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.

Flat-Footed Reptiles to High Stepping Chickens

Most scientists believe that birds evolved from small therapod dinosaurs. The key step was the development of feathers, turning animals that could walk or climb into animals that could fly. In today’s post, Dr. Bakker discusses the evolution of a key feature of Archaeopteryx, the first dinosaur to be discovered with preserved feathers.

Lizard Paws to Chicken Fingers

320 million years ago – the first reptiles evolve, the earliest vertebrates that can lay air-breathing eggs on land.  Legs are sprawling and flat-footed. The front paws have five fingers, all with claws.

250 million years ago – the first archosaurs evolve, the close kin of crocodiles and birds.  Legs are more upright but still flat-footed. The hands have only three claws. The outer two fingers are thin and claw-less.

225 million years ago – the first dinosaurs evolve. Legs are upright and the heel held high, off the ground. The outer two fingers are weak.

160 million years ago – the earliest raptor-like dinosaurs evolve. The outer fingers are gone. Hind-legs are used for running and ankles are tall and thin. The three clawed fingers are long. And there’s a swivel joint on the wrist to let the hand move quickly side-to-side.

150 million years agoArchaeopteryx evolves. Hind legs are like those of raptor-type dinosaurs. The hand is almost exactly like a raptor-dinosaur’s.

110 million years ago – the first modern-style birds evolve. Hind-legs have stiff ankle bones, all fused together. The wrist bones too are all fused together and no fingers have claws.

Want to know more about our current Archaeopteryx exhibit? Check out this article on PlanetEye Traveler.

Interested in learning more about paleontology? Check out our past blogs.