Guest Column: Casey Luskin and the Evolution of Birds

Ed Note: This is a guest column written by Sean Starcher and JA Pourtless. You can read the original version of this column on Sean’s blog.

Casey Luskin of the IDEA Center has really had it piled on lately. We don’t want it to seem like we’re picking on him (there are certainly a healthy number of creationist websites out there that are in serious need of a reality check!), but his primer on “Problems with Evolutionary Explanations of the Fossil Record” contains some serious errors that are in immediate need of correcting.

That there are “some” errors is a bit of an understatement, but for the time being we’re going to focus in on two of his major criticisms. He says:

But what did Archaeopteryx come from? Given the similarities to therapod [sic] dinosaurs, it is usually claimed to be a nice clean relative of the therapods [sic]. The catch? These therapods [sic] are only known from one locality–the Yixian formation in China, and according to the radiometric dates, the Therapods [sic] are “at least 20 Myr younger than Archaopteryx” [sic]. To give an analogy, that’s sort of like saying that the first apes came from modern humans (which appeared out of no where 25 million years ago and then disappeared).

This passage is confused on a number of different counts. Firstly, that bird-like theropods are limited to a single locality, the Yixian, is just flat-out wrong. Dromaeosaurids are known from North America (e.g. Bambiraptor, from the Two Medicine Formation of Montana, Dromaeosaurs and Saurornitholestes from the Judith River Formation of Alberta Canada, Deinonychus from the Cloverly Formation of Wyoming), Europe (teeth, mostly undescribed, from the UK and Portugal), Mongolia (Velociraptor from the Djadoctha Formation, Adasaurus from Nemegtskaya Svita), and Africa (undescribed teeth). Oviraptorosaurs are known from North America, Mongolia, Kazakhstan and Uzbekistan. Therizinosaurs have been found in Mongolia and the United States. Alvarezsaurids are known from Mongolia and the US. This is by no means an exhaustive list.

That there exists some intractable temporal paradox involved with the theropod hypothesis of avian ancestry is also far from accurate. The earliest unquestionable coelurosaur is represented by an incomplete braincase from the Early Jurassic La Boca Formation of Mexico which displays a distinct caudal tympanic recess, strongly suggesting its status as a coelurosaurian theropod (Clark et al. 1994, Munter 1999, Clark et al. 2002). Witmer (2002) and Clark et al. (2002) suggested that “Protoavis texensis” Chatterjee’s dubious Triassic “bird” (which is discussed elsewhere) might in fact represent a coelurosaur. An alleged ornithomimid, also recovered from the Dockum Formation, Shuvosaurus inexpectatus, if valid would push the origin of at least one major coelurosaur clade to the Late Triassic. An isolated troodontid tooth has been recovered from the Morrison Formation of Upper Jurassic age (Chure 1994, Clark et al. 2002) and teeth referable to Dromaeosauridae and Troodontidae are reported from two separate medial Jurassic sites in Great Britain, among other places (Evans & Milner 1994, Metcalf & Walker 1994, Clark et al. 2002). A dentary recovered from the Early Jurassic Lower Lufeng Formation of China displays multiple characters diagnostic of Therizinosauridae (Xu et al. 2001).

In order to successfully argue that these fossils do not indicate a Jurassic or even terminal Triassic adaptive radiation of Coelurosauria, as some have suggested, the characters present in the indicated material must either be shown to be misinterpreted, or greater similarity must be demonstrated to more primitive groupings. To date this has not been done.

It is interesting to document the stratigraphic position of more complete finds as well. Way back in 1994, Feduccia and others subscribing to his heterodox views of avian evolution were telling us that Archaeopteryx’s closest non-avian relations “lived 80 to 100 million years later” (Feduccia 1994, p.g. 32). In 1996 (p.g. vii), it had become “75 million or more years,” and in 1999 (p.g. 4740), “30 to 80 million years after the appearance of the earliest known bird.” The same year this last statement was published, the primitive dromaeosaurid Sinornithosaurus, dated at 125 MYA, pushed back the “gap” in more complete material to 20 million years (Xu et al. 1999), and just recently, another basal dromaeosaurid from the lowest section of the Yixian formation, Graciliraptor, has made it 17 MY (Xu & Wang 2004). The troodontid Sinovenator, a basal member of the group most commonly hypothesized to be the sister to Dromoaeosauridae, is known of the same age (Xu et al. 2002), which was as least tentatively admitted to by Feduccia (2002). Whittled down to next to nothing, how long do Mr. Luskin and the individuals he cites plan on continuing with this sham argument?

Next, Luskin decides to mix it up and have a try at Longisquama:

“To throw a final bone into the problems with reptile-bird evolution, an ancient reptile called Longisquama, found in Krygyztan, Russia in the 1970’s, has recently been re-analyzed and posed as a challenge to the traditional dinosaur-to-bird theories of evolution25. The fossil basically looks like a lizard with feathers, and like Protoavis, was found in strata of about the same geological period as the first dinosaurs. It is interesting because it had feathers which are extremely similar to birds in many fashions…”

Despite Mr. Luskin’s uncritical recitation of the conclusions of Jones et al. (2000), there is little suggesting Longisquama’s dorsal appendages have anything to do with feathers.

According to Senter (2003), the structures are divided into three membranous “lobes”, of which the posterior narrows and disappears as one moves distally. The periodic ridges that Jones et al. interpret as featherlike barbs fused to a rachis are instead pleats on the two larger lobes (Reisz & Sues 2000, Prum 2001, Unwin & Benton 2001, Senter 2003). Proximally, troughs between these ridges on the middle lobe are interpreted as the “air spaces” on the interior of the “rachis” by Jones et al. (2000). Additionally, Prum (2001) observes that “many portions of the membranous “vanes” of the Longisquama appendages lack any such structures,” which is in sharp contrast to the condition in feathers, whereby the vein is composed entirely of barbs. Furthermore, while a “pennaceous feather vane is created by interlocking barbules…the Longisquama “pinnae” lack them.” Perhaps most damaging, the “rachis” is not a continuous element proximodistally (Senter 2003).

Although Jones et al. (2001) and Feduccia (2002) derided Prum’s examination of the fossil material as perfunctory, his observations are consistent with nearly two decades of comments by Feduccia himself. In 1985 (p. 76) he wrote that:

Alan Feduccia wrote:

“Notwithstanding speculations on the nature of the elongated scales found in such forms as Longisquama…as being featherlike structures, there is simply no demonstrable evidence that they in fact are. In 1982 I examined the specimen of Longisquama in Moscow and could see no indication that the elongated scales were particularly feather-like. They are very interesting, highly modified and elongated scales, and are not incipient feathers.”

Although they were to become “featherlike scales” in 1999, he still maintained that “the scales of Longisquama were not transmuted into feathers.” (p.g. 133) To quote Prum (2003: p. 557), “somehow he made a complete and rapid conversion from thinking that Longisquama was “a bizarre and unique solution to the problem of gliding” (Feduccia 1999b: 95) to thinking that Longisquama is the closest known relative of birds (Jones et al. 2000).”

Why did the “featherlike nature” of these structures, “observable facts” (Jones et al. 2001) apparently previously invisible to Feduccia, Sharov (Longisquama’s original describer; Regal 1975), and a host of others, come to light when they did? If forced to speculate, we’d guess it had something to do with the authors, all of whom are outspoken critics of the theropod hypothesis, trying to mount some sort of counteroffensive after the discovery of a host of unambiguously feathered non-avian dinosaurs prior to the paper’s publication. This sort of flim-flam is nothing new, of course.

Back in 1998, Martin et al. argued that the avian hypocleideum was a separate ossification that they identified with an interclavicle. Because interclavicles are unknown in dinosaurs, the wishbones of both groups must be non-homologous. The very same year, Feduccia & Martin (1998), in response to a 1997 paper by Norell et al. in Nature, suggested that the Velociraptor furcula could not be homologous with the avian furcula because now, it was composed of an interclavicle! Now, because Martin has contradicted decades of his own pronouncements and adopted what he calls the “Paulian” (after paleontologist and dino-artist Greg Paul) view of Manirapotra, whereby these dinosaurs are actually flightless birds (pers. comm.), he would now apparently believe they are the same structures. In each case, contradictory statements are interpreted as conclusion proof of pseudo-homology. The first time because dinosaurs don’t have interclavicles, the second because they do, the third because, ostensibly belonging to birds, these wishbones in no way supply evidence for the theropod origin of birds. When the going gets tough, the “thecodont origins” camp seem remarkably skilled at reinterpreting the evidence, but always in a way that supposedly casts doubt on the consensus view.

Mr. Luskin continues by positing what he calls “two bad options”: either “Longisquama is a direct ancestor of the birds (including Archaeopteryx),” in which case “the feathers on Longisquama are ancestral to the feathers on birds,” or, “claim that birds still came from dinosaurs, but then Longisquama is in now way an ancestor of birds.” This second option is unacceptable, he says, because “the evolutionist has to wake up each morning trying to understand how feathers could evolve twice independently.”

Ignoring the preceding discussion and fact that modern systematists cannot and do not posit taxa as ancestral to others, these are not our only options. As Prum & Brush (2002) point out, if Longisquama’s appendages were indeed feathers, it is possible that they were primitive for archosaurs but lost repeatedly in divergent lineages. Like Prum & Brush (2002), we find this an unacceptable conclusion for a number of reasons, and like Luskin, agree that his first option is nearly impossible to defend. What we do not agree with is the need to invoke his second option, for the reasons described above. Hypothetically though, what would truly strain credulity is not the convergence of dinosaur feathers on Longisquama – a single, albeit complex structure – but any supposed Longisquama-bird group on dinosaurs, which at various levels of inclusiveness are united by literally hundreds of derived similarities (Padian & Chiappe 1998, Paul 2002). The number of ad hoc assumptions required to make dinosaurs and birds phony look-alikes simply boggles the mind.

Lastly, we find his suggestion that we “kill two birds with one stone,” throw out evolution altogether and adopt “the hypothesis” that birds are the result of intelligent design, totally unacceptable. We are unaware of any “intelligent design” theory of bird origins that makes testable, falsifiable predictions, or more precisely, are unaware of any scientific ID theory of birds.


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