If creationists keep spewing nonsense about horses and horse evolution, there may come a day when I run out of literary references and idioms involving horses to play off of in my post titles. But today is not that day.
Before I start I want to promise any regular readers of this blog that despite this being yet another post that is (in part) about creationists and horses, I promise there will be no mention of Hyracotherium this time. No quotes of Richard Owen. No references to hyraxes whatsoever, you have my word.
Once again the source of my ire is the Institute for Creation Research (ICR) who sent forth one of their minions, Christine Dao, to dutifully report what the institute’s “creation scientists” had to say about the recent news that the South Korea is going to be altering their school textbooks to pander to creationists in that country.
Dao: Science gained a victory when South Korea’s Ministry of Education, Science and Technology announced last month that textbook publishers will correct editions that contain misinformation regarding evolution.
Yes, absolutely, if there is misinformation in the textbooks we would certainly want to weed that out. The problem is, to a creationist, any of the data that makes up the mountain of empirical evidence supporting evolutionary theory is “misinformation”. Let us examine the two examples of supposed misinformation the South Korean “Ministry of Education, Science and Technology” is planning of removing from textbooks and the “scientific” reasons why the ICR agrees that they should be removed; starting in reverses order with “feathers” (figuratively speaking):
Dao: The push for the corrections is being led by the Society for Textbook Revise. Nature reported that the revisions will remove “examples of the evolution of the horse or of avian ancestor Archaeopteryx.”1
Zoologist and Institute for Creation Research senior lecturer Frank Sherwin said that statement isn’t entirely accurate. “Archaeopteryx has always been Archaeopteryx,” he said. “It didn’t evolve. Paleontologists have unearthed a total of 11 of these specimens, and most agree it was of a single species. So, where’s the evolution?”
Stating that a small collection of fossils representing a single genus: is that genus and always has been, is a taxonomic tautology; he is essentially just saying that “Archaeopteryx is Archaeopteryx” which is true by definition. Furthermore, asking where the evolution is in a single extinct type of organism is nonsensical (dead things don’t evolve). To illustrate the true significance of Archaeopteryx as evidence for evolution one must compare it to other things; in this case theropod dinosaurs and later birds.
Ms. Dao then provides us with a block quote of Mr. Sherwin from a recent Acts & Facts article talking about Archaeopteryx:
Sherwin: The idea that dinosaurs evolved into birds is also misleading.
Yes, technically birds evolved from a particular sub-group (Maniraptorans) of theropod dinosaurs which means taxonomically they still are dinosaurs in the same way we are mammals. However I doubt that is what Mr. Sherwin means.
Sherwin: The poster child of Darwinian change is Archaeopteryx, an alleged link via therapod dinosaurs between reptiles and birds. However, unlike dinosaurs, Archaeopteryx had a large braincase for the increased motor control and sensory input that were required for flight.
First, I fail to understand how Archaeopteryx having a brain that is more adapted to flight is somehow an argument against it being a transitional or intermediate form. It is like he is arguing that Archaeopteryx could not have descended from earlier theropod dinosaurs because its brain evolved too much in the direction of birds.
It is true that Archaeopteryx did have a somewhat larger brain for its size compared to non-avian dinosaurs, however its brain was more basal (“primitive”) in its characteristics and not as large in relation to its body size when compared to later birds. Also other Maniraptorans had large brain to body size ratios when compared to other dinosaurs:
The relatively small hemispheres, lack of posterior rotation of the optic lobes and potentially relatively smaller cerebellum suggest that Archaeopteryx and Enaliornis21 were more primitive than any modern bird.
[…] A plot of endocranial volume against body mass of some birds and modern reptiles (Fig. 4) places Archaeopteryx appreciably closer to birds than Jerison’s estimate does14. Birds with the same body mass as Archaeopteryx have from one-third…to five times…bigger brains14,15. However, the brain of Archaeopteryx is about three times the volume of those of non-avian reptiles of equivalent size.
[…] Few coelurosaurian dinosaur taxa preserve a brain endocast and most show the non-flexed plesiomorphic brain pattern with the optic lobes in dorsal position18,26, except for Troodon18 in which they are laterally placed; however, the cerebellum is comparatively much smaller than in Archaeopteryx. Maniraptorans do, however, show a trend towards brain enlargement and laterally separated optic lobes27, with Archaeopteryx exhibiting a ‘flight adapted’ brain, a stage further towards the modern bird pattern. The remodelling of the brain towards the avian condition must have begun well before the appearance of Archaeopteryx 147 million years ago in the latest Jurassic. (Alonso et al. 2004, pp. 668-669, emphasis mine)
Above is Alonso et al’s “Fig. 4”, referenced in the quote above, which shows Archaeopteryx falling just about right in the middle between “reptiles” and later birds with regards to it brain to body size ratio. So Archaeopteryx did have a larger brain for its body size than most theropod dinosaurs but it was not as large as those found in most modern birds. In other words its brain was intermediate between the two groups.
Sherwin: Theropods had a lizard-like pelvis that was distinct from a bird’s frame. Furthermore, Archaeopteryx had a robust furcula (wishbone), a trait characteristic of strong fliers…
Actually both the pelvis and furcula of Archaeopteryx was more like that of some Maniraptoran dinosaurs than that of modern birds as the illustration below shows (top row are pelvic bones, third row down are the furculae)(Chiappe 2004, p. 104):
Here is a photograph comparing the furculae of various bird species (Nesbitt et al 2009, p. 860).
And here are photos of the furculae of Archaeopteryx (left) and Bambiraptor, a Maniraptoran dinosaur (right)(Nesbitt et al 2009, pp. 870 and 868).
Sherwin: …one [robust furcula] that keeps flight muscles from crushing the bird’s delicate internal air sacs.
Except that the evidence suggests that Air sacs were common amongst all saurischian dinosaurs. This is based on the fact that many saurischians had pneumatic bones (hollow bones) with pneumatic foramen (holes in the bones through which air sacks can connect to hollow spaces within the bones) which are indicative their possessing bird-like air sacks (Wedel 2008).
Also I am not sure about Mr. Sherwin’s claim regarding the function of the furcula in birds. My understanding was that it acts like a sort of spring storing energy on the downward beat of the wings and helping to swing the wings back up on the upstroke and that it may also help in the function of the air sacs (Jenkins et al 1988); not protecting them from being crushed per se. But that’s a nit.
Sherwin: No evidence supports the story that such fully formed wings with fused clavicles “evolved from” the tiny, clavicle-free theropod forelimbs.
The problem is, as we have already seen, Mr. Sherwin’s claim that theropods were furcula (“fused clavicles”) free is simply false (see above). Furthermore many Maniraptoran dinosaurs had robust forelimbs:
Sherwin: Even claw measurements of Archaeopteryx fall within the range of true perching birds [A. Feduccia2].
And? The fact that the hind claws of Archaeopteryx were similar to later perching birds suggests that they may have spend more time in trees than on the ground, but how does this affect its status as a potential intermediate form? Of course Mr. Sherwin neglects to mention that Alan Feduccia (who he cites here) also noted that the fore-claws of Archaeopteryx were very similar to the hind claws of Central and South American tree climbing birds called, appropriately enough, “woodcreepers” (Dendrocolaptinae). Bringing attention to the fact that Archaeopteryx had fore-claws on three independent digits, something no modern bird has,* would be inconvenient:
Yalden (15) discovered that the claws of the manus of Archaeopteryx are very similar to those of trunk-climbing birds and mammals and suggested that Archaeopteryx used the manus claws in trunk-climbing. Morphologically, the manus claws are almost identical to pes claws of neotropical trunk-climbing woodcreepers (Dendrocolaptidae), specifically Xiphocolaptes and Hylexetastes. The claws of a clinging bird, namely, the swift [Streptoprocnezo naris (n = 10)], while morphologically different from those of the manus of Archaeopteryx, had a mean of 131.90 (range 1220 to 1380, SD = 6.4); half of the individuals measured had claw arc measurements that overlapped the manus claw measurements of Archaeopteryx. Manus claws of Archaeopteryx also agree in morphology with those of tree-trunk-climbing or -clinging mammals such as Cynocephalus, Hipposideros, Sciurus, Schoinobates, and Petaurus [a flying lemur, a bat, a squirrel, and two gliding marsupials – T.B.] [see also (15)]. Based on these observations and comparisons of the manus claws of Archaeopteryx with those of woodpeckers, Yalden (15) concluded that Archaeopteryx was a trunk-climber. (Feduccia 1993, p. 791-792)
What, if anything, does this tell us about the theoretical phylogenetic relationships of Archaeopteryx? Not much.
A side note on Alan Feduccia. Feduccia along with people like Larry Martin, are members of a dwindling group of scientists who still question that birds are descended from theropod dinosaurs, preferring the old idea that birds descend from other, hypothetical, archosaurs (crocodilians, pterosaurs, dinosaurs and other extinct types). They argue the hair-like structures interpreted by the majority of paleontologists as possible proto-feathers found on several types of theropod dinosaur fossils (Sinosauropteryx for example) are merely frayed collagen fibers (a taphonomic artifact), and that the several clearly feathered dinosaur fossils (Caudipteryx) that have been found in the last two decades are in reality flightless birds that merely resemble theropod dinosaurs due to convergent evolution.
Their frequent denials that birds are descended from dinosaurs makes them a favorite quote source for creationists. At this point I think they have crossed the line into crank status not too different from the creationists they inadvertently encourage.
Sherwin: It was a bird without a single transitional feature.3
This is an assertion backed by statements that are either flatly wrong, incomplete, or irrelevant.
Here is the skeleton of Archaeopteryx compared, appropriately enough, with a pigeon (Columba) (Heilmann 1927, p. 33). As you can see the skeleton of Archaeopteryx is overall more similar to those of non-avian Maniraptoran dinosaurs than those of modern birds.
Archaeopteryx had a snout with teeth rather than a horny bill; three clawed and unfused fingers; a long bony tail; and unfused metatarsals (foot bones), just to name a few obvious characters, like those of non-avian Maniraptoran dinosaurs but not found in modern birds. It also possessed many bird-like characters: feathers; fused clavicles (a furcula); a backward angled pubis, etc. that are shared with many Maniraptoran dinosaurs. And it had a few characters found in later birds that are not found in non-avian dinosaurs like an opposable hallux (digit 1, homologous to our big toe) and asymmetrical flight feathers.
In other words it was a mixture of non-avian Maniraptoran dinosaur characters, characters birds share with non-avian Maniraptoran dinosaurs and characters possessed by birds, exactly the sort of combination we would expect to see in an organism linking dinosaurs and birds in a descent relationship. In other words, it was a transitional, or intermediate, form.
If Archaeopteryx lacks anything as an example of an intermediate form it would be that it is too much like a non-avian Maniraptoran dinosaur and did not share many of the derived traits of later birds. In other words it is more like non-avian dinosaurs than birds. But creationists have historically committed themselves to the line that it is “just a bird” (a position taken before the discovery of feathers in non-avian dinosaurs) and can’t turn back now.
For more see:
- All About Archaeopteryx by Chris Nedin at the Talk Origins Archive
- Archaeopteryx: An Early Bird (University of California Museum of Paleontology: U.C. Berkeley)
- Archaeopteryx (Wikipedia)
Now we move on to the “horse” section of this folderol.
Mr. Sherwin also said that the removal of horse evolution from textbooks is good for science, especially in light of a 2009 study appearing in the Proceedings of the National Academy of Sciences that called for “revising the recent evolutionary history of equids [animals including horses, zebras, and donkeys] using ancient DNA.”4
“‘Horse evolution’ has fallen upon very bad times,” Mr. Sherwin said. “Consider this: Many specimens placed as separate species are actually variations of the same species. That team of 22 international researchers found that for evolution to be true as taught in textbooks, there had to be sudden bursts of diversification—Cambrian-like explosions within the horse family…
OK, so according to Mr. Sherwin:
- Specimens previous classified as separate species are being lumped (versus split) into other species, which would mean that there is less diversity in the horse Family (Equidae) than previously thought.
- For horse evolution to be true there had to be a “sudden burst of diversification” similar to the Cambrian explosion radiation within Equidae.
- These claims are supported by a study published in the Proceedings of the National Academy of Sciences.
I can’t quite put my finger on it but something doesn’t add up there. However before we get into the PNAS paper and whether it supports Mr. Sherwin’s claims a brief digression on the “Cambrian explosion” (more properly “Cambrian radiation” so that we can better understand the magnitude of what Mr. Sherwin has been discovered regarding horse evolution.
The Cambrian radiation was the geologically rapid (10 million years or so) introduction into the fossil record of a very diverse collection of organisms representing most (but not all) of the extant animal phyla, including (but not limited to) numerous types of annelids, arthropods, mollusks, echinoderms, and even a few chordates. All of which were already somewhat distinct in their body plans. It is one of the great adaptive radiations recorded in the fossil record.
- The Cambrian Explosion (University of California Museum of Paleontology: U.C. Berkeley).
- The Origin of Animal Body Plans by Douglas Erwin et al.
Above is a painting illustrating some of the animal diversity that appeared during the Cambrian radiation in this case from the fossils of the Burgess shale in British Columbia. Image from evolution-textbook.org
So by comparing it to the Cambrian radiation, as Mr. Sherwin has done, it would seem reasonable to assume that whatever the authors of this paper on horses have discovered it must be a big deal. One that perhaps demonstrates a large increase diversity within the Family Equidae, that took place within a relatively short geological time period. So with that in mind let’s now look at the paper that Mr. Sherwin has referenced to support this rather spectacular claim:
The rich fossil record of the family Equidae (Mammalia: Perissodactyla) over the past 55 MY has made it an icon for the patterns and processes of macroevolution. Despite this, many aspects of equid phylogenetic relationships and taxonomy remain unresolved. Recent genetic analyses of extinct equids have revealed unexpected evolutionary patterns and a need for major revisions at the generic, subgeneric, and species levels. (Orlando et al. 2009, p. 21754)
OK but wait a minute, “major revisions at the generic, subgeneric, and species levels”? That’s what creationists would call “microevolution” by which they mean any level of evolutionary change below or above the species level which has been empirically demonstrated beyond rational doubt (but which actually refers to evolution within a species, as opposed to macroevolution which is evolution above the species level, including speciation).
Well at least this has to be a Family wide revision of generic relationships over the last 55 million years within Equidae, from Hyra.., oops I promised I wouldn’t say that word, um, from Mesohippus to Equus, right?
Phylogenetic analyses support a major revision of the recent evolutionary history of equids and reveal two new species, a South American hippidion and a descendant of a basal lineage potentially related to Middle Pleistocene equids. Sequences from specimens assigned to the giant extinct Cape zebra, Equus capensis, formed a separate clade within the modern plain zebra species, a phenotypicically plastic group that also included the extinct quagga. In addition, we revise the currently recognized extinction times for two hemione-related equid groups. However, it is apparent that the current dataset cannot solve all of the taxonomic and phylogenetic questions relevant to the evolution of Equus. In light of these findings, we propose a rapid DNA barcoding approach to evaluate the taxonomic status of the many Late Pleistocene fossil Equidae species that have been described from purely morphological analyses. (ibid.)
So what this paper is really about is a revision of the relationships of the species within the genus Equus (and a couple of closely related extinct genera) from the last few million years. To put this in visual perspective here is a phylogram of the evolutionary history of the Family Equidae, this paper deals only with the part at the top shaded in green.
So Mr. Sherwin is apparently arguing that because scientists are refining the relationships of modern horses, found in the green shaded area, that all the fossil evidence for equid evolution that falls below it somehow disappears. That is quite remarkable.
Sherwin: …That’s contrary to Charles Darwin’s prohibition of great and sudden leaps.”
Oh yes, huge great leaps in morphological change represented by the following pictures of the various types of equids involved. I am sure that your mind will recoil in disbelief at the suggestion that these organisms might be related by common descent:
The extinct Central & South American Hippidion, which the paper argues should either be folded into the genus Equus, or that Equus could be broken into two closely related genera, one of which would include species now classified under the genus Hippidion (Orlando et al. 2009, p. 21755).
As you can see no “great” morphological “leaps” prohibited by Darwinian evolution are involved here. The only obvious difference being that Hippidion would have probably looked in life like a horse with a funny big nose (due to its bizarrely deep nasal notch and nasal bones) . Remember zebras, asses, and horses can still interbreed, though their offspring are sterile.
He [Sherwin] continued, “Reading the research, one concludes these animals suddenly appeared in the fossil record without the expected gradual evolutionary transitions. Horses then appeared quickly all over the world.
There is nothing in this paper about the “sudden” appearance of horses. There is a reference to “rapid radiation events”, which links to a table, but once again this only deals with Equus, Hippidion, and similarly modern equids that everyone would recognize as horses.
Sherwin: Finally, as expected by creation scientists, the skeletal features of fossil horses do not match up with the molecular data (ancient DNA) that they studied.”
“Creation scientists” cannot expect anything, because with God all things are possible. God could make it where the DNA matches previous classifications based on skeletal morphology, or he can make it so that it doesn’t. He can do anything, he’s God and that makes the “God did it” hypothesis consistent with any possible observation of nature. This leaves it untestable and therefore unscientific.
Anyway, the refinement our classification of the various species within Equus is all very interesting but does nothing to affect the evidence for the evolution of horses within the Family Equidae (or the relationship of equids to other Perissodactyls: rhinos, tapirs, an other extinct types). And, again, the level of change we’re talking about falls easily within the range that creationists regularly dismiss as being merely “changes within a kind”.
Furthermore the authors of the study concluded:
In this study, two species of extinct equids have been identified by mtDNA. The first is related to hippidiforms and corresponds to the paleontological genus Onohippidium, which should be reclassified within the Hippidion genus as Hippidion devillei. The second is a unique basal lineage of Old World equid, which appears morphologically related to the Middle Pleistocene Sussemiones, yet survived in southwestern Siberia at least until circa 45–50 KYBP [thousand years before present – T.B.]. In addition, we propose to synonymize a variety of other species [Cape zebras, quaggas, and plains zebras (11, 13) and potentially E. hydruntinus and E. hemionus]. This reinforces similar suggestions for hippidiforms, NWSL, and caballids (15, 16, 18) and E. hydruntinus (17). This pattern of taxonomic oversplitting does not appear to be restricted to equids but is widespread amongst other Quaternary megafauna [e.g., Late Pleistocene bison (49); Holarctic cave lions (50); New World brown bears (51), and ratite moas (52, 53)]. Together, these findings suggest that the morphological plasticity of large terrestrial vertebrates across space and time has generally been underestimated, opening the way to detailed studies of the environmental, ecological, and epigenetic factors involved. Interestingly, in this regard the human lineage shows a rich fossil record over the last 6 MY, spreading over seven possible genera and 22 species (54). The exact number of taxonomic groups that should be recognized is still debated, even within our own genus (55), and in this context it is pertinent to consider the degree of taxonomic oversplitting, from species to generic levels, that aDNA has revealed amongst Late Pleistocene equids and other megafauna. A further important implication of this finding is that the number of megafaunal extinctions and loss of taxonomic diversity from the Pleistocene to modern day may not have been nearly as large as previously thought, at least at the species or subspecies level. Conversely, at the molecular level, aDNA studies on a wide range of large mammal taxa (49, 50, 56, 57) have revealed that the loss of genetic diversity over this time period has been much larger than previously recognized with major implications for the conservation biology of surviving populations (58). (Orlando et al. 2009, p. 21758 emphasis mine)
So they are not arguing for the existence of some Cambrian like explosion in diversity in the late Cenozoic horses, rather they are saying that the paleontologists have overstated the actual level of diversity within the genus Equus, and that they believe that this same “oversplitting” (as opposed to lumping) may have been done in the classification of fossils of other Pleistocene megafauna (large animals). Pretty much the exact opposite of what Mr. Sherwin said they were saying and certainly not related to any Cambrian like diversification of higher level taxa (larger taxonomic groups like Phyla, Class, Family or Order).
Don’t take my word for it, go read the paper yourself and see if you can recognize anything in it that reflects what Mr. Sherwin is saying.
Dao: Students, whether in South Korea or other parts of the world, deserve the best education their countries can offer them. Correcting inaccuracies in textbooks is an important step in the right direction.
Students everywhere do deserve the best education available. Unfortunately it seems that in South Korea, as so often happens here in the United States, their parents have fallen under the influence of the likes of Mr. Sherwin and his colleagues at ICR, who fill their heads with “information” of the sort we’ve looked at here.
Alonso, Patricio Domínguez et al. (2004) “The avian nature of the brain and inner ear of Archaeopteryx“, Nature, 430:666-669
Chiappe, Luis (2004) “The Closest Relatives of Birds“, Ornitologia Neotropical, 15 (Suppl.): 101–116
Feduccia, Alan (1993) “Evidence from Claw Geometry Indicating Arboreal Habits of Archaeopteryx“, Science 259(5096): 790-793
Heilmann, Gerhard (1927) The Origin of Birds, D. Appleton and Company, NY
Jenkins, Farish A. Jr. et al. (1988) “A Cineradiographic Analysis of Bird Flight: The Wishbone in Starlings Is a Spring“, Science 241(4872):1495-1498
MacFadden, Bruce (1994) Fossil Horses: Systematics, Paleobiology, and Evolution of the Family Equidae, Cambridge University Press
Nesbitt, Sterling J. et al (2009) “The Theropod Furcula“, Journal of Morphology, 270:856–879
Orlando, Ludovic et al. (2009) “Revising the recent evolutionary history of equids using ancient DNA“, Proceedings of the National Academy of Science, 106(51): 21754-21759
Sereno, Paul C. et al (2008) “Evidence for Avian Intrathoracic Air Sacs in a New Predatory Dinosaur from Argentina“, PLoS ONE (3(9): e3303
Wedel (2009) “Evidence for Bird-Like Air Sacs in Saurischian Dinosaurs“, Journal of Experimental Zoology, 311A(8): 611–628