs, such as Quetzalcoatlus, had very long, thin hind limb elements, which argues against a bird-like launch.  However, because pterosaurs walked on their folded wings, as well, the incredibly robust forelimb musculature and structure could provide most of the launch power (and sustain the resulting forces) during a quadrupedal launch.  Since pterosaurs were quadrupedal while moving on the ground to begin with, this is actually the most simple model, as well.  Modern bats, particularly vampire bats and New Zealand short-tailed bats, use a quadrupedal launch.

There are a host of other problems with a bipedal launch in pterosaurs, including problems with angle of attack of the wing, trailing edge flutter, Wagner effects, insufficient height and time, and pitching instabilities.  Depending on interest, I may do a summary of these observations at a later date.

There is not much to say specifically about the flight patterns.  One nice thing was that the flapping amplitudes used were pretty reasonable.  The wing cycles are probably a bit too large in some cases (particularly the Quetzalcoatlus models that do flybys), but it's usually much worse.  The problem here is that large animals actually tend to fly with more shallow wing strokes, especially if they have high aspect ratio wings.  This tends to make a distant albatross etc. seem a bit smaller to us than it really is, and the same happens when doing pterosaur models - they just don't look as huge if you model them correctly.  In Clash of the Dinosaurs, I tried very hard to get the animators to reduce the flapping amplitude of the Quetzalcoatlus model to no avail - there was a general feeling from those working on the show that the giant size didn't come across with the lower-amplitude wingbeats that are predicted by anatomy and fluid mechanics.  Oh well, such is life.

Monday, September 12, 2011

Dinosaur Institute hiring paid intern. Please pass along.

Feel free to pass this along to any interested parties/mailing lists.

The Dinosaur Institute at the Los Angeles County Natural History Museum is currently seeking applicants for Proyecto Dinosaurios, a 1-year paid internship designed to encourage under-represented students to pursue careers in the geosciences. In order to apply, students must 1) currently be enrolled in a 2-yr community or junior college, 2) be a minority, preferably hispanic, 3) be eligible to work in the US (citizen or permanent resident), and 4) be interested in the sciences.

It's short notice, but if you know of any potential applicants please pass the information on to them. The application is due Sept 16, so passing this along soon would be greatly appreciated. Feel free to contact me with any questions or interest and I'll pass it on.


Friday, September 9, 2011

Dinosaur Revolution Part 2

On Tuesday September 13, at 9:00PM, episodes 3 and 4 of "Dinosaur Revolution" will air on the Science Channel.  Note the change in date and venue.  One of the featured sequences involves the Early Cretaceous pterosaur Anhanguera.  Since I was a major consultant on that episode, in particular, I will be posting about some of the science background that went into that sequence (after it airs, of course).  Stay tuned!


Thursday, September 1, 2011

Dinosaur Revolution

This Sunday, starting at 9:00PM, Discovery Channel will air the first episodes of their new dinosaur miniseries, "Dinosaur Revolution".  I have been consulting on this show for the last 18 months.  The main page for the show can be found at:


I appear briefly in a couple of the episodes, but my primary involvement was in advising on the models and animations.  The show primarily uses CGI, with limited "talking heads" and narration components.  There are some well known dinosaurs, but there are also quite a few species that are often overlooked and a number of featured Mesozoic animals beyond dinosaurs (pterosaurs, mosasaurs, mammals, etc).  I was primarily involved with the formulation of the pterosaur models.  The art director, David Krentz, is one of my favorite paleoartists, and an outstanding person to boot - his involvement has really helped shape this production into a stunning show.  Check it out this weekend!


Guest Post at Skeletal Drawing

Greetings!  I recently wrote a guest post for Scott Hartman's excellent paleontology blog, Skeletal Drawing.

To check it out, point your cursors here: http://skeletaldrawing.blogspot.com/2011/08/mike-habibs-great-flying-skeletals.html