First specimen was a single feather imprint in a slab of Solnhofen limestone Uncovered in a Bavarian quarry and acquired by Hermann von Meyer

Dinosaurs and Birds

0. Discovery of Archaeopteryx in 1861 burst like a thunderbolt on the Victorian scientific community

1. First specimen was a single feather imprint in a slab of Solnhofen limestone

2. Uncovered in a Bavarian quarry and acquired by Hermann von Meyer

0. von Meyer soon after described a second specimen (acquired by Häberlein)

1. Beautifully preserved small fossil reptile, captured in a limestone so fine it was used to make lithographic plates

2. He named the specimen Archaeopteryx lithographica, meaning "ancient wing"

0. The publication of Origin of Species in 1859 had generated an intense debate among Victorian scientists over the nature of evolution

1. Existence of a "lost age" had only been realized a scant two decades ago

0. Nature of the beasts that populated it was still a matter of heated debate, pitting evolutionists against creationists

1. If the creator was perfect, then his creation must also be perfect

0. But how could a perfect creator allow any part of this perfect creation to go extinct?

1. Were the fossil fish, dinosaurs, and mammals that were now being unearthed actually related to one another?

0. Or had the Earth witnessed successive waves of creation, as the catastrophists claimed

1. Age of Fish swept away and replaced by an Age of Reptiles, which was in turn destroyed to create an Age of Mammals

0. The new geology of Charles Lyell demonstrated the great antiquity of the Earth

1. Far cry from the 4,000 years estimated in the chronology of Bishop Usher

0. Lyell's geology heralded the idea of continuous change - uniform change over time (uniformitarianism)

1. Idea adopted and transformed by Charles Darwin into his developing theory of evolution

0. Catastrophism (Cuvier) invoked powerful forces of nature in the past, to reconcile extinction with special creation

1. Uniformitarianism (Lyell) claimed that the forces of nature are the same intensity now as in the past

0. Lyell maintained that only gradual and continuous change could account for the record of the rocks

1. The earth must be a very ancient place…

0. Catastrophists thought nature progressed ever upwards, culminating in the evolution of Victorian man

1. Lyell’s Geology and Darwin's Origin of Species were mortal blows to the static Victorian view of nature as the expression of a benevolent divine plan

0. Georges Cuvier, William Buckland and other scientists had unearthed gigantic bones of prehistoric animals

1. Filled the vast ages of geologic time with a cast of long-vanished titans

0. Darwin's theory plunged the scientific community into intense debate

1. Thomas Henry Huxley, known as "Darwin's Bulldog" for his fierce defense of Darwin's ideas, was delighted with Archaeopteryx

0. Seized on the newly discovered Archaeopteryx as concrete evidence of a critical "missing link" between birds and reptiles

1. Incontrovertible proof from the fossil record that Darwin was correct

0. So was Huxley correct?

1. Were birds descendants of dinosaurs?

2. Birds are members of the Class Aves

3. Standard classification excludes extinct species

0. Divides Class Aves into two Superorders

1. Superorder Paleognathae - ratites and tinamous

2. Superorder Neognathae - all other modern birds

0. If birds are descended from dinosaurs, then birds must be classified within the dinosaurs

1. Otherwise Dinosauria is a paraphyletic group

2. Excludes birds solely on the basis of their phenetic dissimilarity - don’t look alike, so they can’t be related

0. Avian systematics is especially difficult because all birds share a fundamental similarity

1. Similarity is a design restraint

2. Demands of flight are so great, that they impose a structural uniformity on all birds

0. Ultimate origin of birds is still a mystery

1. Evidence continues to mount that birds are the direct descendants of theropod dinosaurs

0. Is Archaeopteryx a bird or a reptile?

1. In many respects it resembles a small dinosaur

2. In fact, two subsequent specimens of Archaeopteryx were initially misclassified as a pterosaur and a small theropod dinosaur, and languished in drawers for decades

0. Archaeopteryx has a blunt reptilian snout, very unlike the bill that typifies modern birds

1. Full set of reptilian teeth

2. Cranial skeleton also resembles that of a reptile

0. Bones of the hand are not fused, like those of modern birds, but separate, like the limbs of dinosaurs

1. The pelvis is not fused to the sacral vertebrae, as it is in modern birds (the synsacrum)

0. The ribs lack uncinate processes, small projections that link the ribcage of modern birds into a strong and flexible structure

1. It has a long, bony reptilian tail

2. In modern birds, tail is fused and reduced to a short pygostyle

0. Most importantly, it lacks the keeled sternum so prominent in modern flying birds

1. Sternum serves as the attachment point for the major flight muscles

0. 1992 another specimen (the 7th) was found in Solnhofen quarry

1. It has a bony sternum (!) but is much smaller than all other specimens

2. Thought to be a different species, named Archaeopteryx bavarica

0. At the same time, Archaeopteryx has many avian features

1. Most striking are the numerous feather imprints that covered the body

2. Extend out into a feathered wings and tail

0. Has a rudimentary furcula (wishbone) critical adaptation for avian flight

1. The furcula acts to control lateral compression of the chest cavity during the downstroke of the wing

2. Also serves as an attachment point for the pectoral flight muscles

0. Its bones are lightweight, and probably hollow

1. All of these features are designed for flight

0. Is Archaeopteryx ancestral to modern birds?

1. Or is an evolutionary dead end, not directly related to modern birds at all?

0. Such questions are difficult to answer

1. Our knowledge of the earliest evolution of birds is extremely sketchy

0. Archaeopteryx dates back to the Late Jurassic, about 140 million years ago

1. The Jurassic is one of three Periods comprising the Mesozoic Era, the others being the Triassic and the Cretaceous

0. The Mesozoic Era is best known for its most famous inhabitants, the dinosaurs

1. Also the Era in which our modern geography emerges from the breakup of Pangea

0. Age in which angiosperms (flowering plants) evolved, spread throughout the globe

1. Age in which birds evolved

0. Most orders of modern birds are first found in the early Cenozoic

1. There are only a few scattered orders of birds in the Mesozoic

0. Hesperornis and Ichthyornis, are representatives of two major orders of the Mesozoic

1. Hesperornis, discovered in 1870, was a foot-propelled diving bird, similar to the modern loon

2. It had large feet, reduced forelimbs, and lacked a keel on its sternum

0. Ichthyornis - a small tern-like bird with powerful wings, was found in 1872

1. It had sharp teeth and a well-developed keeled sternum

2. In fact, it is still the oldest known bird with a keeled sternum

0. Both genera give their names to an order of Mesozoic birds, the Hesperornithiformes, and Ichthyornithiformes

1. These two orders are still, over one hundred years after their discovery, the best known fossil birds other than Archaeopteryx

0. Recently discovered genera Iberomesornis from Los Hayos in Spain, and Sinornis from mainland China, are typical of several new genera

1. Assigned to the subclass Enantiornithes

0. Enantiornithes may represent the dominant group of Mesozoic birds

1. Globally distributed, and included arboreal perching birds, aquatic birds and shorebirds

0. Sinornis dates back 135 mya, and seems to be a primitive perching bird

1. For example, its tail and trunk are short

2. Center of mass is shifted toward the front, as in modern perching birds

0. Why are Hesperornis and Ichthyornis commonly preserved, while scores of other birds that must have lived in the Mesozoic have not?

0. There is a bias in the fossil record

1. Terrestrial birds are not readily fossilized

2. There is a great difference in taphonomic processes between terrestrial and aquatic habitats

0. Taphonomy is the study of the environmental processes that affect organisms after their death, including fossilization

0. Marine, near-shore, fluvial and deltaic environments offer an excellent environment for rapid burial in soft sediment, good chance of fossilization

1. Terrestrial birds are more likely to be eaten or torn apart by scavengers, or eroded away by wind and rain - So there is an environmental bias against fossil birds
   
   
   

2. Same types of environmental bias extends to other extinct animal, such as dinosaurs

3. We know far more about lowland species of dinosaurs that foraged in great deltas, or along the banks of rivers, than we know about the upland species

0. The lightweight, hollow bones that birds need for flight are less likely to preserved than the more solid bones of mammals

1. So there is also a preservation bias against fossil birds

0. In addition to an environmental bias and a preservation bias, we also introduce a collection bias when we look for fossils

1. Until the last few years, collectors focused entirely on big showy specimens

2. T. rex etc. brought much publicity and many museum visitors