Archaeopteryx is precisely such a transitional form. Archaeopteryx has prominent avian features, including a wishbone, feathers, and a bony sternum in one of the latest specimens (Svitil 1994).
But Archaeopteryx also has many reptilian characteristics, such as a pubic peduncle, a long, bony tail, three well-developed fingers (with the same number of bones as most dinosaurs), three well-developed metacarpal bones, unfused metacarpal bones, separate metatarsal bones, abdominal ribs, the lack of a hypotarsus, and the lack of a pygostyle (list from McGowan 1984:117).
Archaeopteryx also existed at the same time as the theropod reptiles and highly resembled them (Futuyma 1982:188), as one would expect of a transitional form between birds and reptiles.
II. Is Archaeopteryx just a bird?
One creationist objection to Archaeopteryx is that systematics classifies it as a bird. But systematics must classify every intermediate form between reptiles and birds as one or the other, since there is no separate category for intermediates. Were there such a category, then creationists would simply complain that we do not have intermediates between reptiles and this third category, or between the third category and birds. In the case of Archaeopteryx, the deciding factor for systematics was the presence of feathers; but it should be clear that the mere fact that it had feathers does not make it "just a bird" in the sense that the creationists need.
III. Are the Archaeopteryx fossils fakes?
A second creationist objection to Archaeopteryx is that the fossils are fakes. Sir Fred Hoyle, the astronomer who first made this accusation, argued that the fossils were actually reptile fossils with feather impressions either pressed into a thin layer of artificial cement, or chiseled directly into the rock. However, a team of scientists disproved Hoyle's claims by performing a battery of tests on the holotype of Archaeopteryx (Charig et al. 1986). First, they found absolutely no evidence of artificial cement on the fossils: a photographic comparison of the hairline cracks running through the impressions on the slab and counterslab revealed a perfect correspondence between the two sets, demonstrating that "the block was cracked though vertically before it was split horizontally into two slabs, thus indicating the unquestionable absence of any added cement layer on either surface" (Charig et al. 1986:624). Detailed examination of the feather impressions through scanning electron microscopy revealed "a degree of minute detail that [the scientists believed] would be impossible to carve, even today [written in 1986], and a total absence of any chisel marks" (Charig et al. 1986:624). So thoroughly discredited is the claim of the fraudulence of Archaeopteryx that the young-earth creationist organization Creation Ministries International has completely disavowed it (CMI n.d).
IV. Is Archaeopteryx invalidated by modern birds with some reptilian characteristics?
A third creationist objection to Archaeopteryx is that it cannot count as an intermediate since there are modern birds that have some reptilian characteristics. However, in the first place, Archaeopteryx has far more reptilian characteristics than any of the birds offered as examples by creationists. It is a telling point that, as we have seen, when Sir Fred Hoyle erroneously claimed that Archaeopteryx was a forgery, he claimed that it was a reptile fossil with fake feather impressions added. Secondly, and more importantly, Archaeopteryx is not considered a transitional form simply because of its remarkable blend of reptilian and avian characteristics, but because of its resemblance to the theropod reptiles that existed at the same time.
V. Is Archaeopteryx invalidated by Protoavis?
A fourth creationist objection to Archaeopteryx is that it cannot be a transitional form because it is preceded by Protoavis. However, in the first place, Protoavis is still in dispute because the discoverer has not released the fossils for public inspection. Second, even if Protoavis is authentic, this does not eliminate the transitional character of Archaeopteryx. Archaeopteryx still has the intermediate characteristics it does, even if there are more advanced transitional lineages somewhat earlier in the fossil record: all such lineages would show is something paleontologists already believe, namely, that Archaeopteryx was not the common ancestor of all bird-like creatures, but a side-branch in reptile-to-bird evolution (which is what one would expect, given the low probability of a direct ancestor being fossilized and discovered). Finally, even the discoverer uses Protoavis to support the thesis that birds evolved from theropod reptiles, which is the same thesis that Archaeopteryx supports. For more information, consult The Protoavis Controversy at EvoWiki.
VI. The latest specimen
A new fossil of Archaeopteryx was found that preserves its theropod reptile features even better than the previous ones was reported in 2005 (Mayr et al. 2005).
Charig AJ et al. 1986. Archaeopteryx is not a forgery. Science 232:622-625.
CMI. n.d. Arguments we think creationists should NOT use. creation.com/arguments-we-think-creationists-should-not-use. Spotted 21 Nov 2014.
Futuyma DJ. 1983. Science on Trial: The Case for Evolution. New York: Pantheon.
Mayr G, Pohl B, Peters DS. 2005. A well-preserved Archaeopteryx specimen with theropod features. Science vol. 310, 2 December 2005: 1483-1486.
McGowan C. 1984. In the Beginning...: A Scientist Shows Why the Creationists Are Wrong. Buffalo: Prometheus.
Svitil K. 1994. Seven perching dinos. Discover 15(1):52-54. January.
Wheeler TJ. 1993. Were there birds before Archaeopteryx? Creation/Evolution 13(2):25-35.
Last updated: 21 Mar 2008
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