In 1993 some paleontologists hailed a small creature named Mononykus as "a new link between dinosaurs and birds" because it shares some features with modern birds, such as a keeled sternum and some fused wristbones. (On the April 26/93 Time cover, the creature is drawn having feathers instead of scales, which is entirely speculative.)

Mr. Poling:

So what is Mononykus, dinosaur or bird? How does Mononykus help answer the question "Do dinosaur fossils support evolution?"

Mr. Buckna:

The actual fossil material (not conjecture) indicates it is a dinosaur. What do you think it is?

Mr. Poling:

I have no idea. I'm not very familiar with Mononykus. My problem with its mention in your article is that it seems to come out of left field. I don't at all see how it is being used to further the argument that fossils do not support evolution. If it isn't clear to me, it isn't going to be clear to anybody else, either.

Addendum:

.....which, as I've learned thanks to more and more anti-evolutionists/creationists sending me e-mail, is their preferred tactic. Their motto seems to be "Always obfuscate. Never illuminate."

As near as I can tell the reason for inclusion of Mononykus in the article was to mention that drawing feathers on the animal was speculative. Indeed, it was speculative until feather impressions were found on a new fossil of the animal, long after Mr. Buckna's article was written. However, an artist taking what was at the time artistic liberties is not an argument against fossils supporting evolution.

It should be noted that the fossil referred to in Mr. Buckna's article is now called Shuvuuia, meaning "bird" in Mongolian. The fossil is sufficiently different from the type species of Mononykus, found during the famous Roy Chapman Andrews expedition to the Gobi Desert, to warrant placing it in its own genus. The fossil will be referred to by its proper name in the rest of this article, but readers should not lose sight of the fact that it is still the same animal referred to by Mr. Buckna as Mononykus.

Here is a picture of Shuvuuia. As Dr. Tom Holtz says, it's "a really bizarre animal." The strangest thing about this animal is its arms. They have been reduced to almost nothing except a single, large claw. Hence the name of its close relative Mononykus, "single claw."

Mr. Buckna states that Shuvuuia was a dinosaur, although recent fossils show that Shuvuuia was actually a type of flightless bird. Implicit in Mr. Buckna's argument is that Shuvuuia could not possibly have been both bird and dinosaur. This, and use of the term "transitional form" elsewhere in his article, reflects use of a taxonomic system, and its underlying assumptions about evolution, that has been abandoned in the last decade or so.

In the 18th century the biologist Carolus Linnaeus established a taxonomic system for categorizing life that would later become known as Linnean Taxonomy. This system puts animals into groups within a hierarchy of life, each with its own rank. For example, in Linnean Taxonomy we have Phylum Vertebrata, Class Reptilia, Order Dinosauria, Suborder Saurischia, Infraorder Theropoda, and so on. There are also other classes of animals, such as Class Aves and Class Mammalia. The ranking system was adapted from a Christian view of the natural world, one where animals were created by the god Jehovah, remained unchanged through time, and fit into a hierarchical system with man occupying its highest rank, the pinnacle of Creation (hence the phrase "higher form of life").

The Linnean system has several problems. Specific rules that control whether a taxon qualifies for a specific rank do not exist. Ask ten scientists what constitutes a Class, and you will get ten different answers, resulting in ten different hierarchies. The number of extinct and extant animals known has exploded in recent years, to the point where there are more taxa than systematists can invent ranks for. Linnean taxa are often based on primitive characteristics leading to grouping together taxa that are not closely related, such as dinosaurs and synapsids (the direct ancestors of mammals) both being placed within the reptile hierarchy. All of this results in a system that is highly inconsistent and unstable with rankings and membership varying from scientist to scientist, thus making it difficult for anybody to rely on the taxa for their research. Perhaps the biggest problem is that the system was created before evolution was even known, and therefore does not reflect our current understanding of evolution.

The incomplete example figure at right illustrates a hierarchy within the Linnean system. Velociraptor mongoliensis is a theropod, a saurischian, a dinosaur, a reptile and a vertebrate. However, in this system, Archaeopteryx bavarica and other birds are not dinosaurs even though they clearly evolved from a theropod dinosaur similar to Velociraptor (or Velociraptor evolved from a bird similar to Archaeopteryx). Birds, as Class Aves, have been assigned a rank of the same magnitude as the Reptilia, and therefore are placed alongside the Reptilia as the next rank down from Phylum Vertebrata.

This ranking system originally reflected a view that animals did not evolve from any other lifeform and were endowed by their Creator with a specific rank in a hierarchy of life. As the theory of evolution became accepted in the centuries that followed, Linnean Taxonomy was still used as it reflected scientists' theory that as animals evolve they become something "else." Birds are not dinosaurs, a Linneanist might say, because they have evolved a form so different from dinosaurs that they are now something else, and should be removed to a different part of the overall hierarchy. Aves new position would be at a rank appropriate for their degree of "differentness." In this case, birds are placed in the hierarchy with a rank equal to reptiles, which implies that birds are as different from other amniotes as are reptiles. Birds are still vertebrates, tetrapods and amniotes, but they are no longer reptiles nor anything within the reptile hierarchy.

We now understand that evolution does not work this way. As shown on page 3, animals evolve by building upon what is already there, either by modifying existing characteristics or evolving new ones that add to the overall package. They are not something "else," but modified forms of what came before, right down to the retention of the "primitive" DNA sequences that are switched off by, or their effects modified by, new sequences.

Because Linnean Taxonomy is no longer adequate, a new science of taxonomy called Phylogenetic Taxonomy is in use today. Phylogenetic Taxonomy groups animals based on ancestry, or phylogeny, with membership determined only by advanced characteristics. These groupings, called clades, are defined in two ways, either as an animal and all its descendants (a node-based clade) or as an animal and all animals sharing a more recent common ancestor with that animal than with another (a stem-based clade). The node based Dinosauria is defined as the most recent common ancestor of Ornithischia and Saurischia, and all its descendants. The stem-based Carnosauria is defined as Allosaurus and all taxa sharing a more recent common ancestor with Allosaurus than with "birds." Clades are diagnosed by advanced characteristics that set them apart from their ancestors. For example, the clade including snakes is diagnosed by the disappearance of all limbs, an advanced characteristic compared to the primitive (for the clade Tetrapoda) characteristic of having all four limbs expressed. Clades are not family trees as the true ancestry of every animal would have to be known. Clades are hypotheses of ancestry, and are governed by the rules that govern all of science.

A closely related science to Phylogenetic Taxonomy is called Cladistics. Cladistics is the science of discovering and representing the most parsimonious distribution of advanced characteristics among taxa. Cladistics produces branching diagrams called cladograms. Cladistics is used to test phylogenetic hypotheses, as the distribution of advanced characteristics should mirror the taxa's phylogeny, and the resulting cladograms are often used to represent the hypothesized phylogeny. Phylogenetic Taxonomy and Cladistics are therefore often used synonymously, although technically they are two different disciplines.

Phylogenetic Taxonomy has several distinct advantages over Linnean Taxonomy:

1. Stability. The characteristics that diagnose a clade may change if new fossils that clearly belong in the clade do not have, either in full or modified form, the characteristics that diagnose the clade. The characteristics may be moved down the cladistic "tree" to another clade, or they may be removed altogether. In addition, scientists may disagree on what constitute advanced characteristics and therefore may differ in what they think diagnose the clade. However, the definition of the clade will always be the same no matter which scientist is speaking. The Dinosauria, for example, will always be the most recent common ancestor of Ornithischia and Saurischia and all its descendants, no matter what the prevailing opinion is on what physical characteristics diagnose a dinosaur. Linnean taxonomy shares cladistics' fluid diagnoses, but because Linnean groups are also defined by the characteristics that diagnose it, as the diagnoses change so does the definition. The rank of a given group can also vary from scientist to scientist, thus changing the overall hierarchy. These shortcomings cause instability in the taxonomy and inconsistency in its use from scientist to scientist, a problem Phylogenetic Taxonomy eliminates by basing its groupings solely on ancestry and eliminating ranks.

2. Clarifies relationships. Because Linnean groups are often based on primitive characteristics, animal lineages that are not closely related are often grouped together. The most famous example of this is the ancestors of the mammals being included in Class Reptilia. Class Reptilia is diagnosed and defined by "cold-bloodedness" and scales, among other characteristics. However, these are primitive characteristics, inherited by these lineages from their common ancestor ("fish" are cold-blooded and scaled, for example) causing the ancestors of mammals (often called "mammal-like reptiles") to be lumped in with lizards and other reptiles. The ancestors of the mammals are not at all closely related to modern snakes, lizards and turtles, and one can tell this immediately by looking at a cladogram. One cannot tell this at all by looking at a Linnean hierarchy. Phylogenetic Taxonomy also clarifies relationships by putting back animals that were separated out, such as birds being separated from the dinosaurs.

3. Reflects current understanding of evolution. Anything descended from the ancestor forming a clade is a member of that clade. The ancestor of the Ornithischia and Saurischia, and everything that descended from it, including birds, is a dinosaur. This reflects the fact that evolution builds upon what is already there, as shown by the fossil record and modern DNA analyses, rather than becoming something "else" as reflected in modern Linnean Taxonomy. This relegates the term "transitional form," as traditionally used, to the trash heap of history as there is no longer a taxonomic basis (or basis in evolutionary theory) for saying one "type," "kind" or "Class" of animal has evolved into another.

Because Mr. Buckna continues to use the old Linnean taxonomic system, and therefore adheres to an outdated understanding of evolution, Mr. Buckna errs in his statement that

The actual fossil material (not conjecture) indicates it is a dinosaur [and not a bird].

While it is possible Shuvuuia could have been a non-avian dinosaur and therefore not a bird, it is not possible that if it was a bird it was not a dinosaur. If it was a bird then it was a dinosaur too, both in evolutionary and taxonomic terms. The shorthand is that all birds are dinosaurs, although not all dinosaurs were birds.