How To Evolve a Wing

Our Archaeopteryx show has bedazzling fossils – the only Archaeopteryx skeleton in the New World, complete with clear impressions of feathers. Plus frog-mouthed pterodactyls, fast-swimming Sea Crocs, and slinky land lizards. Today we learn the different ways in which wings evoloved on various prehistoric creatures.

Solnhofen show us three ways for Darwinian processes to construct a wing from a normal arm

Dactyls:
Dactyls evolved from very close relatives of early dinosaurs. The dinosaurs and their crocodilian kin are archosaurs. Archosaurs developed a unique asymmetry in the hand. Primitive reptiles, like today’s lizards, have five fingers, each with a strong claw. In archosaurs the outer two fingers are weak and have no claw at all.

Crocodilians and many dinosaurs kept this arrangement -  for example, stegosaurs and Triceratops had five fingers and three claws on the inner fingers. Meat-eating dinosaurs usually evolved three-fingered hands, doing away with those outer two claw-less fingers.

‘Dactyls evolved their archosaur hand in a different manner: they lost the pinky (the outermost finger). The claws on the inner three fingers were strong – useful for climbing trees and the sides of cliffs. The fourth finger evolved into an organ we see in no other creature: Finger four became immense, as thick as the thigh or thicker. The finger could be folded back where it joined the wrist for walking on the ground. When flying, the giant finger four was stretched outwards.

 Schematic of a generic pterosaur wing, pencil drawing, digital coloring
Creative Commons License photo credit: Arthurweasley

Solnhofen fossils showed that the wing surface was attached to the finger four and to the sides of the body and the inner edges of the hind leg. So ‘dactyls could flap like a bat – using up and down strokes of both arm and leg to make the power stroke.

Dinosaurs and Birds:

 Archaeopteryx

Birds evolved their wing by another wonderfully unique method. Their hand bones were 99% identical to those in small meat-eating dinosaurs. Only the three inner fingers were retained. Darwinian processes had clipped off the pinky and fourth finger. Solnhofen fossils prove that specialized wing feathers were attached to the second finger. So Archaeopteryx flew with the feathered arm.

Raptor-type dinosaurs, like Velociraptor and Microraptor, had evolved feathers very like those of birds. But these small dinosaurs evolved hind-leg wings to assist the arms. Flight feathers were attached to knee and shin as well as to the forelimb. When a tiny raptor-like dinosaur evolved into Archaeopteryx, the feathers were lost from the hind-legs, leaving just the arm to do the work of flying.

Bats:

Bats are specialized mammals and no bats had evolved in the Jurassic. The first bats appear much later, about 55 million years ago.

Bats use strong skin to make the wing. But unlike ‘dactyls, who evolved just one finger to support the wing surface, bats use three or four fingers to spread the wing and control the wing in flight.

Don’t miss Archaeopteryx: Icon of Evolution, currently on display at HMNS. Want to learn more? Check out our previous blogs on Archaeopteryx.

Solnhofen – Birthplace of Pterodactyls

Our Archaeopteryx show has bedazzling fossils – the only Archaeopteryx skeleton in the New World, complete with clear impressions of feathers. Plus frog-mouthed pterodactyls, fast-swimming Sea Crocs, and slinky land lizards. Today we learn about the different types of Pterodactyls that have been found at Solnhofen.

The Jurassic Air Was Full of Wings!

The First ‘Dactyl Ever Discovered – 1784, Solnhofen
In that year, Cosimo Collini thoroughly scrutinized a perfect skeleton of a curious creature preserved in the Solnhofen lithographic stone.

Jaws: long, slender, with sharp teeth.
Arms: very long, with an extraordinary finger that could be stretched out and  folded up.
Tail: very short.
Inner construction: bones hollow, like a bird’s.

Verdict: Not a bird, not a bat, but a new life form, never seen before.

More studies produced the name: “Wing-Finger,” Pterodactylus.

Solnhofen gave science a dozen more ‘dactyl species, some as large as a big seagull. Other Jurassic salt-water deposits produced specimens in England and France. Solnhofen still gave the best preserved ‘dactys. Some had the clear impression of the wing skin, connected to the single long finger on each hand.

Science Marches….BACKWARDS!

 William Buckland

Pterodactyl science has made a giant U-Turn in the last decades. Way back in the 1820’s, the best minds of paleontology were convinced that ‘dactyls walked and flew like bats. The Reverend William Buckland – “Mr. Jurassic” in England – drew up cartoons of Pterodactylus hanging onto cliffs like a bat, and fluttering over the Solnhofen lagoon with bat-style wings. His German colleagues agreed:  in design of wings and hind feet, ‘dactyls were definitely batty.

Then came the New Wave of ‘dactyl research in the 1970’s. Young Ivy League scholars went “tsk, tsk….that silly old Buckland. He was wrong.  Dactyls were really built like birds. All dactyls walked upright on their hind legs. They didn’t scuttle about in a bat manner.”

And so textbooks were revised. ‘Dactyls stood up and walked like Jurassic pigeons.

Footprints Back Buckland
But in 1980, a new set of evidence emerged – fossil tracks.  If the New Wave was right, then ‘dactyl tracks should look like bird tracks. The left and right hind feet should have swung back and forth close together, and the hands should have been kept off the ground.

Surprise! Fossil tracks made by small dactyls and by big ‘dactyls showed hind feet that were held out sideways. And the hands were flat on the ground! “Dactyls walked like………BATS!

The case is closed. Hundreds of trackways and bio-mechanical studies of shoulder and hips say the same thing. ‘Dactyls moved on all fours when on the ground, like bats.

Pterodactylus – Sand-Piper ‘Dactyl
The original ‘dactyl, the first species discovered..

Pterodactylus was the commonest ‘dactyl at Solnhofen. No bigger than a tiny sand-piper, Pterodactylus had extra long arms and neck and a compact body with almost no tail.

The thin jaws could be used to snatch small fish. Or the snout might have been used to probe the sand flats, like a shore bird, searching for hidden worms and baby clams.

The long neck, arms and short tail are proof that Pterodactylus was a Jurassic cousin of the enormous ‘dactyls of the Cretaceous, including the Texas Quetzalcoatlus.

Rhamphorhynchus – The Devil-Tailed ‘Dactyl
Rhamphorhynchus was a flying Fish-Trap. The jaws carried long, sharp teeth that slanted forward, and the tips of the snout and lower jaw were pointed too. This ‘dactyl  could dive down on the water and use its strong neck to throw the muzzle at fish and impale them.

The short arms made the wingstroke slower but more powerful than in Pterodactylus, so maximum speed was less but maneuverability was greater.

The long, bony tail was tipped with a vertical rudder of skin, reinforced by stiff fibers.

Mysterious Extinction
Long-tailed ‘dactyls went extinct in the Early Cretaceous and all the common ‘dactyl species of the Cretaceous were short-tailed relatives of Pterodactylus.  Why did the long-tails die out? What gave the short-tails their superiority?

The final extinction of all ‘dactyls struck when the last dinosaurs died out 65 million years ago, at the very end of the Cretaceous.

Anurognathus - Frog-Mouthed Mini-‘Dactyl
Jewel of the Solnhofen Exhibit.

Rarest of the rare, with only two specimens known, is the famous “Frog-Mouthed ‘Dactyl,” Anurognathus.

The Frog-Mouth breaks all the ‘dactyl rules. It’s super-tiny, half the size of Pterodactylus and about as bulky as the average little brown bat that hovers over Texas meadows today. And unlike nearly all other ‘dactyls, the Frog-Mouth doesn’t have a long snout. Instead the mouth is short and very wide.

The Frog-Mouth design is what we’d expect from an aerial insect-hunter, a ‘dactyl that hunted the dragon-flies and beetles of the tropical Jurassic sky. The short tail and abbreviated wrist bones would make quick turns easy. The wide mouth would work like a bug-trap.

Night Flier?
Anurognathus had the biggest eyes for it’s head size of any Solnhofen ‘dactyl. The acute visual system is a clue to unusual habits. Perhaps the Frog-Mouth was an insect-eater who flew in the darkness. More insects get airborne in the evening than during the daylight, so there would be more targets. And the eyes would have to be enlarged to detect  prey in low-light environments.

Don’t miss Archaeopteryx: Icon of Evolution, currently on display at HMNS. Want to learn more? Check out our previous blogs on Archaeopteryx.

The Man Who Made Fossil Fish Famous

Our Archaeopteryx show has bedazzling fossils – the only Archaeopteryx skeleton in the New World, complete with clear impressions of feathers. Plus frog-mouthed pterodactyls, fast-swimming Sea Crocs, and slinky land lizards. Today we learn about the Louis Agassiz and his theories.

Louis Agassiz (1807-1873)

Paris and the Lure of Fish, 1836
Agassiz grew up in Switzerland where he excelled as a student in  chemistry and natural history. He went to Paris to study fish fossils under the Father of Paleontology, Baron Georges Cuvier. The geological history of fish seemed muddled at the time. Agassiz brought order to the fins and scales.

“There’s order in the way fish changed through the ages…” Agassiz concluded. He was the first to map out the long history of fish armor, fish jaws and fish tails.

1) The earliest time periods, the Paleozoic Era, most bony fish carried heavy armor in the form of thick scales covered with dense, shiny bone.

2) In the middle Periods, the Mesozoic, the armored fish became rarer and were replaced by fish with thin, flexible scales.

3) In the later Periods, the Cenozoic, thin-scaled fish took over in nearly all habitats.

4) Today, the old-fashioned thick scales persist only in a few fresh-water fish like the gar.

5) Tails changed too. The oldest bony fish had shark-like tails, with the vertebral column bending upwards to support the top of the fin. Later fish had more complicated tail bones, braced by special flanges, and the base of the tail was more symmetrical.

6) Jaws in the earliest bony fish were stiff, like the jaws of crocodiles. Later fish developed jaw bones that could swing outwards and forwards.

Discovery of the Ice Age
As he traveled across Europe, Agassiz saw evidence of giant ice sheets that had covered the mountains and plains. According to Agassiz’s theory, New England too had been invaded by mile-high ice layers. Giant hairy elephants – woolly mammoths – had frolicked in the frigid habitats. At first,  scholars harrumphed at Agassiz’s idea of a Glacial Period.  But by the mid 1840’s the theory was proven beyond a reasonable doubt.

Boston 1846: Toast of the Town & the New Museum
Fish and glaciers made Agassiz the most famous scientist of his time. When he came to Boston in the 1846, his lectures were so successful that the New England intellectuals wouldn’t let him leave. Poets and politicians, rich merchants and artists all helped raise funds to get Agassiz a professorship at Harvard. He repaid the support by working tirelessly to build a grand laboratory of science and education at Harvard – the Museum of Comparative Zoology. Opened in the 1859,  the MCZ has been a leader in fossil studies ever since.

Design in Nature
Agassiz’s interests spread beyond fish and glaciers. He sought the Plan of Creation, the key to understanding all of Nature. Was it  Evolution? No. Agassiz rejected any notion that natural processes somehow had transformed one species into another. He was a fierce exponent of the theory of Serial Creation: every species of fossil creature was created to fill its ecological role in its special geological time zone.

Darwin and Agassiz
Though he fought Darwin’s theories for his whole life, Agassiz’s work in fact provided support for the new views of evolution. The long trends in fish fins and scales were best explained by Natural Selection. Agassiz’s best students at Harvard went on to become strong supporters of Darwinism.  Endowed faculty positions were established in Agassiz’s name.  Agassiz Professorships were given to Alfred Sherwood Romer, the greatest Darwinian  paleontologist of the 20 century, and to Stephen Jay Gould, the most eloquent defender of Darwin in the last thirty years.

Don’t miss Archaeopteryx: Icon of Evolution, currently on display at HMNS. To read more about Agassiz and Darwin, check out my earlier blog.

Archaeopteryx and Friends

Archaeopteryx and Friends
A virtual visit to a Jurassic wild animal preserve
By Neal Immega, Paleontologist

Is it a bird? or a dinosaur? Archy is both. We have the best-preserved Archaeopteryx on display in our basement and you can see all sorts of significant evolutionary developments such as a semi-lunate metacarpel in the wrist, hallux to the side, elongate tail, furcula, a large second digit claw on the hand, a sternum without a keel and all sorts of other highly abstract features that confirm that Archy is both a bird and and a dinosaur. Come and see me and I will debate both sides of the question until you run screaming out of the room. There are literally oceans of virtual ink written about this critter.

BUT WAIT, we have so much more. I want to introduce you to some of the other things that we have that are really significant and just plain cool.

Geosaurus – A Marine Crocodile with a shark like tail but still has legs.

Marine Crocodile
I know that you are thinking about salties (crocs living in saltwater) down under, but you are still thinking within the box. Envision an island with limited species living on it, protected from outside influences by a deadly ocean. Species would evolve to fill every available niche, just like the kangaroos in Australia occupy all the herbivore niches from squirrel to sheep but are still recognizably ‘roos. What would a croc look like if it evolved to take over the role of a marine predator? It could look a whole lot like an Ichthyosaur (see the one in the paleo hall by the freight elevator).  Amazingly enough, we have caught it part way through the process of adapting to sea life:  it has limbs even though it also has a shark-like tail. I wonder if we will ever find a croc without legs that gave live birth and thus never left the water. What an amazing mix of characteristics!

Marine Lizards
Consider a hypersaline sea that was so toxic that anything that fell in it died and was preserved perfectly because there were no bottom scavengers. Lizards seem to be able to live under the very harshest conditions, but there is only one type on this island. The last surviving remnant of this group is the New Zealand Tuatara, a very strange beast. It has a double row of teeth on the upper jaw and a single row below.  The teeth are just projections of the jaw bone. Another feature that can also be seen in fossils is there is a hole in the top of the skull for a “third eye.” Today, the third eye is non-functional, but I bet it was in the far past. Our exhibit has a whole collection of these lizards that lived on land, and they look a lot like modern lizards. BUT, there are also two specimens with vastly more ribs and tail vertebrae, as if the creature occupied the niche of eels, but eels with legs! This is another transitional form, adapting to marine life but retaining some of the features of land animals.

Tuatara family lizard living on land

If you look at the specimen in Room 13 with a magnifier and a light, you can SEE the place where the third eye was.

Horseshoe Crab
We can make up a story about our horseshoe that’s so sad that you will want to cry. Envision a little horseshoe crab bumbling around the shallow water eating little things from the mud. A wave crashed in and washed the crab out beyond the fringing reef of the Solnhofen sea. The crab landed on the bottom on his back (it swam top-side-down), struggled to turn over and made marks in the soft sediment. The crab was very tough but the environment did not provide any oxygen and the hypersaline water burned its gills. It tried moving, but things did not get better. The current rolled some empty ammonite shells on the bottom, making tire track-like track marks. The crab turned again, and things did not get better. The crisp mark made by its dragging tail became a dashed line on the bottom as it tried to swim out of there, but it could not. Finally, it stopped trying, and died.  Today, we can see the whole narrative on 30 feet of rock.

Squids
Normally, paleontologists do not find much evidence of squids because they do not have many hard parts.  The Solnhofen seabottom, however, preserves nearly everything. One fossil has a long cuttlebone-like internal shell stiffening its soft mantle tissue “wings” on the outside.

Another  of the squid fossils shows hooks on its arms - that show up as lines in the tentacle area - for snagging prey. It even has a modern relative that was given the extreme name, Vampyroteuthis infernalis, or Vampire Squid from Hell. It  dives thousands of feet down in the sea, is red in color, has huge blue eyes and use photophores to confuse preditors, but it is only a few inches long and eats shrimp.

Squid show its pen and soft parts

These are only a few of the more spectacular fossils on display in Archaeopteryx:  Icon of Evoloution. There are many reasons why Darwin loved the fossils from the Solnhofen. Take a walk with a fellow docent or download the guide to the hall from the Guild’s digital library and see what you can find. CAREFUL! If you show any interest, we will tell you enough things about the hall that you will become addicted and start giving tours.