Tag Archives: pterosaurs

The largest pterosaurs have not been grounded yet

In one post (New evidence on the size of pterosaurs) we explored the study by Henderson (2010) in which he modeled pterosaur body forms to generate estimates of body mass. He modeled different areas of the body separately, applying various densities to the different body sections to calculate his masses. His results suggested that the largest pterosaurs like Pteranodon (wing span of 17.5 feet) and Anhanguera (wingspan 13.5 feet) weighed about as much as the heaviest flying birds (41 and 14 pounds respectively). He reasoned that birds represent a reasonable analogy for flying limits in vertebrates, so this range of masses could represent the upper limit of being able to have powered flight in vertebrates.

His results for the giant pterosaur Quetzalcoatlus were astonishing. His calculations suggest that this animal weighed in at 1200 pounds, with a wingspan of almost 37 feet. After discussing various ways to interpret this result, Henderson suggested that maybe these truly giant animals did not fly at all, but were secondarily terrestrial. This evolutionary track can be found among the birds with giants like ostriches and emus growing large and losing the ability to fly.

The giant pterosaur Quetzalcoatlus northropi compared to a modern giraffe. Illustration by Mark Witton.

The giant pterosaur Quetzalcoatlus northropi compared to a modern giraffe. Illustration by Mark Witton.

Henderson’s work and conclusions was challenged by Witton and Habib (2010). Their criticisms involve several arguments. First, they suggest that birds may not be the best models for flight capacity, and that wing structure, overall anatomy, and launch mechanics were very different in pterosaurs. If so, then using birds as models for flight requirements and limitations in pterosaurs could significantly skew the results.

The heart of the arguments of Witton and Habib are the estimates of wingspan and mass suggested previously for pterosaurs. They note that relatively modest difference in wingspan calculations could have dramatic implications for calculations of mass. They state that mass estimates for a pterosaur with a 43 foot wingspan would be almost twice the estimate for a pterosaur with a 33 foot wingspan. Their assessment of the fossil material suggests that no pterosaurs had a wingspan of greater than 33-36 feet.

Likewise, Witton and Habib are critical of the body shape models used by Henderson for Quetzalcoatlus, arguing that his estimates of body size were too large, and were responsible for the very high mass values he obtained. Combined with Witton and Habib’s wingspan estimates, they calculate a body mass for Quetzalcoatlus of about 440 pounds, about one third the value of Henderson.

All of this discussion about wingspans and weights teases us with the question we really want to know—did the largest winged animals ever known actually fly? Could we have looked up into the Mesozoic skies and seen an animal flying overhead with a 34 foot wingspan and weighing as much as a tiger?

The problem, as is often the case in paleontology, is a lack of fossil material. The preserved material of these large pterosaurs is very fragmentary, and this significantly impacts our ability to accurately estimate their overall size and mass. We have in these two studies outlined here two extremes. We need more fossils before we can really know which study is most accurate.

Also, it is likely that birds may not be the best models for pterosaur flight as pointed out by Witton and Habib. Birds do things very differently than bats, our only other modern flying vertebrate, and it is most likely that pterosaurs had unexpected adaptations. For example, Habib (2008) is finding evidence for a vaulting launch in the largest pterosaurs.

Check out this video on the Quadrupedal launch in pterosaurs for an interesting viewpoint.

The largest pterosaurs have not been grounded quite yet.

 

References:

Habib, M.B., 2008. Comparative evidence for quadrupedal launch in pterosaurs. Zitteliana, B28: 159-166.

Henderson, D.M., 2010. Pterosaur body mass estimates from three-dimensional mathematical slicing. Journal of Vertebrate Paleontology, 30(3): 768-785.

Witton, M.P. and Habib, M.B., 2010. On the size and flight diversity of giant pterosaurs, the use of birds as pterosaur analogues and comments on pterosaur flightlessness. PloS One, 5(11): 1-18.

 

New evidence on the sizes of pterosaurs

The flying reptiles, pterosaurs, were an amazing successful group of prehistoric animals. They ranged from the Late Triassic through the end of the Cretaceous periods, a span of time of about 156 million years. That is over 2 times longer than the time since dinosaurs became extinct, and mammals have dominated the terrestrial landscape.

Pterosaurs were the first vertebrates to achieve powered flight, followed later by the birds and bats. However, during their hay-day, pterosaurs achieved an incredible range of diversity in form and size, and occupied countless niches within the Mesozoic world.

Interestingly enough, the first pterosaur remains to come from North America were found in Kansas. Flying reptiles had been known from Europe, but during an 1870 collecting trip through the western territories, O. C. Marsh stopped off in Kansas. Near the end of the trip he spotted a long, slender bone weathering out of the chalk formation, and collected what he could before heading back to Yale on the train. He thought the bone looked like the finger bone of the pterodactyls from Europe, but this bone was much larger. He estimated the wing-span to be 20 feet. The next year, he traveled back to collect the rest of the animal in the Kansas formation, and found that in fact his estimate of its giant size was correct. He named this new animal Pteranodon.

Greg dusts the life-sized models of Pteranodon sternbergii in the Sternberg Museum of Natural History

Greg dusts the life-sized models of Pteranodon sternbergii in the Sternberg Museum of Natural History

As more and more flying reptiles have been found in the fossil record, as basic question about them has puzzled scientists—how well could they fly? Estimating the body mass is a fundamental part of this inquiry. We can look at modern birds and see the constraints that flight dictates for body mass at least today. How do the pterosaurs compare?

In a recent publication, the question of body mass in pterosaurs is addressed (Henderson 2010). In the most detailed study yet of pterosaur body mass, Henderson set out to explore this question and to compare the results to birds. He created a model of body mass based on modern birds by creating digital, three-dimensional models of their bodies. His model was corrected for differences in density from different areas of the body. For example, the wings will have a different average density than the trunk, where the volume of the lungs greatly impacts its overall density.

Using birds, he refined his model to accurately calculate their masses and centers of gravity. Then, he turned to the pterosaurs. What he found was very interesting. The pterosaurs in his study ranged from less than an ounce for Anurognathus to an astonishing 1,200 pounds in mass for Quetzalcoatlus (more on this in a moment).

The giant pterosaur Hatzegopteryx compared to a modern giraffe. Illustration by Mark Witton.

The giant pterosaur Quetzalcoatlus northropi compared to a modern giraffe. Illustration by Mark Witton.

Excluding the giant Quetzalcoatlus for a moment, the other heaviest pterosaurs were Pteranodon at 41 pounds and Tupuxuara at 50 pounds. The estimates for the ancient fliers are not too far off the masses of the largest modern flying bird the Great Bustard, at 35 pounds. So, we know that it is at least possible for an animal of that weight to get airborne on a regular basis.

So, what about the giant Quetzalcoatlus? This animal is known from fragmentary remains from Texas where it was first found in 1971. While mostly known from fragmentary remains it is estimated that it had a wing span of 37 feet or more. Earlier estimates of the weight of this animal vary widely from 141 – 608 pounds. Henderson points out that many of the body mass estimates of the past were influenced by engineering constraints calculated for an animal with this great wing span to be able to fly. The thinking being that an animal evolved from flying animals most likely flew.

But, in an interesting twist, Henderson’s estimate is twice as much as previous estimates, so he turns the issue around and suggests the heresy that maybe giants like Quetzalcoatlus (and I would add Hatzegopteryx by extension) did not fly. Instead, it is perfectly reasonable to assume that a formerly flying species secondarily adapted to a fully terrestrial life style, growing to dramatic size as a protection from predation or for other similar advantage. We certainly can find examples of that in the modern birds too, in the flightless ratites, the emus and ostriches.

No doubt this issue will continue to be explored (for an alternative view see The largest pterosaurs have not been grounded yet) . That is the fun of science—keep probing and answers, and more questions, reveal themselves.

Henderson, D. M. 2010. Pterosaur body mass estimates from three-dimensional mathematical slicing. Journal of Vertebrate Paleontology 30(3):768-785.

Related Posts:
Formations
Niobrara Chalk
My National Geographic moment

My National Geographic moment

“A photographer from National Geographic wants to talk to you.” These words, or words to those effect, met me as I came into the museum office one day back in 2001, and they definitely caught my attention.

It was 2001 and I was Assistant Director of the Sternberg Museum of Natural History. We had just reopened the museum in its new location in Hays, Kansas, a few years before in 1999. The museum had enjoyed some tremendous success at attracting visitors and media attention from across the state. And now someone from National Geographic wanted to talk to us? Wow. I returned Jonathan Blair’s call and began an unusual week of activity.

It turns out that the magazine was going to run a story on pterosaurs, the flying reptiles from the Mesozoic, and they hired Jonathan to get pictures to illustrate it. He had already traveled to some of the great museum collections for pterosaurs in Europe and the United States, but he wanted to visit Sternberg. The Sternberg’s collection of pterosaur material is about the third or fourth largest in the nation, and very significant.

The Sternberg Museum, on the campus of Fort Hays State University, was managed for many years by George F. Sternberg, famed fossil collector. He spent his free time out in the chalk, the Niobrara Formation of western Kansas, collecting the fish and swimming and flying reptiles that left their remains millions of years ago. Sternberg supplemented his salary at the museum by selling specimens to other museums, but if he collected something really nice it went into “his” museum. Over the years, the museum’s collection grew in size and quality.

Besides our amazing collection of fossils, Jonathan had heard about our life-sized pterosaur models we had just installed in our walk-through Cretaceous exhibit. And he had a crazy idea—let’s take a life model of the beast and “fly” it over the very rocks where its remains can be found. He wanted to take one of our life-sized model and photograph it over the chalk beds.

Well, I can bend over backwards for National Geographic, but taking one of our brand new models down from the ceiling, which had not been easy to install in the first place, and which since had walls built up around them, and truck them 70 miles to hang from a crane in the chalk sounded a bit risky to me.

But I did offer to help in any way we could, so I did the next best thing—I found him another pterosaur model.

Over the next several days we made plans and preparations for the big event. We needed to get the model that I was able to find shipped to the museum. It had been kept in storage and was a little beaten up, but the company that supplied it sent a staff member to clean, fix it, and touch up the paint for its big moment. The model, being life-sized, had a twenty foot wing span, flimsy neck with a large head at the end, and feet that stuck out the back, giving the whole thing a cross shape, making it too long in any direction. Not exactly the easiest thing to get into a truck and ship!

We scouted a location for the big photo shoot. I took Jonathan to the Castle Rock area, a well-known outcropping of the chalk that has easy access and grand vistas. We needed to secure special permission as we were going to bring in a crane and another truck to transport the pterosaur model.

We needed to arrange for a crane to make the 70 mile one-way trip from Hays to the chalk beds. On this, and on so many other occasions, I marveled at the “can do” spirit of western Kansas people. You want something done just ask a former farm kid. While he might look at you funny, he will get it done.

In between all this activity, I remember some spectacular meals shared with Jonathan, listening to his many adventures from around the world while taking photographs. He also shot pictures around the museum, and he took a couple of photos of me that I have cherished ever since.

Greg dusts the life-sized models of Pteranodon sternbergii in the Sternberg Museum of Natural History

Greg dusts the life-sized models of Pteranodon sternbergii at the Sternberg Museum of Natural History. Photograph by Jonathan Blair.

The big day arrived and all was going well. The weather cooperated, the truck was loaded with its ungainly cargo, and the crane made it to the site. We had also brought along a number of crew members to help hold the model. We wanted to lift it into the air for the photograph, but if you know anything about western Kansas, you know it is windy. I was not sure what would happen when you lifted such a thing into the gusty winds, and how hard it might be to control. The only control we had were guy-wires coming down from the wing tips to hold it against unruly behavior.

With trepidation we gave the signal to the crane operator to lift, and the hundred pound model took to the air. And in the end, the wind was no issue—the model, like the animal it represented, was built for the air. It found a comfortable equilibrium and settled into the wind easily. Jonathan snapped his pictures, and just like that we had what he had come after.

Life-sized model of a pterosaur, an ancient flying reptile, soars onces again over western Kansas

Life-sized model of a pterosaur, an ancient flying reptile, soars once again over western Kansas

We took more photos at a few other locations, all of which could have made fantastic desktop images, but he knew he was done. We packed up and came home, and all those days preparation resulted in the lead image for the story. It was all Jonathan’s photo and idea, and I enjoyed the part I played in making it happen—one of the perks for working at a museum.

See the National Geographic story.

Jonathan Blair’s web page

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Geologic Formations

Niobrara Chalk

One of the most famous formations is the Niobrara Chalk. This formation is exposed in northwest Kansas and southern Nebraska. Formations are sometimes divided into members, subsections of the formation based upon its rock type. The Niobrara Chalk has two members: the lower Fort Hays Limestone and the upper Smoky Hill Chalk. It is the Smoky Hill Chalk which is best known for its fossils.

The sediments that comprise the Niobrara Chalk were deposited in the Western Interior basin during the Late Cretaceous. At that time sea levels rose and the interior of North America was inundated by a shallow sea, the Western Interior Sea. The sea cut North America in half by spreading from the Gulf of Mexico to the Canadian Arctic. Volcanoes to the west, in what is now Utah and Nevada, spewed ash into the sea and sediments eroded from mountains along the western coast were washed into the sea by rivers. What is today Kansas was much closer to the eastern shore of the sea, a low alluvial plain, also gently washing sediment into the sea basin.

Block diagram of the Western Interior Sea

Image from Hattin, 1982.

The upper member, the Smoky Hill, was deposited from 87 to 82 million years ago, so it preserves a five million year window into the past. Elsewhere we discussed that the Cretaceous sea had a wealth of planktonic organisms. Many of those organisms had calcium carbonate-based shells and body parts, which furnished a steady supply of material to sink to the sea floor. The consistent supply of sediment, both from land and sea, and conditions at the sea floor allowed for the excellent preservation of animals. Those that died and sank to the bottom were rapidly covered by the rain of sediment and entombed until today.

And the diversity of organisms preserved is amazing. In almost every museum with fossils that I have been in, I recognize fossils from Kansas. Giant marine reptiles (mosasaurs and plesiosaurs), flying reptiles (pterosaurs), great toothy fishes, large turtles, and toothed diving birds have all been found. Each of these groups has a very interesting story to share, and we will explore many of them here. An extensive website on fossils from the Niobrara Chalk can be found at OceansofKansas.com.