CASE TEACHING NOTES
for
Seven Skeletons and a Feather

The Mysteries of Archaeopteryx

by
Clyde Freeman Herreid, Department of Biological Sciences
University at Buffalo, State University of New York

INTRODUCTION / BACKGROUND

Archaeopteryx is the most famous fossil in the world. Focusing upon its importance opens up a marvelous variety of fundamental questions in evolution.

This case is structured to be used in a problem-based learning class, but it could easily be run in a discussion format. It was written for the first semester of our freshman biology class in a course called Evolutionary Biology. It is the second case the students encounter.

The major reference for the case and the single best general starting point for our current understanding of Archaeopteryx is the excellent book, Taking Wing: Archaeopteryx and the Evolution of Bird Flight, by Pat Shipman (Simon & Schuster, 1998). The story line of Ostrom comes directly from this book as does all of the dialogue.

OBJECTIVES

MAJOR ISSUES

This case is divided into two parts. In the first part, "Mistaken Identity," we set the scene. Professor John Ostrom, a world authority on pterodactyls, is in Holland at the Teyler Museum where he discovers a fifth specimen of Archaeopteryx. It has been misidentified as a flying reptile for over a century. This leads to a brief recapitulation of the Huxley/Owen feud and Huxley's recognition that Archaeopteryx was an intermediate step in evolution leading from reptiles to birds, and his prediction that dinosaurs were the closest ancestral reptiles to birds.

I include some reading material for students along with this case. I use Internet publications (the Nedin web publications cited at the end of the case and listed below) as well as an excerpt from Gish's book The Fossils Say No. This material focuses on the transitional nature of Archaeopteryx and how evolutionists and creationists have interpreted this fossil species differently. So, in this first part, students should discuss fossil formation, identification, and dating of specimens. Second, they should be able to see the anatomical ambiguity of Archaeopteryx and its dual affinity for both birds and reptiles. Third, they should see one example of the evolutionist/creation debate.

Background for Study Questions in Part I - Mistaken Identity

  1. Any list of reptiles vs. bird characteristics should include the following points. Most are included in Nedin's Internet articles (1996 and 1999).

      Bird Features
      Wings for flight
      True feathers*
      Wishbone (furcula)*
      Bipedal*
      Bones pneumatic*
      Reversed big toe*

      Reptile Features
      Bony tail with free vertebrae
      3 claws on wing
      Long snout; no beak
      Jaws with teeth
      Flat breastbone
      Trunk region vertebrae are not fused
      Elongated cerebral hemispheres
      Skull and brain reptilian
      Concave cervical vertebrae
      Ribs slender and don't join sternum
      6 sacral vertebrae (birds have 11-23)
      Wrist joint flexible
      Nasal opening far forward on snout
      Fibula equal in length to fibula
      Foot bones free
      "Ventral ribs" present in abdominal wall

    Archaeopteryx has many more reptilian features than those of modern birds. Even those listed under birds above are not exclusive; wings were present in pterosaurs, of course, although skin served as the flight membranes rather than feathers. All other features (asterisked, above) are represented in some dinosaurs:

      (1) Recent fossil finds in China show evidence of downy feathers (Gibbons, 1998).

      (2) Wishbones are fused clavicles; once thought to be exclusively avian, they have been found in several theropods.

      (3) The bipedal nature of dinosaurs such as T. rex and its relatives is well known.

      (4) Until recently, air spaces in the bones (pneumatic bones) of modern birds were believed absent in Archaeopteryx and in dinosaurs. They now have been identified in some Jurassic dinosaurs (Nedin, 1996) and in Archaeopteryx (Britt et. al., 1998).

      (5) Modern birds have a big toe located on the back of the foot that is used for perching; theropods have this arrangement, too, but the toe forms a short claw that doesn't reach the ground. Archaeopteryx also has a reversed toe, but it is midway between the positions of dinosaurs and modern birds. A similar situation occurs with the fingers of the front arms; they are long in theropods, tiny nubbins in birds, and midsize in Archaeopteryx.

      No wonder that dinosaurs are believed by most specialists as the most likely ancestors to birds.

  2. Creationists use several arguments to devalue Archaeopteryx as a transitional species.

      (a) The most common argument is that Archaeopteryx is simply a bird.

      "The so-called intermediate is no intermediate at all because, as paleontologists acknowledge, Archaeopteryx was a true bird -- it had wings, it was completely feathered, it FLEW... It was not a half-way bird, it WAS a bird." (Gish 1978, p. 84).

      Gish is correct; we do classify Archaeopteryx as a bird by virtue of its wings and feathers. But it is not like any other bird -- extinct or modern. Except for the feathered wings, it is more like a reptile than a bird. That is why it was misidentified as a small dinosaur on some occasions. We do not have a taxonomic category for a half-way bird/reptile. If we did, we would put Archaeopteryx in it.

      (b) Another argument is to claim that Archaeopteryx is a forgery. They are picking up on the absurd claim made by two controversial astronomers, Hoyle and Wickramasinghe. This allegation, never entertained seriously by paleontologists, was effectively demolished by scientists of the British Museum (Charig et. al., 1986).

      (c) Creationists have argued that Archaeopteryx can't be transitional because true birds existed several million years before Archaeopteryx. It is possible that true birds existed before Archaeopteryx. Sankar Chatterjee of Texas claims that he has a specimen he named Protoavis that predates Archeopteryx by 75 million years. This can't be confirmed because Chatterjee refuses to let other paleontologists examine his specimen, and even he has not been able to find evidence for feathers. Finally, even if Protoavis is a "bird" rather than a small dinosaur, then it would simply assume the title of the earliest reptile-bird transition!

In the second stage of the case, "Ostrom's Dilemma," we deal with the major issues of the origin of flight featuring the famous "ground up" vs. "trees down" argument, the debatable bird-dinosaur connection, and the true story of John Ostrom's ethical decision.

Background for Study Questions in Part II - Ostrom's Dilemma

  1. The naming issue was a problem because, by right of priority, the first name given to a fossil should stand. This would mean that the name given to Ostrom's specimen when it was thought to be a pterodactyl, Pterodactylus crassipes, should be accepted. This would be ridiculous, of course, as it clearly wasn't a pterodactyl. Hence, in this case, Ostrom petitioned the International Commission on Zoological Nomenclature to make an exception to the rules and accept the long-standing name of Archaeopteryx litographica. They agreed with his suggestion.

  2. The dinosaur-bird connection. Several reptile lines have been touted as immediate avian ancestors. Most experts today argue that the reptile-hipped line of the dinosaurs (the Saurischia) is the best bet. The theropods (e.g., T. rex) are probably the ancestors because of many similarities, including their tendency to walk on two legs and their great range in sizes, several being the size of birds. See Shipman (1998) and Feduccia (1996) for the arguments, and see discussion above to the questions posed in Part I.

  3. The exact role of Archaeopteryx in bird phylogeny is unclear. Shipman (1998) and especially Feduccia (1996) discuss this in detail. Even if Archaeopteryx isn't the earliest bird, it certainly is an early bird. And surely there must be even earlier "birds" that existed. There is good reason to believe this based upon recent fossil discoveries that Archaeopteryx may be a side branch on the phylogenic tree leading to modern birds rather than a direct ancestor.

  4. Shipman (1998) and Feduccia (1996) again come to the rescue to discuss the major arguments on the origin of flight, as do several other authors cited in the references.

      The "trees down" argument runs:

        (a) We have examples of animals (e.g., many mammals, amphibians, and reptiles) that jump from trees and glide. Bats are believed to have evolved flight this way. Why not birds?

        (b) The wings of Archaeopteryx seem poorly adapted for power flight. The lack of a keeled sternum, and weak pectoral muscles and poor wing flexibility, seem ill suited to leaping up from the ground in order to start flight. The wings seem specialized for gliding down from trees.

        (c) The claws on the wings could easily have been used to climb trees from which Archaeopteryx could have launched its flight.

        (d) The claws on the feet have a curvature much like a perching bird, and the position of the big toe is directed backward like perchers.

      The "ground up" argument runs:

        (a) Insect flight probably evolved from the ground up. (Their wings probably served as thermoregulatory devices first or were gill plates used in skimming across the water.) Why couldn't something similar have happened in birds?

        (b) Dinosaurs, as the probable ancestors of birds, were not noted for tree climbing; they are bipedal runners.

        (c) The wing structure of Archaeopteryx, though not one of a powerful flier, still falls in the range of birds that are capable of gaining flight by running across the ground.

        (d) It is easy to imagine that early small dinosaurs might have run down their prey of small insects using their forelimbs. Feathers, originally evolved for insulation and temperature regulation, could have been used to capture insects, sweeping them toward their mouth. When these were sufficiently long, they would have made short takeoffs possible.

        (e) The big toe is directed backward in dinosaurs, too, and they don't perch. They are runners.

        (f) The hindlimbs of Archaeopteryx are long and strong and well adapted to bipedalism.

        (g) Feather insulation suggests a high metabolic rate necessary for powered flight.

        (h) There is less risk of injury taking off from the ground than from trees.

        (i) Feathered dinosaurs' fossils have now been discovered in China and this suggests a terrestrial ancestor.

      The advantage of the "trees down" hypothesis is that it explains how takeoff could have been accomplished. The greatest problem is that there are no known ancestors . There are no reptile candidates. Also, some people have argued that there were no trees on the offshore islands in the lagoon area where Archaeopteryx lived.

  5. Should Ostrom have told the curator the truth? I save this for the last stage of any discussion and use it as a wrap up of the case. It does not evoke a heavy discussion for two reasons. First, we know what Ostrom did. Also, as some students astutely have pointed out, we know the truth. Ostrom was honest, yet we know he was the one who made the discovery. Second, students know how scientists are supposed to behave and they hesitate to openly declare that Ostrom should have been selfish.

    In this final session, I do reveal the fact that, indeed, Ostrom did not suffer because of his honesty. When the curator disappeared without a word, Ostrom was stunned and thought he had lost the specimen. He reported later, "So about ten or fifteen minutes later, my host came back, and he was carrying a shoebox: a really battered old shoebox with a piece of string around it. And he presented it to me: 'Here, here, Professor Ostrom, you have made the Teyler Museum famous'.... The two pieces of limestone were in that shoebox."

CLASSROOM MANAGEMENT

The case is structured in two stages. It is designed to be run as the first serious case study in a freshman Evolutionary Biology class. Small permanent groups of students (4 to 5 students per group) work together on the cases.

Part 1, "Mistaken Identity," is given out at the end of one class period along with the reading material. Some preliminary discussion should go on among the members of each group regarding the major issues, but since they will only have time to skim the reading material, and because this is their first real case, the students will leave this class with only the two study questions to guide them. Their assignment should be to individually answer (in typed copy) the two study questions for the next class.

During the second class students should be prepared to hand in these individual assignments. A group project should be handed in as well. Their group assignment--to be handed in at the end of the hour--is this:

During the latter part of the second class period, the second part of the case, "Ostrom's Dilemma," should be given to the students. They should now be allowed to decide what are the critical issues and questions that need to be resolved and to divide up the workload.

During the third class, the group members should share their information and be prepared to participate in a general class discussion of the origin of flight, the dinosaur-bird connection, and finally the ethical question facing Ostrom.

For homework, each student should write a two-page paper focusing on any critical issue that emerged during their studying of the Archaeopteryx problem. But no one in a group can write on the same problem (that is, five group members will produce five different essays). The two typed pages should be structured in this manner:

  1. Title and author
  2. Identify the question, problem, or controversy you are examining
  3. Give our current understanding of the problem with evidence on the issue, pro and con
  4. Give references

Follow-up Assignment

I have given this follow-up assignment for extra credit. It has generated many thoughtful comments.

REFERENCES FOR TEACHING NOTES

INTERNET SITES


Image Credit:
Lithograph of the first Archaeopteryx specimen discovered
Palaeontographica

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