I recently did a G+ hangout interview with Lorena Barba's bio-aerial motion class out at Boston University. I broadcasted from the Natural History Museum of Los Angeles County, along with Justin Hall. Here's the link on YouTube: https://www.youtube.com/watch?feature=player_embedded&v=Mt88TkOlD4g
This was our first go with the "On Air" feature, which automatically records the hangout and sends it to a personal YouTube channel. I talked a lot about pterosaurs, as well as a bit about Microraptor.
Cheers,
--MH
Showing posts with label Pterosaurs. Show all posts
Showing posts with label Pterosaurs. Show all posts
Wednesday, December 12, 2012
Saturday, November 24, 2012
GUEST POST: Felipe Pinheiro and the Raiders of the Lost Palate
2012 has been a good year for pterosaurs, with several new taxa and important papers being published. This trend continued this week with the description of a fragmentary but intriguing pterosaur palate from the famous Cretaceous Santana Formation of Brazil, authored by Felipe Pinheiro and Cesar Schultz of the Universidade Federal do Rio Grande do Sul. Avenida Bento Gonçalves, Brazil, and Bayerische Staatssammlung für Paläontologie und Geologie, Germany, respectively (image of the new material is shown above. Image courtesy Felipe Pinheiro). Felipe asked if we could big up the paper here at the Pterosaur.Net bog, but I'm a little too pushed for time to write a post worthy of the article, which not only describes the specimen but sheds much needed light into pterosaur palatal anatomy. Felipe was kind enough to provide his own illustrated summation of the story however, so we could still cover the paper here at the blog. On that note, I'll hand you over to our guest blogger, and be sure to check out his open access paper for more details on this new discovery.
MPW 24/11/12
--
The fragility of pterosaur skeletons is always working against us, the paleontologists
devoted to understanding these flying archosaurs. Independently if our research
deals with systematics, anatomy or paleobiology, we’re often confronted with
the fact that our research subject is badly crushed and a great deal of useful
information is simply lost. A very good example of this issue is the pterosaur
palate: although new pterosaur taxa are being published all the time, only a
handful of well-known specimens have this structure preserved, thus, limiting
our knowledge of its anatomy and evolution within the group. Luckily, some rare
sedimentary deposits were kind enough and maintained the original,
three-dimensional shape of their fossils, allowing the study of otherwise
inaccessible anatomical features, like, of course, the pterosaur palates.
Our understanding of pterosaur palatal anatomy changed considerably
after the recent work by Attila Ösi and colleagues (2010). Analyzing pterosaur
palates under an evolutionary perspective and utilizing the Extant Phylogenetic
Bracket as a tool, the authors identified homologue structures between
pterosaurs, birds and crocodiles, demonstrating some bones that were misinterpreted
throughout the literature. The best example is the conclusion that, in
pterosaurs, most of the palate is composed by palatal blades of the maxillae,
instead of the palatines. Although this identification was also proposed by
some old researchers, like Newton (1888) and Seeley (1901) and, more recently,
Peters (2000), common sense was still that the palatines composed most of
pterosaur palatal surface.
As the work of Ösi et al.
(2010) was mainly focused on stem “non-pterodactyloids”, especially Dorygnathus, a new look on
pterodactyloid palate was still needed and this is the main subject of our new
paper, titled “An Unusual Pterosaur Specimen (Pterodactyloidea, ?Azhdarchoidea)
from the Early Cretaceous Romualdo Formation of Brazil, and the Evolution of
the Pterodactyloid Palate”.
Besides describing a new fragmentary (but interesting) palate from the
Romualdo Formation (the Early Cretaceous concretion-bearing strata of the
Santana Group, northeastern Brazil), we analyzed and redescribed a number of
well-known pterosaur specimens with palatal preservation, such as “Pterodactylus” micronyx, Anhanguera and Pteranodon. Also, the palate of the Iwaki Tupuxuara specimen is described and illustrated for the first time.
As a result, our work shows that pterodactyloids had often complex palatal morphologies
with, sometimes, interesting “reversions” to the non-pterodactyloid condition,
with three pairs of lateral openings. Also interesting is the extreme reduction
of elements in some taxa, such as the almost vestigial ectopterygoids of
anhanguerids. (Possible evolutionary pathways of the pterosaur palate shown below. Image courtesy Felipe Pinheiro.)
This morphological disparity is probably an evidence of complex feeding
habits among derived pterodactyloids, with ecological implications that is,
presently, the research subject of our working group, at the Universidade
Federal do Rio Grande do Sul, Brazil.
I hope you all read our paper (don’t worry, it’s open access). We’re
opened to all kind of criticism and discussions by my personal e-mail: fl_pinheiro@yahoo.com.br.
Enjoy!
Felipe L.
Pinheiro
Laboratório de
Paleontologia de Vertebrados, Instituto de Geociências, Universidade Federal do
Rio Grande do Sul.
References:
- Ösi A, Prondvai E, Frey E, Pohl B (2010) New interpretation of the palate of pterosaurs. The Anat Rec 293: 243–258.
- Newton ET (1888). On the skull, brain and auditory organ of a new species of Pterosaurian Scaphognathus purdoni), from the Upper Lias near Whitby, Yorkshire. Philos Trans R Soc Lond B Biol Sci 179: 503–537.
- Peters D. (2000). A re-examination of four prolacertiforms with implications for pterosaur phylogenies. Riv Italiana Paleontol Strat 106: 293–336.
- Seeley HG (1901) Dragons of the Air: an account of extinct flying reptiles. New York: Appleton & Co.; London: Methuen & Co.
Monday, November 12, 2012
Pterosaur fact checking
I will keep this brief, since Mark already did a great job of responding to the media release from the recent Chatterjee et al. presentation. One thing to look for in any sort of functional morphology argument is whether the anatomy, the numbers, and the behavior all match up. One reason the Chatterjee et al. abstract is so immediately concerning is that their own information doesn't jive internally.
Example 1: one of their concerns with the quad launch hypothesis is clearance for the wings after launch. Now, I've calculated the expected clearance and everything seems fine, but that doesn't mean I'm right. Maybe someone will find an error at some point. What is clearly not going to be true, however, is the idea that keeping the feet on the ground (biped running launch) is going to give more clearance than a leap. It simply isn't possible to get more clearance by not jumping (it might be true that jumping still isn't enough, but it's not going to be worse). So Chatterjee et al. have a mismatch between their own conclusions and their arguments with the competing model. The numbers and the behavior don't match up.
Example 2: Chatterjee et al. argue that pterosaurs can't work as scaled up bats, and argue instead that they should work like scaled up birds. Anatomically, pterosaurs don't match either of these, so the bat argument is a straw man, and the bird argument is moot. The anatomy and the behavior don't match up.
These are the sorts of arguments that raise red flags in scientific discourse. On a final note, there are some basic fact checking items that should be looked out for, such as claims about living animals. From the media story, Chatterjee is quoted as saying "Like albatrosses and the Great Kori bustards, which weigh 20 to 40 pounds, ground takeoff was agonizing and embarrassing for Quetzalcoatlus."
Aside from the problem with the pterosaur analogy, there is the obvious problem that Kori bustards don't have trouble taking off (though they might find it embarrassing; I haven't asked them). In fact, Kori bustards can leap into flight at a steep angle. Check this out. Yes, the bustard tries running to escape, first, but when pressed, it just leaps into the air. No big runway, no "agonizing" takeoff. In fact, there is no correlation between running launch and size in living birds or bats. More on that some other time, but in general, if a YouTube search quickly demonstrates that your commentary is flawed, that's a bit worrisome.
Example 1: one of their concerns with the quad launch hypothesis is clearance for the wings after launch. Now, I've calculated the expected clearance and everything seems fine, but that doesn't mean I'm right. Maybe someone will find an error at some point. What is clearly not going to be true, however, is the idea that keeping the feet on the ground (biped running launch) is going to give more clearance than a leap. It simply isn't possible to get more clearance by not jumping (it might be true that jumping still isn't enough, but it's not going to be worse). So Chatterjee et al. have a mismatch between their own conclusions and their arguments with the competing model. The numbers and the behavior don't match up.
Example 2: Chatterjee et al. argue that pterosaurs can't work as scaled up bats, and argue instead that they should work like scaled up birds. Anatomically, pterosaurs don't match either of these, so the bat argument is a straw man, and the bird argument is moot. The anatomy and the behavior don't match up.
These are the sorts of arguments that raise red flags in scientific discourse. On a final note, there are some basic fact checking items that should be looked out for, such as claims about living animals. From the media story, Chatterjee is quoted as saying "Like albatrosses and the Great Kori bustards, which weigh 20 to 40 pounds, ground takeoff was agonizing and embarrassing for Quetzalcoatlus."
Aside from the problem with the pterosaur analogy, there is the obvious problem that Kori bustards don't have trouble taking off (though they might find it embarrassing; I haven't asked them). In fact, Kori bustards can leap into flight at a steep angle. Check this out. Yes, the bustard tries running to escape, first, but when pressed, it just leaps into the air. No big runway, no "agonizing" takeoff. In fact, there is no correlation between running launch and size in living birds or bats. More on that some other time, but in general, if a YouTube search quickly demonstrates that your commentary is flawed, that's a bit worrisome.
Friday, July 6, 2012
Cross/Guest Post: Thin vs Thick Wings
I have a special treat this evening. Colin Palmer has been kind enough
to write a guest post on the relative performance advantages and
dynamics of thin and thick wings, especially in the context of animal
flyers. Colin is located at Bristol University. He is an accomplished
engineer with an exceptional background in thin-sectioned lifting
surfaces (particularly sails). Colin has turned his eye to pterosaurs
in recent years, and he has quickly become among the world's best
pterosaur flight dynamics workers. You can catch his excellent paper on
the aerodynamics of pterosaur wings here. Press release on it can be found here.
This is a cross post from Aero Evo. If you want to comment on the post, I recommend going there, as that means Colin only has to watch one site at a time (remember, he supplied this at of the goodness of his heart!)
--MH
------------------------
Thin And Thick Wings
Colin Palmer
In the early days of manned flight the designers took their inspiration from birds. One of the consequences was that they used thin, almost curved plate aerofoil sections. This seemed intuitively right and certainly resulted in aeroplanes that flew successfully. However towards the end of the First World War the latest German Fokker fighters suddenly started to outperform the Allied planes. Counterintuitively their wing sections were thicker-surely these sections would not cut the air so well so how could they possibly have enabled aeroplanes to fly faster and climb more quickly. But that was what was happening, the Germans had done their research and discovered that a combination of a cambered aerofoil with the correct thickness distribution gave superior aerodynamic performance. Subsequently all aircraft had similar teardrop shaped wing sections and soon there was a massive body of experimental and theoretical work available that enabled designers to select just the aerofoil they required.
Fast forward to the period after the Second World War and an explosion of interest in applying the latest aerospace science to the traditional arts of sailing. Many people looked to aircraft and logically assumed that sailboats would perform better if only they could be fitted with wing sails, like up-ended aircraft wings. Surely this had to be more efficient than the old-fashioned sails made of fabric and wire, just like the earliest aircraft. But the results were disappointing. Not only on a practical level where the wing sails proved unwieldy and unsuited to operating in a range of wind conditions, but perhaps more worrying they offered no obvious performance advantage and indeed in light winds they were significantly inferior, area for area. What was going on? Why didn't the massive investment in the development of aircraft wing sections have anything to offer to sailboats?
The answer lay in understanding the effect of Reynolds number. From the very earliest days of manned flight aircraft were operating at Reynolds number approaching 1 million and as speeds increased so did the Reynolds numbers, so it became customary for aerofoils to be developed for operation at Reynolds numbers of 2 to 3 million or more. But sailboats are much slower than even the slowest aircraft so the operational Reynolds numbers are lower than for aircraft, typically in the range from 200,000 to 500,000, right in the so-called transition region. It turns out that in this Reynolds number range the experience and intuition gained from studies at significantly higher values can be very misleading indeed. In the transition region a curved plate, (membrane) aerofoil can be more aerodynamically efficient than a conventional thick aerofoil.
This transition Reynolds number range is also where most birds and bats operate, and from what we know of pterosaurs it was also their domain. Consequently natural forms are not necessarily disadvantaged by having the membrane wings of bats or pterosaurs or the thin foils of the primary feathers in the distal regions of bird wings.
But there is a complication. A curved plate or, to an even greater extent, a membrane aerofoil has very little intrinsic strength and requires some form of structure to keep it in place and keep it in shape. On sailing yachts this structure is a thin tension wire that supports the headsail or the tubular mast in front of the mainsail. In order to tension the wire for the headsail, very large forces are required which places the mast in considerable compression, normally requiring a guyed structure that can have no direct analogue in nature. Natural forms are restricted to using a supporting structure which is loaded in bending and restrained by attached muscles and tendons. Generally speaking, the bending resistance of a structure depends upon the depth of the cross-section, so as bending load increases the diameters of the bones must increase otherwise the wing will become too flexible.
This is where the apparent superiority of the membrane wing may be compromised, because the presence of structural member severely degrades the aerodynamic performance. The structural member may be along the leading edge of the aerofoil as in the case of bats and pterosaurs, or close to the aerodynamic centre as in the case of the rachis of the primary feathers of birds. In all cases the loss of performance is less if the supporting structure is on the pressure side (the ventral side) of the aerofoil. It is therefore most likely no coincidence that this is the arrangement of the wing bones and membrane in bats and the rachis and vane in primary feathers. It was therefore also most likely that the wing membranes of pterosaurs were similarly attached to the upper side of the wing finger. Even in this configuration there is a substantial penalty in terms of drag, although it may result in some increase in the maximum lift capability of the section, due presumably to an effective increase in camber. (Palmer 2010).
This aerodynamic penalty arising from the presence of the supporting structure may perhaps be the reason why birds’ wings have thickness in the proximal regions, where the performance of such a thick aerofoil is superior to a thin membrane obstructed by the presence of the wing bones. More distally, where the wing bones become thinner or are not present, the wing section reverts to a thin cambered plate formed by the primary feathers. On the bird’s wing the proximal fairing of the bones into an aerofoil section is achieved by the contour feathers with very little weight penalty. This is not possible in bats (and presumably also in pterosaurs) where any fairing material would, at the very least, need to be pneumatised soft tissue, resulting in a considerable weight penalty as compared to feathers. In the absence of aerodynamic fairing around the supporting structure, aerodynamic efficiency can only be improved by reducing the cross-section depth of the bones - the general shape of the section having very little effect. But reducing the section depth results in a large increase in flexibility since the bending stiffness varies as the 4th power of section depth, so there are very marked limits to the effectiveness of this trade-off.
It may therefore be no coincidence that where the cross section depth has to be greatest, in the proximal regions of the wing, both bats and pterosaurs have a propatagium, which means that the leading-edge of the wing section is more akin to the headsail of a yacht, stretched on a wire, than a membrane with the structural member along the leading-edge. Wind tunnel tests have shown that moving the structural member back from the leading-edge, while keeping it on the underside of the wing section, results in a significant increase in aerodynamic performance.
This is a cross post from Aero Evo. If you want to comment on the post, I recommend going there, as that means Colin only has to watch one site at a time (remember, he supplied this at of the goodness of his heart!)
--MH
------------------------
Thin And Thick Wings
Colin Palmer
In the early days of manned flight the designers took their inspiration from birds. One of the consequences was that they used thin, almost curved plate aerofoil sections. This seemed intuitively right and certainly resulted in aeroplanes that flew successfully. However towards the end of the First World War the latest German Fokker fighters suddenly started to outperform the Allied planes. Counterintuitively their wing sections were thicker-surely these sections would not cut the air so well so how could they possibly have enabled aeroplanes to fly faster and climb more quickly. But that was what was happening, the Germans had done their research and discovered that a combination of a cambered aerofoil with the correct thickness distribution gave superior aerodynamic performance. Subsequently all aircraft had similar teardrop shaped wing sections and soon there was a massive body of experimental and theoretical work available that enabled designers to select just the aerofoil they required.
Fast forward to the period after the Second World War and an explosion of interest in applying the latest aerospace science to the traditional arts of sailing. Many people looked to aircraft and logically assumed that sailboats would perform better if only they could be fitted with wing sails, like up-ended aircraft wings. Surely this had to be more efficient than the old-fashioned sails made of fabric and wire, just like the earliest aircraft. But the results were disappointing. Not only on a practical level where the wing sails proved unwieldy and unsuited to operating in a range of wind conditions, but perhaps more worrying they offered no obvious performance advantage and indeed in light winds they were significantly inferior, area for area. What was going on? Why didn't the massive investment in the development of aircraft wing sections have anything to offer to sailboats?
The answer lay in understanding the effect of Reynolds number. From the very earliest days of manned flight aircraft were operating at Reynolds number approaching 1 million and as speeds increased so did the Reynolds numbers, so it became customary for aerofoils to be developed for operation at Reynolds numbers of 2 to 3 million or more. But sailboats are much slower than even the slowest aircraft so the operational Reynolds numbers are lower than for aircraft, typically in the range from 200,000 to 500,000, right in the so-called transition region. It turns out that in this Reynolds number range the experience and intuition gained from studies at significantly higher values can be very misleading indeed. In the transition region a curved plate, (membrane) aerofoil can be more aerodynamically efficient than a conventional thick aerofoil.
This transition Reynolds number range is also where most birds and bats operate, and from what we know of pterosaurs it was also their domain. Consequently natural forms are not necessarily disadvantaged by having the membrane wings of bats or pterosaurs or the thin foils of the primary feathers in the distal regions of bird wings.
But there is a complication. A curved plate or, to an even greater extent, a membrane aerofoil has very little intrinsic strength and requires some form of structure to keep it in place and keep it in shape. On sailing yachts this structure is a thin tension wire that supports the headsail or the tubular mast in front of the mainsail. In order to tension the wire for the headsail, very large forces are required which places the mast in considerable compression, normally requiring a guyed structure that can have no direct analogue in nature. Natural forms are restricted to using a supporting structure which is loaded in bending and restrained by attached muscles and tendons. Generally speaking, the bending resistance of a structure depends upon the depth of the cross-section, so as bending load increases the diameters of the bones must increase otherwise the wing will become too flexible.
This is where the apparent superiority of the membrane wing may be compromised, because the presence of structural member severely degrades the aerodynamic performance. The structural member may be along the leading edge of the aerofoil as in the case of bats and pterosaurs, or close to the aerodynamic centre as in the case of the rachis of the primary feathers of birds. In all cases the loss of performance is less if the supporting structure is on the pressure side (the ventral side) of the aerofoil. It is therefore most likely no coincidence that this is the arrangement of the wing bones and membrane in bats and the rachis and vane in primary feathers. It was therefore also most likely that the wing membranes of pterosaurs were similarly attached to the upper side of the wing finger. Even in this configuration there is a substantial penalty in terms of drag, although it may result in some increase in the maximum lift capability of the section, due presumably to an effective increase in camber. (Palmer 2010).
This aerodynamic penalty arising from the presence of the supporting structure may perhaps be the reason why birds’ wings have thickness in the proximal regions, where the performance of such a thick aerofoil is superior to a thin membrane obstructed by the presence of the wing bones. More distally, where the wing bones become thinner or are not present, the wing section reverts to a thin cambered plate formed by the primary feathers. On the bird’s wing the proximal fairing of the bones into an aerofoil section is achieved by the contour feathers with very little weight penalty. This is not possible in bats (and presumably also in pterosaurs) where any fairing material would, at the very least, need to be pneumatised soft tissue, resulting in a considerable weight penalty as compared to feathers. In the absence of aerodynamic fairing around the supporting structure, aerodynamic efficiency can only be improved by reducing the cross-section depth of the bones - the general shape of the section having very little effect. But reducing the section depth results in a large increase in flexibility since the bending stiffness varies as the 4th power of section depth, so there are very marked limits to the effectiveness of this trade-off.
It may therefore be no coincidence that where the cross section depth has to be greatest, in the proximal regions of the wing, both bats and pterosaurs have a propatagium, which means that the leading-edge of the wing section is more akin to the headsail of a yacht, stretched on a wire, than a membrane with the structural member along the leading-edge. Wind tunnel tests have shown that moving the structural member back from the leading-edge, while keeping it on the underside of the wing section, results in a significant increase in aerodynamic performance.
Thursday, July 5, 2012
Meet Bellubrunnus: New Pterosaur in PLoS ONE
Dave Hone and colleagues have just published a fantastic description of a new pterosaur in PLoS ONE. You can read (and download, if desired) the paper here. This new critter is particularly fun because it has wingtips that curve anteriorly; which is unique among pterosaurs known to date. Very cool stuff, and if you want to know more, obviously read the full paper, as well as the discussion by Dr. Hone himself at Archosaur Musings.
Here is a section of the Abstract from the original article:
Methodology/Principal Findings
The specimen was examined firsthand by all authors. Additional investigation and photography under UV light to reveal details of the bones not easily seen under normal lighting regimes was completed.
Conclusions/Significance
This taxon heralds from a newly explored locality that is older than the classic Solnhofen beds. While similar to Rhamphorhynchus, the new taxon differs in the number of teeth, shape of the humerus and femur, and limb proportions. Unlike other derived non-pterodacytyloids, Bellubrunnus lacks elongate chevrons and zygapophyses in the tail, and unlike all other known pterosaurs, the wingtips are curved anteriorly, potentially giving it a unique flight profile.
Cheers!
--MH
Here is a section of the Abstract from the original article:
Methodology/Principal Findings
The specimen was examined firsthand by all authors. Additional investigation and photography under UV light to reveal details of the bones not easily seen under normal lighting regimes was completed.
Conclusions/Significance
This taxon heralds from a newly explored locality that is older than the classic Solnhofen beds. While similar to Rhamphorhynchus, the new taxon differs in the number of teeth, shape of the humerus and femur, and limb proportions. Unlike other derived non-pterodacytyloids, Bellubrunnus lacks elongate chevrons and zygapophyses in the tail, and unlike all other known pterosaurs, the wingtips are curved anteriorly, potentially giving it a unique flight profile.
Cheers!
--MH
Friday, May 11, 2012
The Amazing Pterosaur Pelvis
There is a new paper out in Acta Palaeontologica Polonica on the anatomy and diversity of pterosaur pelvses by Hyder, Witton, and Martill. It's open access, so check it out: http://app.pan.pl/article/item/app20111109.html
Here's the abstract:
Pterosaur pelvic girdles are complex structures that offer a wealth of phylogenetic and biomechanical information, but have been largely overlooked by pterosaur anatomists. Here, we review pterosaur pelvic morphology and find significant differences that correlate well with pterosaur clades identified in some phylogenetic analyses. We find that the length and orientation of the iliac processes, position of the acetabulum, extent of the ischiopubic plate and presence of supraneural fusion in adult individuals are taxonomically informative. Ontogenetic changes in pelvic morphology dictate that osteologically mature specimens are required to assess the development of many of these characteristics. We suggest that pelvic characters can readily be incorporated into pterosaur phylogenetic analyses and may assist in resolving the controversial interrelationships of this group. Distinctive pterosaur pelvic morphotypes suggest considerable differences in stance, locomotory kinematics and hindlimb functionality across the group.
Here's the abstract:
Pterosaur pelvic girdles are complex structures that offer a wealth of phylogenetic and biomechanical information, but have been largely overlooked by pterosaur anatomists. Here, we review pterosaur pelvic morphology and find significant differences that correlate well with pterosaur clades identified in some phylogenetic analyses. We find that the length and orientation of the iliac processes, position of the acetabulum, extent of the ischiopubic plate and presence of supraneural fusion in adult individuals are taxonomically informative. Ontogenetic changes in pelvic morphology dictate that osteologically mature specimens are required to assess the development of many of these characteristics. We suggest that pelvic characters can readily be incorporated into pterosaur phylogenetic analyses and may assist in resolving the controversial interrelationships of this group. Distinctive pterosaur pelvic morphotypes suggest considerable differences in stance, locomotory kinematics and hindlimb functionality across the group.
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