Cocking back the cranium of the Denver Pteranodon

Earlier we added the DMNH Pteranodon skull to the large pterosaur tree and the Pteranodon skull page. What I had for data was the tracing by Chris Bennett from his 1991 PhD thesis. Always looking for more precision, I contacted the stewards of the skull.

Rene Payne and Rick Wicker of the Denver Museum of Natural History (aka Denver Museum of Nature & Science) were kind enough to send me jpegs of  both lateral views of their big crested Pteranodon skull  (DMNH 1732). Their contract stipulated that I not publish the photos themselves. One photograph had to be slightly distorted to remove parallax to exactly match the outlines of the second photo. That made tracing less of a headache. The tracing (Fig. 1, above) comes off data from both sides.

With the tracing in hand, I compared the cranium and jawline to sister taxa and found the occiput angle of the DMNH specimen to be a little too erect. So the revision (Fig. 1, below) cocks the skull back a little bit, rotating on the quadrate axis. Now it more closely matches sister taxa. The dentary was also straightened out at the break.

Figure 1. The Denver Pteranodon, DMNH 1732. Above, traced from the mounted specimen. Below, cranium and jaw slightly rotated to match more complete sister taxa skulls.

Figure 1. The Denver Pteranodon, DMNH 1732. Above, traced from the mounted specimen. Below, cranium and jaw slightly rotated to match more complete sister taxa skulls. Yellow = premaxilla. Dark blue = nasal. Light blue = frontal. Orange = parietal. Pink = restored. And yes, that’s a single tooth in the anterior mandible.

The specimen is incomplete, yet saves some interesting parts. The mandible preserves and exposes the robust anterior tooth. The crest is long, but not the longest of all known crests. It is superbly preserved with long grain on the frontal that looks like parallel lines extending in the direction of growth. The anterior single mandible tooth is preserved.

Figure 2. The DMNH specimen is in color, nesting between the short crest KS specimen and the long crest AMNH specimen.

Figure 2. Click to enlarge. The DMNH specimen is in color, nesting between the short crest KS specimen and the long crest AMNH specimen. Note the cocking back of the cranium of the DMNH specimen more closely matches closest known sisters.

In size and proportion the DMNH specimen nests neatly between the KUVP 2212 and the YPM 2594 specimens of Pteranodon. It’s not quite as unique as once supposed, but does provide clues to the length of the mandible, which is incomplete in YPM 2594.

References
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodon and Systematics of the Pterodactyloidea. [Volumes I & II]. Ph.D. thesis, University of Kansas, University Microfilms International/ProQuest.
Bennett SC 1992. Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests. Journal of Vertebrate Paleontology 12: 422–434.
Bennett SC 1994. Taxonomy and systematics of the Late Cretaceous pterosaur Pteranodon (Pterosauria, Pterodactyloidea). Occassional Papers of the Natural History Museum University of Kansas 169: 1–70.
Bennett SC 2000. New information on the skeletons of Nyctosaurus. Journal of Vertebrate Paleontology 20 (Supplement to Number 3):29A.
Bennett SC 2001. The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Part I. General description of osteology. Palaeontographica, Abteilung A, 260: 1–112. Part II. Functional morphology. Palaeontographica, Abteilung A, 260: 113–153.
Eaton GF 1910. Osteology of Pteranodon.  Memoirs of the Connectictut Academy of Arts and Sciences 2:1-38.
Marsh OC 1876. Notice of a new sub-order of Pterosauria. American Journal of Science, Series 3, 11:507-509.

wiki/Pteranodon

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Gender Dimorphism in Phytosaurs?

Trying to figure out male from female fossils 
is difficult, unless you find several skeletons together in a single site. That seems to be the case here. So, if there’s gender identification in phytosaurs, might pterosaurs be likewise differentiated? Bennett (1992), Lü et al. (2011) and Witton (2013) think so following traditions.

Let’s find out. (Thanks to Rob Gay for the heads up on this phytosaur gender paper.)

Figure 1. Original line drawing and scale bar of the phytosaur Pseudopalatus vs. photographs and scale bars. Something is a little off here. Even so, the case for sexual dimorphism appears to be strong.

Figure 1. Original line drawing and scale bar of the phytosaur Pseudopalatus vs. photographs and scale bars. Something is a little off here. The line drawing indicates the male is a little larger, but the photo doesn’t confirm that. Even so, the case for sexual dimorphism appears to be strong — except when you discover these are the two smallest published specimens.

A paper by Ziegler et. al 2002 claimed to document sexual dimorphism in Pseudopalatus phytosaurs. While the illustrations and figures support the proposition (Fig. 1), I wish they had found at least one big male (Fig 2). Unfortunately, in the sample set from this quarry he(?) is the smallest of the lot. Below (Fig.2) the scale bars are the key. The original photo makes the bulging “male” appear to be the largest and most robust specimen, but when all the scale bars are the same, the male is the punk, the runt, the wee one!

Figure 2. Above, the photograph as published. Note the different length scale bars. Below, all scaled to the same length. The single male Pseudopalatus phytosaur skull is smaller than two females.

Figure 2. Above, the photograph as published. Note the different length scale bars. Below, all scaled to the same length for this blog post. The single male Pseudopalatus phytosaur skull is smaller than two females and no bigger than the third. Presumeably crushing and distortion makes these fossils look more diverse than they likely were in life. Scaled to the same length provides more “truth” in this case.

So the big question is this:
Is it more parsimonious to have two morphs of the same species in the same pond death assemblage? The answer is yes.

Are scale bars important?
Yes!

Are there really two genders here?
It appears so, when you compare the two smallest specimens (Fig. 1). Still wish there was at least one big male here. At present, he’s like a pre-teen compared to the big females.

Does this have anything to do with pterosaurs and their crests?
Yes. We’ll only find out if pterosaur crests have any gender signal when we find a death assemblage with dimorphic adults, like this phytosaur site. So far that hasn’t happened, although the Pterodaustro site is a death assemblage I don’t think very many skeletons were articulated and fewer were complete. All previous claims for gender identity in pterosaurs (Bennett 1992, Witton 2013, others listed below) have been falsified by phylogenetic analysis, something these authors have avoided doing.

And, oddly, 
Yes, these are the same phytosaurs that nest basal to pterosaurs in Nesbitt 2011 here and as a sister taxon once removed in Brusatte et al.  2010 (Fig. 3). I don’t see the resemblance. Perhaps someone does?

I still like lepidosaurs / tritosaurs / fenestrasaurs and wonder why others don’t.

Figure 3. Brusatte et al. 2010 archosaur family tree with hypothetical relationship between phytosaurs and pterosaurs highlighted in yellow. This is obviously bogus.

Figure 3. Brusatte et al. 2010 archosaur family tree with hypothetical relationship between phytosaurs and pterosaurs highlighted in yellow. This is obviously bogus. See the large reptile tree for something a little closer to prehistory.

With regard to pterosaurs
I found that many seemingly congeneric pterosaurs can be differentiated by the variety in their pedal proportions. Rhamphorhynchus is a case in point. It would be nice to find some articulated male and female phytosaur feet from this death assemblage and compare them. If the robust rostrum is a different genus, the pedal proportions might provide the best clue. If the feet are the same, two genders are likely present.

References
Bennett SC 1992. Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests. Journal of Vertebrate Paleontology 12: 422–434.
Bennett SC 2006. Juvenile specimens of the pterosaur Germanodactylus cristatus, with a review of the genus. Journal of Vertebrate Paleontology 26:872–878.
Brusatte SL , Benton MJ , Desojo JB and Langer MC 2010. The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Knell R, Naish D, Tompkins JL and Hone DW E 2012. Sexual selection in prehistoric animals: detection and implications. Trends in Ecology and Evolution28, 38-47.
Lü J, Unwin DM, Deeming DC, Jin X, Liu Y and Ji Q 2011. An egg-adult association, gender, and reproduction in pterosaurs. Science, 331(6015): 321-324. doi:10.1126/science.1197323
Naish D and Cuthill IC 2012. Does mutual sexual selection explain the evolution of head crests in pterosaurs and dinosaurs? Lethaia 45, 139-156.
Naish D, Tomkins JL and Hone DWE 2013. Is sexual selection defined by dimorphism alone? A reply to Padian and Horner. Trends in Ecology and Evolution. 
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Witton M. 2013. Pterosaurs. Princeton University Press. 291 pages.
Zeigler KE, Lucas SG and Heckert AB 2002. The Late Triassic Canjilon quarry (Upper Chinle Group, New Mexico) phytosaur skulls: Evidence for sexual dimorphism in phytosaurs. Upper Triassic Stratigraphy and Paleontology, New Mexico Museum of Natural History and Science Bulletin 21. Online here.

What is Asperoris?

A recent online paper by Nesbitt et al. 2013 introduces us to a new Middle Triassic East African archosauriform, Asperoris mnyama (NHMUK PV R36615), known from several 3D skull pieces (Fig. 1).

Figure 1. Asperoris skull reconstruction. Turns out it's just an ordinary rauisuchid linking Vjushkovia to more derived forms.

Figure 1. Asperoris skull reconstruction. Turns out it’s just an ordinary rauisuchid linking Vjushkovia to more derived forms. Tooth length is pure guesswork.

Nesbitt et al. was unable to resolve what Asperoris was (Fig. 2). So they considered it a “non-archosaurian archosauriform” (incerta sedis). Unfortunately they included rauisuchids within the Archosauria in their analysis AND they included several unrelated taxa: a lepidosauriform (Mesosuchus), a thalattosaur (Vancleavea) and two pararchosauriform supragenera (Proterochampsidae and Phytosauria). That didn’t leave too many related taxa to compare Asperoris to. And they missed the most obvious candidates, like Vjushkovia (Fig. 3). That’s why we turn to the large reptile tree (Fig. 2, subset here) to find out where Asperoris might nest.

Figure 2. The confused nesting of Asperoris according to Nesbitt et al. 2013 (above) and the exact nesting according to the large reptile tree (below).

Figure 2. The confused nesting of Asperoris according to Nesbitt et al. 2013 (above) and the exact nesting according to the large reptile tree (below) as as sister to Vjushkovia.

The large reptile tree data analysis started with a reconstruction of Asperoris (Fig.1), which enabled the employment of several traits not readily apparent from the separated bones. The results nested Asperoris within the Rauisuchidae as the sister to Vjushkovia,  a taxon not included in the Nesbitt (2011) study on archosaurs.

The Nesbitt et al. 21013 definition of Archosauria is not confirmed here.
Nesbitt et al. report, “Archosauria, the crown clade that includes living birds and crocodilians as well as extinct dinosaurs, pterosaurs and pseudosuchians (stem-crocodilians), is one of the most successful evolutionary radiations in the history of vertebrate life on land.” In the large reptile tree, Archosauria includes just crocs and dinos (including birds). Pterosaurs nest with tritosaur lizards. Pseudosuchians, it turns out, are diphyletic with parasuchians and proterochampsids nesting with choristoderes, on a separate branch from the rest of the traditional archosauriforms.

Not far from Vjushkovia
Asperoris shared many skull traits with Vjushkovia and was about the same size. Like Vjushkovia, Asperoris also lacked an antorbital fossa on the maxilla. According to Nesbitt et al. “Asperoris mnyama differs from all known archosauriforms in having highly sculptured cranial elements including the premaxilla, maxilla, nasal, prefrontal, frontal, postfrontal, and parietal, and in having a highly sculptured, dorsoventrally deep orbital margin of the frontal.” This may be a distinct trait indeed.

Vjushkovia.

Figure 3. Vjushkovia had 3 premaxillary teeth and a descending jugal, but otherwise would have been similar to Asperoris in shape and size.

So no great shakes. 
Asperoris was about the size of Vjushkovia and Batrachotomus, so smaller than some rauisuchids. It’s not a key taxon providing new insight into relationships.

Sadly,
having access to data that showed pterosaurs and Vancleavea should not be included in archosauriform studies was not followed by any testing of these oddly nested taxa. Rather Nesbitt et al. (2013) held on to their old traditions — which is a major problem with their study.

Once again, I have not seen the original material (nothing here changes in interpretation anyway), but I do have a larger gamut study from which more accurate and confident nestings can be made. This is available to anyone who wishes to use it. Moreover, the taxonomic clades that result can provide guidance for future inclusion sets. At least they should be tested.

References
Nesbitt SJ 2011. The early evolution of archosaurs: Relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.
Nesbitt SJ, Butler RJ, Gower DJ 2013. A New Archosauriform (Reptilia: Diapsida) from the Manda Beds (Middle Triassic) of Southwestern Tanzania. PLoS ONE 8(9): e72753. doi:10.1371/journal.pone.0072753

NHMUK, The Natural History Museum, London, United Kingdom;

Pteranodon skull evolution movie

Earlier we looked at Pteranodon skulls all to the same scale and in phylogenetic order.  Today there’s a GIF movie that presents the same data (Fig. 1).

Figure 1. Click to animate. Pteranodon skull movie. All the skulls are to the same scale and in phylogenetic order.

Figure 1. Click to animate. Pteranodon skull movie. All the skulls are to the same scale and in phylogenetic order. Each skull appears for 2 seconds and the animation recycles when the page is reloaded. And yes, the long-crested clade does terminate with three smaller taxa.

The first tiny specimen is actually an outgroup Germanodactylus. Long crests and great size evolve from small crests and small size. Learn more about Pteranodon variety here.

Long-crested taxa had digitigrade feet. Tall-crested taxa had flat feet. Other postcranial differences are discussed here.

Pterosaur dipping and skimming – first for drinks, then for floating insects

Last week’s (Sept 18) Nova program on PBS entitled, “Earthflight” showed swallows, with their tiny little beaks, dipping for water while on the wing (see video here). Later the swallows dipped for floating mayflies. Others took quick baths by diving an inch below the water then reemerging without losing too much momentum.

From the BBC special on birds entitled, "Earthflight." Swallows drinking while on the wing.

Click to view. From the BBC special on birds entitled, “Earthflight.” Swallows drinking while on the wing. Note the teeny tiny beaks.

So why can’t certain pterosaurs, like Rhamphorhynchus and others, skim and dip (there is a spectrum between the two based on speed of attack) for surface-dwelling fish? Especially when a fish is found in the throat and belly? We looked at this earlier. The swallows, with their tiny wide, unspecialized for dipping beaks, demonstrate that a flying animal does not need a special beak shape.

Skimming pterosaur

Figure 2. Manipulating the bones of the fish-eating Rhamphorhynchus into a skimming configuration while staying airborne.

Humphries et al. (2007) tried to show that skimming would not be likely for pterosaurs. They used math. Sometimes math isn’t the key. They used morphological comparisons to the modern skimmer, Rynchops, which is ideally suited to high-speed skimming on windless ponds. Swallows demonstrate that’s THAT important. We considered pterosaur skimming earlier here.

Earlier we talked about the key: windspeed. It doesn’t equal groundspeed (or waterspeed) when flying into a breeze or steady wind. A steady breeze at the best glide speed can equal a hover over a particular spot. A little speed isn’t a bad thing either. I’m sure pterosaurs found the ideal circumstances and took advantage of them.

So, like birds, pterosaurs graduated from taking drinks on the wing, to taking floating insects on the wing, to taking surface-dwelling fish while on the wing and some even dived like gannets deep beneath the surface (gannets can descend 70 feet btw). That’s a nice variety of niches.

Nyctosaurus and Pteranodon
On this subject, it’s interesting to note, once again, that Nyctosaurus had a longer mandible and Pteranodon had a longer rostrum, both sharp like a sword and sharpened with a single sharp tooth in the tips of both jaws. Rhamphorhynchus (Fig. 2) does not have these anterior teeth, but has a rostrum and dentary tipped with keratin extensions.

References
Humphries S, Bonser RHC, Witton MP and Martill DM 2007.
 Did pterosaurs feed by skimming? Physical modelling and anatomical evaluation of an unusual feeding method. PLoS Biol 5(8): e204. doi:10.1371/journal.pbio.0050204 online

Padian on Dinosaur Origin Problems

A recent paper by Kevin Padian (2013) promoted two ideas: “I suggest two changes in thinking about the beginning of the ‘‘Age of Dinosaurs’’: first, the event that we call the (phylogenetic) origin of dinosaurs was trivial compared to the origin of Ornithodira; and second, the ‘‘Age of Dinosaurs’’ proper did not begin until the Jurassic.”

Yes, this is a ‘think piece’,
and it’s a great summary of dinosaur thinking throughout the last 200 years, but it doesn’t represent current thinking. Padian is still trotting out old paradigms parked within this “history of paleontology” article. A couple of problems here:

First, there is no such clade as the Ornithodira. 
Because it contains both dinosaurs and pterosaurs, each of which occupy positions on opposite branches in the large reptile tree, the “Ornithodira” includes the same taxa as the Reptilia (= Amniota). Padian still clings to the unsupportable and falsified hypothesis that pterosaurs are sisters to dinosaurs and also keeps the blinders on with regards to the Fenestrasauria.

Second, Padian’s 3 Reasons for a Jurassic Age of Dinosaurs are not news.

1. Ornithischians do not appear until the Jurassic
Granted, but their poposaur dinosaur sisters are known throughout the Triassic (Lotosaurus = Early Triassic). Padian does not realize that poposaurs were dinosaurs. Neither does Padian recognize that Daemonosaurus nests as a basal ornithischian from the Triassic.

2. Saurischian dinosaurs were larger in the Early Jurassic.
Granted, but this is old news. And they don’t get really big until the Late Jurassic, tens of millions of years later. Even so, factor 3 comes into play…

3. All non-crocodylomorphs “pseudosuchians”(= rauisuchians, phytosaurs, aetosaurs) become extinct prior to the Jurassic.
Granted, but this is old news. Their extinction does indeed clear the slate for the radiation of dinosaurs and, lest we forget… crocs, which invaded marine environs.

Padian reports, “This review began by parsing the question of the origin of dinosaurs into three kinds of problems: dinosaur monophyly and relationships; dinosaurian functional-ecological advances; and the timing and pacing of dinosaur origins and diversification.”

Unfortunately Padian shows up with bad data as he reports, “It was not only dinosaurs but also their closest relatives –lagosuchids, lagerpetids, silesaurids and pterosaurs – that shared a suite of structural, functional and metabolic features that differentiated them considerably from other reptiles before the Late Triassic onwards.”

According to the large reptile tree, lagerpetids and pterosaurs were not related to dinosaurs. So those metabolic features did not differentiate ‘ornithodires’ from other reptiles. Rather, these three disparate clades attained similar abilities and morphologies by convergence. Lagerpetids and their chanaresuchid sisters did not survive into the Jurassic. Neither did the nonvolant relatives of pterosaurs.

To his credit
Padian devotes a page to showing how Rotodactylus (Peabody 1948) ichnites do not fit Lagerpeton feet as Brusatte et al. (2011) tried to force fit. We looked at this earlier here.

To his discredit
Padian ignores prior literature (Peters 2000, 2011) that matched Rotodactylus ichnites to basal fenestrasaurs like Cosesaurus. He kept his blinders on.

Reference
Brusatte SL Niedźwiedzki G and Butler RJ 2011. 
Footprints pull origin and diversification of dinosaur stem-lineage deep into Early Triassic. Proceedings of the Royal Society of London, Series B, 278, 1107-1113.
Padian K 2013. The problem of dinosaur origins: integrating three approaches to the rise of Dinosauria. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, Available on CJO 2013 doi:10.1017/S1755691013000431
Peabody FE 1948.  Reptile and amphibian trackways from the Lower Triassic Moenkopi formation of Arizona and Utah.  University of California Publications, Bulletin of the  Department of Geological Sciences 27: 295-468.
Peters D 2000. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605

Pterosaur ornithopters: lessons learned

Following in the success of the Dr. Paul B. MacCready‘s 1985 flying Quetzalcoatlus ornithopter (Fig. 4), a few years ago there was an attempt at getting another very complex pterosaur ornithopter to fly.

Margot Garritsen is a Dutch engineer and Stanford professor who led a team intent on building a flying pterosaur based on Paul Sereno’s ornithocheirid from the Sahara. They were counting on greater success with lighter materials and a more accurate wing movement with not one, but five wing joints for flight control. Several paleontologists were team members and Hall Train provided some of the mechanics. So it had everything going for it. The project was featured in the IMAX film “Sky Monsters.”

Figure x. The Stanford pterosaur ornithopter moments after dropping from its mothership. On this second attempt all the fur and non-essential material had been removed.

Figure 1. The Stanford pterosaur ornithopter moments after dropping from its mothership. On this second attempt all the fur and non-essential material had been removed. A removable horizontal stabilizer with twin rudders is added as a sort of stabilizing tail. Note, this is a deep chord wing membrane configuration, which pterosaurs did not have.

Unfortunately
the new and improved ornithopter failed to flap and failed to fly.

Another inventor, Kazuhiko Kakuta
using a much simpler design (Figs. 2, 3), created a successfully working ptero-ornithopter.

Cheaper. Simpler. Less accurate.
Actually, almost nothing is more pterosaur-like than bird-like here other than the fashioned crest. The key here appears to be the successful creation of sufficient thrust and lift without a cambered airfoil — as in any toy bird-like ornithopter.

For those interested ornithopters are explained here.

Figure 1. Pterosaur ornithopter. This model flies well and for good reason.

Figure 2. Pterosaur ornithopter. This model flies well and for good reason.

An efficient flapping wing must be able to flex and/or rotate: if a static wing is kept at the same angle while moving up and down, it will produce no net lift or thrust. Flexible wings can attain efficiency while keeping the driving mechanism simple. In Ornithopters its the ventral and dorsal curling of the wing during flapping that changes the wing shape and creates lift and thrust.

Read about the model maker here with his other pterosaur YouTube videos listed.

Figure 2. Click to see video. This pterosaur ornithopter folllows the basic plan of bird ornithopters in having a stiff leading edge and a flexible trailing edge. There's no need for complex flapping cycle. Up and down works pretty well.

Figure 3. Click to see video. This pterosaur ornithopter folllows the basic plan of bird ornithopters in having a stiff leading edge and a flexible trailing edge. There’s no need for complex flapping cycle. Up and down works pretty well.

Most ornithopters have extremely simple motions and deep chord wing shapes.

What would happen if the wing had a camber, a narrow chord and a spoon-shaped wing tips, as in pterosaurs? So far, except for the MacCready invention (Fig. 4), no one has built a short chord. long wing ornithopter and even the MacCready invention did not have the proper pterosaur wing shape and leg configuration.

So there’s an opportunity here to do something great for an engineering student: replicate a real pterosaur and make it flap using simple ornithopter techniques.

Figure 3. Quetzalcoatlus model ornithopter by Paul Macready getting walked to its take-off point.

Figure 4. Quetzalcoatlus model ornithopter by Paul Macready getting walked to its take-off point. The tucked in legs are based on the bird-like hypotheses of Dr. Kevin Padian, now widely regarded as wrong. No fossils preserve this configuration. Rather the legs would have been more or less splayed in flight.

Dr. Paul B. MacCready is famous for creating a dang big ornithopter the size and shape of a Quetzalcoatlus back in 1985. Here it is on YouTube. Here is a pdf of the project. It flew very successfully. There’s a Popular Science article here about MacCready’s work.

Still…
It would have been better to extend those hind limbs like horizontal stabilizers on airplanes (Fig. 5), but they were listening to Kevin Padian back then and he saw pterosaurs as very bird-like. Now that we know they were more lizard-like, pterosaur configurations have changed. 

Rhamphorhynchus model by David Peters

Figure 5. Rhamphorhynchus model by yours truly. Note the narrow chord long wings and feet splayed like a horizontal stabilizer. The raised elbows produce more camber proximally. The tail is an unnecessary secondary sexual characteristic.

For a change of pace, here’s a video that shows a small simple pterosaur-shaped airplane powered by propellers. So basically, it’s an airplane.