A Tale of Two Dinosaurs

The Institute for Creation Research has graced us once again with a brilliant display of their scientific prowess. This time the focus of their efforts revolves around the recently published description of a newly unearthed dinosaur species Eodromaeus murphi.

Eodromaeus is a small (slightly over a meter in length) South American dinosaur from the mid-Triassic (230 MYA). This date makes it one of the earliest dinosaurs and its describers, Ricardo Martinez et al., argue that it should be classified as a basal theropod ―the carnivorous branch of the “lizard-hipped” or saurischian dinosaurs (Martinez et al., 2011).

What has ICR’s, or more specifically ICR “science writer” Brian Thomas‘ knickers in a twist is that in the same paper in which they describe Eodromaeus the authors also argue for the reclassification of another dinosaur, Eoraptor (described back in the early 1990’s), which is from the same location and roughly the same time period as Eodromaeus.

In a nutshell Martinez et al. argue that Eodromaeus should be classified as a basal theropod, the most basal yet discovered, and that Eoraptor which had previously held that position should be reclassified as a basal sauropod (the plant eating branch of the saurischian dinosaurs), near the base of the lineage that later gave rise to the super-giants of the dinosaur world, the long necked herbivores like the famous Apatosaurus (Brontosaurus).

In his response to this rejiggering of the saurischian family tree―based on both new fossil evidence (Eodromaeus) and a reexamination of earlier finds (Eoraptor)―Mr. Thomas exposes, yet again, a number of flaws in ICR’s basic understanding of the philosophy of science as well as their understanding of evolutionary theory.

Right off the bat Mr. Thomas illustrates the sharp philosophical distinction between actual science and so called “creation science“:

A newly discovered dinosaur has forced another re-write of the evolutionary dinosaur origins story. The tiny Eodromaeus skeleton unearthed in South America “boots out” the previously designated dinosaur common ancestor. Evolutionary “history” continuously morphs to accommodate fossil data, showing that evolution is primarily conceptual—not scientific. (Thomas, 2011, emphasis mine)

Apparently in Mr. Thomas’ mind the fact that scientific conclusions change in the light of new evidence actually disqualifies them from being science at all. The implication being that in order to be “truly scientific” our ideas about the details of dinosaur evolution should be, like dinosaur fossils themselves, fixed in stone and unchanging, regardless of any new evidence that might later be uncovered.

This truly unscientific way of thinking is reflected in one of my favorite quotes from ICR’s  late founder Dr. Henry Morris concerning the evidence for Noah’s Flood:

But the main reason for insisting on the universal Flood as a fact of history and as the primary vehicle for geological interpretation is that God’s Word plainly teaches it!  No geologic difficulties, real or imagined, can be allowed to take precedence over the clear statements and necessary inferences of Scripture. (Morris, 1970, pp.32-33, emphasis mine)

So you begin with your conclusion, in this case a particular interpretation of the book of Genesis, and stick to it regardless of any “difficulties” you might encounter with the actual evidence.

Let the evidence be damned, literally. This is the very essence of “creation science”.

Another more prosaic problem with Mr. Thomas’ statement above is with the idea that Eodromaeus supposedly removes a previously designated dinosaur common ancestor”, in this case ostensibly Eoraptor. The problem is that while Eodromaeus, or Eoraptor before it, might be described in some popular science reports as being the “common ancestor” to later theropod dinosaurs, such statements are not found in the actual scientific literature describing these organisms.

For example in the paper by Sereno et al. (1993) which originally described Eoraptor they make no such claims about it being the actual common ancestor to later theropods:

We report here the discovery of a primitive dinosaur skeleton from Upper Triassic strata in northwestern Argentina.The 1-m-long skeleton represents a new taxon, Eoraptor lunensis gen. et sp. nov., which is close to the predicted structure and size of the common dinosaurian ancestorAlthough close in overall form to the common dinosaurian ancestor, the functionally tridactyl, grasping/raking hand and other features show that Eoraptor is allied phylogenetically with theropods. (Sereno et al. 1993, p. 64, emphasis mine)

Likewise the describers of Eodromaeus:

Whereas herrerasaurids appear to be more basal in position among theropods (Fig. 3), Eodromaeus is only marginally more derived, has few specializations (autapomorphies) (8), and thus approximates the hypothetical ancestral theropod in body size and morphology. (Martinez et al. 2011, p. 207, emphasis mine)

So whatever some science reporter/blogger might have said or implied, the authors of the papers describing Eoraptor and Eodromaeus in the scientific literature say only that they are “close to the predicted structure and size of the common dinosaurian ancestor” and “approximates the hypothetical ancestor” of later theropods, not that they actually were the ancestors.

Thomas: Eoraptor, “which some believed was a common ancestor to all dinosaurs,” was found there in 1991.1 The nearly knee-high Eoraptor was supposedly from “the era when dinosaurs first arose.”2 

And here is a perfect example of what we’re talking about. The quote Mr. Thomas gives above is from a newspaper article in the USA Today (Weise, 2011) and it misleadingly implies that scientists are making definite claims about Eoraptor being ancestral to later dinosaurs rather than merely looking like it might be the ancestor, or perhaps being closely related to the actual ancestor.

If Mr. Thomas were simply being critical of the fact that some science reporters occasionally mislead their readers with apparent claims of definite ancestral status when describing basal fossils like Eodromaeus or Eoraptor, then I would wholeheartedly agree with him, but somehow I doubt that Mr. Thomas’ true target is really misleading science reporting.

Thomas: Evolutionists have variously proposed it as the ancestor of two of the three major groups of dinosaurs: ornithischians, which included the Triceratops and Hadrosaurs; and saurischians, which included sauropods like Apatosaurus, and theropods like Tyrannosaurus.

This statement is somewhat odd, because I don’t know why Mr. Thomas is bringing up ornithischians (the so called “bird-hipped” dinosaurs) in this context. As far as I can find no one, in the scientific literature, has ever suggested that Eoraptor was a basal ornithischian or even basal within the Dinosauria, in the sense of being in the group ancestral to all dinosaurs, both ornithischian and saurischian. Rather it has, until recently, been primarily considered a basal theropod or perhaps basal within Saurischia, i.e. in the group ancestral to all later saurischian dinosaurs, both theropod and sauropod.

Well, at least Mr. Thomas, unlike some other creationists, seems to generally understand the difference between ornithischian and saurischian dinosaurs. Which is good since the ICR web site lists dinosaurs amongst his specialties.

Thomas: But identifying a single creature as the ancestor of the wide variety of dinosaurs—which include the tank-like Stegosaurus and massive Ultrasaurus, as well as the tiny two-legged Compsognathus—has been notoriously difficult.3 What features could clearly identify such an ancestor? And if it turns out to be impossible to identify, then could such an imagined creature even have existed?

Here we see a classic example of a creationist failing to grasp how evolution works over geologic time scales. Mr. Thomas essentially asks his readers to try and imagine an ancestral dinosaur, implying that such an animal should somehow combine all sorts of derived characteristics. As if the common ancestor of Stegosaurus (an ornithischian) with its plates and spikes, Ultrasaurus (a.k.a. Supersaurus) a massive long necked sauropod, and Compsognathus, a small carnivorous theropod, were all squished together into some improbable chimera.

i1_supersaurus_dinosaur_edited_s220px-compsognathus_bw

The problem is, of course, that these three types of dinosaurs are far removed from their common ancestor which would not have had all the bells and whistles added by millions of years of evolution found in the different branches of their descendants.

Thomas could have used a more obviously derived theropod like Tyrannosaurus to better effect since at least on a superficial level Compsognathus doesn’t seem nearly as derived as Stegosaurus or Supersaurus. I say this because the actual ancestor of all dinosaurs ornithischian and saurischian (both theropod and sauropod) is thought to have been based partly on finds like Eoraptor and Eodromaeus a fairly small (a little over a meter in length) bipedal archosaur the group containing not only dinosaurs (and their avian descendants) but also crocodilians and extinct types like pterosaurs.

So imagine not a combination of the three genera pictured earlier but instead something closer to a combination of the following genera (though even that is not a really accurate way to think about it):

Basal dinosaurs

Image sources: Eodromaeus (Martinez et al. 2011, p. 208) Eoraptor (Langer, 2004, p. 27) and Lesothosaurus (Norman et al. 2004, p. 329)

Pictured here are Eodromaeus (top) a basal theropod, Eoraptor (middle) a basal sauropod (according to Martinez et al.) and Lesothosaurus (bottom) a basal ornithischian. They are all about a meter or so in length and date from the Triassic period. As you can see, imagining a common ancestor between these animals is a bit less difficult than working with their later more derived relatives.

In fact I wouldn’t be surprised if some creationist confronted with these three dinosaurs might argue that they were all part of the same created “kind”. The differences between them certainly aren’t much greater that other groups where creationists have done just this this.

The argument for kicking Eoraptor out of the theropod lineage focuses on the fact that Eodromaeus and Eoraptor lived at the same time and that Eodromaeus has very marked theropod-like features, whereas Eoraptor not only lacks these but also has the inset lower first tooth and enlarged nostrils of a sauropodomorph.

The mistake is understandable, as the differences between the animals come down to very specific details that have only been picked up through comparison to one another. “If the two animals were to run by you with flesh on their bones, it would be a challenge to tell the difference,” says Sereno. (Kaplan, 2011, emphasis mine)

A comparison of the skulls and hands of Eoraptor (A and F) and Eodromaeus (B and G), (Martinez et al., 2011, p. 207)

Once again I must ask: does Mr. Thomas (ICR dinosaur specialist) not know this information or does he know it and chooses not to inform his readers about it? If it is the former then he is too ignorant to making grand pronouncements about the subject. If it is the later then his honesty is much in question.

Thomas: In other words, some scientists believed that the Eoraptor could have been the evolutionary ancestor of all saurischians, or just the theropod saurischians, or just the sauropod saurischians. These authors favor the latter, since Eodromaeus looks more like a theropod than Eoraptor does. In their view, now that Eodromaeus has been designated the new ancestor of theropods, Eoraptor is out.

This type of argument is standard boilerplate at ICR. Dr. Duane Gish (another founding member of ICR) has in the past used a similar argument regarding the basal equid Hyracotherium. He would quote some scientist noting that Hyracotherium is so near the base of the equid Family tree that it could just as easily be the ancestor of one of the other branches of the  Order perissodactyla such as rhinoceroses or tapirs. ‘See’ he would say, ‘they don’t know it if it is a horse or a rhinoceros. So it doesn’t count!’

Of course both Dr. Gish and Mr. Thomas miss the point entirely. That there is sometimes confusion or debate about the classification of animals like Eoraptor or Hyracotherium which are near the base of larger clades of organisms is exactly what is predicted by evolutionary theory.

Sure horses and rhinos are quite different, now, but the farther you go back in their lineages the more they converge until it is difficult if not impossible to tell fossils that belong to one group from the other, or which might perhaps be ancestral to both.

(Monroe, 1985, p. 23)

So Mr. Thomas presents his readers with the scenario of a bunch of scientists quibbling over whether Eoraptor is a theropod or a sauropod and suggests that since there is confusion it must be neither.

The reality is that A) evolutionary theory predicts that distinguishing between organisms at the base of two closely related clades will be difficult (perhaps even impossible); and B) one of the lead scientists in the description of Eodromaeus, who is arguing for the reclassification of Eoraptor as a basal sauropod (instead of a basal theropod) is Paul Sereno, who as it happens was the lead author in the original description of Eoraptor as a basal theropod (Sereno et al., 1993).

Essentially it’s Paul Sereno of 2011 arguing with Paul Sereno of 1993 with some other scientists (the other authors of the recent paper) agreeing with Sereno 2011, and a few others urging caution:

The similarity is so pronounced that not all are convinced at this point. Palaeontologist Mike Benton at the University of Bristol, UK, who was not involved with the study, says, “It’s quite a shift to move Eoraptor from close affinity with theropods to sauropodomorphs, but I can’t say whether I agree or disagree with this interpretation without seeing the material myself.” (Kaplan, 2011, emphasis mine)

Oh, the horror. The horror…

Thomas: So, as has been the case with every single proposed evolutionary ancestor, experts disagree on what evolved into what.5 With no consensus on what is, or even what could or should be, any particular evolutionary ancestor, efforts to fit the fossil data into an imagined evolutionary framework will never rise above the certainty of “your guess is as good as mine.”

Again Mr. Thomas wants to foist his religious sensibilities onto science. If scientists don’t have absolute certainty (like fundamentalists), and they never do, then it’s all just subjective guesswork.

The reality is science does not produce absolute certainty, ever. It conclusions are always tentative even when they reach a high level of confidence, as is the case with atomic theory, the theory of relativity, germ theory and evolutionary theory. Likewise the classifications of organisms are hypotheses which always remain open to being tested against new and better evidence. Modern taxonomic methods such as cladistics work to weed out subjective elements from our classification of organisms by basing them on details of anatomy called synapomorphic characters:

Cladistics is a particular method of hypothesizing relationships among organisms. Like other methods, it has its own set of assumptions, procedures, and limitations. Cladistics is now accepted as the best method available for phylogenetic analysis, for it provides an explicit and testable hypothesis of organismal relationships.

The basic idea behind cladistics is that members of a group share a common evolutionary history, and are “closely related,” more so to members of the same group than to other organisms. These groups are recognized by sharing unique features which were not present in distant ancestors. These shared derived characteristics are called synapomorphies.

Note that it is not enough for organisms to share characteristics, in fact two organisms may share a great many characteristics and not be considered members of the same group. For example, consider a jellyfish, starfish, and a human; which two are most closely related? The jellyfish and starfish both live in the water, have radial symmetry, and are invertebrates, so you might suppose that they belong together in a group. This would not reflect evolutionary relationships, however, since the starfish and human are actually more closely related. It is not just the presence of shared characteristics which is important, but the presence of shared derived characteristics. In the example above, all three characteristics are believed to have been present in the common ancestor of all animals, and so are trivial for determining relationships, since all three organisms in question belong to the group “animals.” While humans are different from the other two organisms, they differ only in characteristics which arose newly in an ancestor which is not shared with the other two. As you shall see on the next page, chosing the right characters is one of the most important steps in a cladistic analysis. (UC Berkeley Introduction to Cladistics, accessed on February 28, 2011)

It isn’t perfect but it is a far cry from simple guesswork as Mr. Thomas would have us believe.

In their paper describing Eodromaeus, Martinez et al. lay out their evidence for classifying it as a basal theropod (this is very technical so you might want to skim it):

Basal theropod status for Eodromaeus is supported by a suite of derived attributes in the skull (promaxillary fenestra, basisphenoid fossa), axial skeleton (cervical pleurocoels, elongate caudal prezygapophyses), forelimb (radioulnar shaft apposition, elongate penultimate phalanges), pelvic girdle (distally tapering pubic blade, pubic foot), and hind limb (femoral extensor depression, tibial crest for fibula) (8). (Martinez et al. 2011, p. 207)

And likewise they spell out their case for reclassifying Eoraptor:

Not only does Eoraptor lack all of the aforementioned theropod attributes in Eodromaeus, but it also exhibits features previously seen only among basal sauropodomorphs. In the skull, these features include an enlarged narial opening, a slender ventral process of the squamosal, and the inset position of the first dentary tooth (Fig. 1B). The toothless anterior end of the dentary, which is flanked by a conspicuous pair of vascular foramina, may have supported a small lower bill as in other basal sauropodomorphs (13). In addition, the form of the crowns (basal constriction, lateral crest, larger inclined denticles) strongly suggests that Eoraptor had an omnivorous, if not wholly herbivorous, diet. In the postcranial skeleton, sauropodomorph features include substantial medial rotation in the shaft of the first phalanx of the thumb (digit I) that directs the tip of the ungual inward (Fig. 1F) (13) and an astragalus with a characteristic shape (anteriorly projecting anteromedial corner) (3). (Martinez et al. 2011, pp. 207-208)

If Mr. Thomas wants to claim that this is all merely guesswork he is going to have to more than shout “is so!” over and over and attempt to refute it in detail, based on observations of the fossils. It’s called doing science rather than propaganda.

Thomas: And Eodromaeus was found fully formed, with no hint of any body part transitioning into another.

Of course it was “fully formed” Mr. Thomas. As I’m sure you’ve been told before, all species under evolutionary theory are fully formed whatever they are; even if they are transitional or intermediate forms. If Eodromaeus murphi was indeed the ancestor to all later theropods (something we can never know with certainty) it was still a fully formed Eodromaeus murphi.

This is just creationist weaseling that literally has no substance. If you try and get them to define exactly what they mean by “fully formed body parts”, it either devolves into nonsense about animals with half an eye (like an eye-ball cut in half) or less often they describe what we actually do find (but what they don’t want to admit); that there are organisms with intermediate characters.

Thomas: Transitional features would be expected in a “basal” dinosaur “at the root of Theropoda,”4 but it was found in a completed two-legged form.6

Ask and ye shall receive. Mr. Thomas is nice enough to provide us with an example of why his talk of things being “fully formed” is nonsense. Here he argues that because Eodromaeus is in a “completed two-legged form” it cannot be transitional (I think he means ancestral).

Now he could mean by this that it has two hind limbs, a character shared by all tetrapods (land animals) since they first crawled out of the water (actually long before that).

Or perhaps he could mean that it is bipedal, walking on its hind limbs, a character shared by all basal dinosaurs and therefore exactly what one would expect in the first dinosaur (quadrupedalism, walking on all fours, in later dinosaurs was re-evolved in some dinosaur lineages).

I wouldn’t want to insult him by asking if he means that they don’t literally have half formed legs (like embryonic limb buds), but who knows.

Regardless, the presence of two fully formed hind limbs (used for bipedalism or not) has no bearing on whether or not Eodromaeus evolved from and earlier dinosaur or was ancestral to later dinosaurs.

Thomas: Since Eodromaeus has no transitional features and is a well-coordinated collection of integrated parts, each of which may or may not be shared with other dinosaur species, this fossil offers no answers to the questions of evolutionary dinosaur origins.

So says the propagandist, the scientists however beg to differ:

With Eoraptor as a basal sauropodomorph [based in part on comparison to Eodromaeus – T.B.], the three principal clades of dinosaurs (ornithischians, sauropodomorphs, theropods) now appear to be converging on an ancestral skeletal plan—a bipedal cursor (tibia longer than femur) with body length less than 2 m. …The discovery of Eodromaeus, the reinterpretation of Eoraptor as a sauropodomorph, and the faunal record of the Ischigualasto Formation provide additional evidence that, by mid Carnian time (~232 Ma), the earliest dinosaurs had already evolved the most functionally important trophic and locomotor features characterizing ornithischians, sauropodomorphs, and theropods (17, 23). These attributes are thus unlikely to have functioned as the competitive advantage to account for the dominance of dinosaurs in abundance and diversity in terrestrial habitats some 30 million years later in the earliest Jurassic (~202 Ma). Eodromaeus increases the range of salient theropod features present in the earliest dinosaurs, and Eoraptor shows that the enlarged naris, basally constricted crowns, and a twisted pollex were present in the earliest sauropodomorphs. (Martinez et al. 2011, p. 208-210)

And they continue on discussing what this evidence suggests about the early evolution of dinosaurs and the environment they lived in.

Thomas: Instead, it looks as though it was fully formed on purpose from the start.

Yes, yes, because it had two legs or something…

References

Kaplan, Matt (2011) “Move over Eoraptor“, Nature, posted on nature.com 13 January, 2011, accessed February 27, 2011

Langer, Max C. (2004) “Basal Saurischia“, chapter 2 in Weishampel, David B. et al. (2004) The Dinosauria (2nd edition)

Martinez, Ricardo N. et al. (2011) “A Basal Dinosaur from the Dawn of the Dinosaur Era in Southwestern Pangaea“, Science 331(6014): 206-210

Monroe, James S. (1985) “Basic Created Kinds and the Fossil Record of Perissodactyls“, Creation/Evolution 5(2):4-30

Morris, Henry (1970) Biblical Cosmology and Modern Science

Norman, David B. et al. (2004) “Basal Ornithischia“, chapter 14 in Weishampel, David B. et al. (2004) The Dinosauria (2nd edition)

Sereno, Paul et al. (1993) “Primitive dinosaur skeleton from Argentina and the early evolution of Dinosauria“, Nature 361, 64-66

Thomas, Brian (2011) “Fossil Discovery Reshuffles Dino Evolution Again“, posted on icr.org, accessed on February, 28, 2011

Weise, Elizabeth (2011) “New dog-sized dinosaur discovered“, USA Today, posted on usatoday.com January 13, 2011, accessed February 27, 2011

Advertisements

5 thoughts on “A Tale of Two Dinosaurs

  1. Hmm —a human five year old looks pretty “fully formed” to me —– how could it possibly change over time into a decrepid wrinkled ninety year old?

    Like

  2. The ICR brain trust is based about 15 miles from me. I became aware of them because I get junk mail addressed to a previous resident of my house. I’m frequently tempted to make the short drive to Chino Valley (aka Methistan) to mock them.

    Like

  3. Pingback: Chicken Wings mal anders: Über die Evolution der Vogelextremitäten | Dance like a monkey

  4. Pingback: So I was on a panel discussion about micro vs. macroevolution… | Playing Chess with Pigeons

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s