Pterosaur physiology

[JimC]

"Recent articles on the impact theory have stated that the Chicxulub event would not have had sufficient energies to cause the global devastation postulated in the classic model,"

What is the energy range currently estimated for the impact?
How many simultaneous Tzar Bombas would that be equivalent to?
I could calculate those numbers myself - but I'm lazy.

Some dinos did survive - we call 'em birds.
As an aside, the effects of the impact were the primary reason for the demise of the pterosaurs (they were not dinos). I would expect that large and small, they were most likely gone worldwide within a month of the impact, possibly less. There were no large soaring birds before the impact, but for the obvious reasons, I would expect small birds to to make it through when pterosaurs couldn't. It took large soaring birds 5 to 10 million years to develop after the pterosaurs were gone.

BTW, this is me out in my front yard holding the left humerus of one of the larger Late Cretaceous pterosaurs. Shoulder is in my right hand, elbow in my left.

 

[JimC]

As an aside (I have a weakness for asides......)
There was a lot of morphological variability between pterosaur species.
The white leg in the attached photo is a cast of the right femur and tibia of the small morph of Quetzalcoatlus (4.8 meter wingspan).
The small brown leg is Anhanguera piscator (5.05 meter wingspan).
The dark grey humerus in my previous post was from the large morph (Quetzalcoatlus northropi -10.4 meter wingspan).

My apologies for not sweeping my driveway before taking the picture.

 

[Vertigo]

As an aside (I have a weakness for asides......)
There was a lot of morphological variability between pterosaur species.
The white leg in the attached photo is a cast of the right femur and tibia of the small morph of Quetzalcoatlus (4.8 meter wingspan).
The small brown leg is Anhanguera piscator (5.05 meter wingspan).
The dark grey humerus in my previous post was from the large morph (Quetzalcoatlus northropi -10.4 meter wingspan).

My apologies for not sweeping my driveway before taking the picture.
View attachment 110887

I thought the pterosaurs had three 'fingers' at about half wing length and the fourth finger braced the remaining length. But that one seems to have four about the same size?

 

[JimC]

Possibly because you are thinking about fingers, and that's a foot.

Another aside - the fingers are always at the distal end of metacarpal IV, but there is a a lot of variability between the relative lengths of bones between species, so the location of fingers along the semispan can vary quite a bit between species.
BTW, in illustrations the fingers are usually shown protruding forward during flight - they can achieve that position, but it isn't how they were carried in flight.

On the ground, the fingers of the hand become the front foot, and when phalange IV is folded aft into the terrestrial position tendon connections pull phalange one so that it is directed forward and somewhat outboard, while phalange two is pulled more outboard. Three is pulled enough to be directed more or less aft. Again, there is a lot of variability between species.

 

[JimC]

Here is a left front foot of the small morph of Quetz seen from outboard looking in toward the midline. Fingers one through three have been omitted. Finger four is folded back up between the elbow and torso for protection.

The other photo is the same joint as seen from below, looking straight up. Other fingers still removed.

Finger three (omitted) lies between this open joint and the ground to protect it.

 

[JimC]

Here's a Pteranodon right foot seen from the bottom looking up. As you can see, the toes are NOT the same length.

The lump sticking out to the side is Metatarsal five. It accepts the distal tensile loads from the uropatagium (the tail membrane) and loads them into the leg as compression. Since pterosaurs can't lift their legs into flight position by muscle power alone, they do it by creating flight loads on the uropatgium and transferring those into the leg.

 

[Matteo]

Mods...please invent a "jealous" emoji so I can respond to @JimC in the way young folk do these days.

 

[JimC]

Matteo, I'm not a young folk, so that went right over my head
Nothing to be jealous of, far as I know.

Another aside, in the photos of the Quetz hand/front foot above, the joint/articulation between metacarpal IV and phalange IV-1 is what I call the wing finger pivot, the joint where your ring finger connects to your palm (pterosaurs didn't have a pinky finger - they did have a pinky toe).

Another aside (that sounds like trivia, but isn't) is that if birds and pterosaurs had palms, birds would fly palms down while pterosaurs fly palms forward - what I am actually describing is major differences in the locus of wrist articulation. Pterosaurs powered their flapping flight very differently from birds and were more powerful flappers - but they couldn't keep it up for as long as birds. They were also better at soaring than birds, but keeping in mind the limited duration of their ability to flap, combined with their limited fat stores as compared to birds meant they couldn't survive as long when conditions were unsuitable for soaring. There was a period after the impact when conditions were unsuitable for soaring throughout most of the world, and it whacked the pterosaurs without nailing the birds.

 

[JimC]

There's a LOT of variability in pterosaur pectoral girdles.
The one shown here is a left scapulocoracoid for the small morph of Quetz.
It has a number of specialized adaptations that greatly enhance the flapping power relative to other pterosaurs (and birds).

 

[JimC]

And here is a Quetz torso. Only 4 vertebrae are unfused. Pterosaur ribcages don't expand like the mammalian ribcage. Instead, flexing the unfused vertebrae in the spine down and up moves the diaphragm fore and aft, deflating and inflating the tiny lungs inside the fixed ribcage. Pterosaurs are more pneumatic than birds, but span for span, their necks tend to be longer, increasing dead air volume, and their lungs smaller, decreasing pumping capacity. Consequently, they are flap-gliders, mostly soaring with occasional intermittant short duration flapping.

 

[JimC]

"How much did pterosaurs act and feed on ground?"

Depends upon the species. Compared to birds, not all that much.
As an aside, they were quadrupedal on the ground though their ancestors were bipedal.

 

[JimC]

In the movies, they get pterosaur flight mechanics wrong too. What particularly bugs me is flexing the wrist and wingfinger pivot in the wrong direction.

 

[chornedsnorkack]

When referring to pterosaurs, what do you mean by 'fledged'??

Ah yes - ambiguous. Because for birds, it often means "having feathers".
Pterosaurs, and bats, do not have feathers. What I mean is "having the ability to fly".

"young of a large pterosaur species from an adult of a small species?"

Generally, by appearance. Bone morphology.

Looking up, seems that pterosaurs generally had determinate growth. Which means a small pterosaur could be identified as a grownup if it is?

 

[JimC]

In some cases, yes. Preservation is usually spotty, particularly so in small specimens.
Small adult pterosaurs are usually insectivores.
Mid to large sized pterosaurs are usually piscavores.
When preserved, their heads are very differently shaped.
Usually their necks are as well.

BTW, you have to be somewhat cautious about what you see in the literature.
For example, the current consensus in the paleo community seems to be that the two morphs of Quetz were shoreline scavengers, largely because the mandible shape of the small morph supposedly wasn't suited to skimming (head of the big guy isn't preserved). However, during virtually all of the half century it has been known, Quetz was embargoed - only about roughly a dozen people have had unfettered access to the original fossils and casts during that time (I'm one of the dozen). As a result, some really goofy stuff has been written about Quetz by people who had no access and have never seen one. As it happens, the Quetz mandible is ideally shaped for off-shore skip-skimming, though unsuited for tuck and pluck feeding. I have no doubt that they would happily scarf down any tasty looking morsal they might happen to see lying about on the shore, but they weren't really well adapted for that.

Here's a Quetz head; draw your own conclusions.
BTW, notice the low position of the eye socket near the jaw hinge.

 

[chornedsnorkack]

In some cases, yes. Preservation is usually spotty, particularly so in small specimens.
Small adult pterosaurs are usually insectivores.
Mid to large sized pterosaurs are usually piscavores.
When preserved, their heads are very differently shaped.
Usually their necks are as well.

BTW, you have to be somewhat cautious about what you see in the literature.

Seems that flaplings fledged at fairly small sizes, even of large species. Which means they grew through large size range while flying.
What did flaplings eat?

 

[JimC]

Nobody really knows. Insofar as I know, no preserved stomach contents have been found for hatchlings. I suspect grubs, insects, minnows, etc - but that's just speculation.

"fairly small sizes, even of large species"

Yeah, adult torsos were quite small. The small morph of Quetz for example was unusually robust, but even with a 4.8 meter span, the distance from hip to shoulder was only about 15 inches (hip to acetabulum 12.25 inches). The torso of a 5 meter Anhanguera was much smaller. In general, there wasn't a lot of volume within the torso available for eggs.

 

[JimC]

Speaking of size, this photo shows the left humerus of the two morphs of Quetz, seen from the front, and the left scapulocoracoid (shoulder girdle) of the small morph seen from the rear. The 'paddle' sticking down from the shoulder is the deltopectoral crest. It is what allowed the azdarchids to become larger than other pterosaurs. Muscles connecting it to the coracoid flange provided additional downstroke power. The shoulder socket was moved downward on the girdle to provide more upstroke power for the back muscles. This photo was taken with a telephoto lens, so my arms in the background are at pretty much the same scale as the bones. The big guy had a 10.4 meter wingspan; the small one about 4.8 meters.

 

[chornedsnorkack]

So the pterosaurs soared well, but tired quickly when they had to flap, and in fair weather were liable to get becalmed, like albatrosses...

How do the proportions of pterosaurs compare to pelagornithids? Wingspan also exceeding 6 m?
Pelagornithids appeared just 4 million years into Tertiary, and died out in Quaternary for some reason. Seems that in the last hundred million years, there has not been five million years in a row that giant soarers have not been skimming the seas...

 

[JimC]

Largest pelagornithids had about a 22 foot wingspan (pretty much the maximum for birds.
Largest pterosaurs had about a 34 foot wingspan.

"and in fair weather were liable to get becalmed, like albatrosses..."

Depends upon what you mean by fair weather. Anytime they had a bit of wind and some waves upon the water after launching, they were good to go. They didn't need either to launch. They were a bit better at soaring than albatrosses and Frigate Birds, and were far more powerful flappers. Their quadrupedal launch from a standing start in a dead calm also got them off the ground far more effectively than birds (which is how they sidestepped the square-cube rule). Their hands (front feet) were the last thing to leave the ground, and they could launch without difficulty in conditions that would ground albatrosses. Couldn't flap as long though - just more powerfully.

 

[JimC]

Here's a teratorn humerus (span about 22 feet).
Compare the robustness against Quetzie.