Thomas Henry Huxley and the Dinosarian Affinities of Birds – A Response to Brian Switek

While browsing the paleontology blogosphere, I came across an article on Brian Switek's blog Laelaps in which he proclaimed that the view that Victorian Era naturalist Thomas Henry Huxley, known as Darwin's Bulldog, arrived at the conclusion that birds had evolved from dinosaurs, and, therefore, are dinosaurs, is a misinterpretation of Huxley's true views. According to Switek, Huxley thought that dinosaurs closely resembled, in anatomical form and structure, to those animals which he deemed as the actual ancestors of birds, which Huxley said had yet to be discovered at the time. Curious, I subsequently read much of Huxley's writings on this topic, and, with all due respect to Mr. Switek, who I have to commend in the highest for his wonderful contributions to paleontology, I am afraid that it is Mr. Switek who has misinterpreted (or rather, more precisely, overlooked) some of Huxley's work. Huxley had used the phrase "intercalary type" to refer to an organism that approximated the form that the ancestor of another species took, but was not actually the direct ancestor, while he used the phrase "linear type" to refer to those organisms that, in his view, represented the actual ancestors of another species.

I reproduce the following excerpt from one of Huxley's works, which Brian Switek had used in his article to show that Huxley did not think that dinosaurs had actually evolved into birds (Ornithoscelida is a broader grouping encompassing the Dinosauria which Huxley utilized at the time; I have intentionally bolded one portion to add emphasis to it):

 "When I addressed you in 1862, I should have been bold indeed had I suggested that palæontology would before long show us the possibility of a direct transition from the type of the lizard to that of the ostrich. At the present we have, in the Ornithoscelida, the intercalary type, which proves that transition to be something more than a possibility; but it is very doubtful whether any of the genera of Ornithoscelida with which we are at present acquainted are the actual linear types by which the transition from the lizard to the bird was effected. These, very probably, are still hidden from us in the older formations."

In this statement, Huxley is merely saying that none of the specific genera of dinosaurs that were known at the time was the direct ancestor of birds. He is not saying, by any means, that dinosaurs in general were not the direct ancestor of birds.

In fact, another excerpt from a September 20, 1876 lecture by Huxley demonstrates that Huxley did, indeed, consider dinosaurs (again, referred to as Ornithoscelidans) to be the direct ancestors of birds (parts that are in bold, are, again, intentionally bolded by me to furnish emphasis):

"I conceive that such linear forms, constituting a series of natural gradations between the reptile and the bird, and enabling us to understand the manner in which the reptilian has been metamorphosed into the bird type, are really to be found among a group of ancient and extinct terrestrial reptiles known as the Ornithoscelida. The remains of these animals occur throughout the series of mesozoic formations, from the Trias to the chalk, and there are indications of their existence even in the later Palæozoic strata."

So Huxley did, indeed, consider dinosaurs to be directly ancestral to birds. He just thought that none of the specific genera of dinosaurs that were currently known at the time were directly ancestral to birds. And, in that respect, he was, of course, correct. It is imperative that Huxley's research and writings be recognized for their several crowning achievements, this being but one of the most notable (another was his proposal that pterosaurs were endothermic, but that's a story for another day).